hyperprolactinemia of portal hypertension in rats.

Plasma prolactin levels are often raised in patients with liver cirrhosis and portal hypertension. To obtain more insight into the underlying mechanisms we examined the synthesis and release of prolactin in male rats with partially ligated portal veins. Portal hypertension led to an increase in pituitary prolactin, plasma prolactin, and plasma 17 beta-estradiol, and a decrease in hypophyseal stalk dopamine levels. Castration decreased plasma prolactin levels and prevented the induction of hyperprolactinemia by portal hypertension. Administration of dihydrotestosterone to castrated animals did not affect prolactin levels in the pituitary gland or in the plasma. Plasma tryptophan and tyrosine concentrations did not change in portal hypertension. A low protein diet caused a decrease in plasma tryptophan and an increase in plasma tyrosine levels without affecting prolactin levels in either controls or portal hypertensive rats. The hyperprolactinemia of portal hypertension is probably caused by elevated estrogen levels which interfere with hypothalamic dopamine release. Changes in plasma amino acid levels are of little importance in the regulation of prolactin release in portal hypertensive rats.U