DIFFERENTIATION OF THE CORPUS-LUTEUM OF THE MINK (MUSTELA-VISON) - MITOGENIC AND STEROIDOGENIC POTENTIAL OF LUTEAL CELLS FROM EMBRYONIC DIAPAUSE AND POSTIMPLANTATION GESTATION

The mink corpus luteum (CL) involutes after ovulation and remains dorm ant, synthesizing low amounts of progesterone until reactivated to ter minate embryonic diapause. We examined the mitotic and steroid synthet ic capacity of luteal cells from the diapause and postimplantation pha ses of mink gestation. Cells from diapause divided in vitro, reaching confluence in 7-8 days. Three phenotypes were distinguishable: a fusif orm cell in whorls, a hypertrophied epithelioid cell, and a small epit helioid cell. The first and second cell types divided in vitro after c onfluence, evidenced by localization of proliferating cell nuclear ant igen (PCNA) in their nuclei. The small epithelioid cells were present in cell nests and showed no PCNA activity. Cells derived from reactiva ted CL did not reach confluence and had no PCNA activity. Progesterone accumulation was enhanced in luteal cells from diapause by LH, FSH, a nd dibutyryl (Bu-2) cAMP, and by LH and (Bu-2)cAMP in cells from react ivated CL. in luteal cells from the diapause phase of gestation, LH an d (Bu-2)cAMP induced increases in mRNA coding for steroidogenic acute regulatory protein, while cytochrome P450 side-chain cleavage enzyme m RNA was increased by prolactin, LH and (Bu-2)cAMP. Cellular concentrat ions of 3 beta-hydroxysteroid dehydrogenase-Delta(5-4)-isomerase mRNA were increased by prolactin and (Bu-2)cAMP. Thus, luteinization in the mink CL does not engender exit from the cell cycle, as both fusiform and hypertrophied cells from diapause divide in vitro. Reactivation ap pears to represent terminal differentiation. LH is capable of stimulat ing steroidogenesis in vitro in luteal cells from diapause, and prolac tin and LH appear to have both specific and overlapping stimulatory ef fects on the CL of this species.