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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.

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

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.

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)

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.

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.

The steroid 11-oxygenation index (i.e. the ratio of the urinary metabolites of cortisol precursors to those of cortisol) has been used by Hill (1960) and by Edwards, Makin & Barratt (1964) in the diagnosis of congenital adrenal hyperplasia. Both showed that any circadian variations in the index were small compared with the gross abnormalities encountered in this condition. In the course of physiological studies on temperature and renal excretory circadian rhythms we have observed a small but definite circadian variation in the steroid 11-oxygenation index in normal men.

Six male subjects (ages ranging from 21 to 55 yr.) followed a routine consisting of rest, light activity, feeding and drinking, which was repeated every 90 min. during a 27 hr. experiment. Urine was collected for 3 hr. periods and the 11-deoxy and 11-oxy 17-hydroxycorticosteroids (11-deoxy and 11-oxy 17-OHCS) were separately estimated (Few, 1968) in each sample. The steroid 11-oxygenation index was