Ac-SDKP reverses cardiac fibrosis in rats with renovascular hypertension

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) is a natural substrate for the N-terminal active site of angiotensin-converting enzyme (ACE). We previously reported that Ac-SDKP prevented cardiac fibrosis in rats with renovascular or aldosterone-salt hypertension. However, it is not clear whether Ac-SDKP reverses cardiac fibrosis in hypertension, nor the mechanism(s) involved. In the present study, we tested the hypothesis that Ac-SDKP reversal of hypertension-induced cardiac fibrosis involves a decrease in transforming growth factor-beta (TGF-beta) and/or connective tissue growth factor (CTGF). In 2-kidney, 1-clip (2K-1C) hypertensive rats, Ac-SDKP at 400 or 800 microg/kg per day SC was started 8 weeks after hypertension and cardiac fibrosis were established and was continued for 8 weeks. Left ventricular (LV) collagen in rats with 2K-1C plus vehicle at 8 and 16 weeks after clipping was similar but higher than in the sham group (P<0.05). Ac-SDKP at 400 and 800 microg/kg per day, which increased plasma Ac-SDKP 2- and 5-fold, respectively, reversed the increase in LV collagen in a dose-dependent manner. The mechanism by which Ac-SDKP reverses LV fibrosis does not appear to depend on ACE inhibition by Ac-SDKP, since we found that Ac-SDKP at various doses did not affect blood pressure responses to exogenous angiotensin I or bradykinin. However, Ac-SDKP reversed the increase in LV TGF-beta and CTGF compared with rats with 2K-1C plus vehicle (P<0.005). We concluded that in hypertension, Ac-SDKP reverses cardiac fibrosis, perhaps due in part to a decrease in TGF-beta and CTGF in the heart.     

Glucose tolerance and insulin secretion in conscious and unrestrained normotensive and spontaneously hypertensive rats

We compared the glucose tolerance and insulin responses to intravenous (IV) glucose administration of a dose of 1 g/kg body weight in a conscious and unrestrained state of spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) with catheters chronically indwelled into artery and vein. Both plasma glucose levels at two minutes and ten minutes following IV glucose load as well as the incremental and total areas of plasma glucose were slightly but significantly lower in SHR than in WKY. Glucose disappearance rate (K value) was 7.7 +/- 0.3%/min in SHR, being slightly but significantly higher than that of 6.8 +/- 0.3%/min in WKY. On the other hand, insulin responses to the glucose load at ten minutes and 30 minutes as well as incremental and total insulin areas were significantly lower in SHR than in WKY. There was no significant difference in insulinogenic index between SHR and WKY. Our observations suggest that in a conscious and unrestrained state, SHR have the greater glucose tolerance associated with reduced insulin secretion than do WKY.     

Glucose tolerance and insulin secretion in hyperthyroidism.

To evaluate the glucose tolerance and insulin secretion in hyperthyroidism patients were examined in the toxic state and after they had been made euthyroid. Fasting values: In 42 untreated patients the glucose- and insulin concentrations in serum were significantly elevated. In 24 treated patients the glucose concentrations became normal, while the insulin concentrations remained elevated. Oral-glucose-tolerance test: In 20 untreated patients the glucose- and insulin responses were significantly increased. In 8 treated patients the glucose response became normal, while the insulin response remained unchanged. Intravenous-glucose-tolerance test: In 28 untreated patients the K-values were significantly decreased and the insulin response increased. In 23 treated patients the K-values rose significantly, but the insulin response remained unchanged. Intravenous-tolbutamide test: In 41 untreated patients the glucose concentration decreased significantly compared with the controls, and the insulin responses were significantly increased. In 23 treated patients the glucose concentrations decreased even more, while the insulin response remained unchanged. The results indicate enhanced sensitivity or an increase in the mass of beta-cells in hyperthyroidism. The glucose tolerance tests point to an increased peripheral insulin resistance. The normalized glucose tolerance and still enhanced insulin secretion during treatment support the assumption, that hyperthyroidism causes an increase in the beta-cell mass.     

