35 PYRUVATE DEHYDROGENASE ACTIVITY IS STIMULATED BY GROWTH HORMONE: A NEW TOOL TO MEASURE RESPONSIVENESS OF HUMAN MONONUCLEAR CELLS TO THE HORMONE

Abstract

No rapid effects of growth hormone (GH) in isolated human cells have been measured until now. Human mononuclear cells were used to examine the effects of human GH (hGH) on the activity of the pyruvate dehydrogenase (PDH) complex. Cells (8×106/ml) were incubated at 37°C for various times in the presence of 10−7M hGH or porcine insulin. PDH activity was determined in sonicated cells by measuring 14CO2 liberation from 1-14C-pyruvate. Increase in basal PDH activity was linear as a function of time (up to 20 min), of pyruvate concentration (up to 0.25 mM) and of proteins (up to 4×106 cells). Ten subjects, aged 5 to 40 years, were studied. Basal PDH activity represented 24 % of the total PDH activity (20.54 ± 1.19 pmol/min/106 cells). Treatment of mononuclear cells by hGH led to an increase in basal PDH activity which was maximal (53 ± 7% above control value) at 15 min. Later on, activation progressively decreased and was no longer detectable at 30 min. Total PDH activity (measured in the presence of 0.5 mM CaCl2 and 20 mM MgCl2) was unaffected by hGH treatment. Incubation of cells with insulin also increased basal PDH activity (65 ± 9% above control value) at 15 min, without changing total PDH activity. In conclusion, hGH as well as insulin, is able to stimulate PDH activity of human mononuclear cells. This hormonal effect allows the rapid evaluation of the cellular responsiveness to GH in various pathophysiologic situations. No effect of GH on PDH activity was observed in cells prepared from two Laron dwarfs.