Circannual rhythm of plasma growth hormone in girls (but not boys) with constitutional short stature.

GH concentrations (in ng/ml) were determined by radioimmunoassay in plasma obtained at about 3-hour intervals during a 24-hr sampling span from 40 boys and 14 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. Circadian parameter comparisons revealed an intergroup difference between the genders in A (P = .012) and, perhaps, in M (P = .078), but not in 0 (P = .957). In the search for circannual variability, individual circadian Ms were fitted by LLS with a 1 year cosine curve. The LLS harmonic analysis shows a circannual rhythm for the girls (P = .037; M = 8.54; A = 5.38; 0 = -214 degrees from January 1), but not for the boys. Moreover, a 3.5 months prominent component was also found for both the individual circadian Ms (P = .010) and As (P = .012) when all subjects are considered for analysis irrespectively of gender. These infradian characteristics complement circadian differences in GH between boys and girls and must be taken into account in the development of any protocol for studies of GH responses to GH-releasing hormone in children with short stature.