Contribution of hGH20K variant to blood hGH response in sauna and exercise

Summary Exercise-induced increases in blood somatotropin (hGH) have always been considered in terms of quantity of the circulating molecules. Knowing that the hypophysis can release several GH species, we investigated the differential release in blood of total hGH (hGH_T) and the main hGH variant (hGH_20K) molecules in six trained male swimmers exposed to three different conditions known to favor GH release in blood: 45 min – 70% maximum oxygen uptake bicycling and swimming, and 20 min of sauna bathing. Based on the binding specificity of hGH antibodies, hGH_20K was isolated then assayed using the Nichols immunoradiometric assay system. All three experimental conditions produced significant (P < 0.001) elevations in blood hGHT and hGH_20K. In all three cases, mean blood hGH_20K contribution to blood hGH_T was relatively constant (11.9, SE 0.7%). Rises in rectal temperature were not statistically related to the changes in blood hGH_T. This demonstration of a relatively constant elevation in hGH_20K during bicycling, swimming, and sauna bathing can hardly explain the large differences in blood hGH_T responses reported in literature under similar conditions.