Biology of Reproduction, Vol 26, 854-860, Copyright © 1982 by Society for the Study of Reproduction

ARTICLES

In vivo and in vitro production of progestins by the corpus luteum of pregnancy of the hamster

C Shaha and GS Greenwald

Synthesis by hamster corpora lutea (CL) in vitro and serum levels of progesterone (P4), 17 alpha-hydroxyprogesterone (17OHP) and 20 alpha- dihydroprogesterone (20DHP) were assessed for different days of pregnancy (Day 1=day of sperm; Day 16=day of delivery). Highest serum levels of the progestins were observed on Day 14 (P4=33 ng/ml; 17OHP=2 ng/ml; 20DHP=3 ng/ml), followed by precipitous declines on Day 16. The highest in vitro levels of luteal P4 and 17OHP were attained on Days 2- 6 (production rates of P4=9-30 ng/mg CL/h; 17OHP=0.6-1.5 ng/mg CL/h), and dropped gradually thereafter. In contrast, the production rate of luteal 20DHP was extremely low on Days 2-8 but abruptly increased on Day 10 and was maintained through Day 14 (4-8 ng/mg CL/h). The in vitro production rates of all 3 progestins dropped abruptly on Day 16. Thus, in the pregnant hamster on the day of parturition (Day 16) there was good agreement between in vivo and in vitro levels of the progestins, contrary to the situation in the rat, where on Day 22 the CL in vitro produce large quantities of P4 and 20DHP while the serum levels are very low (Taya and Greenwald, 1981). Addition of 25 ng/ml of ovine LH to the incubation media containing hamster CL increased production rates of P4 (18-55 ng/mg CL/h) and 17OHP (1.5-2.4 ng/mg CL/h) on Days 2, 4 and 14 of pregnancy but the CL were refractory to this dose of LH from Days 6 to 12. The production rate of luteal 20DHP ws never stimulated by the addition of 25 ng LH. These results indicate that P4 is the principal progestin in the pregnant hamster with 17OHP and 20DHP as minor metabolites. The latter 2 progestins have been measured for the first time in the pregnant hamster and the levels are very low in comparison to the pregnant rat.