Secretion of Oxytocin and Progesterone by Ovine Corpora Lutea in Vitro1

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Abstract
The mechanisms involved in the control of oxytocin and progesterone secretion by the ovine corpus luteum have been investigated in vitro using luteal slice incubations. Oxytocin and progesterone were secreted at constant rates from luteal slices for 2 h of incubation (366 .+-. 60 pg .cntdot. mg .cntdot. h and 18.9 .+-. 0.18 mg .cntdot. mg .cntdot. h, respectively). Secretion of progesterone, but not of oxytocin, was significantly (p < 0.02) stimulated in the presence of ovine luteinizing hormone. Incubation of luteal slices in medium containing 100 mM potassium, however, resulted in increased secretion of oxytocin and, to a lesser extent, of progesterone (294 .+-. 59% and 142 .+-. 15%, respectively, p < 0.05). Basal oxytocin secretion was reduced during incubation in calcium-free medium, compared to secretion in the presence of calcium (70 .+-. 15 and 175 .+-. 25 pg .cntdot. mg .cntdot. 20 min, respectively, p < 0.01), whereas progesterone secretion was not altered in the absence of calcium. Secretion of both hormones by luteal slices was stimulated by the addition of the calcium ionophore A23187 (p < 0.05). Addition of prostaglandin F2.alpha. (2.8 .mu.M) had no effect on secretion of either oxytocin or progesterone. We have demonstrated that oxytocin and progesterone can be stimulated, independently, from corpus luteum slices incubated in vitro. The pattern of release is consistent with the proposal that oxytocin, but not progesterone, is associated with and actively released from luteal secretory granules. Our results also indicated that prostaglandin F2.alpha. does not directly stimulate release of oxytocin or progesterone from luteal cells in vitro.