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Circannual changes of immunoreactive LH and FSH were documented on a circadian basis in January, March, June and October in four groups of subjects: seven young men, six elderly men, six elderly women and six men and women suffering from senile dementia. The sampling was serially dependent only for the young men and the core subgroups of elderly men and elderly women. A circadian rhythm for FSH was not detected in any group of subjects during any of the sampling sessions, whereas a circadian rhythm for LH was detected twice (June and October) in young men, once (October) in elderly demented patients, and not at all in the groups of elderly men and women. Both 24-h and yearly mean levels of gonadotrophins were higher in elderly subjects (two-to 25-fold according to the hormone, sex and season) than in young men. Circannual rhythms of plasma LH with large amplitudes were validated by the cosinor method, with an acrophase located in April or May. A circannual rhythm of plasma FSH was validated only in young men, with an acrophase in October. The persistence of a circannual rhythm of plasma LH with large amplitude in elderly subjects, associated with high mean levels of the hormone, especially in elderly women, suggests that this bioperiodicity of the pituitary gland is independent of gonadal function.
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SUMMARY
Testosterone was measured in the peripheral blood plasma of normal men by radioimmunoassay. The results were analysed to test for the possible existence of a circadian rhythm, for fluctuations superimposed on any such rhythm, and for day-to-day variations. Unequivocal evidence of a circadian rhythm was found in all but one of the subjects studied and the cycle appeared to be accompanied by a series of fluctuations of lower amplitude lasting for 1–2 h. Samples taken from the same subjects on consecutive days showed marked variation between days, but no regular cyclic pattern. The possible existence of such a cycle is not, however, eliminated. On the basis of all the data obtained a regime is suggested for the collection of blood samples from individuals whose androgenic status is to be assessed.
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mediation of seasonal or circadian signals ( Hazlerigg 2001 ). In fact, the duration of the photoperiod affects the structure of TSH cells and TSH β mRNA expression in the PT cells of the Djungarian hamster ( Bergmann et al . 1989 , Bockmann et al
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Biological oscillations with an endogenous period of near 24 h (circadian rhythms) are generated by the master circadian pacemaker or clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus. This clock is synchronised to recurring environmental signals conveyed by selective neural pathways. One of the main chemical constituents of SCN neurones is vasoactive intestinal polypeptide (VIP). Such neurones are retinorecipient and activated by light. Exogenous application of VIP resets the SCN circadian clock in a light-like manner, both in vivo and in vitro. These resetting actions appear to be mediated through the VPAC2 receptor (a type of receptor for VIP). Unexpectedly, genetically ablating expression of the VPAC2 receptor renders the circadian clock arrhythmic at the molecular, neurophysiological and behavioural levels. These findings indicate that this intrinsic neuropeptide acting through the VPAC2 receptor participates in both resetting to light and maintenance of ongoing rhythmicity of the SCN.
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ABSTRACT
Young, growing rats which had been chronically (2 weeks) adrenalectomized or parathyroidectomized were used to define the roles of the adrenal and parathyroid glands on the maintenance of normal circadian rhythms of DNA, collagen and non-collagen protein synthesis in the skeleton. The animals were conditioned to food being available ad libitum and to 12 h light: 12 h darkness (lights on from 08.00 to 20.00 h). The pace of DNA, collagen and non-collagen protein synthesis in different regions of the tibia (tibial growth cartilage, metaphysial bone and diaphysial bone) was measured by the in-vivo incorporation of tritiated thymidine (1 h) and radioactive proline (48 h). In intact rats there were no regional differences in the phasing of the circadian profiles; peak DNA and non-collagen protein synthesis occurred at the onset of the dark period while peak collagen synthesis occurred during the middle of the period of light. Adrenalectomy selectively abolished the regional DNA synthesis rhythms without altering the phases of the serum Ca and phosphorus (P) rhythms, which peak at mid-day and at the onset of darkness respectively. Parathyroidectomy abolished the regional rhythms for collagen and non-collagen protein synthesis and serum Ca rhythms, without altering the phase of the serum P and corticosterone rhythms. Dietary Ca-lactate supplements, which raised serum Ca levels towards normal in parathyroidectomized rats, were able to correct serum corticosterone values but did not normalize bone collagen and non-collagen protein synthesis values. These data indicate that the adrenal rhythm governs the proliferative activities of bone and cartilage cells, and that parathyroid hormone is essential to maintain normal collagen and non-collagen protein synthesis rhythms.
J. Endocr. (1984) 103, 49–57
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SUMMARY
The melatonin (N-acetyl-5-methoxytryptamine) content of the pineal body and serum of White Leghorn cockerels (Gallus domesticus) appears to vary cyclically, with a higher level of both found at the mid-point of the dark period than at the mid-point of the light period when the animals were kept in a diurnal light cycle. These rhythmic variations persisted, although with an apparently lower amplitude, when the animals were maintained in continuous darkness for 2 weeks. The oscillations appeared to be free-running, circadian rhythms and to be phase-locked with the locomotor activity rhythms of the individual birds studied.
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It has been suggested that prolactin secretion exhibits a circadian rhythm and is related to ovine growth hormone (OGH) secretion in the ewe (Davis, 1972; Davis & Borger, 1972, 1973). Prolactin levels in ovine jugular vein blood can fluctuate rapidly, which makes it difficult to establish a temporal pattern of secretion. This problem may be overcome by continuous blood sampling, used here to measure prolactin in rams over 24 h. This secretory pattern is compared with the secretory pattern of OGH in the same animals. In particular, the interrelationship between prolactin and OGH is examined as well as attempting to define a circadian rhythm for the secretion of these hormones.
Five Merino rams were used. Skin folding for the neck and trunk regions of each animal was scored by three independent observers (Carter, 1943). This confirmed that two rams (nos. 174 and 179) had minimal skin folding (mean score 2/18)
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The core oscillatory mechanism consisting of gene transcription and translation is a unique feature and the astonishing discovery in circadian biology is that the rhythm of gene transcription reflects the behavioral rhythm almost perfectly. This means that the clock gene oscillation generated by the core loop in each suprachiasmatic nucleus neuron is coupled and amplified, and harmonized strongly so that oscillating activities are spread into the whole brain and to all those peripheral organs which contain peripheral clocks. Additionally, circadian changes are induced in behavior and hormone secretion. Investigations of biological clocks open the fascinating perspective to analyze the integrational mechanism of 'time', providing a bridge between single genes and the living organism as a whole.
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SUMMARY
The daily rhythm of plasma tyrosine was studied in obese subjects during total fasting, because of the relative constancy of the metabolic processes in this state. The plasma levels of tyrosine showed circadian fluctuations which were similar, although less pronounced, to those observed by other authors. The lowest values occurred at 03.00 h and the highest at 08.00 h with a second rise at 19.00 h.
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Androgen-sterilized female rats were obtained by administering 10 μg testosterone propionate to pups on day 2 after birth. In contrast with ovariectomized adults, androgenized adult female rats are incapable of responding to cervical stimulation by secreting prolactin in the nocturnal surge pattern. In spite of the loss of this pattern the androgenized female rats still exhibited a daily circadian rhythm of prolactin secretion with afternoon levels three times higher than those after midnight.
