Circadian rhythms of testosterone and cortisol in saliva: effects of activity-phase shifts and continuous daylight.

The variations in concentrations of testosterone and cortisol in saliva samples collected by 4 healthy young men whilst on a scientific expedition from Britain to Spitzbergen are described. The rhythms observed in steroid concentrations in saliva were characterized mathematically by cosinor analysis of the levels of testosterone and cortisol determined in saliva samples collected before, during and after the expedition. Whilst in Spitzbergen, the subjects were maintained initially on the British sleep-wake schedule which was later subjected to an 8-h phase change. Variations in testosterone concentrations in saliva appeared to be largely related to subject activity rather than any photoperiodic effect with rapid resynchronization of the circadian acrophase in response to the phase shift of the sleep-wake schedule. In contrast, variation in salivary cortisol levels appeared to be less related to activity and more dependent on the slower resynchronization of an endogenous rhythm of cortisol secretion.