Infradian Biorhythm of Thyroid Hormone Concentrations in Mammals and Birds

Abstract

Studies of the dynamics of thyroid hormone concentrations in the blood revealed a 3-day rhythm that significantly manifested in male Wistar rats and Chinchilla rabbits during intensive growth and in common starlings (Sturnus vulgaris) during moult. Synphasic 3-day biorhythms of thyroid hormonal activities were found in these animals, which attested to an external synchronizer of this biorhythm common for mammals and birds. The maximum level of thyroid hormones coincided with the extrema of daily fluctuations of the Earth rotation velocity, as a result of which this external factor or another factor closely related to it seemed to be involved in synchronization of the 3-day infradian biorhythm of thyroid hormones in mammals and birds.