Prostaglandins and diabetic nephropathy

Abnormalities of renal prostaglandins (PGs) contribute to the pathogenesis of diabetic nephropathy through changes in renal hemodynamics. Our recent studies have demonstrated that urinary excretion ratio of 6-keto-PGF₁ (6KF) to TXB₂ is decreased in patients with non-insulin-dependent diabetes mellitus (NIDDM). In the present study, we evaluated the clinical effects of some drugs on renal PG metabolism and diabetic nephropathy. Ozagrel, a specific thromboxane synthetase inhibitor, reduced urinary TXB₂ excretion, resulting in the improvement of the decreased urinary 6KF/TXB₂ ratio in NIDDM patients. Urinary albumin excretion was decreased and creatinine clearance (Ccr) was increased during ozagrel administration. The similar beneficial effect was also found in the administration of cilostazol, a phosphodiesterase inhibitor, whereas a stable analogue of PGI₂, beraprost sodium, reduced urinary albumin excretion in relation to the reduction of platelet aggregation rate. In conclusion, the drugs modulating renal and platelet PG_S metabolism with direction to an increase in 6KF/TXB₂ ratio and an inhibition against platelet function might be beneficial for the treatment of diabetic nephropathy.     

Postprandial cholesteryl ester transfer and high density lipoprotein composition in normotriglyceridemic non-insulin-dependent diabetic patients

Altered postprandial HDL metabolism is a possible cause of defective reverse cholesterol transport and increased cardiovascular risk in diabetic patients with a normal fasting lipoprotein profile. Ten normolipidemic, normoponderal non-insulin dependent diabetes mellitus (NIDDM) patients and seven controls received a 980 kcal meal containing 78 g lipids with 100000 IU vitamin A. Chylomicron clearance was not different, but area under the curve (AUC) for retinyl palmitate in chylimicron-free serum (remnant clearance) was greater in patients (P < 0.02). LCAT activity increased postprandially to the same extent in both groups. In control subjects, cholesteryl ester transfer protein (CETP) activity (CETA) also increased by 20% (P < 0.01 at 6 h) in parallel with a 20% decrease in HDL₂-CE (r= −0.55, P = 0.009). In NIDDM patients, on the contrary, CETA which was 35% higher in the fasting state (P < 0.005), decreased postprandially yet HDL₂-CE remained unchanged. Postprandial HDL₃ of controls were enriched with phospholipid (PL) (30.3 ± 2.6% at 6 h) with respect to fasting (25.6 ± 2.5%, P < 0.01) and to NIDDM-HDL₃ (25.8 ± 1.7% at 6 h, P < 0.01). These results show that variation in plasma CETA has little impact on HDL₂-CE in NIDDH subjects. They support the concept that, in controls, the combined enrichment of HDL₃ with PL, increased LCAT and CETA create the conditions for stimulation of cell cholesterol efflux and CE transfer to apo B lipoproteins. In NIDDM, because of the lesser HDL₃ enrichment with PL and of the inverse trend of CETA, these conditions fail to occur, depriving the patients of a potentially efficient mechanism of unesterified cholesterol (UC) clearance, despite their strictly normal preprandial profile.     

Reactive oxygen species in essential hypertension and non–insulin-dependent diabetes mellitus

To evaluate whether increased levels of reactive oxygen species (ROS) are involved in the pathogenesis of essential hypertension (EH) and non–insulin-dependent diabetes mellitus (NIDDM), both resting and stimulated levels of intracellular ROS were measured in lymphocytes from patients with EH (n = 10), NIDDM (n = 16) and age-matched healthy individuals (control subjects, n = 19). ROS was monitored with the dye, dihydrorhodamine-123 (DHR; 1 μmol/L) in the presence or absence of superoxide dismutase (superoxide scavenger), sodium azide (singlet oxygen/hydrogen peroxide scavenger), genistein (tyrosine kinase inhibitor), or bisindolylmaleimide (protein kinase C inhibitor). Simultaneous monitoring of cytosolic [Ca²⁺]_i was done with fura-2. Resting ROS levels were significantly higher in NIDDM (4.71 ± 0.25 nmol/10⁶ cells; mean ± SEM, P < .05) compared with EH (4.03 ± 0.22 nmol/10⁶ cells) or controls (4.05 ± 0.15 nmol/10⁶ cells). The formyl-Met-Leu-Phenylalanine-(fMLP)–induced ROS generation was significantly higher in NIDDM (21.92 ± 2.23 nmol/10⁶ cells; P < .05) compared with EH (14.58 ± 1.90 nmol/10⁶ cells) or control (16.06 ± 1.22 nmol/10⁶ cells). The fMLP-induced ROS increase was significantly reduced in the presence of sodium azide in all groups (P < .01) but was largely unaffected in the presence of SOD. Genistein and bisindolylmaleimide significantly inhibited the fMLP-induced ROS in all groups. The fMLP-induced [Ca²⁺]_i increase was significantly higher in NIDDM (71 ± 12 nmol/L, P < .01) compared with EH (42 ± 4 nmol/L) and control subjects (35 ± 3 nmol/L). Phytohemagglutinin was more effective in increasing [Ca²⁺]_i than ROS. It is concluded that ROS may play a role in the metabolic syndrome of NIDDM but not in EH.     

