The influence of hyperinsulinaemia on calcium-phosphate metabolism in renal failure

Background. Patients with renal failure are characterized by impaired insulin-mediated glucose uptake. Insulin plays a major role in the maintenance of phosphate homeostasis but it remains to be determined whether in uraemia insulin-dependent renal and extrarenal phosphate disposal is also affected. Methods. The effects of hyperinsulinaemia on serum concentrations of phosphate, ionized calcium and intact PTH as well as renal excretion of calcium and phosphate was studied under euglycaemic conditions (glucose clamp technique) in patients with advanced renal failure and in healthy subjects. Fifteen patients with renal failure (mean serum creatinine 917 &mgr;mol/l) and 12 control subjects were included. All subjects underwent a 3-h euglycaemic clamp with constant infusion of insulin (50 mU/m²/min) following a priming bolus. The urine was collected for 3 h before and throughout the clamp. Results. The tissue insulin sensitivity (M/I) was lower in patients with renal failure than in control subjects (5.3±2.4 vs 6.7±1.8 mg/kg/min per mU/ml, P=0.001) but the phosphate lowering action of insulin was larger in patients with renal failure than in control subjects. Urinary calcium excretion increased (P<0.05) and phosphate excretion did not change during the clamp in both groups. Despite a decrease of serum ionized calcium in the group of patients with renal failure and no change in the control group, plasma PTH fell significantly in both groups but this effect was still significant after 180 min only in the renal failure group. A significant correlation was observed between changes in serum phosphate and PTH induced by hyperinsulinaemia (r=0.48, P<0.01). Conclusions. Phosphate-lowering effect of insulin is well preserved in severe renal failure despite the resistance to insulin-stimulated glucose uptake. The decrease of serum PTH observed during hyperinsulinaemia appears to be independent of serum ionized calcium.     

Stability of access resistance during haemodialysis

Background: Access blood flow (Qac) is considered a useful indicator in the surveillance of haemodialysis access function. However, changes in Qac may be due to changes in blood pressure and/or to changes in access resistance (AR). Methods: Weekly readings of Qac, cardiac output, and arterial blood pressure measured early and late during haemodialysis were obtained in 11 patients for a period of 3 weeks. Qac was determined from thermodilution of extracorporeal blood returning to the patient with reversed placement of blood lines and by measurement of arterial and venous blood temperatures in the extracorporeal circulation. Data are given as mean±SE. Results: Qac dropped as mean arterial pressure (MAP) and total peripheral resistance (TPR) decreased, but increased when MAP and TPR increased. Linear regressions between the change in access flow and the change in MAP (&Dgr;Qac%=0.80*&Dgr;MAP%-1.6, r²=0.39), and the change in TPR (&Dgr;Qac=0.54*&Dgr;TPR%-9.2, r²=0.35) respectively, were significant (P<0.001). Whereas Qac significantly decreased (-8.4±3.3%, P<0.01) during the same treatment. AR remained unchanged (4.7±3.2%; P=NS). AR for all studies was 16.5±1.0 peripheral resistance units (1PRU=2.226 kPa min l^-1). There was a trend for resistance to increase (5.1±2.6%, P=NS) and for flow to decrease (-6.1±2.3%, P=NS) during the 3 weeks of the study. Conclusion: Qac measured during haemodialysis is variable and depends on haemodynamics, but AR is constant. AR is related to the physical structure of the peripheral access. Because of its intradialytic stability AR may be better suited as an indicator of access function.     

Acute effects of recombinant human erythropoietin on plasma levels of proendothelin-1 and endothelin-1 in haemodialysis patients

