Estimation of growth hormone secretion rate: impact of kinetic assumptionsintrinsic to the analytical approach

We compared four common mathematical techniques to determine daily endogeno us growth hormone (GH) secretion rates from diurnal plasma GH concentration profiles in 24 women (16 upper- or lower-body obese and 8 normal-weight in dividuals). Two forms of deconvolution analysis and two techniques based on a priori determined GH clearance estimates were employed. Deconvolution an alyses revealed significant differences in the 24-h GH secretion rate betwe en normal-weight and upper-body obese women, whereas the other two techniqu es did not. Moreover, deconvolution analyses predicted that the reduction i n mean plasma GH concentrations in upper- body obese women was accounted fo r by impaired GH secretion, whereas the other methods suggested that obesit y increases GH metabolic clearance. Thus we infer that disparate conclusion s concerning GH secretion can be drawn from the same primary data set. The different inferences likely reflect dissimilar kinetic assumptions and the particular limitations intrinsic to each analytical approach. Accordingly, we urge caution in the facile comparison of calculated GH secretion data in humans, especially when kinetic and secretion measurements are performed u nder different conditions. The most appropriate way to determine the GH sec retion rate in humans must be balanced by the exact intent of the experimen t and the acceptability of different assumptions in that context.