The regulation of glucocorticosteroid secretion during the perinatal period

Abstract

Summary. The regulation of adrenal activity during the perinatal period raises different experimental problems ; studies are often limited and their conclusions vary with the species studied. During the perinatal period, the profile of the ratio of adrenal weight to body weight reaches a minimum earlier the more mature is the species ; this minimum occurs before birth in sheep, at birth in guinea-pigs and 10 days after birth in mice.In mature species, fetal plasma cortisol is higher than that of the mother ; it rises sharply near term. In other species, maternal plasma cortisol remains higher than that of the fetus which also rises during the days before birth. In all species, the fetal adrenal is activated concomitantly with a sharp increase of the action of corticosteroid binding globulin on fetal plasma. The (Jost, 1954(Jost, , 1957(Jost, , 1966 (Wintour et al., 1975). In these species, the induction of parturition by the fetal adrenal gland has been extensively described and reviewed (Liggins et al., 1973). 4) Guinea-pigs : these laboratory animals present a relatively long gestation period with fetuses large enough to permit fetal surgical procedures and vessel catheterization. Moreover, the guinea-pig placenta appears to be very active and broadly resembles that of women (Duval, 1889 ;Myers et al., 1936 ;Kaufmann and Davidoff, 1977 (Gay, 1976 (Comline and Silver, 1961), pigs (Dvorak, 1972), goats (Currie and Thornburn, 1977) and calves (Boshier et al., 1980 ;Richet et al., 1984) Thornburn, 1977 ; pigs : F6vre, 1975 (Khaldoun, 1977) and macaques (Robinson and Bridson, 1978).The profile of CBG in neonatal plasma parallels this decrease. Furthermore, a half-life T1 /2 value of about 5 days for CBG has been measured in sheep (Ballard et al., 1982), rats and humans (Sandberg et al., 1964 (Koch, 1969) or in neonatal rabbits (Sereni et al., 1966). In newborn guinea-pigs, the glucocuronide conjugating system is defective (Brown and Zuelzer, 1958), and Dalle et a/. (1985) have demonstrated that, in this species, cortisol metabolism depends on its degradation in the liver and on its distribution volume. This volume develops during the neonatal period (Dalle et al., 1985), paralleling body growth after 10 days postpartum, but more slowly before this stage. Fetal steroid metabolism cannot be investigated without keeping in mind maternal influence on fetal plasma corticosteroid levels. Furthermore, the role of placental enzymes in steroid metabolism has been well documented in several species, especially in humans (Diczfalusy, 1962(Diczfalusy, , 1969Murphy, 1981) (Osinski, 1960 ;Villee et al., 1961 ; Goldkrand et al., 19761. We demonstrated a similar process in guinea-pigs (Dalle and Delost, 1976) showing that the cortisone/cortisol ratio in newborn plasma might be used as an index of adrenal maturity.The origin of fetal corticosteroids was investigated and their metabolism measured by infusing radioactive cortisol to pregnant guinea-pigs or to their fetuses.At the end of gestation, 90 % of the fetal cortisol...

Ontogeny of Plurihormonal Cells in the Anterior Pituitary of the Mouse, as Studied by Means of Hormone mRNA Detection in Single Cells

“…The rise in POMC expression at birth in the plurihormonal cell population suggests that cell types other than the classical corticotrope might express POMC at this age, possibly in response to an augmented demand of POMC products at that developmental stage. It is known that adrenocorticotropic hormone (ACTH) and glucocorticoid secretion are enhanced at birth (31) and that these high glucocorticoid levels are needed for lung development (32, 33). On the other hand, gonadotrope‐shaped cells in neonatal male rats have been shown to contain both ACTH and gonadotropins (21), identifying gonadotropes as candidate cells to coexpress POMC when requirement of the latter has raised.…”

The Regulation of Growth by Insulinlike Growth FactorII

“…Thus, in rats, down-regulation of hepatic IGF-II does not normally occur until 2 wk after birth. It coincides CHAPTER 22: REGULATION OF GROWTH BY IGF-II 715 with a sharp increase in circulating corticosterone concentration (81,372,395).…”

Distribution between Protein-Bound and Free Forms of Plasma Cortisol in the Gilt and Fetal Pig Near Term

“…Species exhibiting rapid prepartum adre nal growth with elevated corticosteroid secre tion (e.g., sheep) [9,28] and having minimal fetal-maternal transplacental exchange must produce its own binding proteins to protect itself from the effects of rising levels of both total and free corticosteroids on premature maturation and initiation of labor [7], Indeed, as documented in the fetal sheep. CBG con centrations parallel rising total cortisol levels thus keeping free cortisol levels constant until initiation of parturition [9,10].…”

“…113 (5). and 114 (7). For all day-114 gilts, mammary secretion was success fully obtained following manual expression of the teats.…”

“…The mechanism by which increasing activity of corticosteroids is achieved varies with species and is correlated with the maturity of the whole animal just before birth [7,8], In the fetal sheep, total cor ticosteroid levels rise during late gestation and are preceded by a major increase in CBG binding capacity [9,10]. Apparently, a higher adrenal production of corticosteroids, relative to CBG concentration, results in a prepartum rise in free corticosteroid levels [10].…”