Estradiol binding in different parts of the rabbit oviduct during egg transport

Binding of estradiol (E2) was determined in the nuclei and cytosols from ampullary (A), ampullary-isthmic junction (AIJ) and isthmic (I) segments of the rabbit Fallopian tube during the passage of the egg. In the estrus rabbits, low concentration of cytosol and high concentration of nuclear bindings in I was recorded in contrast to that of A. However AIJ had similar levels as that of A. Important alterations were recorded when binding of estradiol was compared at 12, 14, 24, 48, 70 and 144 h post coitum (p.c.). At 12 h the nuclear binding was decreased in all portions of the oviduct, while cytosol binding was increased. When ova are present in the ampulla (14 h p.c.) level of nuclear binding decreased while that of cytosol increased; but both types of bindings increased when eggs are normality in AIJ (24 h p.c.). The level of nuclear binding begins to increase in the isthmus reaching maximum at 48 h and then gradually declines at 70 h. The estradiol binding further declined in A and AIJ, but I showed no significant change at 144 h (the eggs being in uterus). In cytosol maximum binding was obtained at 70 h, thereafter the level in all portions recorded a decrease at 144 h p.c. On the basis of these findings it is concluded that there is some correlation between egg transport and different levels of estradiol binding in tubal segments. Increased influence of estradiol is required for the retention of egg at AIJ and also for the transport through the isthmus. However, a decrease in the level of the hormone would be necessary for the release of tubal lock at AIJ.