Suppression of Plasma Luteinizing Hormone by Prolactin in the Male Rat

Abstract

The secretion of LH [luteinizing hormone] and FSH [folicle stimulating hormone] was studied in response to the stimuli of castration and LH releasing hormone administration in adult male rats made hyperprolactinemic with ectopic pituitary glands. Although plasma LH and FSH levels were similar in non-castrate hyperprolactinemic rats vs. controls, LH concentrations 24 h postcastration were less in hyperprolactinemic animals as compared to controls. The level of LH achieved was inversely correlated with the PRL [prolactin] concentration generated. LH suppression was evident in hyperprolactinemic rats at 1 and 3 days postcastration but was no longer observable at 7 days postcastration. After LH releasing hormone administration to non-castrate rats the rise in plasma LH was significantly less in the hyperprolactinemic animals. PRL directly inhibits LH secretion, presumably at the pituitary level.