Glucose tolerance and insulin release in l-asparaginase treated rabbits

Male New Zealand White Rabbits were injected intravenously with either a single dose of 10,000 IU Escherichia colil-asparaginase/kg body weight containing 80 mg of d-mannitol/10,000 IU E. colil-asparaginase or 80 mg d-mannitol kg/body weight alone. Elevated fasting glucose (G) and elevated fasting immunoreactive insulin (IRI) levels were observed in the l-asparaginase treated rabbits at 1 wk. They peaked at 3 wk and declined thereafter. However, fasting G and IRI levels remained significantly elevated at the end of the study (9–15 wk after injection) compared to preinjection levels and levels of the controls. Glucose and IRI levels 0.5 hr post an intravenous glucose load (1 g/kg body weight) also became elevated post l-asparaginase and followed a time course similar to that of the fasting G and IRI levels. These 0.5-hr levels also remained significantly elevated at the end of the study. These data show that a single dose of 10,000 IU/kg body weight produces a hyperinsulinemic diabetes in New Zealand White Rabbits that appears to persist in a mild form for at least 9–15 wk.     

Glucose tolerance and insulin release in adolescent female.

The increase in insulin requirement at the onset of adolescence is compensated by an increase of insulin secretion. This metabolic pattern persists during adolescence but is no longer present in adults. It is supposed to depend on a decrease of insulin sensitivity of uncertain origin. We compared the metabolic pattern of late adolescent girls (13-16 year old) with young women (21-30 year old) with similar body mass indexes, testing subjects with iv glucose tolerance test (IVGTT) (glucose 0.33 g/kg) and arginine test (ATT) (arginine 30 g in 30 min). In late adolescent vs adult women we observed: i) IVTT: similar k of glucose tolerance and higher insulin and C-peptide responses; ii) ATT: unmodified plasma glucose, insulin and glucagon values, higher GH plasma levels; iii) in adolescent girls GH and CPR incremental areas significantly correlated (r = 0.755, p less than 0.05). These data show that: i) the adolescent pattern of glucose metabolism persists after completion of sexual development and, ii) there is a positive correlation between GH response to arginine and beta-cell response to glucose. So GH should play a role in the impairment of glucose metabolism during adolescence.     

Glucose tolerance and plasma insulin response to intravenous glucose infusion and test meal in rats with microencapsulated islet allografts

Summary Albino Oxford rats made diabetic with 75 mg/kg streptozotocin were intraperitoneally transplanted with 2500–2900 alginate-polylysine microencapsulated Lewis islets (n=9, total islet tissue volume 8.0–11.0 l), or a similar volume of non-encapsulated Lewis islets (n=5). All rats with microencapsulated islets became normoglycaemic, and remained normoglycaemic for 5–16 weeks. In rats with non-encapsulated islet grafts, only a temporary decrease in blood glucose was observed, and all were again severely hyperglycaemic at 1 week after implantation. At 5–6 weeks after transplantation, glucose tolerance in rats with microencapsulated islets was tested by intravenous glucose infusion (10 mg/min over 20 min) and test meal administration (n=4). During glucose infusion, maximum glucose levels were 13.0±0.4 mmol/l in rats with microcapsules and 8.9±0.4 mmol/l in healthy control rats (p<0.01). Concomitant maximum plasma insulin levels were 215±17 pmol/l in rats with microcapsules and 715±85 pmol/l in controls (p<0.001). After the test meal, maximum blood glucose was 10.6±0.9 mmol/l in rats with microcapsules and 6.2±0.1 mmol/l in controls (p<0.001), with concomitant maximum plasma insulin levels of 247±11 pmol/l and 586±59 pmol/l, respectively (p<0.001). In conclusion, although the glucose tolerance is impaired and plasma insulin responses to intravenous glucose-load and test-meal are reduced, the alginate-polylysine membrane does provide adequate immunoisolation for the prolongation of allograft survival, resulting in prolonged normoglycaemia in streptozotocin diabetic rats.     