Abnormal pH-sensing of platelet Na+/H+ exchanger in patients with cardiac syndrome X

An enhanced activity of Na⁺/Li⁺ countertransport, studied as a surrogate of Na⁺/H⁺ exchanger, has been described in red blood cells of patients with cardiac syndrome X. In this study we investigated whether abnormalities in the activity of platelet Na⁺/H⁺ exchanger (NHE) also existed in syndrome X patients and whether such abnormality was associated with platelet activation. Platelet NHE activity was evaluated in 21 syndrome X patients and 18 controls by measuring the pH recovery in platelets after acid loading and/or thrombin stimulation. The linear correlation existing between the initial intracytoplasmic pH (pH_i) values and the maximal velocity of pH recovery allowed to calculate the values of slope and intercept at pH_i=6.6 (I_pH6.6) for each individual. Urinary excretion of the major TXB₂ metabolite, 11-dehydro-TXB₂ was measured in 15 syndrome X patients and 15 controls. The acidification-induced NHE activity resulted significantly higher in syndrome X patients compared to controls. Indeed, slope values were 0.75±0.29 and 0.5±0.23 min⁻¹ in patients and controls, respectively (P=0.01), while I_pH6.6 values were 0.24±0.1 and 0.17±0.1 ΔpH/min (P=0.04). The thrombin-stimulated NHE activity, however, was not different in the two groups and no significant difference in the urinary excretion of 11-dehydro-TXB₂ between patients and controls (median 920 vs. 765 pg/mg creatinine, respectively) (P=0.32) was also found. Thus our data demonstrate an alkaline shift in pH-dependence of platelet NHE of syndrome X patients. This abnormality does not seem to be associated with increased platelet activation.     

Effects of digitalis on ventricular myocardial and His-Purkinje refractoriness and reentry in man

The effects of digitalis on retrograde conduction and refractoriness of the His-Purkinje system, ventricular myocardium and reentry within the His-Purkinje system were studied in 17 patients using the ventricular extrastimulus (V₂) technique. Studies were performed, before and 30 minutes after intravenous administration of ouabain, 0.01 mg/kg. After treatment with ouabain, there was a significant decrease in the functional refractory period (266 ± 19 to 254 ± 18 msec, P < 0.001), relative refractory period (253 ± 17 to 240 ± 16 msec, P < 0.001) and effective refractory period (242 ± 23 to 231 ± 24 msec, P < 0.005) of the ventricular muscle. In contrast, there was no significant change in retrograde His-Purkinje conduction and refractoriness. The phenomenon of reentry within the His-Purkinje system characterized by the reentrant beat (V₃) at critical retrograde conduction delays in the His-Purkinje system (V₂-H₂) within a narrow range of V₁–V₂ intervals was seen in 10 of 17 patients. Ouabain increased and shifted to the left the zone of reentry within the His-Purkinje system in 7 of 10 patients (36 ± 23 to 55 ± 23 msec, P < 0.001) and decreased it by 10 to 30 msec in the remaining 3 patients. The critical V₂-H₂ (186 ± 29 to 193 ± 27 msec, difference not significant [NS]) and V₁–V₂ (299 ± 30 to 294 ± 36 msec, NS) intervals for reentry did not significantly change after ouabain. However, the minimal V₁–V₂ intervals (266 ± 26 to 253 ± 25 msec, P < 0.025) decreased significantly, whereas the maximal V₂-H₂ intervals (266 ± 40 to 239 ± 37 msec, P < 0.01) increased significantly.

Thus, in the intact human heart, digitalis (1) significantly decreased all measures of ventricular myocardial refractoriness, (2) had no significant effect on retrograde conduction and refractoriness of the His-Purkinje system, and (3) widened the zone of reentry within the His-Purkinje system due to shortening of the functional refractory period of the ventricular muscle with attainment of longer V₂-H₂ delays.     

