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Biomedical subjects

J Arendt

Publications and source records attributed to J Arendt.

At least 163 records · Page 9Linked to original sources
PubMed1985

Immunoassay of 6-hydroxymelatonin sulfate in human plasma and urine: abolition of the urinary 24-hour rhythm with atenolol.

An assessment of the rhythmic characteristics of melatonin secretion in man and other species requires the determination of 24-h secretion profiles. Measurement of a major excreted metabolite would allow noninvasive study of pineal function, applicable in particular to pediatric and long term circadian rhythm studies. This report describes a simple and rapid RIA for 6-hydroxymelatonin sulfate in human plasma and urine. Physiological studies revealed that both plasma and urinary levels of 6-hydroxymelatonin sulfate were closely related to plasma melatonin, and that the urinary 24-h rhythm was abolished by the beta 1-adrenergic anagonist atenolol.

Animals↗
PubMed1985

Differential effects of melatonin on the stimulated release of LH from dispersed pituitary cells of the prepubertal female rat.

The effect of melatonin on the stimulated release of LH from prepubertal female rat pituitary cells in vitro was investigated. Significant inhibition of LH-releasing hormone and calcium ionophore-induced LH release was seen but not of potassium-induced release. These results suggest a specific interaction between melatonin and the endogenous events leading to LH release, and may implicate melatonin as an important neuroendocrine component of pubertal development in this species.

Animals↗
PubMed1984

The effects of chronic, small doses of melatonin given in the late afternoon on fatigue in man: a preliminary study.

In a double-blind cross-over study, melatonin (2 mg) or placebo, was administered daily for 4 weeks to 12 volunteers (10 men and 2 women) at 17.00 h during February and March. Self-rated fatigue (tiredness) was significantly increased in the evening during melatonin treatment. No other consistent effects on sleep ratings or mood parameters were observed and the dose was well tolerated.

Adult↗
PubMed1983

How does the indoleamine production of the pineal gland respond to variations of the environment in a non-mammalian vertebrate, Testudo hermanni Gmelin?

The relative effects of environmental factors, photoperiod and temperature on pineal indoleamine production have been investigated in male Tortoises, Testudo hermanni, at different times of their seasonal reproductive cycle. Photoperiod appears to be an important factor in the regulation of the seasonal and diurnal variations of pineal serotonin content, while temperature has a more drastic effect on the diurnal production of melatonin. These results reinforce, at least partly, the concept that the pineal gland responds to several kinds of information about the state of the environment in order to synchronize some cyclical functions such as reproduction.

Animals↗
PubMed1983

Plasma melatonin in ewes after ovariectomy.

Six ewes were ovariectomized in late November and kept in natural light with 5 intact controls. LH levels were monitored approximately weekly. On Days 16 and 58 after ovariectomy plasma melatonin was determined at 3-h intervals for 24 h in all the ewes. Plasma melatonin concentrations were greater in the ovariectomized ewes than in the controls especially at 16 days when total 24 h secretion was almost 3 times that in the control ewes. These data indicate that, in the ewe, the gonads exert an inhibitory influence on melatonin secretion.

Animals↗
PubMed1983

Melatonin can induce early onset of the breeding season in ewes.

Patterns of plasma melatonin, similar in the duration of high levels to those found in winter, were induced in Suffolk-cross ewes kept in summer light (16 h light: 8 h darkness) by daily oral administration of melatonin (3 mg/13 mumol). The onset of oestrous cycles in these sheep occurred in August, 2-8 weeks before the onset of oestrous cycles in untreated ewes kept in natural light. The onset of oestrous cycles in a further group of ewes kept in winter light (8 h light: 16 h darkness) from mid-June was indistinguishable from that of the melatonin-treated ewes. Rams were excluded from the premises. These data indicate that melatonin alone in physiological quantities is sufficient to induce early onset of the breeding season in the ewe, and provide strong evidence for a hormonal role of melatonin in a short-day breeder.

Animals↗
PubMed1983

Melatonin feeding decreases prolactin levels in the ewe.

Three groups of Suffolk-cross ewes were kept in (A) summer photoperiod plus melatonin feeding in such a way as to mimic the plasma levels found in winter photoperiod, (B) winter photoperiod or (C) natural light/dark from mid-June onwards. Prolactin levels remained high in group C throughout July and August but were dramatically reduced in both groups A and B. The rise in prolactin levels associated with dusk, however, was still apparent in all three groups. Appropriate administration of melatonin can thus influence prolactin secretion in the same way as an extension of the dark phase. This effect is associated with an early onset of the breeding season in the ewe.

Animal Feed↗
PubMed1982

Reduced nocturnal melatonin secretion in chronic schizophrenia: relationship to body weight.

Melatonin was estimated by RIA in samples taken at 24.00 h and 08.00 h from twenty-one male chronic schizophrenics and twelve age--sex matched controls and subsequently in more frequent nocturnal samples from nine of the chronic schizophrenics. The 24.00 h melatonin level and the 24.00/08.00 h melatonin ratio were significantly reduced in the chronic schizophrenic patients. Similar results, with no evidence of subsidiary peaks of melatonin secretion, were obtained in those patients who were retested. No relationships between melatonin secretion and age or anterior pituitary hormone secretion were demonstrated, but an effect of body weight was noted which accounted, in part, for the difference between schizophrenics and controls. These results suggest that the low levels of melatonin noted in studies on depressed patients may not be specific and that body weight must be controlled in subsequent studies of melatonin secretion in patients with psychiatric disease.

Adult↗