Serotonin stimulation of the period of in vitro LHRH release is estradiol dependent.

The neurotransmitter serotonin (5-HT) has well known effects on the release of luteinizing hormone (LH) which may be estrogen and photoperiod dependent. An in vitro superfusion system was used to assess the potential role of 5-HT and photoperiod in modulating the release of luteinizing hormone releasing hormone (LHRH) from the mediobasal-suprachiasmatic-preoptic area (MBH-POA-SCN) in the ovariectomized (OVX) and OVX estradiol (E2) implanted rat model of LH release. Regularly cycling female Holtzman strain rats, maintained on a photoperiod of 0500-1900 or 0100-1500 hr light were OVX, and silastic capsules containing estradiol-17 beta (150 micrograms/ml) or sesame oil implanted SC. Two days later the rats were killed at 1000 hr and the MBH-POA-SCN isolated. Tissue was superfused in vitro with Krebs-Ringer-Phosphate buffer (KRP) for 2 hours followed by 3 hours of KRP with intermittent superfusion of 5-HT at increasing concentrations: 1 X 10(-10) M (1st hour); 1 X 10(-8) (2nd hour); 1 X 10(-6) M (3rd hour). Superfusate was collected every 10 min for the entire 5 hour incubation period and LHRH measured by RIA with the following results. In the OVX rat 5-HT significantly (p less than 0.05) increased the period of LHRH pulses and decreased the release of LHRH compared to control superfusions, while in the OVX E2 rat 5-HT significantly (p less than 0.05) decreased the period of LHRH release and increased the release of LHRH.(ABSTRACT TRUNCATED AT 250 WORDS)