BABOON CORPUS-LUTEUM - AUTONOMOUS PULSATILE PROGESTERONE SECRETION AND EVIDENCE FOR AN INTRALUTEAL OSCILLATOR DEMONSTRATED BY IN-VITRO MICRORETRODIALYSIS

Pulsatility of serum progesterone (P) is usually ascribed to stimulati on of the corpus luteum (CL) by pulsatile release of pituitary LH. We investigated P secretion by the primate CL by performing micro-retrodi alysis on 6 fresh CL obtained at laparotomy from baboons (Papio anubis ) with well defined menstrual cycles. individually microdialyzed for 2 4-26 h with Dulbecco's Modified Eagle's Medium and Ham's F-12 enriched with HEPES buffer in a perifusion chamber, the retrodialyzed fluid wa s collected every 10 min and measured for P, estradiol, and 17 alpha-h ydroxyprogesterone by specific and sensitive RIAs. The chronodynamics of hormone secretion were analyzed for pulse detection by PC-Pulsar 3. 0. All 6 CL (2 each from early, LH +1 to +5; mid, LH +6 to +10; and la te luteal phases, LH +11 to +15) demonstrated pulsatile secretion of P in vitro, with distinct and detectable peaks over the 24-26 h studied . The CL secreted 23-27 pulses of P in 24 h in early luteal, 8-20 puls es in midluteal, and 6-19 pulses in late luteal phases. Peak lengths m ere 23.8 +/- 18.5 to 35.7 +/- 17.1 min. Four CL gave interpeak interva ls of 46-55 min, whereas two gave intervals of 136-137 min. Analysis o f distribution of pulses against different interpulse intervals in ind ividual CL and all CL together revealed a bell-shaped distribution, wi th the largest number of pulses seen at an interpulse interval of 21-4 0 min. Because of the low concentrations of estradiol and 17 alpha-hyd roxyprogesterone retrodialyzed, a similar analysis of these data was n ot possible. Histological examination of the tissue at the termination of the experiment using hematoxylin and eosin and localization of 3 b eta-hydroxysteroid dehydrogenase activity indicates that the steroidog enic potential of the tissue is minimally affected, although some morp hological changes do occur. Our findings suggest autonomous pulsatile P secretion by the primate CL, indicating local control by and the pre sence of an intraluteal oscillator or pulse generator for P secretion.