oxytocin and Anovulation

A major limiting factor in the resumption of postpartum ovarian cycles in cattle is the inhibitory influence of the suckling calf on central regulatory elements controlling the release of GnRH from the median eminence. This inhibitory influence occurs only as a consequence of specifically defined behavioural interactions between the cow and calf in the presence of a maternal bond, cannot be simulated experimentally using thermal, electrical or mechanical stimuli, and is not dependent upon sensory ennervation within the udder. Indeed, the identity of the calf, either own or unrelated, appears to define the neuroendocrine events that attend the maintenance of the anovulatory state under controlled experimental conditions. Hence, new hypotheses that focus upon the relationship between physiological correlates of maternal behaviour and hypothalamic regulation of LH secretion are currently being tested. Specific aspects of these relationships remain conjectural, but are postulated to include the regulation of opioid tone, intracerebral oxytocin, and modulation of synthetic or excitatory activity of GnRH secretory neurones. Defining the role of the special senses in transduction of signals from calves that influence these neuronal processes may provide insight for developing practical intervention strategies of the future.

Topics: Animals; Anovulation; Cattle; Feedback; Female; Gonadotropin-Releasing Hormone; Gonadotropins, Pituitary; Lactation; Luteinizing Hormone; Maternal Behavior; Models, Biological; Oxytocin

Although it is clear that the initial endocrine deficit contributing to the length of the postpartum anovulatory period in suckled cows is of pituitary origin, this limitation is only operative for about the first 2 weeks of the puerperium. Thereafter, the pattern of LH secretion required for the final stages of follicular development and ovulation is blocked or attenuated through a more centrally regulated phenomenon. Hence, much of the recently published work in this area has focused on regulatory processes within the hypothalamus. This focus ignores the critical issue of exteroceptive signalling. Recent observations in this laboratory suggest that exteroceptive cues responsible for suckling-mediated anovulation are specifically attributable to the dams' own calf, but are not teat-specific. In fact, suckling does not produce an extended anovulatory state in the absence of a maternal-offspring bond. This review provides an historical perspective of investigations leading to this conclusion, and proposes a conceptual working model that links the special senses, maternal behavior and neuroendocrine centers that drive gonadotropin secretion during the puerperium.

Topics: Animals; Anovulation; Cattle; Female; Gonadotropin-Releasing Hormone; Lactation; Luteinizing Hormone; Maternal Behavior; Oxytocin; Postpartum Period

This study was undertaken to compare the effect of oxytocin and human chorionic gonadotrophin (hCG) on ovulation and conception. A total of 100 women with anovulatory infertility were allocated into two equal groups to take clomiphene citrate plus hCG or clomiphene citrate plus oxytocin. The size and number of follicles by transvaginal sonography determined the administration of hCG or oxytocin. The serum progesterone concentration was measured to provide evidence for ovulation. The ovulation and pregnancy rate of the two groups were compared. There was no significant difference between the groups with respect to mean number of follicles, mean follicular size and rate of ovulation in three cycles. The rate of pregnancy was higher in the oxytocin group compared with the hCG group (12% vs 4%) but it failed to reach statistical difference (p = 0.140). Mild pain was the only side-effect observed in the two groups. Oxytocin was found to be a viable alternative to hCG for triggering ovulation in infertile patients.

Topics: Adult; Anovulation; Chorionic Gonadotropin; Double-Blind Method; Female; Humans; Ovulation Induction; Oxytocin; Pregnancy; Pregnancy Rate; Prospective Studies; Reproductive Control Agents

Some component of the suckling process inhibits LH secretion and delays postpartum ovulation in beef cows. To investigate a possible role for maternal behavior in suckling-mediated anovulation, 27 crossbred beef cows were randomly allotted to 1 of 3 groups: 1) alien (dam suckled by alien calf; n = 11); 2) own (dam suckled by own calf; n = 8); and 3) weaned (calf removed for 6 days; n = 8). Beginning 14-17 days after parturition (experimental Day 0), cows were control suckled (10 min every 6 h) in stanchions for 6 days by either their own calf or by an alien calf or were weaned. Mean LH pulse frequencies in the alien and weaned groups were similar but were elevated (p < 0.02) on experimental Days 2 and 4 compared to those in the own group. The incidence of luteal activity by experimental Day 10 was greater (p < 0.01) for the alien (72.2%) and weaned groups (75.0%) than for the own group (12.5%). Frequency of oxytocin release following suckling was greater (p < 0.01) in the own group than in the alien group (Day 2: 100% vs. 36.4%; Day 4: 100% vs. 54.6%), whereas suckling-induced release of prolactin was similar for both groups. Data provide evidence that the mother-offspring bond is an important link in suckling-mediated inhibition of LH secretion and ovulation.

Topics: Aggression; Animals; Animals, Suckling; Anovulation; Cattle; Estrus; Female; Lactation; Luteinizing Hormone; Maternal Behavior; Oxytocin; Prolactin

Four normally menstruating subjects were studied throughout the menstrual cycle to investigate changes in plasma LH, arginine vasopressin (AVP), oxytocin (OT) and oxytocin associated neurophysin (NPOT). A clear mid-cycle LH peak was observed in each subject. Mean levels of AVP, OT and NPOT were 2.2 pmol/l, 1.1 pmol/l and 39 pmol/l, respectively. There were no significant differences between plasma levels during follicular, mid-cycle and luteal phases for each of these. Two further subjects with anovulatory cycles were studied in a similar way. In the first subject, with polycystic ovarian disease, posterior pituitary peptide levels were in the normal range, whereas the other subject, recovering from anorexia nervosa, had raised plasma levels of all posterior pituitary peptides (AVP 8.1 pmol/l, OT 1.8 pmol/l, NPOT 131 pmol/l, mean values) despite a normal osmolality. Administration of ethinyl oestradiol, 100 micrograms or 500 micrograms, had no effect of either AVP or OT, but 100 micrograms caused a marked rise in NPOT levels in all cases within 12 h (from mean 64 pmol/l to mean 196 pmol/l) and the levels remained elevated for 3 d.

Topics: Adult; Anorexia Nervosa; Anovulation; Arginine Vasopressin; Ethinyl Estradiol; Female; Humans; Luteinizing Hormone; Menstrual Cycle; Oxytocin; Pituitary Gland, Posterior; Pituitary Hormones; Polycystic Ovary Syndrome; Radioimmunoassay