Does sympathetic nerve stimulation and norepinephrine infusion affect vascular resistance and lipolysis in canine omental adipose tissue?
Sympathetic nerves play a physiologically important role in regulating vascular reactions and lipid metabolism in canine omental adipose tissue.
Vascular resistance, capillary filtration coefficient (CFC) and changes in blood volume were determined in canine omental adipose tissue. Release of glycerol and free fatty acids (FFA) were measured. Basal values in acutely denervated tissue for blood flow and CFC were 11 ml/min/100 g (range 4 to 26, N = 36) and 0.05 ml/min/100 g/mm Hg (range 0.018 to 0.090, N = 38), respectively. Stimulation of the sympathetic nerves (1 to 9 Hz) caused initial vasoconstriction, maintained for 1 to 3 minutes. At lower frequencies (1 to 3Hz), the blood flow increased gradually after the initial decrease. At higher frequencies, the constriction often reverted to vasodilatation. The CFC was not changed or increased initially. The clearance rate of locally injected 125 I decreased in spite of a constant blood flow and blood volume was reduced initially. After α-receptor blockade, nerve stimulation caused vasodilatation, which in turn was inhibited by β-receptor blockade. Infusion of norepinephrine produced a pattern of vascular and lipolytic responses similar to those evoked by nerve stimulation. The release of glycerol and FFA was increased by nerve stimulation and by norepinephrine. The lipolytic response was inhibited by β-receptor blockade. It is concluded that sympathetic nerves are physiologically important for the regulation of vascular reactions and control of lipid metabolism in omental adipose tissue. Whether this is also the case for circulating catecholamines remains to be established.
Ballard et al. (1971) studied this question.