Endocrine Abstracts

Circadian, 24 hr, timing is a conserved feature of physioloogy and behaviour across eukaryotes. In mammals the principal clock resides in the suprachiasmatic nuclei of the hypothalamus (SCN). Through neural and endocrine linkages the SCN direct the daily temporal programme of brain and peripheral tissues. The core clockwork is based on a cell-autonomous, self-sustaining feedback loop of gene expression. Mutations of mammalian homologues of 'clock' genes identified in lower spe...

For many animals anticipation of future changes in environmental conditions is a critical adaptation for survival. Seasonal changes in reproductive activity, body weight and adiposity, metabolism and coat condition are examples of such adaptive physiology. Clearly each of these involves neuroendocrine control. The environmental cue that triggers these changes is photoperiod, which is translated into the hormonal signal, melatonin, a product of the pineal gland. A considerable ...

Appropriate biological timing is essential for optimal physiological function. Driven by the central pacemaker, circadian rhythms in physiology and behaviour require time cues, primarily light, to maintain synchrony with the 24h day and adapt slowly to abrupt changes of time cues. Extrinsic rhythm disorder results from the desynchrony of the internal clock with a new behavioural and/or light dark schedule. The numerous health problems of shift workers (poor sleep, alertness, p...

We carried out a series of experiments to identify common principles underlying the temporal organization of diverse circadian rhythms in endocrine and other functions in humans. Profiles of rhythms in plasma hormone levels, body temperature, and arousal state were measured while subjects remained at rest in continuous dim ( < 1 lux) light, after they had been exposed to artificial 'days' and 'nights' of different lengths. Subjects gave written informed consent for their pa...