Countercurrent Transfer of Testosterone by the Ovarian Vascular Pedicle of the Cow: Evidence for a Relationship to Follicular Steroidogenesis1

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Abstract
Utilizing an in vitro perfusion procedure, the current studies were performed to determine whether [3H]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 in ovarian arterial blood of all preparations tested. [3H]T was also infused directly into the arterial circulation. During constant-rate infusion, .apprx. 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 min 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 T was markedly lower (P < 0.001) and concentrations of estriol, dihydrotestosterone/androsterone, androstanedione, estradiol-17.beta., androstenedione, androstanediol, and estrone were consistently higher (P < 0.001) in FF, granulosa (Gr) and theca (Th) relative to concentrations in the highly purified infusate (> 99.5% T). In 60 min experiments, in which perfusion continued for 30 min after termination of [3H]T infusion, sequestered radiolabel as T declined (P < 0.001) in both follicles (17-20%) and ovarian venous effluent (2-5%) relative to that present in the infusate. Coincident with this decline in [3H]T was a marked (P < 0.001) increase of all 7 metabolites studied in FF, Gr and Th. All of these steroids, except androstanediol and estradiol-17.beta., 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.