Glucose and insulin responses to intravenous glucose challenge in relatives of Nigerian patients with non-insulin-dependent diabetes mellitus

We analysed blood insulin and glucose concentrations before and during frequently sampled intravenous glucose tolerance tests (FSIGT) in 2 groups of Nigerian subjects: (A) Control group (n = 18), without a positive family history of diabetes mellitus, and (B) Experimental group (n = 16), comprising age-, sex- and body mass-matched first-degree relatives of patients with non-insulin-dependent diabetes mellitus (NIDDM). In comparison with Group A subjects, those in Group B had: (i) higher fasting plasma glucose level (mean ± S.E.M., 4.1 ± 0.1 vs. 3.8 ± 0.11 mmol/l, P < 0.05); (ii) similar fasting serum insulin levels (6.7 ± 5.0 vs. 5.8 ± 5.6 mU/l, P = NS); (iii) lower mean incremental area under the first-phase (t = 0–10 min) post-glucose challenge insulin curve (376.9 ± 8.8 vs. 435.6 ± 5.6 mU/min l⁻¹, P < 0.05); (iv) increased incremental area under the second-phase (t = 10–182 min) post-glucose challenge insulin curve (432.9 ± 11.5 vs. 161.3 ± 8.7 mU/min l⁻¹, P < 0.05); (v) reduced K_G rate constant of glucose elimination (0.97 ± 0.12 vs. 1.41 ± 0.12%/min, P < 0.05). These results suggest that the subjects with a positive family history of NIDDM have a reduced beta-cell insulin secretory reserve (from reduced first-phase insulin response), tendency to rebound hyperinsulinemia during the latter phase of the insulin secretory response, a degree of tissue insulin insensitivity (as evident from high fasting plasma glucose despite similar insulin levels) and a diminished glucose disposal rate, in comparison with subjects without a family history of NIDDM. These features predict subsequent development of diabetes and suggest that as in Caucasians, first-degree relatives of Nigerian patients with NIDDM are at greater risk for future development of the disease.     

Improved right ventricular systolic time intravals after digitalis in patients with cor pulmonale and chronic obstructive pulmonary disease

Although digitalis has been used to treat patients with cor pulmonale secondary to chronic obstructive pulmonary disease, its effect on right ventricular performance has not been conclusively determined. This study assessed the effects of acute digitalization on measurement of right ventricular systolic time intervals in patients with chronic obstructive pulmonary disease and cor pulmonale. The intervals were recorded before and 40 minutes after administration of ouabain, 1 mg intravenously, in nine men (mean age 58 ± 5 [standard deviation] years) with chronic obstructive pulmonary disease (mean maximal mid expiratory flow rate 0.29 ± 0.08 1 liters/sec) and electrocardiographic evidence of right ventricular hypertrophy.

Ouabain produced significant reductions in right ventricular systolic time intervals, including the right ventricular preelection period (from 117 ± 23 to 102 ± 16 msec; P < 0.01), right ventricular ejection time index (from 397 ± 33 to 375 ± 24 msec; P < 0.01) and mean Q-P₂ index (from 509 ± 23 to 474 ± 8 msec; P < 0.001). In eight patients with simultaneously measured left ventricular systolic time intervals, similar changes were observed, including shortening of the left ventricular preejection period index (from 135 ± 9 to 117 ± 11 msec; P < 0.01), ejection time index (from 395 ± 18 to 379 ± 20 msec; P < 0.01), and the mean Q-A₂ interval (from 530 ± 16 to 495 ± 16 msec; P < 0.001). There were no significant changes in aortic or pulmonary arterial pressures. The results demonstrate that acute administration of digitalis produces significant improvement in right ventricular performance in patients with chronic obstructive pulmonary disease and cor pulmonale. The simultaneous shortening of right and left ventricular systolic time intervals is of comparable magnitude.     

Thromboxane A2 Production in Allergen-Induced Immediate and Late Asthmatic Responses: Its Possible Role in Inducing the Late Response

To determine whether thromboxane A₂ (TXA₂) participates in allergen-induced asthmatic responses, we measured plasma TXB₂ levels during allergen-induced immediate and late asthmatic responses (IAR and LAR) in atopic asthmatics. We also examined the effect of a TXA₂ synthetase inhibitor, OKY-046, on the responses.

Plasma TXB₂ levels increased in both IAR and LAR, being 2.2 times higher in LAR than in IAR. Plasma TXB₂ levels in LAR reached the peak 4 hours after allergen challenge when FEV₁ had just begun to decrease in LAR. OKY-046 inhibited both IAR and LAR with decreased plasma TXB₂ levels.

