Time structure of endocrine secretion. II. Circannual variations in the free fractions of tri- and tetraiodothyronine, cortisol, human growth hormone and plasma insulin in healthy subjects

Abstract Circadian and circannual variations of several endocrine activities and their biological implications in health and diseases were described in men. Aim of our work was to perform a further observation on circannual bioperiodicities of some hormone: free fractions of T3 and T4, cortisol, HGH, PTH and serum insulin. Four healthy young males volunteered to be submitted to the study from June and their blood-samples collected six times a day, every other month, in the course of one year. Our data were analysed by macroscopic (mean chronogram) and microscopic (Cosinor test) methods. First we could document a circadian phase-shift of the highest peak of secretion, occurring in the course of the year, for FT3, FT4, Cortisol, HGH and serum basal insulin. Then we could detect a circannual oscillation of the highest diurnal secretion for FT3 (October), cortisol (December) HGH (April) and serum basal insulin (February). FT4 showed the lowest secretion in October. Almost the same cyclic variations were demonstrated when Mesors and Amplitudes of the same values were examined except for slight shiftings. PTH showed no cyclic variation during the period of observation.