Vascular and lipolytic responses to infused norepinephrine in canine subcutaneous and omental adipose tissues

Vascular and lipolytic responses to intravenously administered norepinephrine (NE, 1 mug/kg-min for 30 min) were examined in autoperfused canine subcutaneous and omental adipose tissues. In response to NE, arterial perfusion pressures increased initially and then returned gradually to the pre-infusion levels. Shortly after the onset of NE infusion, the blood flow increased greatly in both adipose tissues. The higher blood flow was maintained throughout the whole infusion period in the subcutaneous adipose tissue, whereas in the omentum the initial high flow fell gradually to the pre-infusion level. Vascular resistance started to decrease after 2-5 min from the onset of NE infusion in the subcutaneous adipose tissue and the reduction of resistance was consistent and persistent as the infusion continued. NE infusion increased the net output of FFA from the subcutaneous adipose tissue, but not in the omentum. The increased FFA output seemed to coincide with the decrease in vascular resistance. Omental adipose tissue may not be influenced by NE at the concentration tested in this experiment. A marked fall in the blood flow was observed in the hindleg of the same animals. Such fall in blood flow was not observed in the adipose tissues in this experiment. It was concluded from the present results that there was a qualitative difference in the effects of norepinephrine on adipose tissues from different locations in the same animal and lipolytic response occurred only if active vasodilatation was present in these tissues.