Lipolytic effects of insulin in adipocytes isolated from hypophysectomized rats

Adipocytes isolated from the epididymal fat of hypophysectomized rats by digestion with collagenase failed to respond to insulin with an increase in glucose utilization. These cells also exhibited an anomalous response to insulin when added in the presence of epinephrine. While insulin antagonized the lipolytic actions of epinephrine in normal adipocytes or in segments of epididymal fat from normal or hypophysectomized rats, it potentiated lipolysis in adipocytes isolated from hypophysectomized rats. This anomalous effect was also evident when isoproterenol, ACTH, or glucagon was used as the lipolytic agent, but the expected antilipolytic response was obtained when theophylline served as the lipolytic agonist. The lipolytic effects of insulin were not seen until 4-7 days after hypophysectomy. Treatment of hypophysectomized rats with a combination of GH (100 micrograms/rat . day), cortisone acetate (1 mg/rat . day), and T3 (1 micrograms/rat . day) for 5 days restored the antilipolytic response to insulin in cells of hypophysectomized rats, but no one hormone alone was effective. The data indicate that adipocytes of hypophysectomized rats retain their ability to recognize and response to insulin, but the ability of insulin to stimulate glucose oxidation or antagonize epinephrine-induced lipolysis is abolished by the cell isolation procedure. The findings underscore the need to consider the impact of hormonal status on the ability of cells to retain normal responsiveness during the rigors of the cell isolation procedure and suggest that failure to do so might lead to erroneous interpretations of the physiological actions of hormones.