Possible role of the pineal gland in pituitary prolactin secretion in female rats.

Wistar female rats housed under conditions of 12 hr dark/12 hr light were pinealectomized (PX) or underwent sham-operation (SO) 21 days after ovariectomy, on the 7th or on the 15-17 th day of pregnancy. Serum and pituitary prolactin (PRL) levels in ovariectomized (OVX) rats were determined 9 days after pinealectomy. In the case of OVX rats receiving estrogen and progesterone injections (OVX-EP), PRL levels were determined 48 hr after injection administered 7 day after pinealectomy. PRL levels in pregnant rats were determined on the 20th day of pregnancy and in postpartum rats, on the 3rd day following parturition. As compared with the SO control, pinealectomy resulted in a significant decrease in the serum PRL level in the OVX-EP rats but in a significant increase in that level in the OVX, pregnant and postpartum rats. In OVX-EP rats, exogenous estrogen raised the serum PRL level less in PX than in SO rats, probably because the pineal gland is closely related to the facilitation of PRL secretion by estrogen. The high estrogen level in OVX-EP rats seemed to trigger pineal stimulation of PRL release, but low estrogen levels in OVX and postpartum rats or markedly high levels of progesterone in pregnant rats on the 20th day are thought to cause pineal inhibition.