Background: The pathogenesis of rHuEpo-induced hypertension in haemodialysis (HD) patients still remains uncertain. Endothelin-1 (ET-1) is produced from proendothelin-1 (proET-1) by an endothelin-converting enzyme. Since proET-1 is known to have approximately 1/100 the potency of ET-1 for contracting an isolated blood vessel, the change in the activity of endothelin-converting enzyme (ECE) has been proposed as an important factor in the pathophysiology of various hypertensive diseases. However there is no report on whether a change in the rate of conversion of proET-1 to ET-1 may be involved in the pathogenesis of rHuEpo-induced hypertension. The purpose of this study was to ascertain the potential role of ECE in the development of rHuEpo-induced hypertension. Methods: The levels of plasma erythropoietin, proET-1, ET-1, and mean arterial blood pressure (MAP) were measured following a single dose of rHuEpo (100 U/kg) in HD patients with 24-h ambulatory blood pressure monitoring. Different routes of administration (19 intravenous group, 10 subcutaneous group) were compared to a placebo-injected control group (10 HD patients). Results: Plasma erythropoietin levels reached maximal value 5 min after i.v injection of rHuEpo (13.1±2.4 vs 2780.9±290.1 mU/ml, P<0.01), whereas it was 6h in the s.c. group (14.7±3.8 vs 38.8±17.7 mU/ml, P<0.05). A significant increase in MAP was noted 30 min after rHuEpo injection, which lasted for 3 h in the i.v. group. However, no significant changes in MAP were noted in patients given rHuEpo subcutaneously. Both the plasma concentrations of proET-1 and ET-1 started to increase from 10 min after i.v. rHuEpo administration, with the pro-ET-1 reaching a peak level at 30 min (13.5±7.4 vs 21.6±3.8 pg/ml, P<0.05) and the ET-1 at 1 h (4.2±2.6 vs 9.9±4.8 pg/ml, P<0.05). In patients with significant interdialysis hypertension following a single i.v. injection of rHuEpo, the molar ratio of ET-1 over proET-1 (ET-1/proET-1) was significantly higher than in patients without hypertension. In addition, the increase in ET-1 levels was significantly greater in patients with interdialysis hypertension, while changes in proET-1 level were similar in both hypertensive and non-hypertensive groups. Changes in interdialysis MAP (Dgr;IDMAP) was significantly correlated with &Dgr;ET-1 during the interdialysis period, but not with &Dgr;proET-1. Conclusion: Differences in ET-1/proET-1 ratio in relation to changes in MAP after a single intravenous administration of rHuEpo suggest a potential role for ECE in the pathogenesis of rHuEpo-induced hypertension. Key words: endothelin-1; endothelin-converting enzyme; haemodialysis; proendothelin-1; rHuEpo-induced hypertension      

A calcium-channel blocker, amlodipine, attenuates insulin antinatriuresis but does not modulate insulin-mediated attenuation of cardiovascular reactivity in healthy man

Background: Insulin exerts an antinatriuretic effect when administered acutely in vivo. Interestingly, insulin fails to reduce sodium excretion in rats receiving verapamil. The present study was undertaken in order to investigate whether the calcium-channel blocker amlodipine attenuates the antinatriuretic effect of insulin in humans. Method: Eight healthy lean men (32±2 years) were investigated on three different occasions; i.e. time-control, insulin infusion alone, and insulin infusion following pretreatment with amlodipine (5 mg x 1 during 10 days). During the experiments renal haemodynamics (insulin and PAH clearances) and segmental tubular sodium handling (sodium and lithium clearances) were investigated. The cardiovascular reactivity was also assessed by a graded noradrenaline infusion at the end of each experiment. Results: Insulin infusion alone was accompanied by a significant 50% reduction in urinary sodium excretion. Following amlodipine pretreatment, euglycaemic insulin infusion was associated with an attenuated antinatriuretic response and the cumulative sodium excretion following 135 min of insulin infusion was significantly higher (24±4 vs 18± mmol; P <0.05) as compared to insulin infusion alone. No significant differences in the proximal and distal tubular sodium handling respectively, were seen following CCB pretreatment. The results also show that the doses of noradrenaline required to increase the basal mean arterial blood pressure by 10 mmHg (262±38 vs 150±25 ng/g/min; p <0.05) and by 20 mmHg (431±36 vs 350±38 ng/kg/min; P<0.05) respectively, were significantly higher during the insulin infusion than during the time-control experiment. Pretreatment with amlodipine did not further modulate the cardiovascular reactivity. Conclusion: Pretreatment with a calcium-channel blocker, amlodipine, attenuates the antinatriuretic effects of insulin leading to a significantly higher cumulative sodium excretion at the end of insulin infusion, which may be of clinical importance. Moreover, insulin attenuates the cardiovascular reactivity to a graded noradrenaline infusion, suggesting that insulin causes vasodilatation in healthy man.     

Norepinephrine-induced blood pressure rise and renal vasoconstriction are not attenuated by enalapril treatment in microalbuminuric IDDM

