Michael B. Given

Changes in protein kinase C in early cardiomyopathy and in gracilis muscle in the BB/Wor diabetic rat

Hyperglycemia can upregulate protein kinase C (PKC), which may be an important mediator of the progression from normal heart and muscle function to diabetic myopathy in the myocardium and skeletal muscle in type 1 insulin-dependent diabetes mellitus (IDM). We evaluated this possibility during the early stage of IDM in BB/Wor diabetic (D) rats and age-matched BB/Wor diabetes-resistant (DR) rats. Interventricular septal thickness, E wave peak velocity of tricuspid inflow (both minimum and maximum), and left ventricular (LV) weight index were increased, and the rate of change in LV pressure (LV dP/dt) decreased in D rats subjected to M-mode and two-dimensional echocardiography and hemodynamic recording of heart rate, LV pressure (LVP), + LV dP/dt, -LV dP/dt, and LV end-diastolic pressure (LVEDP) in vivo and in vitro 41 days after the onset of hyperglycemia. Whole ventricle basal PKC activity was increased by 44.4 and 18.4% in the particulate and soluble fractions, respectively, from D rats compared with that from DR rats using r-32P phosphorylation of appropriate peptide substrates. When measured by Western blot gel densitometry, particulate PKC-alpha and PKC-delta content increased by 89 and 24%, respectively, but soluble PKC-beta and soluble and particulate PKC-epsilon were unchanged compared with that of DR rats. Similarly, gracilis muscle PKC activity and PKC-alpha and PKC-delta were elevated in the gracilis muscle, whereas that of the circulating neutrophil did not differ between the D and DR rats. Thus, in vivo, the early diabetic cardiomyopathy of the D rat is characterized by a restrictive LV with increased septal thickness and is associated with elevated PKC activity and increased amounts of myocardial particulate PKC-alpha and PKC-delta, which are also seen in the skeletal muscle. We conclude that increased PKC isozymes may play a pivotal role during IDM in the development of diabetic cardiomyopathy and skeletal muscle myopathy.Hyperglycemia can upregulate protein kinase C (PKC), which may be an important mediator of the progression from normal heart and muscle function to diabetic myopathy in the myocardium and skeletal muscle in type 1 insulin-dependent diabetes mellitus (IDM). We evaluated this possibility during the early stage of IDM in BB/Wor diabetic (D) rats and age-matched BB/Wor diabetes-resistant (DR) rats. Interventricular septal thickness, E wave peak velocity of tricuspid inflow (both minimum and maximum), and left ventricular (LV) weight index were increased, and the rate of change in LV pressure (LV dP/d t) decreased in D rats subjected to M-mode and two-dimensional echocardiography and hemodynamic recording of heart rate, LV pressure (LVP), +LV dP/d t, -LV dP/d t, and LV end-diastolic pressure (LVEDP) in vivo and in vitro 41 days after the onset of hyperglycemia. Whole ventricle basal PKC activity was increased by 44.4 and 18.4% in the particulate and soluble fractions, respectively, from D rats compared with that from DR rats using r-32P phosphorylation of appropriate peptide substrates. When measured by Western blot gel densitometry, particulate PKC-α and PKC-δ content increased by 89 and 24%, respectively, but soluble PKC-β and soluble and particulate PKC-ε were unchanged compared with that of DR rats. Similarly, gracilis muscle PKC activity and PKC-α and PKC-δ were elevated in the gracilis muscle, whereas that of the circulating neutrophil did not differ between the D and DR rats. Thus, in vivo, the early diabetic cardiomyopathy of the D rat is characterized by a restrictive LV with increased septal thickness and is associated with elevated PKC activity and increased amounts of myocardial particulate PKC-α and PKC-δ, which are also seen in the skeletal muscle. We conclude that increased PKC isozymes may play a pivotal role during IDM in the development of diabetic cardiomyopathy and skeletal muscle myopathy.

