CHANGES IN HYPOTHALAMIC NE AND DA TURNOVER RESULTING FROM STEROID-INDUCED LH AND PROLACTIN SURGES IN OVARIECTOMIZED RATS

Treatment of ovariectomized, estrogen primed rats wirh progesterone (P) resulted in a LH and prolactin (PRL) surge. A 2-fold increase in anterior hyopthalamic fragment (AHF) norepinephrine (NE) turnover was observed by 4 hr after P treatment and returned to control (Pre-P) levels by 6 and 9 hr after P administration. AHF dopamine (DA) turnover decreased by 6 and 9 hr after P treatment. No change in posterior hyopthalamic fragment (PHF) catecholamine turnover occurred after P administration. The increased AHF-NE turnover preceded the LH surge and occurred at the peak of serum PRL. The decrease in AHF-DA turnover occurred when both LH and PRL were elevated. Treatment with alpha-methyl-para-tyrosine (αmpt) at the time of P administration completely blocked the subsequent P-induced LH release observed in control animals. Alpha-mpt treatment 1 hr before blood collection decreased serum LH in animals killed at 4 and 6 hr, but not at 0 and 2 hr after P administration. Sustained treatment with the DA agonist, piribedil mesylate (1 mg/kg), did not affect peak levels of LH but blocked the PRL rise, indicating that the decrease in DA turnover after P administration is not essential for mediating the subsequent LH surge, but may be involved in the P-induced PRL surge. It is concluded that the transient increase in AHF-NE turnover is necessary for the P-induced increase in serum LH, whereas a decrease in hypothalamic DA turnover may be involved in the P-induced surge of PRL.