LUTEAL AND PLACENTAL CHARACTERISTICS OF CARNIVORE GESTATION - EXPRESSION OF GENES FOR LUTEOTROPHIC RECEPTORS AND STEROIDOGENIC ENZYMES

Experiments were carried out to investigate the abundance of mRNA for luteotrophic receptors and steroidogenic elements in the ovaries and c orpora lutea of mink during the embryonic diapause, peri-implantation and postimplantation pregnancy. The second aim was to determine whethe r the mink placenta synthesized progesterone. Homologous cDNA probes f or the mink LH and prolactin receptors were generated by the polymeras e chain reaction. Heterologous cDNA probes for steroidogenic acute reg ulatory protein (StAR), cytochrome P450 side chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase-Delta(4)-Delta(5) isomerase (3 beta HSD) were also used. The abundance of mRNA encoding the prolacti n receptor was low during the period of embryonic diapause and increas ed concurrent with circulating progesterone. The abundance of LH recep tor message reached peak values during the peri-implantation period fo llowed by maintenance of a steady-state after implantation. The abunda nce of StAR and P450scc messages appeared not to vary during gestation , while that for 3 beta HSD was correlated with changes in circulating progesterone. There was no evidence of 3 beta HSD activity or transcr ipts in the placenta. These results indicate that prolactin and LH are necessary for activation of the corpus luteum during the period of em bryonic diapause, and for its maintenance during postimplantation gest ation. The mink placenta does not synthesize progesterone.