Porcine growth hormone and prolactin: concentrations in the fetus and secretory patterns in the growing pig.

The concentrations of growth hormone (GH) and prolactin (PRL) were measured in serum harvested from umbilical arterial blood of fetal pigs from 40 to 112 days of gestation and the secretory patterns of these hormones determined in plasma obtained from jugular blood samples at 5, 13, 18, and 24 wks after birth. Fetal serum concentrations of GH appeared to parallel the changes in fetal weight until approximately 75 days of fetal age, after which minimal change in GH concentrations occurred. The PRL concentrations in fetal sera reached 1 to 1.5 ng/ml on days 40 to 50 of fetal age and declined approximately 50% through 80 days of fetal age. Near day 80 of gestation, fetal serum PRL concentrations began to increase from nadir concentrations to 3 ng/ml on day 112. In postnatal pigs, the level of GH secretion declined with age and this decline was mainly associated with a reduction in the amplitude of secretory peaks. Decreases in incidence and amplitude of PRL secretory peaks were the only significant age-associated changes observed in PRL secretion postnatally.