Dopaminergic regulation of circadian rhythms of blood pressure, renin and aldosterone in essential hypertension

SUMMARY

This study examines the influence of bromocriptine, a dopamine agonist, circadian mean arterial blood pressure (MAP) levels and circadian secretory patterns of plasma renin activity (PRA) and plasma aldosterone in essential hypertension. Nine patients with sustained essential hypertension were studied after they had reached metabollic equilibrium on a constant 100 mmol sodium and 80 mmol potassium intake. MAP measurements and PRA and aldosterone determinations were made at 30 min intervals over 24 h during a control (no medication) and a bromocriptine period (bromocriptine, 2.5 mg three times a day for 5 days). In the control period there was a clear circadian rhythm in blood pressure in these hypertensive patients with lowest MAP occurring during sleep. Bromocriptine treatment was associated with a depression in MAP throughout the 24 h cycle. Circadian patterns for both PRA and plasma aldosterone were observed in all patients before and after bromocriptine treatment. PRA demonstrated peaks between 1600 and 2000 h and again between 2400 and 0600 h. Peak aldosterone occurred in the late hours of sleep, 0400 to 0630 h, and shortly after awakening, 0800 to 0900 h. Although bromocriptine did not significantly affect the circadian rhythm of PRA and aldosterone it did decrease (P<0.05) mean 24 h recumbent PRA from 2.3±0.1 ng/cm³·h⁻¹ to 1.40±0.1 ng/cm³·h⁻¹ and plasma aldosterone from 8.5±0.3 ng·dl⁻¹ to 6.8±0.2 ng·dl⁻¹. 24 h recumbent blood pressures were not correlated with PRA or plasma aldosterone, and PRA and aldosterone were not correlated. These observations suggest that hour-to-hour maintenance of blood pressure is not dependent on the renin-angiotensin-aldosterone system in patients with essential hypertension. Dopaminergic mechanisms do not appear to account for the circadian periodicity of renin and aldosterone secretion.