Background: In non-diabetic subjects, an attenuated systemic norepinephrine (NE) responsiveness may contribute to the mechanisms of action of angiotensin-converting enzyme (ACE) inhibitor treatment. We determined whether ACE inhibitor treatment influences systemic and renal haemodynamic responsiveness to exogenous NE, as well as urinary albumin excretion during NE, in microalbuminuric insulin-dependent diabetic (IDDM) patients, representing a patient category that benefits by strict blood pressure control. Methods: In seven microalbuminuric IDDM patients, systemic and renal responsiveness to NE, infused at individually determined threshold (&Dgr;mean arterial pressure (MAP)=0 mmHg], 20% pressor (&Dgr;MAP=4 mmHg) and pressor (&Dgr;MAP=20 mmHg) doses, were compared before and after 8 weeks treatment with enalapril, 10 mg daily. Blood glucose was clamped at 5 mmol/l and insulin was infused at 30 mU/kg/h. Results: Enalapril decreased MAP (P<0.05) and microalbuminuria (P<0.05), whereas effective renal plasma flow (ERPF) increased (P<0.01) and glomerular filtration rate remained unaltered. The filtration fraction tended to decline (P=0.09). The ACE inhibitor-induced fall in MAP disappeared at NE pressor dose, and the overall mean increase in MAP in response to NE was even higher with than without enalapril (P<0.05). After enalapril, the ERPF remained higher at all NE doses (P<0.05), but the magnitude of the NE-induced fall in ERPF was not altered by ACE inhibition treatment. Overnight urinary albumin excretion fell with ACE inhibition (P<0.05), but this effect was not seen during NE infusion. The angiotensin II/active renin ratio and serum aldosterone levels remained lower with enalapril at all NE doses (P<0.05). <It>Conclusions:Enalapril does not attenuate systemic and renal vascular responsiveness to exogenous NE in microalbuminuric IDDM despite adequate inhibition of the renin-angiotensin-aldosterone system. These findings suggest that the effect of NE on vasoconstriction is not counteracted effectively by ACE inhibition treatment alone.     

Parathyroid hormone decreases in vivo insulin effect on glucose utilization

Hyperparathyroidism is associated with impaired glucose tolerance, and parathyroidectomy may improve carbohydrate homeostasis. It has been suggested that parathyroid hormone (PTH) suppresses insulin secretion but it is unclear whether it also interferes with the peripheral action of insulin. To evaluate in vivo effects of PTH on insulinmediated glucose utilization, 15 male Sprague Dawley rats were continuously infused with rat PTH (1–34) using an Alzet miniosmotic pump at a rate of 0.03 nm/hour. Controls were infused with the vehicle alone. Following 5 days of PTH infusion, plasma calcium (Ca) levels were higher in the PTH-infused rats (12.3±0.2 versus 9.9±0.1 mg/dl, P<0.01). On the 5th day, glucose (700 mg/kg) and insulin (0.175 U/kg) were given as a bolus infusion through the left femoral vein, blood samples were obtained from the right femoral vein, and plasma glucose and insulin were measured at basal (0 minutes) and at 2, 5, 10, and 20 minutes postinfusion. Basal, nonfasting glucose levels were higher (166±4 versus 155±4 mg/dL, P<0.04) in the PTH-infused rats but their insulin levels were similar to those of controls (6.5±0.6 versus 5.6 ±0.5 ng/ml). Postinfusions and maximal (2 minutes) glucose and insulin levels were similar in both groups. However, although insulin levels were similar in both groups at all measured time points, glucose levels at 20 minutes were higher in the PTH-treated rats (205±13 versus 173±9; P<0.03). Also, calculated glucose disappearance rates (Kg) were decreased in the PTH-infused rats (4.05±0.3 versus 4.63±0.8; P=0.054), suggesting an impaired peripheral effect of insulin on glucose utilization. To gain insight into the potential contribution of the hypercalcemia or the PTH to these abnormalities, correlation evaluations were performed. Only in PTH-infused rats did plasma Ca correlate with plasma glucose at 0 and 20 minutes (r=0.6, P=0.02; r=0.7, P=0.01) and with the area under the glucose curve (r=0.6, P=0.03) during the glucose-insulin infusion. Also only in PTH-infused rats did PTH correlate with 0 (P=0.07) and 20-minute (P=0.02) plasma glucose levels. There was no correlation between either Ca or PTH and basal insulin levels or the area under the insulin curve in either group. Consequently, we suggest that in the rat, PTH infusion associated with hypercalcemia impairs insulin effect on glucose utilization in vivo and this defect may be induced by the Ca, PTH, or both.This study was presented in part at the 76th Annual Meeting of the Endocrine Society, Anaheim, CA, USA, June 1994.     

Insulin resistance precedes microalbuminuria in patients with insulin-dependent diabetes mellitus

Background. Insulin resistance has been associated with hypertension and with renal complications in patients with type 1 diabetes mellitus. Causal relationships have not been fully explained. Methods. We investigated whether insulin resistance precedes microalbuminuria by measuring insulin resistance with a euglycaemic clamp in combination with indirect calorimetry in 16 uncomplicated type 1 diabetic patients and in six healthy control subjects. The patients had over 10 year duration of diabetes, and were expected to experience either a complication-free or complicated disease course within the next few years. They have thereafter been followed for the development of microalbuminuria for 3 years. Results. In a euglycaemic insulin clamp glucose disposal was lower in diabetic patients compared with control subjects (7.5±2.9 and 12.6±2.0 mg/kg LBM/min; P<0.002), mainly due to impaired glucose storage (4.3±2.3 vs 8.6±1.6 mg/kg LBM/min; P<0.001). Three years later seven IDDM patients had albumin excretion rate over 30 mg/24 h; glucose disposal (5.5±2.1 vs 9.0±2.2 mg/kg LBM/min; P<0.01) had been lower in patients who developed microalbuminuria compared with those who remained normoalbuminuric. Conclusions. Insulin resistance predicts the increment in urinary albumin excretion. Insulin resistance depends mainly on impaired glucose storage in uncomplicated IDDM.     

