Effect of advancing age on cardiopulmonary baroreceptor function in hypertensive men

Blood pressure, heart rate, forearm vascular resistance, and hormonal responses to graded lower body negative pressure were investigated in 15 hypertensive men younger than 55 years of age (mean age, 44 +/- 2 years) and 13 comparably hypertensive men older than 55 years of age (mean age, 63 +/- 2 years). Baseline forearm vascular resistance was greater in the elderly group compared with the younger hypertensive men. However, forearm vascular resistance responses to selective unloading of low pressure cardiopulmonary baroreceptors were similar in the two groups. This finding suggests that normal vascular responses to the unloading of cardiopulmonary baroreceptors are preserved in subjects with advancing age and mild to moderate hypertension. Baseline plasma norepinephrine levels, as well as norepinephrine responses to lower body negative pressure, were comparable in the two groups. This finding suggests that, unlike normotensive subjects, essential hypertensive subjects do not have an age-related increase in sympathetic nervous system activity.

Effects of hydrochlorothiazide and diltiazem on reflex vasoconstriction in hypertension

The purpose of our study was to determine the effects of treatment with hydrochlorothiazide (n = 10) or diltiazem (n = 8) on reflex humoral, hemodynamic, and vascular responses to graded lower body negative pressure in subjects with mild to moderate hypertension (supine diastolic pressure, 95-114 mm Hg). All subjects received placebo for 2 to 4 weeks followed by either hydrochlorothiazide (25-50 mg b.i.d.) or diltiazem (120-180 mg b.i.d.) to achieve a reduction in supine diastolic pressure of 10 mm Hg or more and a final pressure below 90 mm Hg. Mean arterial pressure, forearm vascular resistance, plasma norepinephrine, and renin responses to graded lower body negative pressure (-10, -20, -40 mm Hg) and head-up tilt were examined before and after 12 weeks of treatment with either drug. Pretreatment basal values of mean arterial pressure (114 +/- 2 vs 117 +/- 2 mm Hg), forearm vascular resistance (29 +/- 3 vs 35 +/- 7 units), and plasma renin activity (0.7 +/- 0.2 vs 0.6 +/- 0.2 ng angiotensin I/ml/hr) were not significantly different between groups. There were no significant differences in basal plasma norepinephrine or in the increases of norepinephrine in response to lower body negative pressure before and after treatment in either group. Forearm vascular resistance responses to lower body negative pressure were virtually abolished in the diltiazem-treated group but not in the hydrochlorothiazide-treated group despite similar levels of mean arterial pressure and basal forearm vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of calcium-entry blockers and diuretics in the treatment of hypertensive patients

This review compares the calcium antagonists with diuretics in the management of mild-to-moderate essential hypertension. The antihypertensive efficacy of calcium antagonists appears comparable to that of oral diuretics such as hydrochlorothiazide when used as monotherapy. Peripheral vascular dilation appears to be the principal mechanism of the long-term blood pressure-lowering effects of both calcium antagonists and diuretics. Peripheral vasoconstrictor responses to cardioreflex-mediated sympathetic nervous system activation is attenuated by calcium antagonists but not by diuretics. Long-term calcium antagonist therapy is generally not associated with reflex activation of the sympathetic nervous system or of the renin-angiotensin-aldosterone axis, whereas diuretic therapy results in considerable activation of the renin-angiotensin-aldosterone system. Calcium antagonists appear to have a greater beneficial effect than diuretics with respect to maintenance of renal blood flow and glomerular filtration rate. Calcium antagonists, because of their effects on coronary blood flow and heart rate-blood pressure product, offer advantages over diuretics in the treatment of hypertensive patients with concomitant ischemic heart disease. Metabolic abnormalities associated with diuretic antihypertensive therapy, such as hypokalemia, hypercalcemia, hyperuricemia, lipid changes, and hyperglycemia, are generally not observed with calcium antagonists. Many of these deleterious metabolic changes observed with diuretic therapy may be minimized by the use of smaller doses of these agents than have generally been employed in the past. Diuretics are less expensive and require less frequent dosing than calcium antagonists. Thus, they continue to be preferable first-line antihypertensive agents in many patients with mild-to-moderate hypertension.

