Secretion of estradiol-17β by porcine mammary gland of ovariectomized steroid-treated sows

Although the mammary gland of many species secretes estradiol (E2), nothing is known of E2 secretion in the porcine gland. The present study was designed to investigate whether porcine mammary gland was a source of E2, and to test the influence of individual and combined effects of exogenous progesterone and estradiol benzoate (EB) on the secretion of E2. Immature crossbred gilts were ovariectomized at 7 months of age followed by 4 weeks later by steroid hormone replacement therapy to produce estradiol and progesterone (P4) blood concentrations similar to those observed during a normal estrous cycle. Arterial and venous blood plasma (from carotid artery and anterior mammary vein, respectively) were sampled for 2 h at 10 min intervals. Plasma concentrations of progesterone, androstenedione (A4), testosterone (T), estrone (E1) and estradiol were determined by RIA. In all gilts treated with progesterone alone or in combination with EB, concentrations of P4, A4 and E1 in blood collected from venous outflow were lower compared to concentrations in arterial blood, whereas concentrations of E2 were higher in blood plasma from the anterior mammary vein compared to plasma from the carotid artery. The results indicated that the porcine mammary gland secreted E2. Increased concentrations of plasma E2 collected only from P4-treated animals suggested that progesterone activated enzymes involved in steroidogenesis in porcine mammary gland, or those utilized in its metabolism.