CIRCANNUAL RHYTHMS OF PLASMA LUTEINIZING HORMONE, FOLLICLE‐STIMULATING HORMONE, TESTOSTERONE, PROLACTIN AND CORTISOL IN PREPUBERTY

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Abstract
For a period of 4 yr 106 healthy males and 66 healthy females, aged 6-10, were studied by cross-sectional design, to look for evidence of a circannual rhythm in LH [luteinizing hormone], FSH, testosterone, PRL [prolactin] and cortisol secretion. Plasma samples were taken at 0800 h and all hormones were measured by RIA [radioimmunoassay]. A cosine function was fitted to the single data to indicate any significant circannual (about 1 yr) rhythm and to estimate its parameters: mesor, amplitude and acrophase. Annual changes were validated in the secretion of LH (annual crest time in Jan. in both sexes), testosterone (studied only in males, annual crest time in July), and PRL (significant rhythm only in females with annual crest time in March). FSH and cortisol did not show an annual rhythm in both sexes. Apparently, sex influences the circannual hormonal rhythms from prepuberty onwards.