Do intraoperative hemodynamic factors of the recipient influence renal graft function?

Purpose

To assess the importance of intraoperative management of recipient hemodynamics for immediate versus delayed graft function.

Methods

The retrospective study of 1966 consecutive renal transplants performed in our department between June 1980 and December 2009 analyzed several perioperative hemodynamic factors: central venous pressure (CVP), mean arterial pressure (MAP) as well as volumes of fluids, fresh frozen plasma (FFP), albumin, and whole blood transfusions. We examined their influence on renal graft function parameters: immediate diuresis, serum creatinine levels, acute rejection, chronic transplant dysfunction, and graft survival.

Results

Mean CVP was 9.23 ± 2.65 mm Hg and its variations showed no impact on graft function. We verified a twofold greater risk of chronic allograft dysfunction among patients with CVP ≥ 11 mm Hg (P < .001). Mean MAP was 93.74 ± 13.6 mm Hg; graft survivals among subjects with MAP ≥ 93 mm Hg were greater than those of patients with MAP < 93 mm Hg (P = .04). On average, 2303.6 ± 957.4 mL of saline solutions were infused during surgery. Patients who received whole blood transfusions (48%) showed a greater incidence of acute rejection episodes (ARE) (P = .049) and chronic graft dysfunction (P < .001). Patients who received FFP (55.7%), showed a higher incidence of ARE (P < .001). Only 4.6% of patients (n = 91) received human albumin with a lower incidence of ARE (P = .045) and chronic graft dysfunction (P = .024). Logistic binary regression analysis revealed that plasma administration was an independent risk factor for ARE (P < .001) and chronic dysfunction (P = .028). Volume administration (≥2500 mL) was also an independent risk factor for chronic allograft dysfunction (P = .016). Using Cox regression, we verified volume administration ≥ 2500 mL to be the only independent risk factor for graft failure (P < .001).

Conclusion

MAP ≥ 93 mm Hg and perioperative fluid administration <2500 mL were associated with greater graft survival. Albumin infusion seemed to be a protective factor, while CVP ≥ 11 mm Hg, whole blood, and FFP transfusions were associated with higher rates of ARE and chronic graft dysfunction.     

Calcium infusion and left ventricular diastolic function in patients with chronic renal failure

Background. Left ventricular (LV) function is sensitive to disorders in calcium metabolism. Most previous reports have focused on the effects of calcium on systolic performance. We studied the acute effect of calcium infusion on LF diastolic function in patients with moderate to severe chronic renal failure (CRF) and secondary hyperparathyroidism (SHP). Methods. We infused calcium gluconate at a constant rate of 45 &mgr;mol/kg/h to 14 patients with severe to moderate CRF and SHP. Our aim was to reach slightly supranormal levels of serum ionized calcium (1.35-1.45 mmol/l). LV diastolic function was assessed by pulsed Doppler echocardiography before and after the calcium infusion. The echocardiographic indices were compared to those of 14 age- and sex-matched healthy controls. Results. Before calcium infusion the patients had significantly greater LV dimensions than the controls, but there was no differences in the diastolic indices. During calcium infusion, serum ionized calcium increased from 1.18±0.03 to 1.40±0.03 mmol/l (P<0.0001) and plasma intact PTH decreased from 38.6±5.6 to 9.0±2.2 pmol/l (P<0.0001). Calcium infusion did not affect the LV dimensions or fractional shortening. The peak early diastolic velocity (Emax) decreased and peak late diastolic velocity (Amax) increased, and their relationship decreased significantly (1.552±0.586 vs 1.414±0.535 m/s, P=0.03). These changes reflect impairment of LV diastolic function. Conclusions. Induction of acute hypercalcaemia by calcium infusion impairs LV diastolic function in patients with CRF and SHP.     