We conclude that TXA₂ is produced in allergen-induced asthmatic responses and participates in the responses, especially in inducing LAR.     

Adrenoceptor antagonists, but not guanethidine, reduce glucopenia-induced glucagon secretion from perfused rat pancreas

This study was designed to investigate (1) whether norepinephrine is released in response to glucopenia in vitro, thereby stimulating glucagon secretion and, (2) the modulating effects of norepinephrine on insulin and glucagon secretion, using isolated perfused rat pancreas preparations. Simultaneous addition of the adrenergic receptor antagonists yohimbine, prazosin and propranolol, each at a concentration of 10⁻⁵ mol/l, significantly potentiated glucose-stimulated insulin secretion (6.23 ± 0.76 vs. 2.11 ± 0.72 (control) nmol/min, P < 0.01), and suppressed glucopenia-induced glucagon secretion (0.59 ± 0.10 vs. 1.34 ± 0.18 (control) ng/min, P < 0.05). Also, 10⁻⁵ mol/l yohimbine alone significantly potentiated glucose-stimulated insulin secretion (4.86 ± 0.50 nmol/min, P < 0.05). The norepinephrine release inhibitor, guanethidine, significantly inhibited tyramine-induced secretion of both norepinephrine (7.86 ± 0.77 vs. 49.7 ± 2.3 nmol/min, P < 0.01) and glucagon (0.31 ± 0.08 vs. 1.21 ± 0.15 ng/min, P < 0.01), but exerted no effects on glucopenia-induced secretion of either norepinephrine or glucagon. We conclude that these results further support the concept that the neurotransmitter norepinephrine is released in response to glucopenia in vitro, and modulates insulin and glucagon secretion. Our data do not, however, provide evidence indicating that glucopenia-induced glucagon secretion is mainly mediated by activation of sympathetic nerve terminals around the -cells in the isolated perfused rat pancreas.     

Pulse waveform analysis of arterial compliance: relation to other techniques, age, and metabolic variables

T o assess the physiologic and clinical relevance of newer noninvasive measures of vascular compliance, computerized arterial pulse waveform analysis (CAPWA) of the radial pulse was used to calculate two components of compliance, C1 (capacitive) and C2 (oscillatory or reflective), in 87 normotensive (NlBP, n = 20), untreated hypertensive (HiBP, n = 21), and treated hypertensive (HiBP-Rx, n = 46) subjects. These values were compared with two other indices of compliance, the ratio of stroke volume to pulse pressure (SV/PP) and magnetic resonance imaging (MRI)–based aortic distensibility; and were also correlated with demographic and biochemical values.

The HiBP subjects displayed lower C1 (1.34 ± 0.09 v 1.70 ± 0.11 mL/mm Hg, significance [sig] = .05) and C2 (0.031 ± 0.003 v 0.073 ± 0.02 mL/mm Hg, sig = .005) than NlBP subjects. This was not true for C1 (1.64 ± 0.08 mL/mm Hg) and C2 (0.052 ± 0.005 mL/mm Hg) values in HiBP-Rx subjects. The C1 (r = 0.917, P < .0001) and C2 (r = 0.677, P < .0001) were both closely related to SV/PP, whereas C1 (r = 0.748, P = .002), but not C2, was significantly related to MRI-determined aortic distensibility.

Among other factors measured, age exerted a strong negative influence on both C1 (r = −0.696, P < .0001) and C2 (r = −0.611, P < .0001) compliance components. Positive correlations were observed between C1 (r = 0.863, P = .006), aortic distensibility (r = 0.597, P = .19) and 24-h urinary sodium excretion, and between C1- and MR spectroscopy-determined in situ skeletal muscle intracellular free magnesium (r = 0.827, P = .006), whereas C2 was inversely related to MRI-determined abdominal visceral fat area (r = −0.512, P = .042) and fasting blood glucose (r = −0.846, P = .001).

Altogether, the close correspondence between CAPWA, other compliance techniques, and known cardiovascular risk factors suggests the clinical relevance of CAPWA in the assessment of altered vascular function in hypertension.     

