Plasma levels of progesterone in the domestic hen related to the maturation of ovarian follicles, and changes in the secretion of progesterone by granulosa cells cultured for 24 hours.

Hens in their sixth month of lay were injected with a series of doses of ovine LH, either following the oviposition of a mid-sequence egg (which is closely associated with an ovulation), or following the oviposition of the last egg of a sequence. The concentrations of steroid hormones were subsequently measured by radioimmunoassay in blood withdrawn at intervals after injection. No changes were observed in the concentrations of either testosterone or 17 beta-oestradiol, irrespective of the dose of LH or the stage of the ovulatory cycle. An increase in delta-4-androstenedione was observed in all cases. This increase was minimal and unrelated to the dose of LH at the mid-sequence stage, but a dose-response relationship was observed in hens injected following the terminal oviposition of a series. Consistent, dose-related changes in the concentrations of progesterone in plasma were found at both stages of the ovulatory cycle, and the magnitude of these changes was 3.5-5 times greater than those observed for androstenedione. Granulosa cells from the first, second and third ovarian follicles were dispersed by collagenase and stimulated with ovine LH either immediately or following a 24 h pre-incubation in medium 199. The amount of progesterone released into the medium after 3 h was assessed by radioimmunoassay. A progressive decrease in this response was observed in cells derived from the first to the third follicles in all cases. Cells challenged after 24 h always showed increased responses, cells from the second follicle secreted similar amounts of progesterone as cells from the first follicle that were challenged immediately, without pre-incubation. The responses obtained after 24 h were attenuated if no bovine serum albumin was present in the medium, or if ovine LH had been present in the medium continuously. These results are interpreted as evidence for an increase in the secretion of progesterone by the granulosa cells of the hen which is linked to the maturation of the follicle. The final stages of this maturation may proceed in the absence of LH.