Alterations in Adipogenic and Mitogenic Activity of Porcine Serum in Response to Hypophysectomy*

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Abstract
The importance of the pituitary in postnatal regulation of peripheral preadipocyte proliferation and differentiation was examined by hormone supplementation of hypophysectomized pig serum in primary cultures of preadipocyte and stromal-vascular cells derived from rat inguinal adipose tissue. Hypophysectomized pig serum promoted at least 25% less preadipocyte proliferation, less differentiation of sn-glycerol-3-phosphate dehydrogenase activity, and less histochemical differentiation than serum from intact pigs. Porcine GH supplementation of hypophysectomized serum-stimulated [3H]thymidine incorporation by preadipocytes and stromal cells and also histochemical differentiation of preadipocytes, but not enzymatic differentiation. Insulin-like growth factor I (IGF-I) stimulated [3H]thymidine incorporation by preadipocytes and stromal cells. Enzyme differentiation by developing cells was stimulated by IGF-I. Hydrocortisone supplementation of hypophysectomized serum inhibited [3H]thymidine incorporation and stimulated enzymatic differentiation. Thyroid hormones (T3 and T4) stimulated [3H]thymidine incorporation by preadipocytes in a dose-responsive manner when supplemented to hypophysectomized serum. Thyroid hormones stimulated differentiation of enzyme activity at the lowest concentrations examined. The mitogenic effects of GH, IGF-I, and T4 were not specific to the preadipocyte population, since the stromal-vascular cells responded in a similar manner. However, hypophysectomy resulted in a specific reduction in preadipocyte proliferation while stimulating multiplication of stromal-vascular cells. These results suggest that these hormones are nonspecific mitogens in adipose tissue, while unidentified factors of pituitary origin may be important for the specific regulation of proliferation of preadipocytes. Additionally, hypophysectomy appears to remove mitogenic inhibitors that are specific for the stromal-vascular cells.