Stimulation of lipolysis but not of leptin release by growth hormone is abolished in adipose tissue from Stat5a and b knockout mice

The present studies examined the effects of growth hormone (GH) on lipolysi s and leptin release by adipose tissue from mice incubated for 24 h in prim ary culture. In adipose tissue from control mice GH enhanced lipolysis with out affecting leptin release. The lipolytic action of GH was unaffected in adipose tissue from Stat5b-/- male mice but leptin release was enhanced by GH in fat from Stat5b-/- mice. In adipose tissue from Stat5ab-/- female mic e no significant lipolytic action of GH was seen but leptin release was enh anced by GH. An insulin-like effect of GH on glucose conversion to lactate was also seen in mice deficient in Stat5ab-/-. These results suggest that t he lipolytic action of GH involves the Stat5 proteins while the insulin-lik e effects of GH on glucose metabolism and leptin release involve different mechanisms. (C) 1999 Academic Press.