In vivo effects of a treatment with antibodies to adipocyte plasma membranes in the rabbit

Antibodies against rabbit adipocyte plasma membranes were injected in 6-week-old rabbits. Controls received normal IgG. Animals were killed 1, 2, 5 or 9 weeks after treatment. Body weight and food intake were reduced significantly until the 7th week for the live weight and the 5th week for the intake. Whatever the anatomical location considered, adipose tissue was markedly reduced: -75% for week 1 and -20% for week 9 respectively for the total adipose mass. Cell volume and enzymatic activities of G3PDH, LPL and LDH were highly decreased during the first 2 weeks after treatment. Simultaneously the plasma levels of triglycerides and plasma free fatty acids were increased. As shown by others in the rat, it is possible to induce a long-term fatness reduction in the rabbit by treatment with antibodies to adipocyte plasma membranes. The cytotoxic effects of antibodies have also been discussed.     

Reevaluation of lipolytic activity of growth hormone in rabbit adipocytes

The lipolytic activities of porcine pituitary fractions and purified growth hormone (GH) from human (h), porcine (p), ovine (o) and rabbit (Rb) origin as well as ovine placental lactogen (oPL), were compared to that of ACTH on rabbit adipocytes. All the GH preparations and oPL were equivalent in inhibiting the binding of labelled oGH to liver plasma membranes from pregnant rabbits. ACTH, and to a lesser extent porcine pituitary fractions and hGH, stimulated free fatty acid production by isolated adipocytes. The sensitivity of the adipocytes to these factors was increased when adenosine deaminase was added to the incubation medium. But, RbGH, pGH, oGH and oPL had no effect. We conclude that GH is not directly involved in the control of lipolysis in rabbit adipocytes and that the effect of hGH is rather due to a contamination of this preparation by other pituitary factors.     

Differentiation of rabbit adipocyte precursor cells in a serum-free medium

Summary A serum-free, hormone-supplemented medium containing insulin, transferrin, and triiodothyronine (ITT medium), able to support differentiation of rat adipose precursor cells, has been used to study the regulation of the development of adipocytes in the rabbit. Adipose conversion was assessed by the appearance of glycerol-3-phosphate dehydrogenase activity. Stromal-vascular cells from rabbit perirenal adipose tissue differentiated to a very low extent or not at all in ITT medium. Supplementation of ITT medium with growth hormone or fibroblast growth factor did not increase the proportion of differentiated cells. In contrast, rabbit stromal-vascular cells were able to differentiate in ITT medium supplemented with glucocorticoids (dexamethasone, corticosterone) whereas sex steroids (β-estradiol, testosterone, progesterone) did not affect the differentiation process. In the presence of both dexamethasone and insulin, 20 to 50% of rabbit stromal-vascular cells differentiated into adipocytes within 2 wk of culture. The stimulatory actions of dexamethasone or insulin were dose-dependent. Insulin-like growth Factor-I (IGF-I), did not replace insulin under our culture conditions and had only a slight effect when added along with dexamethasone (100 nM) and insulin (1.7 nM). The results suggest that glucocorticoids, in association with insulin, may play an important role in the development of adipocytes from rabbit precursor cells. This work was supported by grant 4388 from the Institut National de la Recherche Agronomique, France.