Comparison of nitrendipine and hydrochlorothiazide for systemic hypertension

Left ventricular (LV) hypertrophy with associated LV systolic and diastolic dysfunction is frequently found in patients with systemic hypertension, and is multifactorial in origin. Although a reduction in blood pressure (BP) often results in regression of hypertrophy, the pharmacologic profiles of the antihypertensive agents used may determine the probability of such regression despite similar levels of BP reduction. Thiazide diuretic drugs may actually result in increased LV hypertrophy; calcium channel antagonists may cause regression or no change. The effects of treatment with nitrendipine (20 mg/day) or hydrochlorothiazide (50 mg/day) were compared in an 8-week, double-blind study of 18 hypertensive subjects aged 50 years or older. BP was significantly reduced (p less than 0.05) by both nitrendipine (from 161 +/- 29/102 +/- 4 to 145 +/- 24/92 +/- 7 mm Hg; mean +/- standard deviation) and hydrochlorothiazide (from 162 +/- 15/105 +/- 6 to 143 +/- 20/95 +/- 7 mm Hg). Plasma norepinephrine increased in the nitrendipine group, from 202 +/- 110 to 332 +/- 220 pg/ml at 8 weeks of therapy and in the hydrochlorothiazide group, from 147 +/- 130 to 313 +/- 277. Plasma renin activity changed from 3.2 +/- 2.4 to 3.5 +/- 2.1 during nitrendipine treatment, but from 2.1 +/- 2.1 to 10.5 +/- 10.8 ng angiotensin l/ml/90 min (p less than 0.05) during treatment with hydrochlorothiazide. Left ventricular mass index did not change significantly with either therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between circulating peptides and the central nervous system in hemodynamic regulation.

Enkephalins and endothelins are endogenous peptides, which, at least at pharmacologic doses, produce complex hemodynamic responses after intravenous administration. The enkephalins, when injected into conscious animal models and humans, increase blood pressure, heart rate and minute ventilation. This response occurs by activation of specific opiate receptors located outside the bloodbrain barrier; the actual mechanism involves an increase in adrenergic autonomic nervous system tone and a decrease in cholinergic tone. These opiate receptors may activate afferent fibers, perhaps nicotinic cholinoceptors; in many ways their properties are suggestive of chemoreceptors. Furthermore, enkephalin responses appear to be modulated by gamma-aminobutyric acid complexes, in that the reversal of the excitatory hemodynamic responses seen in the conscious state to vasodepressor responses after barbiturate anesthesia may result from alteration of the state of activation of the gamma-aminobutyric acid complex. The enkephalin receptors are localized to the vertebral artery vascular distribution; the specific site may be the area postrema, a blood-brain barrier-deficient circum-ventricular organ demonstrated to modulate heart rate and blood pressure and to represent a target site for circulating angiotensin II. Endothelin increases heart rate and blood pressure when infused slowly into conscious or anesthetized dogs, although barbiturates do blunt the increase in heart rate. The mechanism appears to involve modification of autonomic tone, but also some element of direct vasoconstrictor activity. Interestingly, rapid bolus doses of endothelin produce only vasodepressor responses, suggesting that the rate and concentration at which circulating endothelin reaches afferent receptors or vasoconstrictor sites on vascular smooth muscle may determine the net hemodynamic response observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin and platelet function

The effects of newly discovered vasoconstrictor peptide endothelin was studied on human, rabbit and canine platelet function. Endothelin (0.01 nM-1 microM) did not promote platelet aggregation. In human platelets, endothelin (0.1 microM) did not significantly affect aggregation responses to ADP, collagen, epinephrine, arachidonic acid, PGH2 or thrombin. Endothelin did not promote the mobilization of intracellular calcium in Fura2 loaded human platelets. In rabbit and canine platelets endothelin produced significant potentiation of platelet aggregation mediated by low concentrations of ADP. Aggregation responses to higher concentration of ADP (5 microM) were unaffected by endothelin. These data reveal that under certain circumstances endothelin may potentiate rabbit and canine platelet aggregation responses to ADP, however endothelin does not produce direct effects on human platelet function.

