Pulsatile characteristics of spontaneous growth hormone (GH) concentration profiles in boys evaluated by an ultrasensitive immunoradiometric assay: evidence for ultradian periodicity of GH secretion.

To investigate underlying ultradian periodicities in spontaneous circulating GH concentration, blood samples were drawn from 15 normal short boys every 20 min over a 24-h period, and plasma GH concentrations were measured using an ultrasensitive immunoradiometric assay. The limit of detection for the GH assay was 0.01 microgram/L. The GH time series were analyzed using the Cluster program, Ultra program, cosinor analysis, and autocorrelation analysis. Plasma GH concentrations in 1095 samples derived from 15 normal short boys were all within the detectable range of the assay and ranged from 0.07-52.2 micrograms/L. Thirty-six percent of the GH values in the 1095 samples from 15 normal short boys were below 1 microgram/L, and 82% of them occurred during the diurnal awakening period. Cluster analysis disclosed a total of 176 peaks in 15 normal short boys, with a mean +/- SEM number of significant GH peaks of 12.1 +/- 0.5/24 h. Twelve percent of the 176 peaks were below 1 microgram/L, and 95% of them occurred during the diurnal awakening period. In addition, Cluster analysis disclosed 161 interpulse intervals in total, with a mean +/- SEM interval of 116.5 +/- 4.3 min. The GH interpulse interval did not show a significant 24-h rhythm, whereas the GH peak height increased significantly at night. An independent discrete peak detection program, Ultra, identified 12.6 +/- 0.5 GH peaks/24 h. This result was in good agreement with that from analysis by the Cluster program (P = NS). Autocorrelation analysis revealed that GH time series were significantly autocorrelated in 9 of the 15 boys, with maximal autocorrelation coefficients at 115.5 min, on the average. The mean autocorrelation coefficient for a group of 15 normal short boys was significantly positive at a 100-min lag. These findings suggest that there could be a regularly occurring periodicity of approximately 100-120 min in the human GH time series.