Inverted response of arginine vasopressin to postural change in patients with essential hypertension

1. This study was designed to compare the response of plasma arginine vasopressin (AVP) to head-up tilt in hypertensive patients and in normals. 2. As expected, plasma AVP showed a consistent increase (P less than 0.005) in normal subjects after tilt while plasma volume decreased significantly (P less than 0.02). On the contrary, in hypertensive patients, after tilt both plasma AVP (P less than 0.025) and plasma volume (P less than 0.05) decreased. 3. These findings, thus, indicate that essential hypertension is characterized by an inverted response of arginine vasopressin to postural change.

The reflex control of arginine-vasopressin release in essential hypertension

1. The reflex control of arginine-vasopressin release was studied in 12 essential established hypertensive patients and in 12 age-matched normal subjects by comparing the effects of head-up tilt and a variable-pressure neck-chamber. 2. After 45 min 85 degrees head-up tilt, normal subjects showed an increase in plasma arginine-vasopressin and in plasma renin activity, while plasma volume decreased. In hypertensive patients, plasma arginine-vasopressin showed changes after tilt opposite to those of controls, while the changes in plasma renin activity and plasma volume were similar to those observed in the normal group. In both groups the changes in systolic and diastolic blood pressure were not statistically significant. A reduction in carotid sinus transmural pressure obtained by increasing neck-tissue pressure (+50 mmHg) by means of a neck-chamber, evoked different responses in mean blood pressure in the two groups, but failed to induce any significant change in plasma arginine-vasopressin concentration both in the normal and in the hypertensive subjects. 3. These results seem to suggest that carotid sinus baroreceptors, though active in blood pressure control, do not play a direct role in arginine-vasopressin release and, therefore, the opposite response of arginine-vasopressin observed after tilt in the two groups of subjects should be ascribed to more complex mechanisms.

Baroreflex responsiveness in borderline hypertensives: a study with neostigmine

The baroreflex response to changes in transmural pressure throughout the arterial tree or limited to the carotid sinus was evaluated in ten borderline hypertensives and compared with that observed in ten normal subjects and in ten established hypertensives. Baroreceptor sensitivity was tested by evaluating both heart rate response to phenylephrine-induced increase in arterial pressure and heart rate and blood pressure changes induced by increased neck tissue pressure by means of a neck chamber. The heart rate response to phenylephrine (evaluated by the regression of the R-R interval versus the systolic blood pressure) was depressed both in borderline and established hypertensives as compared with controls. Similarly, the heart rate and the pressor response to increased neck tissue pressure were depressed in both groups of hypertensives. In borderline, but not in established hypertensives, neostigmine administration improved consistently the pressor baroreflex response to increased neck tissue pressure and the heart rate reflex response to both the employed stimuli. These findings indicate that a reduced parasympathetic activity is one of the components involved in the altered baroreflex sensitivity in borderline hypertensives.

Mechanisms underlying systemic hemodynamic responses to experimental coronary artery occlusion. A preliminary study with hexamethonium

The hemodynamic changes induced by coronary occlusion were investigated in anesthetized dogs. Coronary occlusion elicited an immediate but transient increase in the systemic blood pressure and in the vascular resistance of the hind limb perfused at constant flow. Thereafter, systemic hypotension and vasodilatation in the perfused region were observed. Vagotomy abolished the initial increase of the systemic and perfusion pressure and reduced significantly the late vasodilator response both systemically and in the perfused hind limb. After the subsequent administration of hexamethonium the vasodilatation in the hind limb was no longer manifest but the fall in blood pressure was unmodified. These results seem to suggest that multiple mechanisms are involved in the hemodynamic response to coronary occlusion.

Disopyramide and mexiletine: which is the agent of choice in the long term-oral treatment of lidocaine-responsive arrhythmias? Efficacy comparison in a randomized trial

Forty patients with serious lidocaine-responsive ventricular arrhythmias were randomly assigned to treatment with either oral disopyramide (100 mg 4 times daily) or mexiletine (200 mg 4 times daily) for 3 weeks. A satisfactory arrhythmias control (greater than 75 % reduction of premature ventricular complexes per minute as compared to the control period prior to lidocaine administration) was achieved in 19 patients in the mexiletine group and in 16 in the disopyramide treated patients. Furthermore, disopyramide failed to maintain the reduction of the number of ventricular extrasystoles per minute obtained with lidocaine, while mexiletine succeeded. Finally, the number of ventricular extrasystoles per minute in the mexiletine treated group was significantly lower than in the other group. Gastrointestinal disturbances were more frequent during mexiletine administration.