Stimulatory effect of insulin on tubular sodium reabsorption in normotensive subjects with a positive family history of hypertension

BACKGROUND: Insulin resistance and hyperinsulinaemia has been suggestedas a pathogenetic mechanism in hypertension. METHODS: In this investigation the renal response to insulin was studiedin normotensive subjects with a positive family history of hypertensionin two generations (n = 14), in one weight-matched (n = 11)and one lean (n = 13) control group. During hyperinsulinaemia(euglycaemic hyperinsulinaemic clamp technique) we determinedrenal haemodynamics (clearances of ⁵¹Cr-EDTA and PAH) and urinarysodium excretion. Lithium clearance was used to estimate thesegmental tubular reabsorption of sodium. RESULTS: In subjects with a positive family history of hypertension,hyperinsulinaemia did not influence renal plasma flow (RPF)or glomerular filtration rate (GFR) but urinary sodium excretiondecreased by 50%. Estimated proximal tubular sodium reabsorptionwas unaffected by insulin while estimated distal fractionalsodium reabsorption increased, P<0.01. At the end of theclamp a low-dose infusion of angiotensin II (0.1 ng/kg per min)was superimposed. GFR and RPF then decreased significantly concomitantwith urinary excretion of sodium. In control subjects hyperinsulinaemia caused an unchanged GFRin both groups, increased RPF in the lean control group and15–25% reduction in sodium excretion. No alteration wasseen in estimated proximal tubular sodium reabsorption, butestimated distal tubular sodium reabsorption increased (P<0.05)in the lean control group. Angiotensin II elicited a furtherincrease in distal fractional tubular sodium reabsorption inboth control groups (P<0.05). CONCLUSIONS: In normotensive subjects with a positive family history of hypertension,in contrast to control subjects without such history, hyperinsulinaemiacaused a marked decrease in urinary sodium excretion in presenceof unchanged RPF and GFR indicating a renal tubular effect ofinsulin located at a distal site of the renal tubules. AngiotensinII caused further sodium retention, probably due to an effecton renal haemodynamics.     

Effects of Hyperinsulinaemia under Euglycaemic Condition on Liver Fat Metabolism in Dairy Cows in Early and Mid‐lactation

The objective was to examine the effects of insulin under euglycaemic conditions on liver long chain fatty acids (LCFA) metabolism with special focus on the aetiology of hepatic lipidosis in early lactation. A 4‐day hyperinsulinaemic–euglycaemic clamp (clamp) was conducted on four dairy cows starting in weeks 4 and 17 postpartum. Insulin was infused continuously (1 μg/kg BW per h) and a 50 % glucose solution was infused to maintain euglycaemia. Liver biopsies were taken 6 days before, the last day of, and 5 days after the clamp, and blood samples were taken in the same period. In the liver tissue, the relative triglyceride content decreased (P < 0.01) and the glycogen content increased (P < 0.0001) in response to the clamp. Hepatic in vitro palmitate oxidation capacity was lowest during the clamp period and could be explained by a significant decrease in incomplete oxidation (ketogenesis) (P < 0.04) and a tendency to a decreased complete oxidation of palmitate (P < 0.10). Plasma non‐esterified fatty acids concentration was decreased during the clamp in early lactation (P < 0.05) but there was no effect on the mid‐lactation clamp. The present study shows that increased insulin under euglycaemic conditions seems to depress hepatic LCFA oxidation capacity. However, in terms of preventing hepatic lipidosis, the anti‐lipolytic effect of insulin on adipose tissue, which results in decreased mobilization of and hence hepatic load with LCFA, appears more important.     

Intravenous insulin decreases protein breakdown in infants on extracorporeal membrane oxygenation

Background/Purpose

Infants requiring extracorporeal membrane oxygenation (ECMO) have the highest rates of protein catabolism ever reported. Recent investigations have found that such extreme protein breakdown is refractory to conventional nutritional management. In this pilot study, the authors sought to use the anabolic hormone insulin to reduce the profound protein degradation in this cohort.

Methods

Four parenterally fed infants on ECMO were enrolled in a prospective, randomized, crossover trial. Subjects were administered an insulin infusion using a 4-hour hyperinsulinemic euglycemic clamp followed by a control saline infusion on consecutive days in random order. Whole-body protein flux and breakdown were quantified using a primed continuous infusion of the stable isotope l-[1-¹³C]leucine. Statistical analyses were performed using paired t tests.

Results

Serum insulin levels were increased 15-fold during the insulin clamp compared with the saline control (407 ± 103 v 26 ± 12 μU/mL; P < .05). During the insulin infusion, infants had decreased rates of total leucine flux (214 ± 25 v 298 ± 38 μmol/kg/h; P < .05) and leucine flux derived from protein breakdown (156 ± 40 v 227 ± 54 μmol/kg/h; P < .05) when compared with saline control. Overall, insulin administration produced a 32% reduction in protein breakdown (P < .05).

Conclusions

In this pilot study, the anabolic hormone insulin markedly reduced protein breakdown in critically ill infants on ECMO. Because elevated protein breakdown correlates with mortality and morbidity, the administration of intravenous insulin may ultimately have broad applicability to the metabolic management of critically ill infants.     