Impairment of cardiopulmonary baroreflex after cardiac transplantation in humans

There is ample evidence for efferent cardiac denervation in patients after cardiac transplantation. However, little is known regarding the effects of the cardiac deafferentation that also results. We examined responses to graded lower-body negative pressure and thus cardiopulmonary baroreceptor unloading in 23 patients 3 to 12 months after cardiac transplantation and compared their responses with those of nine normal subjects. Responses of mean arterial pressure, forearm vascular resistance, and plasma norepinephrine were assessed during lower-body negative pressure and the cold pressor test. Reflex increases in forearm vascular resistance (1.5 +/- 1, 5.0 +/- 1.4, and 6.4 +/- 2.1 vs 14.5 +/- 4.5, 20.3 +/- 6.5, and 34 +/- 11 units) and plasma norepinephrine (42 +/- 12, 58 +/- 15, and 62 +/- 13 vs 49 +/- 14, 94 +/- 25, and 173 +/- 36 pg/ml) during lower-body negative pressure (at -10, -20, and -40 mm Hg) were strikingly smaller in cardiac transplant patients than in normal subjects. The impaired responses of the cardiac transplant patients were not the result of a nonspecific depression of cardiovascular reflexes, since increases in mean arterial pressure (12 +/- 3 vs 10 +/- 2 mm Hg), forearm vascular resistance (19.5 +/- 3.4 vs 18 +/- 5.8 units), and plasma norepinephrine (56 +/- 8 vs 42 +/- 11 pg/ml) during cold pressor test were not significantly different in the two groups. Furthermore, the impaired responses were not caused by the immunosuppressive agents used to treat the cardiac transplant patients, since patients with renal transplants on similar regimens had augmented forearm vasoconstrictor responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial norepinephrine, epinephrine and dopamine concentrations after cardiac autotransplantation in dogs

Myocardial norepinephrine is markedly reduced after cardiac transplantation because of interruption of postganglionic cardiac sympathetic nerves. There are also substantial stores of dopamine in the myocardium, but the influence of cardiac denervation on dopamine remains unknown. The effect of cardiac transplantation was determined and, thus, the effect of denervation on myocardial norepinephrine, dopamine and epinephrine. Myocardial catecholamines were measured with high-performance liquid chromatography with electrochemical detection in five dogs 6 to 8 weeks and in four dogs 8 to 12 years after cardiac autotransplantation and in six sham-operated dogs with intact cardiac innervation. Norepinephrine, dopamine and epinephrine levels were determined from samples obtained from the right and left atria and ventricles. Samples from the left ventricular apex and base were analyzed separately. There was a striking depletion of norepinephrine in all cardiac chambers after short-term autotransplantation. The norepinephrine content of the left atrium in sham-operated dogs (1,659 +/- 219 ng/g) was significantly higher than that of dogs with long-term autotransplanted hearts (754 +/- 372 ng/g). Sham-operated dogs and dogs with long-term autotransplanted hearts had statistically significant (p less than 0.05) differences in norepinephrine content in the left ventricular apex (480 +/- 197 versus 294 +/- 198 ng/g), left ventricular base (876 +/- 2204 versus 654 +/- 156 ng/g) and right ventricle (766 +/- 133 versus 247 +/- 29 ng/g). In contrast to norepinephrine, dopamine concentrations were relatively preserved in the short-term group despite the virtual depletion of myocardial norepinephrine.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent reinnervation of the autotransplanted heart in dogs

Patients have been observed with a chest pain syndrome after cardiac transplantation. For this pain to be cardiac in origin the afferent nerves carrying sensory information from the heart would have to reinnervate the heart. A previous study in dogs indicated that afferent reinnervation is uncommon during the first 2 years after transplantation. The purpose of this study was to determine whether afferent reinnervation of the heart occurs in the long term. The decreases in arterial pressure and renal nerve activity resulting from chemical stimulation of left ventricular sensory receptors with vagal afferents with cryptenamine (veratrum alkaloid) were assessed in three dogs 8 to 12 years and in four dogs 6 to 8 weeks after cardiac autotransplantation and in six sham-operated dogs (thoracotomy-pericardiotomy 6 to 8 weeks before study). Responses of renal nerve activity to physiologic stimulation of cardiac receptors by volume expansion were also determined. Left ventricular cryptenamine inhibited renal nerve activity by 72 +/- 8% in dogs with long-term and by 10 +/- 6% in dogs with short-term autotransplantation and by 92 +/- 5% in sham-operated dogs. Decreases in mean arterial pressure in these groups were 34 +/- 4, 11 +/- 3 and 67 +/- 16 mm Hg, respectively. Volume expansion inhibited renal nerve activity in long-term autotransplant (43%) and sham-operated (48%) groups but less in the short-term transplant group (33%) for comparable increases in cardiac filling pressure. It is concluded that in dogs there is extensive afferent reinnervation of the long-term autotransplanted heart that results in relatively normal cardiopulmonary baroreflex responses to volume expansion.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of diltiazem on hormonal and hemodynamic responses to lower body negative pressure and tilt in patients with mild to moderate systemic hypertension

