Dose-dependency and reproducibility of the prolactin response to metoclopramide

Oxytocin does not modify the prolactin response to metoclopramide in normal women

The present study was undertaken in order to establish whether oxytocin (OT) affects the dopaminergic control of PRL secretion in normal women during follicular, periovulatory and luteal phase of their menstrual cycle. For this purpose, 22 normal women were tested with a lower (1 mg) or higher (10 mg) dose of the dopaminergic antagonist metoclopramide (MCP) with or without the concurrent treatment with OT (2 IU injected plus 0.033 IU/min infused for 2 h). Since OT was found unable to modify the effect of either 1 or 10 mg MCP, in additional experiments the same doses of MCP and OT were administered after dopamine (0.04 micrograms/kg/min for 2 h) infusion. Also in these experimental conditions OT failed to modify the PRL response to MCP. These data argue against a role of OT in modulation of the dopaminergic control of PRL secretion in normal women.

Prolactin secretion in essential hypertension

This study was designed to evaluate prolactin (PRL) secretion in patients with essential hypertension. PRL secretory pattern was assessed by hourly blood sampling between 2200 and 0800 hours. Additional samples were collected at 0810 and 1000 hours (10 and 120 minutes after assumption of upright posture), as well as at 1200, 1400, and 1800 hours under normal simulated activities. No difference could be detected between the two study groups at any of the sampling times, and the number of secretory episodes were similar. Basal plasma renin activity levels were inversely related to simultaneous PRL levels in the hypertensive patients (r= -0.60, p less than 0.05). In the normal subjects mean overnight PRL levels were inversely related (r= -0.78, p less than 0.05) to the overnight urinary Na/K excretion. There was no PRL response to posture in either group. Hypertensive patients had a greater early response to the dopamine antagonist, metoclopramide than did normal subjects. Our data do not support the previously introduced concept of enhanced PRL responses to normal physiologic stimuli in essential hypertensives. However, it appears that dopaminergic control of PRL secretion may be altered in this disease state.