Intravascular catheters were placed in the umbilical, uterine and maternal peripheral circulations of 16 Jersey cows between 240 and 260 days of gestation. Fetal plasma cortisol, blood gases and pH, and maternal plasma estrogen, progesterone and cortisol were measured in ten animals during late pregnancy and throughout spontaneous parturition; all delivered live fetuses, although parturition was earlier than normal and the placenta was generally retained. The gradual pre partum rise in fetal plasma cortisol during the last wk of gestation (from 10 to 20 ng/ml 7 days before parturition to 51±5 ng/ml in the last 3 hr before delivery) was much less marked than the abrupt increase immediately after birth when the cortisol concentration invariably doubled. Maternal plasma estrogen rose from 0.35±0.04 ng/ml to 1.20±0.11 ng/ml during the wk before parturition. Progesterone concentrations remained stable until a sudden fall 1 to 2 days before delivery. The slight alterations in maternal plasma cortisol during this period were not statistically significant. The maternal plasma estrogen levels were higher in the uterine vein than in the periphery, whereas uterine venous progesterone concentrations were significantly lower than in the peripheral circulation. The hormonal changes associated with the artificial induction of labor were investigated by the administration of cortisol, dexamethasone or corticotrophin to the fetus (four animals). In each case, premature delivery occurred 5 to 6 days later; the maternal hormonal changes were very similar to those in untreated catheterized cows. These findings contrasted sharply with the known, rapid effect of dexamethasone given directly to cows in late pregnancy. This action of dexamethasone was confirmed in two catheterized cows (at 257 and 260 days of gestation); one dose of 25 mg (i.m. to the cow) was sufficient to cause delivery within 40 hr. No changes in fetal plasma cortisol concentration occurred until the increase immediately after delivery but the usual maternal hormonal changes were telescoped into a sudden rise in estrogen and fall in progesterone. The changes in fetal and maternal hormone levels during induced and naturally occurring parturition are discussed in relation to findings in other species.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism