PROGESTERONE FACILITATES THE LRH RELEASING ACTION OF ESTROGEN

The effects of progesterone (P) on the release of LHRH and LH [luteinizing hormone] were examined in a sequential double chamber superfusion system by superfusing the medial basal hypothalamus (MBH) and/or pituitaries excised randomly from cycling female rats. Addition of 10 .mu.l of 10-6 M estradiol (2) to the first chamber resulted in a gradual and significant (60-160%) increase in LH release above the pre-injection level from the pituitary in series with MBH. Administration of 10-8 M after 10-6 M E2 caused a prompt and marked increase (300%) of LH (P < 0.05), while 10-8 M P alone had no effect. Administration of 10-6 M E2, 10-8 M P or E2 plus P did not significantly change LH secretion from the pituitary superfused alone. The concentration of LHRH in the efflux was significantly increased (150-200%) 150 min after 10-6 M E2 administration. P administration after E2 injection produced a prompt and significnat increase of LHRH and the increase of LHRH (300-600%) was 2- to 3-fold that produced by E2. P alone had no effect. P enhances E2-induced LH release by increasing LHRH secretion from the MBH.