In-vitro effects of corticosterone, synthetic ovine corticotrophin releasing factor and arginine vasopressin on the release of adrenocorticotrophin by fetal rat pituitary glands

Abstract

The in-vitro release of ACTH by fetal rat pituitary glands on days 17, 19 and 21 of pregnancy was measured using radioimmunoassay. The spontaneous release of ACTH, expressed in pg ACTH/gland per h, increased with fetal age, in correlation with the sharp rise in pituitary ACTH content. However, since pituitary ACTH content was nearly sevenfold higher at term than on day 17, while basal release of ACTH was only threefold higher, one can speculate that the spontaneous release of ACTH was proportionally greater on day 17 than on day 21 of gestation. As corticosterone, at a physiological concentration (865 nmol/l), reduced ACTH release, it was concluded that the pituitary gland was one site of the negative feedback action of the corticosteroids during fetal life. Quantities of synthetic ovine corticotrophin releasing factor (CRF) which gave concentrations of 0.3-30 nmol/l in the incubation medium induced a sharp rise in ACTH release which was log-dose dependent between 0.3 and 3 nmolCRF /1 on day 17 and between 0.3 and 30 nmolCRF /1 on days 19 and 21. The response to CRF increased with fetal age. Quantities of arginine vasopressin (AVP) which gave concentrations of 2-200 nmol/l stimulated ACTH release at all stages of gestation investigated. However, the response to AVP was much lower than that to CRF. Potentiation of CRF-induced ACTH release was not observed when whole pituitary glands from 21-day-old fetuses were incubated with AVP (20 nmol/1) + CRF ( 3nmol /1). Such results were correlated with the ontogenesis of immunoreactive vasopressin- and CRF-containing fibres in the median eminence of the rat fetus, as well as with the CRF-like immunoreactivity present in adult rat pituitary portal plasma and the AVP content of the fetal rat hypophysis.

ACTH secretion from isolated hypophysial anterior lobes of male and female newborn rats: effects of corticotrophin-releasing factor, arginine vasopressin and oxytocin alone or in combination

“…Basal as well as CRF-induced ACTH release in vitro were equivalent for anterior lobes of 8-day-old male and female rats and similar to previous findings for whole pituitary glands at the end of gestation (Dupouy & Châtelain, 1984). In the two experiments, 0-2 nmol rCRF/1 induced an ACTH secretion equal to three to four times that of the basal level.…”

Pituitary Corticotroph Function during the Stress Hyporesponsive Period in Neonatal Rats

“…3). Dupouy et al [21], using superfused whole pituitaries from fetal rats at gestational days 17, 19 and 21, found a direct relationship between the quantity of ACTH spontaneously released in vitro (basal release) and the ACTH content of the fetal pituitary gland. Furthermore, at gestational day 21, just prior to parturition, CRF stimulation gave a 7-fold increase in ACTH release.…”

Maturation of the Pituitary-Adrenal Function in Rat Fetuses

“…These Fibers are abundant on day 19, when they establish connections with the external zone of the hypophysial portal vasculature. The pituitary glands from 17-to 21-day-old fetuses respond to in vitro incuba tion with synthetic CRF and AVP by a large increase in ACTH release [14]. It has been well established that y-globulins cross the placental barrier.…”

“…Besides CRF, other factors may play a physiological role in the reg ulation of fetal ACTH secretion. These factors include AVP, oxytocin, epinephrine, and angiotensin II (14,23]. AVP has been detected by immunohistochemistry in the hypothalamo-hypophysial system on the 14th day of fetal life [34].…”