Circadian rhythm of TSH in adult men and women

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Abstract
The circadian rhythm of TSH [thyrotropin] secretion and its typical pattern were investigated during the spring of 2 successive years in a group of 12 adult women, and then in a group of 12 adult men, both having normal thyroid function. Blood samples were obtained from each individual every 2 h for 24 h. TSH was measured by radioimmunoassay. Data were processed by inferential analysis and represented using the cosinor method. The chronobiological rhythm of TSH is in good agreement with the typical function of circadian rhythms both in men and in women, significance averaging 1.permill.. The typical parameters of the rhythm (M = mesor, i.e. the mean level of the rhythm; A = amplitude of the sinusoidal function approximating the rhythm; .vphi. = acrofase, i.e. the lag from a reference timepoint of the crest time in the function) under the conditions used in our investigation were shown to be: Male subjects: mean .+-. SE = 3.72 .+-. 0.21 mU/l, A (95% C.I.) = 1.15 (0.93-1.47) mU/l; .vphi. (95% C.I.) = 3.9.degree. (-8.6.degree. + 23.8.degree.). Female subjects: mean .+-. SE = 5 .+-. 0.13 mU/l; A (95% C.I.) = 0.96 (0.86-1.11) mU/l; .vphi. (95% C.I.) = 8.8.degree. (-0.2.degree. + 20.5.degree.). The patterns of TSH biorhythm are practically identical in both sexes. Taking into account the methods used and the results obtained it was concluded that the circadian rhythm of TSH secretion is programmed in both sexes in order to meet the cyclic requirements of the target gland, while several other factors which mark the course of the day at the level of central nervous structures function as rhythm harmonizers.