Impact of intensive venous sampling on characterization of pulsatile GH release

The effect of sampling intensity on quantitative properties of pulsatile growth hormone (GH) release was tested using an objective, statistically based pulse detection algorithm (Cluster). Seven normal young men had blood withdrawn at 5-min intervals for 24 h. The number of GH peaks/24 h (mean ± SE) detected in the 5-min series (5.93 ± 0.66) was significantly greater than the number of peaks documented in the constituent 10-min (3.45 ± 0.28), 15-min (2.79 ± 0.31), 20-min (2.86 ± 0.64), 30-min (2.5 ± 0.36), 45-min (2.21 ± 0.21), and 60-min (1.93 ± 0.23) series. The increased number of peaks detected with 5-min sampling reflected high-frequency pulsatile GH release occurring within the major GH secretory episodes. Both the mean widths and areas associated with peaks identified in the 5-min series were smaller than those documented with less intensive sampling. Peak amplitude did not change with sampling intensity. These data suggest that the major secretory episodes of GH release in normal young men encompass high-frequency GH secretory activity. That these high-frequency GH secretory events have not previously been described probably reflects the relatively infrequent sampling paradigms (e.g., every 20-30 min) commonly used in the past.