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 lipolysis and leptin release by adipose tissue from mice incubated for 24 h in primary culture. In adipose tissue from control mice GH enhanced lipolysis without 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 mice no significant lipolytic action of GH was seen but leptin release was enhanced 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 the lipolytic action of GH involves the Stat5 proteins while the insulin-like effects of GH on glucose metabolism and leptin release involve different mechanisms.