Amelioration of hypertension and insulin resistance by 1,25-dihydroxycholecalciferol in hemodialysis patients

The effects of i.v. 1,25-dihydroxycholecalciferol (DHCC) on blood pressure and insulin sensitivity were studied in 7 patients on maintenance hemodialysis and compared with 7 healthy controls. Three days after discontinuing oral 1,25-DHCC, the dialysis patients were evaluated by glucose clamp studies to quantitate insulin sensitivity, with (+D) and without (–D) a prior single dose of i.v. 1,25-DHCC at 2g/m². Blood pressure was measured just before the glucose studies. During –D studies, the patients were hypertensive (mean arterial blood pressure 108±2 mmHg, controls 84±4 mmHg,P<0.02) and insulin resistant (insulin sensitivity index 7.5±0.4 mg/kg·min per U per ml, controls 14.2±0.7,P<0.01) i.v. 1,25-DHCC significantly reduced the mean arterial blood pressure (96±3 mmHg,P<0.05) and increased insulin sensivity (10.9±0.5 mg/kg·min per U per ml,P<0.02) in the dialysis patients. I. V. 1,25-DHCC did not change blood pressure and insulin sensitivity in the control subjects. During –D studies, serum concentrations of 1,25-DHCC were significantly lower in patients than controls (P<0.02). Serum 1,25-DHCC during the +D studies increased to supraphysiological levels in both patients and controls. Serum concentrations of intact parathyroid hormone, total and ionized calcium, magnesium, potassium, urea nitrogen and creatinine were not different between the +D and –D studies in either the dialysis patients or the controls. These results suggest that pharmacological doses of 1,25-DHCC may have therapeutic value in the treatment of hypertension and insulin resistance in dialysis patients.     

Inhibition of AAA in a rat model by treatment with ACEI perindopril

Background

The purpose of the present study was to evaluate the effect of a new angiotensin converting enzyme inhibitor perindopril on the formation of experimental abdominal aortic aneurysms (AAAs) in a rat model induced by intraluminal elastase infusion and extraluminal calcium chloride (CaCl₂) application.

Materials and methods

Thirty-six male Sprague–Dawley rats were randomly distributed into three groups (n = 12 per group): model (A), sham (B), and perindopril (C). Rats in model and perindopril groups underwent intra-aortic elastase perfusion and extraluminal CaCl₂ application to induce AAAs. Rats in the sham group received aortic perfusion and extraluminal application of saline. A dose of 3 mg/kg/d of perindopril was fed orally in the perindopril group. The maximum abdominal aortic diameter was measured in vivo on days 0 and 28 and by ultrasound on days 7, 14, and 21. The arterial blood pressure was measured directly using a pressure transducer after cannulation in surgery and before death. AAA tissue samples were harvested at day 28 and evaluated using normal hematoxylin and eosin stain, Verhoeff-van Gieson stain for elastin, and image analysis technique.

Results

Aortic diameters of rats in the model group consistently increased within 28 d, coinciding with the development of a transmural inflammatory response, thickening of intima, and destruction of the elastic media. Without alteration in blood pressure, the AAA formation rate and mean maximal diameter of aorta at day 28 were significantly lower in the perindopril group compared with the control group (1.71 ± 0.20 versus 2.70 ± 0.69 mm, P < 0.001; 0% versus 90.91%, P < 0.001) and were similar to those in the sham group (1.79 ± 0.29 mm, P = 0.175; 0%, P = 1). The thickness of intima in the perindopril group was lower than that in the model group (20.68 ± 9.96 versus 58.49 ± 32.01 μm, P = 0.001), but higher than that in the sham group (7.23 ± 2.68 μm, P = 0.005). The intensity of elastin fiber showed the opposite trend (0.8541 ± 0.0495 in sham group versus 0.7376 ± 0.1024 in perindopril group versus 0.5413 ± 0.0912 in model group, P < 0.001).

Conclusions

Perindopril inhibited the aortic degeneration and AAA formation in the experimental AAA model induced by elastase and CaCl₂. This effect, which was independent of its influence on hemodynamics, appeared to be induced by the suppression of the inflammatory cell influx and intimal thickening and the preservation of aortic medial elastin.     