Abnormal diurnal changes in in-vivo platelet activation in patients with atherosclerotic diseases

We measured the urinary excretion of beta-thromboglobulin in timed urine samples collected by 2 groups of healthy volunteers, (group I, N = 20, mean age 34 years, group II, N = 15, mean age 64 years) and by patients (n = 40) with symptomatic atherosclerotic diseases. Older healthy subjects were found to excrete high amounts of BTG in comparison to young subjects (302.25 ± 50.61 vs 219.65 ± 59.31 ng/day, P < 0.05). Higher (P < 0.01) levels of urinary BTG were observed in patients with coronary (427.61 ± 179.96 ng/day), cerebral (422.13 ± 223.2 ng/day) and peripheral (454.16 ± 269.05 ng/day) arterial diseases and in diabetic patients with diffuse vascular complications (613.71 ± 253.07 ng/day). The diurnal variability of BTG excretion, measured as coefficient of variation (C.V. %) of the mean daily excretion rate, was higher (P < 0.001) in atherosclerotic patients (70.59 ± 26.57) as compared with the similar values observed in the control groups of young (32.05 ± 14.54) and older subjects (26.38 ± 8.4). Comparable diurnal variabilities of the creatinine excretion rate were observed in the control groups and in patients. These data indicated that in vivo platelet activation may occur in atherosclerotic patients with a distinctive high fluctuation rate.     

Regression of left ventricular hypertrophy by AT1 receptor blockade in renal transplant recipients

AT₁ receptor antagonists control blood pressure (BP) effectively and reduce left ventricular hypertrophy in patients with essential hypertension. Because left ventricular hypertrophy is very common in renal transplant recipients, we examined the cardiovascular effects and the safety profile of the AT₁ receptor antagonist losartan in hypertensive renal transplant recipients. In 20 renal transplant recipients with stable renal graft function 50 mg of losartan was added to the preexisting antihypertensive treatment (no angiotensin-converting enzyme inhibitors) at least 6 months after renal transplantation. Twenty-four–hour ambulatory BP, two-dimensional-guided M-mode echocardiography, and duplex sonography, as well as renal function, red blood cell count, cyclosporine A and FK 506 levels, erythropoetin, and angiotensin II concentration were determined at baseline and after 6 months of therapy. With 24-h ambulatory BP measurement, systolic blood pressure (SBP) was reduced by 7.5 ± 2.4 mm Hg and diastolic blood pressure (DBP) by 4.5 ± 1.8 mm Hg (P < .01 and P < .05, respectively). Posterior, septal, and relative wall thickness decreased by 0.95 ± 0.2 mm, 0.91 ± 0.2 mm and 0.04 ± 0.01 mm, respectively (all P < .001). Left ventricular mass index decreased by 18.1 ± 4.7 g/m² (P < .01). Ejection fraction and midwall fractional fiber shortening as systolic parameters and the relation of passive-to-active diastolic filling of the left ventricle were unaltered. Serum creatinine and cyclosporine A concentration remained stable in all patients. Hemoglobin and hematocrit decreased by 1.0 ± 0.3 g/dL and 3.6% ± 0.9%, respectively (P < .002 and P < .001) without a change in serum erythropoetin level. In renal transplant recipients the AT₁ receptor antagonist losartan reduces left ventricular hypertrophy without altering systolic or diastolic function. It is safe with regard to renal function and immunosuppression, but slightly decreases hemoglobin level.     

The effect of PGI2 analogue on vascular endothelial function and platelet aggregation in patients with NIDDM

The effect of the short-term administration of beraprost sodium, an analogue of prostaglandin I₂ (PGI₂), on the function of vascular endothelial cells and platelet in non-insulin-dependent diabetes mellitus (NIDDM) patients was investigated. Seven nonobese NIDDM patients with microalbuminuria were recruited for this study. They received a dose of 20 μg of beraprost sodium three times daily for 1 month. Before and after this treatment, various factors concerning functions of vascular endothelial cells and platelet were measured. Treatment with PGI₂ analogue caused a decrease in basal levels of plasma lipoprotein (a) from 16.8 ± 5.3 to 13.2 ± 4.4 mg/dL (p < 0.05), immunoreactive-(i-)endothelin from 2.4 ± 0.3 to 1.6 ± 0.2 pg/mL, and i-thrombomudulin from 9.3 ± 3.7 to 7.9 ± 3.0 FU/L, respectively, and caused a significant increase in basal plasma i-tissue type plasminogen activator (tPA) from 5.3 ± 0.7 to 8.3 ± 1.5 ng/mL (p < 0.01). This treatment also increased maximum response of i-tPA induced by desmopressin infusion. Platelet aggregation due to ADP was inhibited in five of six patients after this treatment. In conclusion, treatment with PGI₂ analogue caused a decrease in the presumed promoting factors of angiopathy such as lipoprotein (a) and endothelin and an increase in the protecting endothelial factor of angiopathy, tissue type plasminogen activator in patients with NIDDM. And immunoreactive thrombomodulin levels which reflect the vascular endothelial cell injury tended to decrease with the treatment. Therefore, it is suggested that this treatment preserves the vascular endothelial function in diabetes.     

