Effects of Ovine Growth Hormone and Other Anterior Pituitary Hormones on Lipolysis of Rat and Ovine Adipose Tissue In Vitro1

Ovine growth hormone (oGH) was tested for its effects on lipolysis of rat and ovine adipose tissue in vitro. Ovine growth hormone at 1, 5 and 25 μg/ml stimulated lipolysis (P<.05) of chopped rat adipose tissue and isolated rat adipocytes incubated in the presence of 100 mU/ml adenosine deaminase and .2 μg/ml dexamethasone, but had no effect on lipolysis of chopped ovine adipose tissue or isolated ovine adipocytes. Isoproterenol, a β-adrenergic agonist, stimulated lipolysis (P<.05) of both rat and ovine adipose tissue. Contaminants of the oGH preparation used were examined for lipolytic effects. Thyroid stimulating hormone (TSH), luteinizing hormone (LH) and adreno corticotropic hormone (ACTH) content in oGH were measured by radioimmunoassay. When quantities of these hormones contaminating 5 and 25 μg oGH were tested for lipolysis in rat adipose tissue, the TSH contamination could account for some (30%) of the lipolysis observed with oGH, while the other hormones had no effect. Also, preincubation of oGH with anti GH, but not with anti-TSH or anti-LH, removed the principle in oGH responsible for the lipolytic effect on rat adipose tissue. At relatively higher levels, TSH (60 ng/ml), LH (600 ng/ml) and ACTH (300 ng/ml) stimulated lipolysis (P<.01) of rat adipose tissue, but prolactin (PRL) and follicle stimulating hormone (FSH) were without effect. None of these hormones stimulated lipolysis of ovine adipose tissue. Based on these data, we suggest that there is a species difference in the lipolytic response of adipose tissue to anterior pituitary hormones. Neither GH, nor the other anterior pituitary hormones tested, have a direct, acute lipolytic effect on adipose tissue in sheep, however, lipolysis of rat adipose tissue can be increased by several anterior pituitary hormones.