EFFECT OF HISTAMINE AND ACETYLCHOLINE ON HYPOPHYSEAL STALK PLASMA DOPAMINE AND PERIPHERAL PLASMA PROLACTIN LEVELS

To further define the role of dopamine in the regulation of prolactin secretion, we studied the effect on prolactin and hypothalamic dopamine secretion of histamine and acetylcholine (ACh) injected into the lateral ventricle of urethane anesthetized diestrus-1 rats. Histamine (10 μg) caused a 592% increase in plasma prolactin levels and a 26% decrease in stalk plasma dopamine levels. ACh (50 μg) caused a 2090% increase in plasma prolactin levels but no significant change in stalk plasma dopamine concentration. To determine if the 26% fall in stalk plasma dopamine following histamine administration could account for the 6-fold increase in plasma prolactin, we measured the effect on prolactin secretion of a similar decrease in administered dopamine. During an infusion of physiologic levels of dopamine, a 25% decrease in arterial plasma dopamine concentration resulted in only a 2-fold increase in prolactin secretion. The results of these experiments suggest that the effect of histamine on prolactin secretion may be mediated in part by decreased hypothalamic secretion of dopamine but that an additional hypothalamic hormone is probably involved. The stimulatory effect of ACh on prolactin secretion is not mediated by dopamine. These data are consistent with the growing evidence for the participation of multiple hypothalamic factors in the regulation of prolactin secretion. © 1979.