Preservation of left ventricular function and coronary flow by angiotensin I-converting enzyme inhibition in the hypertensive-diabetic Dahl rat.

The effect of the angiotensin I-converting enzyme (ACE) inhibitor benazepril (55 mg/kg orally) on the preservation of cardiac performance in diabetic-hypertensive Dahl S rats was investigated. Diabetes mellitus was produced by streptozotocin. Fasting (4-h) blood glucose levels were 279 +/- 50 mg/dL in diabetic Dahl salt-sensitive v 79 +/- 5 mg/dL in nondiabetic Dahl salt-sensitive rats. Cardiac performance was determined at the end of 8 weeks in an isolated perfused working heart apparatus. Peak left ventricular pressure (LVPmax), left ventricular peak negative dP/dt, and coronary flow were depressed in diabetic Dahl S rats (P < or = .05 v control). These deficits in cardiac function were not observed in diabetic Dahl S rats chronically treated with benazepril. The beneficial effects of benazepril apparently were independent of systolic blood pressure reduction. Although plasma ACE activity was increased in diabetic Dahl S rats, plasma renin activity was reduced. This suggests that the beneficial effects of ACE inhibition may be due to an effect upon the kinin system rather than the renin-angiotensin system. The benazepril-associated preservation of cardiac function in this study suggests that ACE inhibitors may be beneficial in the treatment of diabetic heart disease.

Hemodynamic actions of endothelin in conscious and anesthetized dogs.

The newly described endogenous peptide, endothelin, was administered to five chronically instrumented conditioned dogs. Endothelin produced significant and simultaneous increases in both heart rate (HR) and mean arterial pressure (MAP) in conscious dogs. Endothelin also produced significant increases in MAP in anesthetized animals. Ganglionic suppression induced by hexamethonium (10 mg/kg) and atropine (0.1 mg/kg) blocked HR responses and markedly inhibited the pressor responses to endothelin in conscious animals. These results suggest that endothelin in part acts to elevate blood pressure and heart rate through modification of autonomic nervous system tone. When endothelin and angiotensin II were administered in mole equivalent doses, angiotensin II produced a pressor response of greater magnitude than did endothelin in conscious animals.

Intravenous Captopril in Congestive Heart Failure

Hemodynamic and neurohumoral effects of intravenous captopril were studied in ten patients with severe chronic congestive heart failure (NYHA Functional Class III and IV). Incremental bolus doses of captopril, titrated to a maximum cumulative dose of 15 mg, were given at 10‐minute intervals. Systemic arterial pressure, mean pulmonary capillary wedge pressure, systemic vascular resistance, mean pulmonary artery pressure, and heart rate decreased (P < .05). Cardiac index and stroke volume index increased (P < .05). Maximum hemodynamic effects occurred after cumulative doses of 7 mg and were seen within 30 minutes after initiation of therapy; responses persisted for 30–90 minutes after the last dose. Plasma renin activity increased, and plasma atrial natriuretic factor concentration decreased. No adverse effects were observed with the use of intravenous captopril. Thus, intravenous captopril produces rapid and favorable hemodynamic improvement in advanced heart failure patients.

Efficacy of Nicardipine in Angina Pectoris

The dose‐related efficacy and safety of nicardipine, a new calcium antagonist of the dihydropyridine class, was assessed by exercise tolerance testing in a randomized, double‐blinded, placebo‐controlled study in 19 patients with chronic, stable effort angina pectoris. Four patients were assigned to each of four treatment sequences receiving nicardipine three times daily in an extended Latin‐Square study design. An increase in total exercise capacity, time to onset of angina and time to 1 mm ST segment depression was observed with nicardipine 90 mg/day compared to placebo (P < .05). Gradual upward dose titration in 30 mg/day increments starting from 30 mg/day appeared to produce maximal increase in exercise capacity. Two patients developed adverse side effects attributable to the drug when administered nicardipine 90 mg/day directly from placebo.