The structure of steroids and their diffusion through blood vessel walls in a counter-current system.

Several substances including prostaglandin F2 alpha, progesterone and 85-krypton have been shown to be transferred from the venous side to the arterial side of the circulation in the ovarian vascular pedicle. Experiments were therefore carried out to study the transfer of three pairs of steroids (progesterone and 20 alpha-dihydroprogesterone, C-21; androstenedione and testosterone, C-19; and estrone and estradiol-17 beta, C-18) in which each member of a pair differed by one hydroxyl group. Each pair of steroids, one labeled with 3H and the other with 14C, were infused in sequence for 30 minutes into a side branch of an ovarian vein near the hilus of the ovary with a rest period of 90 minutes between infusions. An increase in radioactivity in ovarian arterial plasma compared to the radioactivity in an equal volume of aortic plasma sampled simultaneously was used as the index for a direct transfer of steroids from the ovarian vein to the adjacent ovarian artery. All six steroids showed such a transfer which began 3 to 6 minutes after the start of each infusion and decreased rapidly after the infusion was stopped. The results of this study also showed that a larger quantity of the less polar (ketonic) form of each steroid pair examined was transferred than its hydroxyl counterpart.