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On Days 13 and 14 of gestation in the rabbit, injections of cortisone acetate interrupt pregnancy by causing resorption of conceptuses (Robson & Sharaf, 1952). In the later stages of pregnancy, glucocorticoids administered to the mother have a shortening effect on gestation which is independent of a lethal effect on fetuses (Adams & Wagner, 1969). Large doses of glucocorticoids injected into the mother are known to induce premature delivery in sheep (Fylling, 1971), cows (Adams & Wagner, 1970) and goats (van Rensburg, 1970). Detailed investigations of the physiological significance of glucocorticoids in the termination of pregnancy in sheep and goats have revealed no consistent change in the plasma levels of maternal corticosteroids with advancing gestation (Paterson & Harrison, 1967; Thorburn, Nicol, Bassett, Shutt & Cox, 1972; Paterson

Summary. Prolactin secretion was stimulated in 5 cyclic gilts during the luteal phase (Day 10–13) with 5 mg haloperidol given i.v. Stimulation of prolactin secretion was also attempted by inducing milk let-down by suckling (4 sows), or by the injection of 1 mg oxytocin i.v. followed by hand milking (3 sows). Plasma prolactin concentrations increased significantly 1–2 h after haloperidol injection, and in 3 of 4 sows during suckling (P = 0·001); plasma relaxin concentrations did not change significantly at these times. No change was observed in plasma prolactin or relaxin concentrations at 15 min or 1–2 h after oxytocin injection and hand milking. Plasma relaxin concentrations ranged from below the sensitivity of the assay (100 pg/ml) to 450 pg/ml in lactating sows and from 100 to 2000 pg/ml in cyclic gilts. The results suggest that in cyclic gilts treated in the luteal phase with a dopaminergic receptor blocker, and in lactating sows during suckling, elevations in plasma prolactin concentrations were not accompanied, during the same period, by detectable changes in relaxin concentrations.

Summary. Myometrial activity was abolished abruptly but reversibly in 4 out of 5 ewes by the intravenous injection of 1 mg (500 GPU) porcine relaxin. Recovery began only after about 90 min and was not complete until 3–4 h after the injection. During the relaxin-induced inhibition the myometrium responded to oxytocin administered intravenously in doses of 250 mU. One ewe received intrauterine infusions of 2·5 and 5·0 μg PGF-2α per min during the period of relaxin inhibition: the former dose evoked a slight, and the latter a marked, response from the myometrium. The rate of rise of intrauterine pressure and the mean amplitude of pressure cycles were significantly depressed at 1, 1·5 and 2 h after the relaxin injection.

Summary. To determine the effects of prolonged hCG treatment in vitro upon granulosa cells from follicles of various sizes previously exposed to clomiphene citrate and hCG in vivo, progesterone and relaxin concentrations of spent media were correlated with light microscopic and ultrastructural characteristics. Intact, freshly dispersed cells were characterized by numerous lipid droplets, elliptical mitochondria with tubular or lamellar cristae, moderate rough-surfaced endoplasmic reticulum (RER), sparse smooth-surfaced endoplasmic reticulum (SER), and few Golgi. After 10–24 days in culture, 2 morphologically distinct cell types, 'granulosa-type' and 'luteal-type', were noted at the light microscopic level. Ultrastructurally, lipid droplets decreased in number, mitochondria became pleomorphic, RER became more prominent and dilated, and Golgi became more widely dispersed. Tubular SER became abundant and annular nexuses became more numerous after hCG treatment in vitro. Granulosa cells generated from all follicles responded to hCG treatment with significantly increased progesterone secretion after 4 days in culture. Relaxin was not detectable in any sample of medium. This study shows that human granulosa cells from 15–25-mm follicles retain their differentiated function of progesterone secretion in long-term culture and recover responsiveness to hCG in vitro, as demonstrated by enhanced progesterone secretion and development of prominent SER and increased annular nexuses.