Circadian rhythm in plasma immunoreactive somatomedin-C in children.

Fifteen boys and 27 girls, 11 +/- 2 years of age were studied over a single 24-hour span during the month of June. Statistically significant circadian rhythms of plasma immunoreactive somatomedin-C (SM-C) concentration, immunoreactive growth hormone (hGH) and cortisol concentration were found, which show marked differences in timing. The highest values of somatomedin-C occurred in the early evening hours (acrophase 19:08) in contrast to growth hormone which showed its peak values during the night and cortisol, which peaked in the morning hours. These observations are of interest for the physiologic regulation of somatomedin-C as well as for the clinical evaluation of plasma immunoreactive somatomedin-C concentrations, and for studies of the response of somatomedin-C to hormonal and/or pharmacologic manipulation.