Dynamic change in collateral flow associated with myocardial ischemia in humans

Background: This study sought to investigate how collateral flow changes during myocardial ischemia in patients. Methods: Myocardial contrast echocardiography (MCE) and rapid atrial pacing were performed in 20 patients with angiographically evidenced coronary collaterals from the right coronary artery (RCA) to the occluded left anterior descending coronary artery. Sonicated contrast medium was injected into the RCA before and immediately after atrial pacing to determine the peak background-subtracted contrast intensity (PI) in the collateral territory (PIA) and its ratio to PI in the control territory (PI ratio) as parameters of collateral blood flow. Lactate production in the coronary circulation during pacing was determined to assess myocardial ischemia in the collateral territory. Results: PIA showed a significant correlation with regional wall motion either before (r(squared)=−0.64, P<0.01) or after pacing (r(squared)=−0.65, P<0.01). Similarly, PI ratio was significantly correlated with regional wall motion either before (r(squared)=−0.54, P<0.05) or after pacing (r(squared)=−0.64, P<0.01). Rapid atrial pacing decreased both PIA and PI ratio significantly greater in patients with lactate production than in those without (PIA: −67±53 vs. −15±34%, P<0.05; PI ratio: −68±49 vs. −8.2±32%, P<0.05, respectively), while neither PIA nor PI ratio differ between the two groups of patients before pacing (PIA: 13.8±19. vs. 16.2±13.3U, P=0.75; PI ratio: 0.70±0.71 vs. 0.87±0.65, P=0.58, respectively). Conclusions: We concluded that (1) collateral flow determined by MCE was closely associated with regional cardiac function, and (2) not the amount of collateral flow at rest, but pacing-induced change of collateral flow seemed to be a determinant of regional ischemia in patients with coronary collaterals.     

Role of thromboxane A2 in the hypotensive effect of captopril in essential hypertension

We have previously reported that captopril stimulates thromboxane A2 synthesis in patients with essential hypertension. In the present study, the hypotensive effects of captopril and OKY-046, a selective inhibitor of thromboxane A2 synthetase, were studied in nine patients with essential hypertension to determine whether thromboxane A2 is involved in the regulation of blood pressure. A single oral dose of OKY-046 (400 mg) decreased urinary thromboxane B2 (a stable metabolite of thromboxane A2) excretion significantly (from 113 +/- 19.0 to 51.0 +/- 6.1 pg/min; p less than 0.01) and increased urinary sodium excretion significantly (from 73.0 +/- 15.3 to 113.0 +/- 14.4 microEq/min; p less than 0.01), but no change was observed in mean arterial pressure. The administration of OKY-046 (600 mg/day) for 3 days induced a significant and sustained decrease in urinary thromboxane B2 excretion, but it did not affect the mean arterial pressure. Although captopril (50 mg) alone induced a significant increase in urinary thromboxane B2 excretion (from 91.4 +/- 11.0 to 297.3 +/- 30.8 pg/min; p less than 0.001) and a significant decrease in mean arterial pressure (from 97.0 +/- 4.7 to 88.1 +/- 5.1 mm Hg; p less than 0.01), captopril in combination with OKY-046 induced a decrease both in urinary thromboxane B2 excretion (from 70.8 +/- 12.3 to 54.2 +/- 14.7 pg/min; p less than 0.01) and in mean arterial pressure (from 105.1 +/- 3.8 to 84.2 +/- 3.6 mm Hg; p less than 0.01). Thus, the hypotensive effect of captopril was potentiated by OKY-046. OKY-046 did not affect the changes in plasma renin activity and plasma aldosterone concentration and blunted urinary prostaglandin E2 and 6-keto-prostaglandin F1 alpha excretion in response to captopril. These results indicate that thromboxane A2 counteracts the hypotensive effect of captopril in patients with essential hypertension.     

