Chronic effects of somatotropin treatment on response of subcutaneous adipose tissue lipolysis to acutely acting factors in vivo and in vitro

ABSTRACT: The basis of the chronic lipolyticeffect of somatotropin on adipose tissue was inves-tigated in sheep. Lipolytic rate was assessed insubcutaneous adipose tissue both in vivo, by microdi-alysis, and in vitro. Somatotropin treatment resultedin a small increase in basal (unstimulated) lipolysisand also in the maximum lipolytic rate observed in thepresence of catecholamines both in vivo and in vitro.There was a small increase in the number of b-adrenergic receptors but no change in the amount ofthe two isoforms of the stimulatory GTP-bindingprotein, Gs. Treatment with somatotropin decreasedthe response to antilipolytic agents such as theadenosine analog N 6 -phenylisopropyladenosine andprostaglandin E 1 . There was, however, no change inthe number of adenosine receptors or amounts of theinhibitory GTP-binding proteins (Gi-1 plus Gi-2).Somatotropin also decreased prostaglandin E 2 produc-tion by subcutaneous adipose tissue in vivo.Somatotropin treatment thus alters lipolytic regula-tion in sheep and this is characterized by changes in anumber of proteins involved in this process.Key Words: Somatotropin, Lipolysis, Adipose Tissue, SheepJ. Anim. Sci. 1996. 74:562–568