EFFECTS OF CYCLOSPORINE ON CIRCULATING LEVELS OF PROLACTIN, LH, FSH, TSH AND GH IN CHRONIC HYPERPROLACTINEMIC MALE-RATS

The effects of cyclosporine (CyA) on pituitary hormone secretion in an imals with previously high plasma prolactin levels have been studied. Hyperprolactinemia was either induced in 30 day old male rats by the t ransplantation of one anterior pituitary gland from a litter mate dono r or they were sham-operated to be used as controls. Both pituitary-gr afted and sham-operated animals were injected s.c. with the vehicle or CyA (5 mg/kg weight per day) for 10 days, beginning 30 days after sur gery. As expected, pituitary grafting markedly increased plasma prolac tin levels as compared with the values found in control animals. Hyper prolactinemia was associated with reduced plasma LH and GH levels, inc reased plasma TSH levels and with no changes in circulating FSH levels . CyA administration to control animals increased plasma prolactin and TSH levels, decreased plasma levels of LH and did not modify circulat ing values of FSH and GH. Furthermore, CyA administration to pituitary -grafted animals decreased plasma prolactin and TSH levels, whereas pl asma concentrations of GH and gonadotropins did not change. These data suggest that CyA differentially affect the release of pituitary hormo nes and that there is an interrelationship between previously high pla sma prolactin levels and CyA to modulate pituitary hormone secretion.