Postnatal Development of Circadian Rhythm of Corticotropin-Releasing Activity in the Rat Hypothalamus

Abstract

SynopsisPostnatal development of circadian rhythm of the hypothalamo-pituitary-adrenocortical axis was examined by sacrificing rats twice a day, i. e., 8:30 a. m. and 6:30 p.m. Circadian rhythm of plasma corticosterone level became evident during the third week of life. Hypothalamic content of corticotropin-releasing factor (CRF) was not detectable till the end of the second week after birth. A significant increase of CRF activity became manifested in the evening during the third week of postnatal life, whereas the CRF activity in the morning remained undetectable. Thus, it is apparent that a significant circadian rhythm of hypothalamic CRF activity also begins during the third week of postnatal life in the rat under our experimental conditions. The finding may provide further support for the existence of a circadian rhythm in the hypothalamic CRF content with the peak value in the evening and the nadir in the morning.

The Effect of Perinatal Thyroxine Treatment on the Development of the Plasma Corticosterone Diurnal Rhythm

“…Intact and vehicle-treated animals in experiment 1 exhibited a pronounced a.m.-p.m. difference in plasma corticosterone content on days 23 and 28 of life, which is in accordance with data in the literature [A llen and K e n d a ll, 1967; A d er, 1969; HiROSHiGEand Sato, 1970;R amaley, 1973]. Experiment 2 showed, however, that this a.m.-p.m. difference begins to develop earlier, e.g., during the 3rd week of life.…”

“…A significantly higher p.m. than a.m. plasma corticosterone level is present on either day 21 [Ader, 1969;Hiro sh ig e and Sato, 1970] or day 25 [Allen and Kendall, 1967], It is well decumented that the time of development of these functions can be influenced by perinatal hormonal manipulations, particularly with gluco corticoids [K rieg er , 1972; R o n n ek leiv et al, 1975; T u rn er and T a y lor, 1976]. On the other hand, perinatal hypothyroidism lengthens [M eserve and L eathem , 1973] while hyperthyroidism shortens [M eserve and L eathem, 1974] the stress non-responsive period.…”

Rat‐Liver Cholesterol 7α‐Hydroxylase

“…The rhythm of cholesterol 7a-hydroxylase appears on the 20th postnatal day, in other words at the time when the animal abandons liquid foods (milk) for solid foods [35]; this is also the period when the circadian activity of the hypothalamo-hypophysoadrenal axis begins to develop [36]. This rhythm is directly dependent on the endocrine activity, since it is completely abolished following hypophysectomy or adrenalectomy.…”

Orcadian and Ultradian Variations of ACTH and Cortisol Secretion

“…This periodicity in CRF secretion becomes detect able at about 3 weeks of age in rats (Hiroshige and Sato, 1970), just prior to the developmental stage at which the rhythm of plasma corticosterone concentra tions becomes apparent (Allen and Kendall, 1967;Hiroshige and Sato, 1970). In direct evidence of such a maturation process also exists in man: diurnal varia tions in plasma corticosteroids are not present at birth, but progressively appear throughout childhood, with a magnitude becoming comparable to that of adult patterns beyond 3 years of age (Franks, 1967).…”