Mean arterial blood pressure, forearm vascular resistance, plasma norepinephrine, plasma renin activity and aldosterone responses to graded lower body negative pressure and tilt at 80 degrees were examined in 10 men with mild to moderate essential hypertension before and after 12 weeks of diltiazem (240 to 360 mg/day) therapy. Diltiazem therapy lowered basal supine systolic and diastolic blood pressures without affecting basal heart rate. Mean arterial blood pressure and forearm vascular resistance were decreased from 114 +/- 1.5 to 105 +/- 1 mm Hg, p less than 0.01 and from 29.3 +/- 3.5 to 18.9 +/- 2.1 units, p less than 0.01, respectively. Diltiazem therapy had no effect on basal supine levels of norepinephrine, plasma renin activity or aldosterone, nor on the responses of these hormones to lower body negative pressure. Diltiazem did decrease the forearm vascular resistance responses to lower body negative pressure and tilt. Diltiazem abolished an orthostatic increase (10 +/- 0.3 mm Hg) in mean arterial blood pressure and this was associated with a greater plasma norepinephrine response to tilt. These results suggest that diltiazem decreases vascular resistance through a reduction in the postjunctional effects of norepinephrine on vascular smooth muscle.

Dopaminergic regulation of natriuretic response to acute volume expansion in dogs

Effects of carbidopa, a dopa (3,4-dihydroxyphenylamine) decarboxylase inhibitor, on the renal, haemodynamic and hormonal responses to acute volume expansion were examined in six healthy mongrel dogs which were infused intravenously with 0.9% sodium chloride solution (saline; 30 ml h-1 kg-1) over 2 h. Saline infusion studies were performed in the absence (control) and in the presence of carbidopa given by nasogastric tube in a dose of 1 mg/kg every 8 h beginning 24 h before the infusion. Saline infusion resulted in an increase in renal excretion of dopamine (3,4-dihydroxyphenylethylamine) and a decrease in renal excretion of noradrenaline. Carbidopa treatment decreased urinary sodium excretion and eliminated the increase in renal production of dopamine in response to saline infusion without affecting renal or haemodynamic response to acute vascular volume expansion with saline. Carbidopa treatment obliterated the suppression of aldosterone produced by saline infusion. Thus, dopamine appears to play a significant role in mediating both the natriuretic and aldosterone response to acute volume expansion.

Relationship between urinary dopamine production and natriuresis after acute intravascular volume expansion with sodium chloride in dogs

The role of renal production of dopamine in mediating the natriuretic response to acute vascular volume expansion was investigated. The effect of infusion of 0.9% saline (30 ml/kg X h) over 2 h on urine excretion of sodium and catecholamines, as well as other hemodynamic and renal function parameters, was examined in seven dogs during control and carbidopa (1 mg/kg every 8 h for 24 h before saline infusion) treatment periods. Acute vascular volume expansion with saline resulted in a rise (P less than 0.01) in the renal excretion of dopamine and a depression (P less than 0.01) in renal excretion of norepinephrine which paralleled the natriuretic response to saline infusion. Epinephrine excretion was not altered by saline infusion. Carbidopa treatment was not associated with changes in left ventricular filling pressure, arterial blood pressure, glomerular filtration rate, renal blood flow, renal excretion of norepinephrine or epinephrine. However, carbidopa eliminated the increase in renal production of dopamine and markedly attenuated the natriuretic response to saline infusion. Since carbidopa blocks tissue conversion of dopa to dopamine, it appears that renal production of dopamine is an important mechanism mediating the natriuretic response to acute volume expansion.

Atrioventricular block and supraventricular arrhythmias with X-linked muscular dystrophy

This report describes a family showing muscular dystrophy and atrioventricular block with an x-linked hereditary transmission. Among a known pedigree of 101 family members, 12 males were found to have skeletal muscle involvement and six needed pacemakers around age 30 years. Unlike the x-linked muscular dystrophies of Duchenne and of Becker, the predominant skeletal involvement was in humeral muscles, was usually very mild, and did not produce incapacitation. Cardiac involvement consisted of various atrial arrhythmias and atrioventricular block. The few sporadic reports of other families that describe the same disease under different names are briefly reviewed. Recognition of this subtle muscular dystrophy is important for early detection of incipient complete atrioventricular block to prevent fatal complications by pacemaker insertion.