Glucose tolerance and gastric emptying in thyrotoxic rats

To clarify the contribution of gastrointestinal function to impaired oral glucose tolerance in hyperthyroidism, gastric emptying rate and portal and peripheral blood glucose responses to intragastric or intraduodenal glucose administration were investigated in experimental thyrotoxic rats. Glucose absorption from perfused intestine of thyrotoxic rats was also examined. Thyrotoxicosis was induced by subcutaneous (SC) thyroxine injection (50 micrograms/kg/d) for seven days. In intragastric glucose tolerance test, although insulin and glucagon responses were not significantly altered, increments in portal and peripheral blood glucose were significantly higher in thyrotoxic rats than in controls at 30 minutes. This phenomenon was almost normalized by the preadministration of phentolamine (2 mg/kg SC). In intraduodenal glucose tolerance test, blood glucose, insulin, and glucagon responses were similar in thyrotoxic and control rats. Gastric emptying rate in thyrotoxic rats was significantly higher than that in controls at 30 minutes, and that was also normalized by phentolamine administration. Absorption of glucose from perfused intestine was similar in thyrotoxic and control rats. These results suggest that an altered glucose tolerance to intragastric glucose load in thyrotoxic rats may primarily be due to rapid gastric emptying induced by increased alpha-adrenoceptor responses, and that glucose absorption from small intestine was not increased in short-term thyrotoxic rats.     

Glucose tolerance, plasma insulin levels and insulin sensitivity in elderly patients.

The oral glucose tolerance test (OGTT) and the intravenous glucose tolerance test (ivGTT) were carried out in 23 elderly patients (mean age 79 years) and in 14 healthy young adults (mean age 28 years). The ivGTT was followed immediately by a second injection of glucose, this time with insulin added. The percentage rate constants for the disappearance of glucose alone (KG, % min-1) or with added insulin (KG+I, % min-1) were calculated. Seventeen of the elderly patients had a blood glucose value at 120 min in the OGTT greater than or equal to 7.7 mmol/1 (140 mg/100 ml) or had KG less than or equal to 1% min-1 and 13 were 'diabetic' by both criteria. This was associated with a sluggish pattern of insulin release and with diminished insulin sensitivity (KG+I). Since these changes could reflect impaired inhibition of hepatic glucose output, a preliminary attempt was made to assess gluconeogenic capacity. After the injection of substrate levels of L-alanine, plasma levels of glucose and alanine both rose but fell more slowly in the elderly than in young adults, suggesting impaired transmembrane transport of both substances in old people. After injection of alanine, plasma insulin rose to a lesser extent and glucagon to a greater extent in the elderly than in young adults.     

Inhibition of left ventricular fibrosis by tranilast in rats with renovascular hypertension

BACKGROUND: Growth factors such as transforming growth factor-beta (TGF beta) are believed to have an essential role in cardiac fibrosis. Tranilast (N(3,4-dimethoxycinnamoyl) anthranilic acid) attenuates the increased expression of TGF beta mRNA in vitro. OBJECTIVE: To investigate whether tranilast reduces cardiac fibrosis in rats with two-kidney, one-clip (2K1C) renovascular hypertension. In addition, we tested the in-vitro effects of tranilast on cardiac myocytes and non-myocyte cells. METHODS: We analysed hearts from four groups of rats: sham-operated controls; rats with 2K1C renovascular hypertension; rats with 2K1C renovascular hypertension treated for 12 weeks with the angiotensin converting enzyme (ACE) inhibitor, quinapril (6 mg/kg per day); rats with 2K1C renovascular hypertension treated for 12 weeks with tranilast (400 mg/kg per day). RESULTS : Systolic blood pressure was reduced after quinapril treatment. Tranilast did not alter blood pressure (2K1C: 223 +/- 19 mmHg; 2K1C + quinapril: 149 +/- 15 mmHg (P < 0.01 compared with 2K1C); 2K1C + tranilast: 204 +/- 32 mmHg). Left ventricular weight was likewise reduced significantly by quinapril, but not significantly by tranilast (2K1C: 1.52 +/- 0.2 g; 2K1C + quinapril: 1.26 +/- 0.18 g (P < 0.05 compared with 2K1C); 2K1C + tranilast: 1.37 +/- 0.27 g). Using a computer-aided image analysis system, we demonstrated that tranilast prevented cardiac fibrosis in a blood-pressure-independent manner (P < 0.01 compared with 2K1C). Determination of the cardiac hydroxyproline content similarly revealed a significant reduction in cardiac fibrosis by tranilast (2K1C: 4.92 +/- 0.48 mg/mg; 2K1C + tranilast: 3.97 +/- 0.46 mg/mg; P < 0.05). The effect of tranilast on cardiac fibrosis was comparable to the effects of a blood-pressure-decreasing dose of the ACE inhibitor, quinapril. Cell culture experiments revealed that tranilast significantly decreased the proliferation of cardiac non-myocyte cells. Proliferation of cardiac myocytes was not altered. CONCLUSION: This study revealed that long-term treatment with tranilast markedly attenuated left ventricular fibrosis in rats with renovascular hypertension. This was most probably the result of an antiproliferative effect of tranilast on cardiac non-myocyte cells. Tranilast thus offers a unique new therapeutic approach to the reduction of TGF beta-mediated cardiac fibrosis in vivo.     

