Effects of Synacthen on lipid metabolism in the perfused epididymal fat pad of the rat

Rats were treated with Synacthen, a synthetic corticotrophin analogue, to induce hypercorticism. The epididymal fat pad was selectively cannulated and perfused. In fasted rats acetone ether powder lipoprotein lipase (LPL) activity rose during treatment to levels found in fed controls. In fed animals no further rise in LPL activity was observed during Synacthen treatment. However, the heparin-elutable LPL activity did not change during this treatment in fasted nor fed animals. Pharmacologic levels of insulin in the perfusion medium caused an increase in heparin-releasable LPL activity as a percentage of total fat pad LPL activity (15% v 48%). Hydrolysis of chylomicrons was higher in fasted three days treated animals then in controls (10 ± 4% v 2 ± 2%). In this group a higher uptake of liberated free fatty acids was found (2.6 ± 1.5% v 1.0 ± 0.5% in controls). The increase in hydrolysis rate and uptake of fatty acids in the treated fasted animals could not be explained by an increase in releasable LPL activity. Fatty acid release from the fat pad was lower in treated animals than in controls (fasted and fed), basally as well as after adrenalin stimulation. The observation that the epididymal fat pad retains its weight during hypercorticism may therefore be ascribed to an increased influx of fatty acids from increased hydrolysis of TG-rich particles and to an inhibited efflux of fatty acids from the adipocyte. The discrepancy between the LPL activity extractable from an acetone ether powder and the heparin releasable LPL activity suggests impairment of the transport of LPL from the adipocyte to the heparin releasable pool at the endothelium.