SECRETION OF PROGESTERONE AND 20\g=a\-DIHYDROPROGESTERONE BY CORPORA LUTEA AND INTERSTITIAL TISSUE OF PREGNANT RABBITS

lutea (c.l.), follicles and interstitial tissue are normally present in the ovaries of pregnant rabbits, it has been difficult to determine whether interstitial tissue and c.l. both secrete both steroids (Dorrington & Kilpatrick, 1965), or whether, as is frequently assumed, 20\g=a\-dihydroprogesteronecomes predominantly from inter-stitial tissue and progesterone from c.l. (Hilliard, Archibald & Sawyer, 1963; Hil-liard, Spies, Lucas & Sawyer, 1968). Recently it has been shown that progesterone comes from c.l. and not from interstitial tissue by experiments using unilaterally X-irradiated ovaries of pregnant rabbits: these contained either c.l. and interstitial tissue or interstitial tissue alone (Keyes & Nalbandov, 1968). In this paper, further evidence of the site of progesterone secretion is reported from experiments using normal ovaries of pregnant rabbits. White rabbits in mid-pregnancy were anaesthetized with pentobarbital (25 mg./ kg.) and each blood sample from the ovarian vein was collected for 30 min. before and after surgical removal of c.l. by cauterization. Evidence that cautery destroyed only c.l. was obtained histologically. The techniques used for ovarian vein cannulation