VARYING RESPONSE TO LUTEINIZING-HORMONE OF 2 LUTEAL CELL-TYPES ISOLATED FROM BOVINE CORPUS-LUTEUM

Luteal cell suspensions obtained by enzymatic digestion of pregnant cow corpus luteum were found to be heterogenous and mainly made up of two types of cells of different sizes. The large cells (37μm, average diameter) could be separated from the small ones (18 μm, average diameter) by sedimentation at unit gravity in a gradient of Ficoll-bovine serum albumin. A comparative in-vitro study of the synthesis of progesterone by the two types of cells indicated striking differences between them. The average content and the synthesis of progesterone in the absence and presence of a saturating dose of bovine LH after incubation for 2 h were 0.07, 0.12 and 6.9 pg/cell for the small cells and 0.65, 2 and 10 pg/cell for the large ones. Moreover, the sensitivity to low concentrations of LH was 100 to 1000 times higher for the small cells than for the large ones. Oestradiol-17β at concentrations ranging from 5 x 10-10 to 5 x 10-4 mol/l exerted a dose-dependent inhibition on the stimulation of LH in both cell types. These results suggest a possible involvement of both cell types in the synthesis of progesterone in vivo with a greater contribution by the small cells to stimulation induced by LH. Moreover, it appears that small cell suspensions could be a useful model system for in-vitro studies of the control of the synthesis of progesterone in cow corpus luteum.