title: [Sex difference in the circadian rhythm of corticotropin-releasing activity in the rat hypothalamus (author's transl)].
abstract: Sex difference in the circadian rhythm of the hypothalamic content of Corticotropin-Releasing Factor (CRF) and plasma corticosterone levels was examined in the rat. In the male rat the CRF content was higher in the afternoon than in the morning. In contrast, the hypothalamic CRF content in the female rat was higher in the morning. The peak value was found at 8 a.m. and it fell rapidly around noon with a concomitant sharp rise in the plasma corticosterone. Thus, the whole pattern of CRF content during a 24-hour period makes a mirror image of that of plasma corticosterone. The influence of gonadal hormones on the sex difference was then examined by following variations in the CRF content after ovariectomy. Even after chronic ovariectomy, essential features of the female pattern of CRF rhythm persisted: rapid fall of the CRF content was accompanied by a sharp rise in the plasma corticosterone level. It is noteworthy however that ovariectomy reduced the morning level of CRF activity without elevating the afternoon level, resulting in a peak shift toward noon. The female pattern of CRF rhythmpersisted similarly after bilateral ganglionectomy which is known to affect the biogenic amine rhythm in the pineal gland. The persistence of the female pattern may suggest some endogenous nature of the rhythm. It was then possibly that sex differentiation in the central nervous system (CNS) might be related with manifestation of the female pattern. In order to elucidate this point, postnatal development of circadian rhythm of CRF activity was examined in male and female rats separately. It was found that the CRF rhythm became manifest both in male and female rats around the third week of postnatal life and there was no essential difference in their rhythm pattern. In other words, both male and female rats begin their CRF rhythm with so-called male pattern, with higher values in the afternoon than in the end of the third week of life. In contrast, the CRF rhythm in females rats showed a marked change at ages of five to six weeks during which the onset of puberty intervened in our series of experiment;during this period, the CRF rhythm in female rats turned into the so-called female pattern, with higher values of CRF activity in the morning than in the afternoon. It was of interest that a marked rise in the plasma corticosterone, characteristic of mature female rats, concomitantly appeared. Further attempt were made to examine the effect of gonadal hormones in the periratal period. The hypothalamic CRF content in androgen sterilized female rats as well as in neonatally castrated male rats showed no circadian rhythm. The results implicate subtleness of hormonal effect in simulating physiological processes. In fact, CRF rhythms are variable depending on stages of the estrous cycle: during proestrus and estrus, the CRF content was markedly higher in the morning (9 a.m.) than in the afternoon (4 p.m.). But no significant difference was observed between them during diestrus I and II...
mesh_terms: D000367:Age Factors; D000818:Animals; D002369:Castration; D002940:Circadian Rhythm / Q000187:drug effects; D003345:Corticosterone / Q000097:blood; D003346:Corticotropin-Releasing Hormone / Q000032:analysis / Q000502:physiology*; D004971:Estrus; D005260:Female; D005725:Ganglia, Autonomic / Q000601:surgery; D007031:Hypothalamus / Q000032:analysis*; D008297:Male; D011247:Pregnancy; D051381:Rats; D012737:Sex Factors; D013739:Testosterone / Q000494:pharmacology
chemical_list: D013739:Testosterone; D003346:Corticotropin-Releasing Hormone; D003345:Corticosterone