Effect of insulin-induced hypoglycemia on adrenergic responsiveness and forearm haemodynamics in low- and normal-high-renin hypertension

Abstract

In order to elucidate possible differences in adrenergic responsiveness and forearm haemodynamics between patients of different renin-status, hypoglycemia was induced by insulin in seven patients with low-renin and in seven patients with normal-high-renin hypertension. Nearly identical nadir plasma glucose values were obtained 45 min after insulin administration. Simultaneously, plasma adrenaline and plasma noradrenaline concentrations as well as plasma renin activity increased in both groups of patients indicating an increased sympathetic nervous activity whereby renin release was stimulated. However, plasma renin activity remained significantly lower in the low-renin group compared with the normal-high-renin group during hypoglycemia. No significant differences were found between the two groups in basal values or in changes of plasma catecholamines. Mean blood pressure and calculated forearm vascular resistance decreased, whereas forearm blood-flow increased, which indicates that the β₂ receptor vasodilator action of adrenaline overweighed the vasoconstrictor action of angiotensin II and noradrenaline. No significant differences were found between the two groups in the basal state of forearm haemodynamics, and changes in mean blood pressure and calculated forearm vascular resistance did not differ significantly. However, forearm blood-flow increased significantly more in low-renin patients than in normal-high-renin patients during hypoglycemia. The results support an equal adrenergic responsiveness and favour a different response of forearm hemodynamics mainly due to differences in blood pressure in low and high-renin hypertension during insulin-induced hypoglycemia.

Key Words:

• adrenergic responsiveness
• arterial hypertension
• catecholamines
• forearm hemodynamics
• plasma renin activity