LOCAL STEROID CONCENTRATING MECHANISM IN THE REPRODUCTIVE VASCULATURE OF THE EWE

A local counter current exchange mechanism for progesterone was demonstrated between the uteroovarian vein and the ipsilateral ovarian artery in nonpregnant and pregnant ewes. [3H]-progesterone ([3H]-P; 55.7 Ci/mmol) was infused into the uterine vein (1.3 μCi/min, 7.5 ng/min) and simultaneous measurements of the amount of [3H]-P in plasma from the ovarian artery and a mesenteric artery of similar size were made. In both pregnant and nonpregnant ewes, infusion of [3H]-P into the uterine vein significantly increased (P<0.001) the concentration of [3H]-P in ovarian arterial plasma but not in control samples from mesenteric arterial plasma (P>0.10). Pregnant ewes had consistently lower levels of [3H]-P in ovarian arterial plasma when compared with nonpregnant ewes. The results indicate that tissues vascularized by the ovarian artery are exposed to higher levels of progesterone than are peripheral tissues and that ewes are capable of counter current transfer of progesterone in the reproductive vasculature. We suggest that counter current transfer of progesterone and possibly other steroids may provide an important means of local regulation within the reproductive tract.