Ontogeny of endocrine control of osmoregulation in chick embryo : I. Role of pituitary gland in distribution of water and ions among embryonic and extraembryonic compartments

Abstract

Distribution of water and of Na+ and Cl- ions in blood and in allantoic, amniotic, and yolk sac fluids were observed during ontogeny of the chick embryo. A possible osmoregulatory role for pituitary hormones was inferred from differences in ionic concentrations and volumes of these compartments in partially decapitated (hypophysectomized) embryos and in intact and windowed-control embryos observed on Day 16.5 of incubation (20-21 days to hatching). Na+-K+-ATPase activity was also measured in both mesonephric and metanephric kidneys in control and in hypophysectomized and pituitary transplanted embryos. Some osmoregulatory defects in hypophysectomized embryos were reversed by transplantation of anterior and posterior lobes of the pituitary for 1 week beginning on Day 9 of incubation. Allantoic fluid volume was reduced and Na+ and Cl- concentrations were elevated in this compartment in hypophysectomized embryos. Pituitary transplantation restored both measurements to control values. Amniotic fluid volume was not significantly changed by hypophysectomy when compared with windowed controls. Amniotic Cl- concentration was also insensitive to hypophysectomy. Pituitary transplantation lowered amniotic fluid volume slightly, but elevated its Cl- concentration significantly. Hypophysectomy reduced the percentage water content in yolk sac and significantly increased hydration of the embryo. Pituitary transplantation partially restored fractional water content of yolk to control levels and reversed body hydration. Hypophysectomy and transplantation had no significant effects on serum Na+ concentrations in the 16.5-day-old embryo. Activities of renal Na+-K+-ATPase were not significantly changed in mesonephros or metanephros by hypophysectomy or transplantation of one pituitary gland. Hormones of the pituitary gland appear to be required for normal distribution of water and ions in the chick embryo at 16.5 days of incubation. Possible target organs include both embryonic kidneys, but activities of renal Na+-K+-ATPase seem to be independent of pituitary hormones. Certain corrective actions obtained in response to metabolic hormones (thyroxine and corticosterone) suggest that some osmoregulatory defects observed in hypophysectomized embryos could result from impaired metabolism and a reduced rate of maturation rather than from the absence of specific osmoregulatory hormones of the pituitary gland.