Diadenosine Polyphosphates’ Action on Calcium and Vessel Contraction

The effects of the endogenous, platelet-derived vasoactive compounds, diadenosine tetraphosphate (AP₄A), diadenosine pentaphosphate (AP₅A), and diadenosine hexaphosphate (AP₆A) on the vasoconstriction of isolated rat renal resistance vessels and rat aortic strips were measured using a vessel myograph. In addition, the effects of AP₄A, AP₅A, and AP₆A on the cytosolic free calcium concentration ([Ca²⁺]_i) were evaluated in cultured rat vascular smooth muscle cells (VSMC) using the fluorescent dye technique. Diadenosine polyphosphates dose-dependently increased the force of renal resistance vessels and isolated aortic strips. The administration of 10 μmol/L AP₄A, AP₅A, or AP₆A significantly increased the force of isolated renal resistance vessels by 3.48 ± 0.43 mN (n = 8), 2.14 ± 0.40 mN (n = 12), or 2.70 ± 0.31 mN (n = 11, each P < .01 compared with resting tension), respectively. The administration of 10 μmol/L AP₄A, AP₅A, or AP₆A significantly increased the force of isolated aortic strips by 2.45 ± 0.97 mNewton (n = 10), 2.70 ± 0.30 mN (n = 6), or 1.48 ± 0.20 mN (each P < .01 compared with resting tension), respectively. The administration of 10 μmol/L AP₄A, AP₅A, or AP₆A significantly increased [Ca²⁺]_i in VSMC to a peak concentration of 314 ± 60 nmol/L (n = 6), 247 ± 25 nmol/L (n = 15), or 332 ± 100 nmol/L (n = 5), respectively (each P < .01 compared with resting value). Both the diadenosine polyphosphate-induced vasoconstriction and [Ca²⁺]_i increase was significantly reduced in the absence of extracellular calcium or after administration of a specific inhibitor of P2 purinoceptors. It is concluded that diadenosine polyphosphates increase [Ca²⁺]_i and hence cause vessel constriction.     

Determinants of lipid and lipoprotein level in elderly men

In an effort to better understand the relationship existing between lipoprotein pattern and longevity, we studied the lipid and lipoprotein distribution of 94 men over age 80 who lived in a nursing home, and assessed the role of selective mortality, body mass and sex hormone secretion in determining these distributions. High density lipoprotein subfraction and serum testosterone measurements were obtained on subsamples. The main findings were: (a) Presence of a lipoprotein pattern characterized by low LDL (total serum cholesterol: 179.6 ± 36.0 mg/dl; LDL cholesterol: 106.3 ± 31.2 mg/dl) and high HDL₂ cholesterol (18.5 ± 10.2 mg/dl) levels. (b) Occurrence of a positive association between LDL and HDL₃ (r = 0.51, P < 0.01), resulting in an overall high HDL₂/HDL₃ ratio. Mortality over a 6-month period was directly related to LDL level and possibly inversely related to HDL₂ level, suggesting that selective mortality played a major role in determining the pattern observed. Body mass and serum testosterone concentration, which tended to be low, were independently correlated with lipoprotein level, a particularly strong correlation (positive) existed between free testosterone and triglyceride (r = 0.68, P < 0.01). The latter results suggest that changes related to senescence also influenced lipid and lipoprotein levels.     

Inhibition of lipoprotein lipase induced cholesterol ester accumulation in human hepatoma HepG2 cells

It has been suggested previously that lipoprotein lipase may act as a ligand to enhance binding and uptake of lipoprotein particles. In the present study we have examined the capacity of bovine milk lipoprotein lipase to induce intracellular accumulation of triglyceride and cholesterol ester by VLDL (S_f 60–400) isolated from Type IV hypertriglyceridemic subject (HTg-VLDL) in HepG2 cells, independent of its lipolytic activity. We have also attempted to elucidate the cellular receptor mechanisms responsible for these effects. HTg-VLDL-mediated increases in intracellular triglyceride and cholesterol ester were dependent on the presence of an active lipase. Bovine milk lipoprotein lipase (LPL) increases triglyceride mass by 301% ± 28% (P < 0.0005) and cholesterol ester mass by 176% ± 12% (P < 0.0005). These HTg-VLDL-mediated increases in intracellular triglyceride and cholesterol ester did not occur when heat-inactivated lipase was used. Rhizopus lipase could replace LPL and cause equivalent increases in intracellular triglyceride and cholesterol ester (472% ± 61% (P < 0.005) and 202% ± 25% (P < 0.025) respectively vs. control). HTg-VLDL treated with LPL and reisolated also caused equivalent increases (274% ± 18% (P < 0.01) and 177% ± 12% (P < 0.005) for triglyceride and cholesterol ester). LDL also caused increases in intracellular cholesterol ester (189% ± 20% (P < 0.005)), although three times more LDL cholesterol had to be added to achieve the same effect. These LDL-induced increases were effectively blocked by monoclonal antibodies directed against the B,E receptor binding domains of apo B (−97% ± 13% (P < 0.0005) with anti-apo B 5E11 and − 68% ± 13% (P < 0.05) for anti-apo B B1B3) or by anti-B,E receptor antibodies (− 77% ± 7% (P < 0.01) antibody C7). These same antibodies had little effect on the HTg-VLDL + LPL-induced increases in cholesterol ester (+21%, + 15% and − 22% for 5E11, B1B3 and C7, respectively). Monoclonal anti-apo E antibodies also had no effect on LDL-mediated increases in intracellular cholesterol ester, but had a small and significant effect on VLDL-mediated increases in cholesterol ester. However, heparin, which interferes with cell surface proteoglycan interaction, was very effective at blocking HTg-VLDL-mediated increases in cholesterol ester in the presence of LPL (− 86% ± 8% P < 0.0005). Heparin was also effective in the presence of Rhizopus lipase (−79%) or lipolyzed re-isolated HTg-VLDL (−95%). These results suggest that lipoprotein lipase may enhance the uptake process beyond its role in lipolytic remodelling but does not appear to be an absolute requirement. In contrast, heparin had no effect on LDL-mediated cholesterol ester accumulation. Lactoferrin, which inhibits interaction with the low density lipoprotein receptor-related protein (LRP), was also very effective at inhibiting HTg-VLDL increases in intracellular cholesterol ester (− 95% ± 6%, P < 0.01). However, there was no effect of either heparin or lactoferrin on HTg-VLDL-mediated triglyceride accumulation. Thus cell surface heparin sulphate may facilitate intracellular lipid acquisition by providing a stabilizing bridge with the lipoproteins and enhance uptake through receptor-mediated processes such as LRP.     

