The substitutive role of ACTH in supporting aldosterone response to head-up tilt during acute renin suppression in patients with essential hypertension

Response of the renin-angiotensin-aldosterone system to upright tilting and to intravenous frusemide: effect of prior metoprolol and propranolol

1 Upright tilting in normal volunteers caused increases in plasma active and total renin, angiotensin II and aldosterone; a slight but significant fall in inactive renin accompanied these changes. 2 The alterations in the renin-angiotensin-aldosterone system on tilting took up to 1 h upright to become fully established. 3 Large intravenous doses of propranolol or metoprolol attenuated, without abolishing, the rises in active renin, angiotensin II, and aldosterone; the attenuation was most evident soon after tilting and was largely overcome by 1 h upright. Inactive renin did not fall significantly after beta-adrenoceptor blockade. 4 Intravenous frusemide caused immediate rises in plasma active, total and inactive renin, angiotensin II, and aldosterone, which then declined over 2 h despite increasing cumulative sodium losses. 5 Intravenous propranolol or metoprolol attenuated, without abolishing, these early increases in the components of the renin-angiotensin-aldosterone system after frusemide. 6 Prior oral metoprolol or propranolol, while significantly slowing the heart, did not limit the early rise in plasma angiotensin II following intravenous frusemide. 7 Thus in contrast to previous workers, we did not find that propranolol eliminated the response of the renin-angiotensin system to upright tilting; in part this difference appeared to be due to the longer tilt we employed. 8 Also in contrast to earlier work, we found attenuation by both intravenous propranolol and metoprolol of the immediate rise in renin after intravenous frusemide.

Plasma catecholamines and cardiovascular responses during converting enzyme inhibition in normotensive and hypertensive man

The hemodynamic and plasma catecholamine responses to isometric exercise and head up tilt were investigated in normotensive and hypertensive subjects during normal and low sodium intake and before and during the administration of the converting enzyme inhibitors teprotide or captopril. Although teprotide and captopril decreased significantly the mean arterial pressure during both sodium intakes the normal pattern of hemodynamic response to hand grip and head up tilt was preserved. Moreover changes of plasma catecholamines during hand grip and head up tilt were not affected either by teprotide or captopril. When following the administration of teprotide or captopril fainting occurred either in the seated position or during head up tilt it was associated not only with a decrease in arterial pressure but also with a concurrent reduction in cardiac output and/or hypovolemia. It is concluded that converting enzyme inhibition does not impair significantly the cardiovascular responses which are mediated via the sympathetic nervous system either in normotensive or in hypertensive subjects.

Effect of beta-adrenergic receptor blockade with propranolol on the response of plasma catecholamines and renin activity to upright tilting in normal subjects

1 Relationship between plasma catecholamines (measured as noradrenaline and adrenaline) and plasma renin activity (PRA) were examined at rest and during passive head-up tilting for 30 min in nine normal subjects, before and after treatment with propranolol 160 mg daily for 7 days. 2 Noradrenaline (NA) and adrenaline (A) increased substantially after tilting for 15 min. There were no changes in PRA. After 30 min tilting, NA remained elevated, whereas A had returned to resting levels. A significant increase in PRA was apparent at 30 min. Pulse rate and diastolic blood pressure increased progressively during tilting. Systolic pressure did not change. 3 Treatment with propranolol reduced pulse rate and systolic blood pressure at rest and during tilting. Resting catecholamine concentrations and the response of NA to tilting were unaffected. In contrast, treatment prolonged the A response leading to significantly higher levels after 30 min tilting. Propranolol reduced PRA in six of the nine subjects and prevented the increase with tilting observed before treatment.

Effects of change in body posture on plasma and serum electrolytes in normal subjects and in primary aldosteronism

We observed that change in body posture from the supine to the erect position in normal volunteers was associated with a rise in circulating potassium and a fall in sodium concentrations, irrespective of whether the electrolytes were measured in serum or plasma, or whether head-up tilt or ambulation was used. In patients with primary aldosteronism, the fall in serum sodium and rise in serum potassium with ambulation tended to obscure the characteristic electrolyte abnormalities of that syndrome. These changes in potassium and sodium could contribute to the rise in aldosterone secretion on orthostasis. The body posture of patients should be considered in the interpretation of plasma and serum electrolyte levels.