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Summary.Basal adenylate cyclase values for corpora lutea (CL) removed from cyclic gilts on Days 3, 8, 13 and 18 were 178 ± 61, 450 ± 46, 220 ± 25 and 208 ± 18 pmol cAMP formed/min/mg protein, respectively. Basal activity was significantly elevated on Day 8 (P< 0·001). LH-stimulatable adenylate cyclase values for CL from Days 3, 8, 13 and 18 were 242 ± 83, 598 ± 84, 261 ± 27 and 205 ± 17 pmol cAMP formed/min/mg protein respectively. Serum progesterone concentrations of 12 gilts bled every 2 days through one complete oestrous cycle ranged from 1·1 to 26·9 ng/ml with highest values between Days 8 and 12. The decline in serum progesterone concentrations was coincident with the decrease in basal adenylate cyclase activity. There was no LH-stimulatable adenylate cyclase activity present in the CL at the specific times of the oestrous cycle examined. We conclude that progesterone secretion by the pig CL is apparently dependent on basal activity of adenylate cyclase.

The objective was the immunocytochemical localization of steroidogenic enzymes in the corpus luteum of Hokkaido brown bears during the period of delayed implantation. Cholesterol side-chain cleavage cytochrome P450 (P450scc), 3β-hydroxysteroid dehydrogenase (3βHSD), 17α-hydroxylase cytochrome P450 (P450c17) and aromatase cytochrome P450 (P450arom) were localized as biosynthetic sites of pregnenolone, progesterone, androgens, and oestrogens, respectively. Ovaries containing corpora lutea were obtained from three mature bears during the expected delayed implantation period and ovarian sections were immunostained by the avidin–biotin–peroxidase complex method using polyclonal antibodies generated against steroidogenic enzymes of mammalian origin. P450scc and 3βHSD were localized in all luteal cells, whereas P450c17 (0.4–5.1% of 1000 cells) and P450arom (7.1–11.2% of 1000 cells) were localized in only a few luteal cells. These data suggest that luteal cells contain steroidogenic enzymes required for progesterone synthesis but also have a minimum capability for synthesizing androgen and oestrogen during the delayed implantation period in Hokkaido brown bears.