GROWTH-HORMONE TREATMENT OF HYPOPHYSECTOMIZED RATS INCREASES CATECHOLAMINE-INDUCED LIPOLYSIS AND THE NUMBER OF BETA-ADRENERGIC RECEPTORS INADIPOCYTES - NO DIFFERENCES IN THE EFFECTS OF GROWTH-HORMONE ON DIFFERENT FAT DEPOTS

Growth hormone (GH) has a lipolytic effect in adipose tissue but this effect may differ in adipose tissue from various fat depots. This latt er possibility was investigated in the present study, in which the eff ects of GH in vivo on catecholamine-induced lipolysis and the number o f beta-adrenergic receptors in isolated adipocytes from different fat depots of hypophysectomized rats were investigated. Female and male Sp rague-Dawley rats were hypophysectomized or sham-operated at 45 days o f age. One week after the operation, hormonal replacement therapy with L-thyroxine and hydrocortisone acetate was given. In addition, groups of rats were treated with GH (1.33 mg/kg per day, given as two daily subcutaneous injections). After 1 week of hormonal treatment, adipocyt es were isolated from the parametrial, epididymal and inguinal fat pad s, and glycerol release after catecholamine-stimulation and I-125-cyan opindolol binding were measured. Hypophysectomy resulted in a marked d ecrease in the lipolytic response to catecholamines. GH treatment sign ificantly increased catecholamine-induced lipolysis with similar effec ts in adipocytes from parametrial or epididymal and inguinal fat depot s in both female and male rats. There were no differences between nore pinephrine compared with isoproterenol-induced responses. I-125-cyanop indolol binding was reduced after hypophysectomy and normalized by GH treatment, without differences between parametrial and inguinal adipos e tissue regions. We conclude that the lipolytic effects of GH in the rat may partly be mediated by a stimulatory effect on beta-adrenergic receptors in adipocytes. In addition. GH exerted similar effect on cat echolamine-induced lipolysis and beta-adrenergic receptors in adipocyt es from parametrial, epididymal and inguinal fat depots.