Circadiane rhythmen von hormonen bei der Ratte Eine Übersicht

Abstract

Circadian rhythms of hormones in the rat are reviewed: In female rats, the oscillations of both corticotrophin and corticosterone show the same phase. There may be a slight phase difference between adrenocortical and plasma corticosterone levels. Adrenalectomy leads, apart from the expected increase in concentration, to a phase shift of the corticotrophin rhythm. A circadian periodicity of luteinizing hormone can be demonstrated only in the plasma of ovariectomized rats. Nonetheless, there are circadian changes of cholesterol levels in the ovaries of immature, PMSG‐HCG treated rats, suggesting rhythmic estrogen synthesis. The maxima of pituitary luteotrophic hormone and of ovarian progesterone possibly coincide; hypophysectomy results in a loss of rhythmicity of the progesterone levels. Although there is no sufficient evidence for a circadian rhythm of thyrotrophin, protein‐bound iodine is shown to be oscillating. The other hypophyseal hormones, growth hormone and adiuretin, also exhibit a circadian pattern, maximum and minimum of the latter being in good agreement with minimum and maximum of urine production, respectively. Slight circadian changes, if any at all, occur in the serotonin content of the whole brain, whereas hypothalamic and, more markedly, pineal serotonin rhythms are clearly expressed. A sudden decrease in pineal serotonin concentration coincides with a sudden increase of melatonin formation and a decrease in the concentration of the other serotonin derivative, 5‐hydroxyindole acetic acid. Distinct circadian differences in norepinephrine levels occur in the pineal and submaxillary glands. The diurnal periodicity of adrenal epinephrine concentration appears to be somewhat variable. Circadian histamine rhythms are reported for the mid‐brain, the caudate nucleus, and for the excretion rate.