Antinatriuretic action of insulin is preserved after angiotensin I converting enzyme inhibition in normal man

To examine the potential role for intrarenal angiotensin IIin mediating the antinatriuretic action of insulin, seven normalmales were studied on three occasions, twice during euglycaemichyperinsulinaemia (40 mU.m^–2.min^–1) after double-blindtreatment for 1 week with placebo and the converting enzymeinhibitor perindopril, and on a time control day. Lithium carbonate250 mg was given before each study as an indirect marker oftubular sodium handling. Renal haemodynamics did not changeduring hyperinsulinaemia. Insulin infusion reduced both theabsolute and fractional urinary excretion rates of sodium (P<0.0001) and potassium (P<0.00l); these effects of insulinwere not altered after converting enzyme inhibition. Lithiumclearance did not change during insulin infusion on either day.The antinatriuretic effect of hyperinsulinaemia is mediatedat a tubular site distal to the proximal tubule. The data doesnot support the hypothesis that intrarenal generation of angiotensinII plays a part in this action of insulin.     

Insulin resistance is a common denominator of post-transplant diabetes mellitus and impaired glucose tolerance in renal transplant recipients

Background. Post-transplant diabetes mellitus is a known complication of steroid therapy in renal transplant recipients. Both insulin resistance and insulin deficiency have been shown to be necessary for development of post-transplant diabetes mellitus. It is not known whether recipients with impaired glucose tolerance have similar degree of insulin resistance or deficient insulin response as recipients with post-transplant diabetes mellitus. Methods. To address this question, we used an oral glucose tolerance test to categorize 46 renal transplant recipients on triple immunosuppressive medication to groups with normal glucose tolerance, impaired glucose tolerance or post-transplant diabetes mellitus. Insulin sensitivity was measured using a hyperinsulinaemic euglycaemic clamp. Insulin response was calculated from the increase in serum insulin concentration during the oral glucose tolerance test. Results. Twenty-five were categorized to normal glucose tolerance, 15 to impaired glucose tolerance and six to post-transplant diabetes mellitus. There were no statistically significant differences between the groups regarding prednisolone dose, azathiprine dose, use of {beta}-blocker, age, gender, weight, waist-hip ratio, body mass index, donor source, smoking habits, or first-degree relatives with histories of diabetes mellitus. The impaired glucose tolerance and post-transplant diabetes mellitus groups showed a significant reduction in insulin-stimulated glucose disposal rate (mg/kg^.min) compared to the normal glucose tolerance group (4.6±1.6 and 3.4±1.3 respectively vs 7.1±2.4, P<0.05). The insulin response (picomol/l) was not different between the normal glucose tolerance and impaired glucose tolerance groups but was significantly reduced in the post-transplant diabetes mellitus group (448±310 and 450±291 respectively vs 170±128, P<0.05).Conclusion. Insulin resistance is a common denominator of post-transplant diabetes mellitus and impaired glucose tolerance in renal transplant recipients.     

Effect of ipriflavone on bone mineral density and calcium-related factors in elderly females

The effects of ipriflavone (7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one) on bone mineral density (BMD) of the 3rd lumbar vertebra and on calcium (Ca)-related factors, including serum calcitonin (CT) levels before and after rapid calcium infusion (4 mg/kg for 5 minutes), were studied in 11 elderly female subjects (80 ± 2 years of age, mean ± SE). Ipriflavone (IP) administration (600 mg/day, 7 months) resulted in inhibition of BMD loss in 7 patients (responders, mean change of BMD value 2.2 ± 2.3%), whereas 4 patients showed a loss of BMD (nonresponders, mean change of BMD value -13.1 ± 2.6%) compared with pretreatment values. The responder group showed a significant increase in mean pretreatment serum CT levels (from 20 ± 2 pg/ml to 42 ± 7 pg/ml,P < 0.05) after treatment with IP, and a significant decrease in the mean basal serum level of corrected Ca (from 9.6 ± 0.2 mg/dl to 8.7 ± 0.1 mg/dl,P < 0.01) after treatment with IP; nonresponders did not show these changes. For responders, both the percentage of change and the maximal value of serum CT in response to Ca infusion were maintained at rather high levels, both before and after IP treatment; nonresponders showed almost no response to a stimulation test for CT. These findings suggest that IP inhibits bone loss in elderly female subjects possibly through the mechanism of increasing CT secretion.     

Renal effects of losartan and amlodipine in hypertensive patients with non-diabetic nephropathy

Background. The objective of this study was to examine the effects of angiotensin II receptor blocker losartan versus the calcium channel blocker amlodipine on proteinuria, renal haemodynamics, glomerular sieving and tubular function in hypertensive patients with non diabetic nephropathy. Methods. The study design was a prospective, double blind, placebo controlled, randomized crossover trial with amlodipine and losartan. Renal parameters were measured at baseline and at the end of each 4-week active treatment period. Fifteen patients with a diagnosis of non-diabetic renal disease and hypertension were included. Results. Mean arterial blood pressure decreased from 123±13 mmHg at baseline to 113±10 mmHg (P<0.01) on losartan and to 114±10 mmHg on amlodipine (P<0.01). Urinary albumin excretion significantly decreased from 3510±2586 mg/24 h at baseline to 2684±2051 mg/24 h (P<0.01) on losartan and increased non-significantly to 3748±3355 mg/24 h on amlodipine. Filtration fraction significantly decreased from a baseline value of 22.8±9.3% to 21.2±10.2% (P<0.05) on losartan and increased to 23.6±8.9 (ns) on amlodipine. Either drug did not significantly alter glomerular sieving of neutral dextrans. Conclusion. Our results demonstrate that losartan, but not amlodipine, decreased albumin excretion in hypertensive patients with non-diabetic nephropathy.     

