Circadian and ultradian characteristics of plasma growth hormone in children with normal and short stature.

Circadian and ultradian variations characterize plasma growth hormone (GH) in 40 boys and 10 girls of short stature, and 15 boys and girls of normal stature, 6-14 yr of age, living on a diurnal waking (approximately 07:00 to approximately 22.00), nocturnal resting routine. Blood was drawn at about 3-h intervals during a 24-h span and serum stored frozen at -60 degrees C until radioimmunoassay for GH concentration. A linear least-squares spectrum analysis of those data reveals the anticipated statistically significant circadian rhythm as the principal spectral feature for all groups. Prominent components with a period of 12 h were also found for the groups of short boys and short girls, and of 8 h for short boys. A parameter comparison indicates similar circadian characteristics between short and normal children, whether one compares boys (p = .52, .30 and .84 for comparison of rhythm-adjusted means (M), amplituedes (A) and acrophases (phi), respectively), girls (p = .65, .37 and .92), or all children (p = .53, .31 and .87). These results notwithstanding, studies of GH responses to GH-releasing hormone in children with short stature and healthy controls should be extended to evaluate any possible difference in terms of gender and circadian or ultradian timing.