Segments of epididymal fat from normal and hypophysectomized rats were incubated in vitro for 4 hr in the presence of growth hormone (0.01–1.0 μg/ml) and the synthetic glucocorticoid, dexamethasone (0.16 μg/ml). The 2 hormones in conjunction increased the release of glycerol and free fatty acids (FFA) from the fat of normal rats but had no effect on lipolysis when tissues of hypophysectomized rats were studied. The addition of theophylline (0.9 mg/ml) to the incubation medium evoked maximal lipolysis in the normal tissues whether or not the hormones were present. The same concentration of theophylline increased the basal lipolysis in the adipose tissues of hypophysectomized rats and caused these tissues to respond to dexamethasone and growth hormone in a manner that was quantitatively and qualitatively similar to the response of normal tissues in the absencs of theophylline. Pretreatment of hypophysectomized rats with L-triiodothyronine (5 μg/rat/day for 2 days) or cortone acetate (2.5 mg/rat/day for 2 days) failed to restore the capacity of their adipose tissue to respond to the lipolytic action of dexamethasone and growth hormone in vitro. The administration of growth hormone (100 μg/rat/lday) for at least 2 days restored responsiveness to dexamethasone and growth hormone, but a single injection of 100 μg/ of growth hormone administered 18 hr before sacrifice was without effect in this regard. It was concluded that, in promoting lipolysis, growth hormone must act on more than one aspect of the lipolytic system. (Endocrinology83: 300, 1968)
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H. M. Goodman (1968) studied this question.