Effects of dopaminergic antagonists on dopamine-induced cardiovascular and insulin secretion actions in hypertensive patients.

A comparative study between two dopaminergic antagonists: metoclopramide and domperidone, was undertaken in nineteen (19) hypertensive patients at the Vargas Hospital, Caracas. The patients were pretreated with labetalol, 800-1,200 mg/day, orally, over a period of one week, after which they were divided into two groups: group A, a total of eleven patients were intravenously infused with dopamine hydrochloride 0.5-3 micrograms/kg/min, before and after treatment with metoclopramide (10 mg, i.v. as a bolus); group B (n = 8), was pretreated with domperidone, 20 mg b.i.d., p.o. over a period of one week and intravenously infused with dopamine hydrochloride, 0.5-3 micrograms/kg/min. In group A, dopamine induced a decrease of blood pressure from 171.9 +/- 6.35/103.6 +/- 3.12 to 152.7 +/- 7.55/93.8 +/- 2.97 mmHg (p < 0.001) without altering heart rate, and it increased plasma insulin levels from 8.29 +/- 0.70 microunits/ml to 12.09 +/- 1.83 microunits/ml (p < 0.01). Metoclopramide caused no changes of blood pressure or plasma insulin levels. However, hypotensive responses and plasma insulin rises due to dopamine were blocked by metoclopramide. In group B, domperidone also blocked dopamine-induced antihypertensive effect (from 170.0 +/- 9.23/102.8 +/- 3.80 to 160.2 +/- 9.84/95.5 +/- 2.50 mmHg) although it was less effective than metoclopramide. Domperidone also blocked dopamine-induced increase of plasma insulin levels from 9.65 +/- 4.50 microunits/ml to 11.78 microunits/ml. We conclude that a dopaminergic receptor may be involved in some cardiovascular responses and in modulating insulin secretion in man.