Prolactin and the renin-aldosterone axis in human pregnancy

In view of observations suggesting an osmoregulatory role for prolactin (PRL) and the central role of the renin-aldosterone system in the regulation of pressure-volume homeostasis, this study was undertaken to determine whether acute drug-induced alterations in circulating PRL had any effect on mean arterial blood pressure (MAP), serum osmolality, and the renin-aldosterone response during early pregnancy. Bromocriptine suppressed mean baseline PRL by 83% (p > 0.05), whereas chlorpromazine increased it more than twofold (p < 0.05) during a 180-minute study period. MAP, mean serum osmolality, plasma renin activity, and aldosterone concentrations were not significantly different from mean baseline values after the administration of either drug. These data suggest that, during early pregnancy, the renin-aldosterone axis is independent of PRL and resistant to the beta-adrenergic agonist effect of chlorpromazine.