Relationship between systolic time intervals and heart rate during atrial or ventricular pacing in normal subjects

Systolic time intervals (STI) are regarded as good indices of cardiac performance in many heart diseases. It must be considered, however, that they are temporally related to the cardiac contraction cycle and, therefore, may be modified by heart rate changes. Thus, it is necessary to define the possible relationship between STI and heart rate changes. In this study, changes in heart rate were induced by atrial and ventricular pacing. Tachycardia caused a proportional decrease of left ventricular ejection time (LVET) (y=275.142-1.0025 x, r=0.76, p less than 0.001 for atrial pacing and y=298.28-0.691 x, r=-0.75, p less than 0.001 for ventricular pacing, respectively), but did not modify the pre-ejection period (PEP) and the isometric contraction time (ICT) and the electromechanical interval (QS1). These results demonstrate that while LVET must be corrected for the changes in heart rate, no correction of PEP and ICT is necessary.

Long term comparative study of guanfacine and alpha-methyldopa in essential hypertension

The hypotensive action of guanfacine and alpha-methyldopa has been compared in 30 patients wth moderate essential hypertension. After 2 weeks of placebo treatment, the patients were randomly allocated to a 12 week treatment with either of the two drugs. The treatment was started with guanfacine, 1 mg twice daily p.o., or alpha-methyldopa, 250 mg three time a day p.o. This dose of guanfacine was able to induce a satisfactory control of blood pressure in all patients while the dose of alpha-methyldopa was gradually increased to a predetermined maximum daily dose (2 g) in those patients with unsatisfactory blood pressure control, i.e., systolic blood pressure above 160 mmHg and diastolic above 95 mmHg. Then the two treatments were dicontinued for one week. Both drugs induced a significant reduction of systolic and diastolic blood pressure. However, guanfacine induced a more marked decrease in systolic blood pressure after the 14th day of treatment while the reduction of diastolic blood pressure was significantly higher only at the end of the final wash-out period, thus indicating a longer lasting effect of guanfacine as compared to alpha-methyldopa. Two patients treated with guanfacine developed dryness of the mouth and three of those in the alphamethyldopa group complained of excessive sedation.

Effect of furosemide on plasma concentration and beta-blockade by propranolol

Although propranolol and furosemide are used together for hypertension, the effects of furosemide on plasma levels and beta-blocking action of propranolol are not known. Ten healthy subjects received propranolol 40 mg orally; the mean plasma propranolol levels in 60, 90, 180, and 300 min were 85 +/- 16, 90 +/- 7, 82 +/- 8, and 58 +/- 8 ng/ml. Propranolol was then given together with furosemide (25 mg orally) and the propranolol blood level was measured. Mean propranolol plasma levels were 106 +/- 11 ng/ml at 60 min, 120 +/- 12 ng/ml at 90 min (p less than 0.01), 102 +/- 8 ng/ml at 180 min (p less than 0.05), and 78 +/- 8 ng/ml at 300 min (p less than 0.01). Six additional subjects were given an infusion of 1 microgram/min isoproterenol increased by 0.5 microgram/min every 2 min until the heart rate rose by 25% after oral administration of furosemide 25 mg. This procedure was repeated after propranolol (40 mg orally) and propranolol with furosemide (25 mg orally). The amount of isoproterenol which raised the heart rate by 25% was 2.6 +/- 0.3 micrograms after furosemide alone and 17.7 +/- 2 micrograms after propranolol (p less than 0.01). After propranolol with furosemide the dose of isoproterenol required to elevate heart rate by 25% was 109 +/- 15 micrograms (p less than 0.001).

Histamine mediation in muscular vasodilatation induced by beta adrenoceptor stimulation in dogs

This study was designed to investigate the possibility of a histamine mediation in muscular vasodilation induced by beta adrenoceptor stimulation. Accordingly, in seven dogs the effects of isoproterenol administration on the release of 14C-histamine from the perfused gracilis muscle were studied. Beta adrenoceptors stimulation induced a vasodilatation, as shown by a decrease in perfusion pressure(-43 +/- 12 mm Hg); simultaneously, a significant increase of the radioactivity measured in the venous blood effluent from the gracilis muscle was observed. Both these events were blocked by propranolol. In the other five dogs, chlorpheniramine was able to reduce the vasodilatation induced by the injection in the gracilis muscle of isoproterenol. Under control conditions, isoproterenol induced a fall in perfusion pressure of 44 +/- 5 mm Hg while, after chlorpheniramine, perfusion pressure decreased by only 24 +/- 4 mm Hg. The results of this study seem to confirm the possibility of a histamine mediation in isoproterenol-induced vasodilatation. However, further investigation is needed in order to identify the exact role of histamine in the geneis of this phenomenon.

Effects of guanethidine on histamine release during reflex vasodilatation in the dog

1 The effects of guanethidine pretreatment on the release of [14C]-histamine during the reflex vasodilatation induced in the atropinized gracilis muscle by rapid intravenous administration of noradrenaline, were studied in dogs. 2 After guanethidine treatment the haemodynamic reflex response was completely abolished and no appreciable modification of [14C]-histamine release from the gracilis muscle following intravenous noradrenaline was observed. 3 These results suggest the hypothesis that the withdrawal of the sympathetic discharge represents the mechanism of histamine release during the reflex vasodilatation. Therefore, guanethidine would suppress both the passive and the histaminergic component of the baroreceptor reflex through the abolition of the sympathetic tone.