MIFEPRISTONE TREATMENT DEMONSTRATES THE PARTICIPATION OF ADRENAL GLUCOCORTICOIDS IN THE REGULATION OF ESTROGEN-INDUCED PROLACTIN SECRETION IN OVARIECTOMIZED RATS

Accumulated evidence indicates that the adrenal cortex is able to regu late prolactin (PRL) secretion in rats. The aim of this study was to d etermine the participation of adrenal steroids on the regulation of PR L release in ovariectomized (OVX) and oestrogen-treated rats, by using mifepristone or a specific progesterone antiserum. Blood samples were obtained at 13:00 and 18:00h 3 days after priming with oestradiol ben zoate (OB). A significant increase in serum PRL at 13:00 and 18:00 h w as induced by OB treatment. The administration of mifepristone to OVX and oestrogen-primed rats enhanced serum PRL increase at 13:00 h, with out modifying the values at 18:00 h; while the administration of proge sterone antiserum did not modify PRL levels, indicating that the effec t of mifepristone on PRL secretion is due to its antiglucocorticoid ac tion. Adrenalectomy induced a release of PRL at 13:00 h similar to tha t observed in the OVX and oestrogen-primed rats after mifepristone adm inistration. Treatment with a low dose of progesterone (0.1 mg/rat) to OVX, adrenalectomized and oestrogen-primed rats did not modify the ef fect of adrenalectomy in serum PRL. Progesterone (2 mg/rat) given at 0 8:00 h to OVX and oestrogen-primed rats increased serum PRL 5 h later. Mifepristone treatment partially reverted the PRL increase induced by progesterone. These results suggest that after a previous sensitizati on of the pituitary by oestrogen, circulating glucocorticoids may exer t a direct inhibitory effect on PRL release. This inhibition takes pla ce at 13:00 h on day 3. On the other hand, the lack of effect of mifep ristone or adrenalectomy on the PRL release at 18:00 h may also indica te that neither progesterone nor glucocorticoids modify PRL release in duced by oestrogen at this time.