Baboon corpus luteum: autonomous pulsatile progesterone secretion and evidence for an intraluteal oscillator demonstrated by in vitro microretrodialysis.

Abstract

Pulsatility of serum progesterone (P) is usually ascribed to stimulation of the corpus luteum (CL) by pulsatile release of pituitary LH. We investigated P secretion by the primate CL by performing microretrodialysis on 6 fresh CL obtained at laparotomy from baboons (Papio anubis) with well defined menstrual cycles. Individually microdialyzed for 24-26 h with Dulbecco's Modified Eagle's Medium and Ham's F-12 enriched with HEPES buffer in a perifusion chamber, the retrodialyzed fluid was collected every 10 min and measured for P, estradiol, and 17 alpha-hydroxyprogesterone 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 late 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 pulses in midluteal, and 6-19 pulses in late luteal phases. Peak lengths were 23.8 +/- 18.5 to 35.7 +/- 17.1 min. Four CL gave interpeak intervals of 46-55 min, whereas two gave intervals of 136-137 min. Analysis of distribution of pulses against different interpulse intervals in individual CL and all CL together revealed a bell-shaped distribution, with the largest number of pulses seen at an interpulse interval of 21-40 min. Because of the low concentrations of estradiol and 17 alpha-hydroxyprogesterone retrodialyzed, a similar analysis of these data was not possible. Histological examination of the tissue at the termination of the experiment using hematoxylin and eosin and localization of 3 beta-hydroxysteroid dehydrogenase activity indicates that the steroidogenic potential of the tissue is minimally affected, although some morphological changes do occur. Our findings suggest autonomous pulsatile P secretion by the primate CL, indicating local control by and the presence of an intraluteal oscillator or pulse generator for P secretion.