In-vitro steroidogenesis of newly formed corpora lutea and the non-luteal ovary in the rat, rabbit, hamster and guinea-pig.

Abstract

The steroidogenic abilities of the newly formed corpus luteum (8–10 h after ovulation) and the non-luteal ovary were compared in the guinea-pig, hamster, rabbit and rat using an invitro incubation technique. Histologically, newly formed rat corpora lutea (CL) were highly luteinized whereas the CL of the rabbit and guinea-pig were only partially luteinized. The CL of the hamster showed the least amount of luteinization. Serum progesterone was highest in the rat (18 ± 3 (s.e.m.) ng/ml). In the hamster, it was about 8 ng/ml, whereas in the rabbit and guinea-pig it was about 1 ng/ml. Serum androstenedione ranged between 0·5 and 1 ng/ml. Serum testosterone was lowest in the hamster (60 pg/ml) and highest in the rabbit (470 pg/ml), whereas in the rat and guinea-pig, testosterone levels were similar (about 240 pg/ml). Serum oestrogens were at baseline levels in all species. The CL of the rat exhibited considerably greater steroidogenic ability than the CL of the other species, producing 70 ± 6 ng progesterone/mg per h, 215 ± 14 pg androstenedione/mg per h, 49 ± 3 pg testosterone/mg per h, 3 pg oestrone/mg per h and 1 pg oestradiol/mg per h. Rabbit CL produced only progesterone (7 ± 2 ng/mg per h). Newly formed hamster CL produced none of the above steroids. In general, the ability of the CL to produce progesterone in vitro correlated with the degree of luteinization found by histological observation. Guinea-pig CL were embedded deeply in the ovary and could not be obtained without damage. Consequently, a portion of the ovary containing a corpus luteum was incubated. There was no difference in the steroid production by this portion of the ovary compared with the non-luteal ovary. The non-luteal ovary of the rat produced the highest amount of progesterone (10 ± 2 ng/mg per h). The guinea-pig non-luteal ovary produced about 5 ± 2 ng progesterone/mg per h, whereas the non-luteal ovary of the rabbit did not produce any. On the other hand, the hamster non-luteal ovary lost progesterone. Non-luteal ovaries from all species produced androgens. The non-luteal ovary of the guinea-pig contained especially large numbers of atretic antral follicles. The guinea-pig non-luteal ovary produced extremely large amounts of androstenedione (1110 ± 210 pg/mg per h) and testosterone (606 ± 154 pg/mg per h) compared with the amounts produced by the non-luteal ovary of the rat, hamster and rabbit. In the non-luteal ovary, interstitium and atretic antral follicles are the probable source of androgens. Oestrogen production by the non-luteal ovary was at baseline levels in the four species studied correlating with the absence of healthy antral follicles. The results indicate the extreme species differences that exist in ovarian function in the early postovulatory period.