The effects of prolactin on rat ovarian function

Hyperprolactinemia has been associated with several reproductive disorders. To investigate whether hyperprolactinemia directly affects rat ovarian function, we examined the ovarian histopathology and the activities of the four ovarian enzymes 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), 17-hydroxylase (17-OH), 17,20-desmolase (17,20-D) and aromatase in hyperprolactinemic rats and controls. Hypophysectomized, gonadotropin-treated Fisher rats were made hyperprolactinemic by isografting pituitary glands under the kidney capsule. The control animals received skeletal muscle. The ovaries were resected, pooled according to prolactin levels and microsomal enzyme activities were measured from each pool. Prolactin (PRL) levels were 344 +/- 23 ng/ml in the hyperprolactinemic rats and 18 +/- 5 ng/ml in the controls (p less than 0.001). Estradiol concentrations were 609 +/- 47 pg/ml in the hyperprolactinemic animals and 56 +/- 13 pg/ml in the controls (p less than 0.001). Ovarian and uterine weights were significantly higher in the hyperprolactinemic rats (p less than 0.02). Ovarian histopathology demonstrated benign polycystic transformation in the hyperprolactinemic animals. Hyperprolactinemia had no effect on 3 beta-HSD, but was associated with significant decreases in the 17-OH, 17,20-D and aromatase activities when compared to controls (p less than 0.001). We conclude that prolactin has a direct effect on rat ovarian function which appears to be independent of changes in gonadotropin secretion.