Cyclic Nucleotides, DNA, and Steroid Levels in Ovarian Follicles and Corpora Lutea of the Cyclic Hamster

Abstract

The largest follicles present on each day of the 4-day hamster estrous cycle and the corpora lutea (CL) were isolated and incubated independently for 1 h. The serum and incubation medium wre analyzed for steroids; tissue levels of DNA, cyclic nucleotides and steroids were also determined. Day 1 of the cycle corresponded to the day of ovulation and Day 4 to proestrus. Based on a value of 6.4 pg DNA/cell, the CL contained approximately the same theoretical number of cells through the first 3 days of the cycle: 1.23 .times. 105 cells. Cyclic AMP and cGMP in the CL were maximal on Day 3 when luteolysis was advanced as evidenced by nondetectable levels in the serum of progesterone (P) and low levels of P, 17.alpha.-OH-progesterone (17-OH-P), 20.alpha.-OH-progesterone (20-OH-P) and testosterone (T) in the incubation media. The medium following luteal incubation on days 1-4 of the estrous cycle contained increasing amounts of estradiol (E2) but this appears to be of follicular origin. Thus, on day 3 although it seems that the luteal adenylate cyclase increased cAMP formation, the link to steroidogenic stimulation was broken. The largest follicles (fol) present on day 1 (preantral) released low levels of E2 and T (25 and 16 pg/fol) into the incubation medium while values for P, 17-OH-P and 20-OH-P were slightly elevated (0.66, 0.37 and 0.08 ng/fol). Between 0900 h Day 2 and 0900 h Day 4, E2 in serum and medium rose steadily (from 22 to 91 pg/ml, serum; from 51 to 180 pg/fol, medium) while the other steroids remained constant (T) or decreased (P, 17-OH-P and 20-OH-P). Cellular numbers (based on DNA values) rose during this period and reached a maximum in preovulatory follicles on Day 4, 1400 h (5.2 .times. 105 cells/fol). From Day 1 until 0900 h Day 4, tissue levels of cGMP/fol were higher than cAMP. However, beginning at 1400 h, Day 4 (the onset of the surge in LH) there was an abrupt increase in cAMP and steroids with a concomitant decline in cGMP. The peak level of cAMP at 1700 h was an increase of 14 times above the 0900 h value. Both in vitro (in follicular incubations) and in vivo (in serum) the surge of E2 and T at 1400 h Day 4 was followed by a precipitous decline at 1700 h. In serum and follicles, P, 17-OH-P and 20-OH-P continued to increase through 1700 h. However, levels of 17-OH-P and P in the incubation medium remained consistently higher than 20-OH-P on Day 4 and throughout the cycle. The high level of 17-OH-P following the luteinizing hormone surge in the hamster differ from the decline observed in the rat. Apparently, in the hamster C17-20 lyase is a pivotal enzyme controlled by gonadotropins or steroids and 17-OH-P may represent a metabolic endpoint similar to 20-OH-P in the rat.