Plasma Renin Activity, Active and Inactive Renin Concentrations, and their Responses to β₁-Adrenoceptor Blockade with Metoprolol in Hyperthyroidism

Summary

Plasma renin activity (PRA), plasma renin concentration (PRC), inactive renin concentration (IRC) and total renin concentration (TRC) were measured in 31 normal controls and in 8 patients with hyperthyroidism. TRC was determined as angiotensin I generated with sheep renin substrate after an acid activation of plasma. The angiotensin I of non-acidified plasma was expressed as PRC. IRC was calculated as TRC minus PRC. The mean values for PRA, PRC, IRC and TRC were significantly (P < 0.05 to P < 0.01) higher in the hyperthyroid patients than in the normal or euthyroid controls. The administration of a beta₁-adrenergic blocker, metoprolol (120 mg/day for 14 days), produced a significant (P < 0.05 to P < 0.01) fall in levels of T₄, PRA and TRC, and reduced the active renin ratio calculated from PRC/TRC significantly (P < 0.025), as compared to the pretreatment values. Our observations support the idea that the higher PRA in hyperthyroidism is due to an increased secretion of renin. Furthermore, the results may indicate that the conversion of inactive to active renin is accelerated in hyperthyroidism, possibly by an increased sympathetic activity.

Key-Words

Plasma Renin Activity - Plasma Renin Concentration - Inactive Renin Concentration - Metoprolol - Hyperthyroidism