Infradian characteristics of plasma cortisol in children of short stature.

CT concentrations (in micrograms/dl) were determined by radioimmunoassay in plasma obtained at about 3-hour intervals during a 24-hour sampling span from 42 boys and 16 girls of short stature, 6-14 years of age, living on a diurnal waking (approximately 07:00 to approximately 22:00), nocturnal resting routine. Circadian rhythm parameters were first computed by the single and population mean cosinor fits of a 24-hour cosine curve. A parameter-comparison shows similar circadian rhythm parameters for both genders, the Ps for a comparison of Ms, As, 0s and (A,0) pairs being .69, .14, .73 and .32, respectively. In the search for infradian variability, individual circadian Ms were first fitted by LLS. The LLS harmonic analysis shows prominent components with periods of 8, 7, 4, 3 and 1 months, with ordering P-values of .031, .011, .009, .018 and .024, respectively. The rhythm parameters thus obtained were used as initial values for the NLLS method. This approach only detects the circaseptrigintan (7 months) component, with estimated period, M, A and 0 of 5023.96 hours, 10.32 micrograms/dl, 3.34 micrograms/dl and -273 degrees, respectively. These not anticipated infradian characteristics of the adrenal cortisol cycle may constitute quantitative parameters in dealing with risk in health and may serve to monitor any possible progression of a condition into a disease.