GROWTH-HORMONE INHIBITS LIPOPROTEIN-LIPASE ACTIVITY IN HUMAN ADIPOSE-TISSUE

The in vitro effects of GH on human adipose tissue Lipoprotein Lipase (LPL) activity and messenger ribonucleic acid (mRNA) levels were studi ed using a tissue incubation technique. After preincubation for 3 days , abdominal sc adipose tissue pieces mere exposed to cortisol (1000 nm ol/L) for 3 days to induce LPL activity. Addition of GH (50 mu g/L) to the cortisol-containing medium during the last 24 h (day 6) caused a decrease by 84 +/- 4% (P < 0.01) in heparin-releasable LPL activity an d by 65 +/- 4% (P < 0.01) in total LPL activity. Moreover, the heparin -releasable fraction was reduced from 42% of the total LPL activity wi th cortisol alone to 17% when both GH and cortisol were present in the incubation medium during the last 24 h (P < 0.01). The reduction in L PL activity in response to GH was not accompanied by a decrease in the level of LPL mRNA measured by a solution hybridization ribonuclease p rotection assay. In adipose tissue incubated in the control medium for 6 days, the addition of GH alone during the last 24 h caused an insig nificant decrease in heparin-releasable LPL activity. Low control acti vities Limited the scope for further decrease. It is concluded that GH counteracts the potent stimulatory effect of glucocorticoids on LPL a ctivity without affecting LPL mRNA levels. Therefore, the inhibition o f LPL activity by GH probably occurs during translation and/or posttra nslational processing of the enzyme, and the mechanism may involve a d ecreased channeling of the lipase to the cell surface.