Countercurrent transfer of testosterone by the ovarian vascular pedicle of the cow: evidence for a relationship to follicular steroidogenesis.

Abstract

Utilizing an in vitro perfusion procedure, the current studies were performed to determine whether [3H]T testosterone ([3H]T) is transferred from ovarian vein to artery by countercurrent penetration during Days 18–19 of the bovine estrous cycle. The possible relationship of such a transfer to follicular steroidogenesis was also examined. Infusion of [3H]T, but not 51Cr-red blood cells, into the ovarian vein 1–2 cm below the ovarian hilus resulted in the recovery of radiolabel (ⵐ4.7%:range=2–1 3%) in ovarian arterial blood of all preparations tested. We also infused [3H]T directly into the arterial circulation. During constant-rate infusion, approximately 43% of the [3H]T infused into the vein and 37% of that infused into the ovarian artery remained sequestered within the periovarian tissue-fluid complex. At the end of 30-mm experiments, a markedly higher (P<0.001; P<0.05) amount of radioactivity per ml follicular fluid (FF) was observed in the largest follicle compared to that observed in small-medium follicles. Radioactivity remaining in follicles as testosterone (T) was markedly lower (P<0.0O1) and concentrations of estriol, dihydrotestosterone! androsterone, androstanedione, estradiol-17β, androstenedione, androstanediol, and estrone were consistently higher (P<0.O01) in follicular fluid (FF), granulosa (Gr) and theca (Th) relative to concentrations in the highly purified infusate (>99.5% T). In 60-mm experiments, in which perfusion continued for 30 mm after termination of [3H]T infusion, sequestered radiolabel as T declined (P<0.001) in both follicles (17–20%) andovarian venous effluent (2–5%) relative to that present in the infusate. Coincident with this decline in ([3H]T was a marked (P<O.001) increase of all seven metabolites studied in FF, Gr and Th. All of these steroids, except androstanediol and estradiol-17β, increased (P<0.05) in ovarian venous effluent of ovaries bearing the largest follicle or small-medium follicles. Results suggest an important countercurrent concentrating mechanism for T in the ovarian vascular pedicle which provides additional substrate for follicular metabolism/aromatization.