Glucose tolerance during moderate alcohol intake: insights on insulin action from glucose/lactate dynamics

Moderate alcohol (ETOH) intake has been associated with a significant reduction in risk for infarction among general populations. In this study, we assessed the effects of low-dose ETOH (40 g over 3-h period as vodka) on the interaction between glucose (G), insulin, and lactate (L) during the insulin-modified frequently sampled i.v. glucose tolerance test (FSIGT) (0.3 U/kg body weight between 20-25 min) in eight normal volunteers. In the control (C) study, water was administered. An insulin-independent two-compartment model was used to describe G and L kinetics. Insulin sensitivity (S(I)) was significantly higher in the ETOH study than in the C study (2.49 +/- 0.52 vs. 0.92 +/- 0.20 10(-4) min(-1)microU(-1)ml, C vs. ETOH; P = 0.0391). No significant differences were observed in G effectiveness (0.029 +/- 0.004 vs. 0.033 +/- 0.004 min(-1)). Blood L levels were higher during FSIGT when ETOH was administered [area under the curve (AUC), 201 plus minus 16 vs. 123 +/- 23 mmol/liter in 240 min; P = 0.0001]. The dynamic analysis of blood L concentrations showed that ETOH also significantly decreased L clearance (0.0016 +/- 0.0011 vs. 0.0029 +/- 0.0002 min(-1); P = 0.0156), whereas no difference was observed for the fractional conversion of the rate of G disappearance to L (0.0033 +/- 0.0012 vs. 0.0031 +/- 0.0005 min(-1)). ETOH decreased baseline plasma FFA concentration; AUC of FFA was markedly reduced with ETOH (65 +/- 14 vs. 109 plus minus 17 mmol/liter in 240 min; P = 0.0063) and inversely correlated with S(I) (r = 0.693; P = 0.0029). The amount of C-peptide in 240 min as well as the amounts before and after insulin administration were not different between the two tests. We concluded that G and L kinetics derived from FSIGT shows that moderate ETOH intake: 1) improves insulin action; 2) decreases L clearance; and 3) does not affect beta cell function. Because ETOH at moderate doses has a marked antilipolytic action, it might improve insulin action by improving substrate competition. The present findings suggest that moderate alcohol consumption in the diet should not be discouraged.     

Estrogen receptor agonists alleviate cardiac and renal oxidative injury in rats with renovascular hypertension

Although endogenous estrogen is known to offer cardiac and vascular protection, the involvement of estrogen receptors in mediating the protective effect of estrogen on hypertension-induced cardiovascular and renal injury is not fully explained. We aimed to investigate the effects of estrogen receptor (ER) agonists on oxidative injury, cardiovascular and renal functions of rats with renovascular hypertension (RVH). Female Sprague-Dawley rats were randomly divided as control and RVH groups, and RVH groups had either ovariectomy (OVX) or sham-OVX. Sham-OVX-RVH and OVX-RVH groups received either ERβ agonist diarylpropiolnitrile (1 mg/kg/day) or ERα agonist propyl pyrazole triol (1 mg/kg/day) for 6 weeks starting at the third week following the surgery. At the end of the 9^th week, systolic blood pressures were recorded, cardiac functions were determined, and the contraction/relaxation responses of aortic rings were obtained. Serum creatinine levels, tissue malondialdehyde, glutathione, superoxide dismutase, catalase levels, and myeloperoxidase activity in heart and kidney samples were analyzed, and Na⁺, K⁺-ATPase activity was measured in kidney samples. In both sham-OVX and OVX rats, both agonists reduced blood pressure and reversed the impaired contractile performance of the heart, while ERβ agonist improved renal functions in both the OVX and non-OVX rats. Both agonists reduced neutrophil infiltration, lipid peroxidation, and elevated antioxidant levels in the heart, but a more ERβ-mediated protective effect was observed in the kidney. Our data suggest that activation of ERβ might play a role in preserving the function of the stenotic kidney and delaying the progression of renal injury, while both receptors mediate similar cardioprotective effects.     

