The cytosol receptors for progesterone in the different parts of rabbit fallopian tube and uterus during ovum transport.

Progesterone receptors were determined in the cytosol from the ampulla, ampullaryisthmic junction and isthmus of rabbit fallopian tube and uterus of estrus and pregnant rabbits. The receptor levels when compared among its various anatomical segments, were the same in ampulla, isthums and uterus but maximum in ampullary-isthmic junction. Significant differences were observed in mated animals at 14, 24, 34, 48, 70 and 144 h after coitus. The receptor concentrations in portions of the fallopian tube showed no significant change between 14 and 24 h after coitus, except for a decrease in ampullary-isthmic junction at 24 h. At 34 h the concentration of receptor further decreased in all parts of the tube. At 48 and 70 h after coitus, receptor concentrations decreased gradually in ampulla and ampullary-isthmic junction, while isthmus showed a gradual increase. At 144 h, the receptor concentration showed no further change in ampulla and ampullary-isthmic junction; however, isthmus showed a decline. The uterine receptor concentration declined steadily from estrus till 70 h after coitus, however, it was increased at 144 h. The dissociation constant (Kd) of cytosol receptor in all the tissues at estrus and during early pregnancy was found similar. The implications of these changes in relation to the normal ovum transport have been correlated in this paper.

The binding of progesterone in different parts of the rabbit uterus during implantation.

Progesterone receptors, both nuclear and cytosolic, were determined in the embryonic and inter-embryonic segments of the rabbit uterus at 6, 7 and 8 day post-coitum. At day 6 postcoitum a higher concentration of nuclear receptor in the embryonic segment was observed compared with that in the inter-embryonic segment. A reverse situation was observed in the case of cytoplasmic receptors. On the 7th day post-coitum, no significant alteration in the concentration of either kind of the receptors was observed. However, on day 8, a higher concentration of both nuclear and cytosolic receptors at the embryonic site was observed compared to that in inter-embryonic segment. Since receptors are influenced only in the immediate vicinity of the blastocyst, it can be suggested that the blastocyst plays a role in the induction of its own implantation. Further, at day 8 increase in receptor concentration at the embryonic site may be related to the presence of decidual tissue at this site.