Hemodynamic results of percutaneous aortic balloon valvuloplasty as assessed by sequential Doppler echocardiographic studies

We determined the sequential hemodynamic changes after percutaneous aortic balloon valvuloplasty by means of two-dimensional and Doppler echocardiographic examinations in 25 patients immediately before, immediately after, and 24 to 36 hours after valvuloplasty. An aortic valve area was determined at all three time periods by using the continuity equation from the Doppler velocity profiles. The aortic valve area by Doppler echocardiography immediately before valvuloplasty correlated with that determined by cardiac catheterization (r = 0.85, SEE = 0.08 cm²). The mean aortic valve gradient by Doppler echocardiography was 50 ± 22 mm Hg before the procedure, decreasing to 29 ± 12 mm Hg (P < 0.001), with a small, but significant, increase 1 day later to 33 ± 13 mm Hg (P < 0.001). The mean subvalvular velocity increased from 0.44 ± 0.13 to 0.52 ± 0.15 m/sec immediately after valvuloplasty (P < 0.001), increasing further to 0.60 ± 0.16 m/sec 1 day later (P < 0.001). The resultant aortic valve area increased from 0.45 ± 0.11 to 0.73 ± 0.18 cm² immediately after (P < 0.05). One day later, the aortic valve area increased further to 0.86 ± 0.19 cm² (P < 0.05). Because of the dynamic changes occurring during the first 24 to 36 hours after balloon valvuloplasty, hemodynamic measurements taken immediately after the procedure may underestimate the efficacy of this technique.     

Reduced sympathetic inhibition in salt-sensitive Japanese young adults

The purpose of our study was to investigate the sympathetic response to excess salt loading of 54 normotensive young adults with and without a family history of hypertension. We examined muscle sympathetic nerve activity, plasma concentration and urinary excretion of catecholamines, and ambulatory blood pressures during low (4 g NaCl) and high (16 g NaCl) salt diet intake. Ambulatory blood pressure and urinary excretion of catecholamines are known to be reduced during sleep. These parameters were therefore calculated during waking and sleeping periods. The subject was defined as salt-sensitive when mean ambulatory systolic pressure during the waking period was ≥3mm Hg higher during high salt intake than during low salt intake (n = 26: 21.4 ± 0.3 years old). When mean systolic pressure was either lower or equal during high salt intake than during low salt intake, the subject was defined as salt-resistant (n = 24: 21.3 ± 0.3 years old). Muscle sympathetic nerve activity, plasma concentration and urinary excretion of norepinephrine in salt-resistant subjects were significantly reduced (P < .05) by salt intake, wheras plasma concentration of epinephrine was unchanged and urinary excretion of epinephrine was reduced. In contrast, urinary excretion of epinephrine in salt-sensitive subjects was significantly elevated (P < .05) during high salt intake, whereas muscle sympathetic nerve activity and urinary excretion of norepinephrine remained unchanged despite a significant increase (P < .01) of ambulatory blood pressure. Of the salt-sensitive subjects, 73% (19 of 26) had a positive family history of hypertension, whereas only 5 of 24 salt-resistant subjects had a positive family history. These data indicate that the inhibition of sympathetic activity during a high salt intake did not occur in salt-sensitive young adults, and this may be linked with a hereditary predisposition to hypertension.