Glucose, insulin, and lipid metabolism in doxazosin-treated patients with hypertension.

The metabolic changes associated with doxazosin treatment of hypertension were evaluated in ten patients with mild hypertension (mean +/- SEM = 150 +/- 3/100 +/- 1 mm Hg) and a plasma triglyceride (TG) concentration > 1.50 mmol/L. The blood pressure was lower after 4 to 6 months of doxazosin treatment (mean +/- SEM = 134 +/- 4/87 +/- 1 mm Hg), which was also associated with a significantly lower plasma insulin response to a 75 g oral glucose load, and lower plasma TG and cholesterol concentrations. In addition, insulin-mediated glucose uptake was significantly greater after doxazosin treatment. These data suggest that doxazosin treatment of patients with mild hypertension is associated with changes in insulin and lipid metabolism that should decrease the risk of coronary heart disease.     

Relationship between glucose tolerance,insulin secretion,and insulin action in non-obese individuals with varying degrees of glucose tolerance

Summary Plasma glucose and insulin concentration following a 75 g oral glucose challenge and glucose uptake during a hyperinsulinaemic glucose clamp study were determined in 50 non-obese individuals. The study population was divided into five groups on the basis of their glucose tolerance: normal, impaired glucose tolerance, Type 2 (non-insulin-dependent) diabetes mellitus with fasting plasma glucose of less than 8 mmol/l, between 8–15 mmol/l, and more than 15 mmol/l. The plasma insulin response was significantly greater (p<0.001) than normal in those with either impaired glucose tolerance or Type 2 diabetes and a fasting plasma glucose concentration less than 8 mmol/l. In contrast, the plasma insulin response was similar to normal in the other two groups of patients with Type 2 diabetes, i.e. fasting plasma glucose concentration 8–15 mmol/l or greater than 15 mmol/l. Glucose uptake rates were significantly lower (p<0.001) than normal in subjects with impaired glucose tolerance and all three groups of patients with Type 2 diabetes. Although glucose uptake rates during the glucose clamp studies were relatively similar in all four groups of glucose intolerant subjects, the values were significantly lower in those patients with Type 2 diabetes who had a fasting plasma glucose concentration greater than 8 mmol/l (p<0.01), These data indicate that a significant degree of insulin resistance exists in patients with impaired glucose tolerance or Type 2 diabetes, relatively independent of fasting plasma glucose concentration. Indeed, glucose uptake during glucose clamp studies fell 8-fold over a range in fasting plasma glucose concentration of from 4.5 to 6.5 mmol/l. In contrast, the plasma insulin response increased over the same range of fasting plasma glucose concentrations. The fact that this defect in insulin action can be seen in patients who are hyperinsulinaemic, not hypoinsulinaemic, and only modestly hyperglycaemic, is consistent with the hypothesis that resistance to insulin-stimulate glucose uptake is a basic characteristic of patients with impaired glucose tolerance or Type 2 diabetes.     

Myocardial imaging with 123I-metaiodobenzylguanidine in essential hypertension and renovascular hypertension

Iodine-123 metaiodobenzylguanidine (MIBG) myocardial imaging is considered to reflect cardiac sympathetic function. We performed myocardial MIBG scintigraphy and echocardiography in 27 patients with essential hypertension (EHT), 7 patients with renovascular hypertension (RVHT), and 8 normotensive subjects (NT) to investigate alterations in MIBG myocardial imaging in the presence of hypertension and left ventricular hypertrophy (LVH). EHT were divided into two groups based on LV wall thickness; EHT with LVH group (> or = 13 mm, n = 15) and EHT without LVH group (< 13 mm, n = 12). The delayed uptake of MIBG was decreased, and the washout rate of MIBG was greater in the EHT with LVH group than EHT without LVH group or NT group. The washout rate was correlated with LV mass and LV diastolic function (as assessed by mitral flow). In RVHT group, the MIBG washout rate increased even without LVH, compared with NT and EHT without LVH groups. In summary, the washout rate of MIBG increased in parallel with the development of LVH in EHT and increased independently of the LV mass in RVHT. Cardiac sympathetic function could be altered in hypertensive LVH and in renovascular hypertension.