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 were 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 three days of the cycle: 1.23 × 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, 17α-OH-progesterone (17-OH-P), 20α-OH-progesterone (20-OH-P) and testosterone (T) in the incubation media. The medium following luteal incubation on Days 14 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 adenylyl 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/mI, 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 × 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 and was more striking than values reported for the whole ovaries of cyclic or prepubertal rats treated with pregnant mare’s serum (PMS). Both in vitro (in follicular incubations) and in vivo (in serum) the surge of E, 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 levels of 17-OH-P following the LH surge in the hamster differ from the decline observed in the rat. It appears that in the hamster Cl 7–20 lyase is a pivotal enzyme controlled by gonadotropins or steroids and that 17-OH-P may represent a metabolic endpoint similar to 20-OH-P in the rat.