IN-SITU REGULATION OF LIPOLYSIS BY INSULIN AND NOREPINEPHRINE - A MICRODIALYSIS STUDY DURING EUGLYCEMIC HYPERINSULINEMIC CLAMP

Lipolytic responsiveness of subcutaneous and epididymal adipose tissue to norepinephrine (NE) was measured by microdialysis before and durin g a euglycemic-hyperinsulinemic clamp in male Sprague-Dawley rats (280 +/- 7 g, n = 8). Microdialysis probes were perfused with standard Kre bs-Ringer buffer without (basal condition [BC]) or with NE 10(-6) mol/ L to determine basal and stimulated rates of lipolysis. The dialysate concentration of glycerol was measured (lipolytic index). NE infusion resulted in 3.0- and 4.2-fold increases in glycerol release in abdomin al subcutaneous and epididymal adipose tissues, respectively. A euglyc emic-hyperinsulinemic clamp at 6 mU/kg . min increased by ninefold the insulinemia (120 +/- 9 U/L). Hyperinsulinemia suppressed basal glycer ol release by 57% and 42% in subcutaneous and epididymal adipose depot s, respectively (BC + I). Lipolytic responses to NE infusion during a euglycemic-hyperinsulinemic clamp (NE + I) were reduced by 45% and 33% in subcutaneous and epididymal adipose tissues, respectively, as comp ared with BC. Under BC, the lipolytic response to NE was greater in ep ididymal than in subcutaneous adipose tissue. Physiological levels of insulin regulated basal lipolysis and counteracted adrenergic stimulat ion of lipolysis to a similar extent in both superficial (subcutaneous ) and intraabdominal (epididymal) adipose tissues. Our findings show t hat lipolysis is more responsive to NE in epididymal than in subcutane ous adipose tissue, The antilipolytic effects of insulin are similar i n both superficial and deep intraabdominal adipose tissues. Furthermor e, physiological plasma insulin levels cannot fully antagonize the lip olytic effects of NE. Copyright (C) 1995 by W.B. Saunders Company