Neuroendocrine regulation of growth hormone and luteinizing hormone in fetal and neonatal pig.

Ontogeny of the production and the regulation of growth hormone and Luteinizing hormone is studied in a series of experiments utilizing male and female pigs at different fetal and neonatal stages. Growth hormone mRNA is detectable in both sexes as early as d. 50 p.c. The mRNA levels increase to reach the maximum levels at d. 95-110 p.c. Plasma levels of GH follow the developmental patterns of GH mRNA. A sex difference is evident around d. 80-90 p.c. with males having higher GH levels than females. The stimulatory but not the inhibitory mechanisms of GH secretion are fully functioning in the pig fetus. LHbeta mRNA is detectable earlier in females (d. 50 p.c.) than in males (d. 65 p.c.). Plasma concentrations of LH increase with fetal age in female fetuses, but in male fetuses there is no distinct developmental pattern evident. Basal LH secretion achieves maximum levels in both sexes after birth. Opioids do modulate fetal LH secretion, however, the mode of their action is age-dependent.