Hypertension in stroke patients: Relationship with hyperinsulinaemia

Summary: In an attempt to determine the presence of hypertension in stroke patients and its relationship with hyperinsulinaemia, a case-control study was carried out in the outpatients clinic, Department of Neurology, Sardjito General Hospital, Yogyakarta. Patients included in the study were those who had survived a stroke at least 3 months after the first attack. the exclusion criteria included: diabetes mellitus, renal failure, heart failure, malignancy, myocardial infarction, current antihypertensive and hypolidaemic treatment. Controls were selected from non-stroke patients at the same department matching for sex and age. During the study 51 stroke patients (39 male and 12 female, aged 58.7 ± 10.3 years) and 51 controls (40 male and 11 female, aged 58.6 ± 9.8 years). There were no significant differences in baseline clinical characteristics; namely, smoking, body mass index, blood sugar and blood lipids except triglyceride (169 ± 61 vs 141 ± 60 P<0.05) of cases and controls. Although there was no significant difference of fasting plasma insulin levels (9.3 ± 8.3 vs 8.3 ± 2.6 mU/L, P= >0.05), significantly higher levels of postprandial insulin (94.8 ± 86.7 vs 55.2 ± 49.1 mU/L, P<0.05) were found in cases than controls. There were a significantly higher levels of blood pressure, both systolic (160 ± 24 vs 131 ± 11 mmHg, P<0.05) and diastolic (101 ± 13 vs 79 ± 4 mmHg, P<0.05), and more frequent hypertension defined as BP ± 140/90 mmHg (72.5 vs 2.0%, P<0.05) in cases than controls. No significant difference of plasma insulin levels (94.9 ± 82.3 vs 94.3 ± 119.2 mU/L, P>0.05) between hypertensive and normotensive stroke patients. However, significantly higher levels of insulin (94.3 ± 119.2 mU/L vs 55.2 ± 49.1 mU/L, P<0.05) were found in normotensive stroke patients than controls. the relationship between 2 h post-prandial blood sugar levels and post-prandial insulin levels was positive and nearly significant relationship (r=0.62, P=0.05). the relationship between mean arterial pressure (MAP) and post-prandial insulin levels of the whole patients (cases and controls) were poor but significant (r = 0.22, P<0.05). the relationship between MAP and post-prandial insulin levels are poor and not significant both in stroke patients (r = 0.00, P>0.05) and controls (r = 0.17, P>0.05). the slope of both curves in both scattered diagrams seemed to be slightly different. We conclude that hypertension and post prandial hyperinsulinaemia may play a role in the genesis of stroke, while hyperinsulinaemia may an independent factor.     

Regulation of renal calbindin-D28K: The role of calcitonin

Infusion of calcitonin lowers circulating calcium, but in the distal tubule of the kidney, pharmacological doses of calcitonin increase the active calcium reabsorption. Calbindin-D28k plays a significant role in the calcium reabsorption in the distal convoluted tubule of the kidney. The effect of calcitonin on renal calbindin-D28k in relation to calcium metabolic changes was therefore examined. In study 1, thyroparathyroidectomy followed by autotransplantation of the parathyroid glands (TX) was compared with a sham operation in rats. TX reduced plasma calcitonin from 54±2 to 9±1 pg/ml (P<0.001), whereas ionized calcium and parathyroid hormone were returned to the control value after an initial decrease, indicating a successful implantation of the parathyroid glands. No changes were seen in calbindin-D or plasma 1,25(OH)₂D. In study 2, subcutaneous infusion of salmon calcitonin 2.5 U/kg/hour via osmotic pumps was compared with infusion of vehicle in rats. Ionized calcium was reduced from 1.37±0.01 to 1.33±0.02 mmol/liter (P<0.05), whereas no changes were seen in renal or intestinal calbindin-D or in plasma 1,25(OH)₂D. After TX, only calcitonin decreased whereas the other calcium metabolic parameters showed no change. This indicates that in rats, selective elimination of calcitonin does not influence other parameters of the calcium metabolism and that the effect of calcitonin on calcium transport in the distal tubule is not mediated via an increase in renal calbindin-D28k.