Heparin-induced release of lipase activity from perfused canine subcutaneous adipose tissue

An in situ perfusion protocol of rat epididymal adipose tissue useful in metabolic studies

Experimental approaches involving the perfusion of tissues and organs offer the advantage of improved physiological relevance over the use of isolated tissues or cells while at the same time being much more controlled and tissue-specific than studies in vivo. Nevertheless, there have been few metabolic studies performed in perfused white adipose tissue, largely because of the difficulty of the surgical technique involved. Although some methods have been described, they are difficult to use as perfusion protocols and their reproducibility is poor. We have modified a rat perfusion method, based on a modification of the Ho and Meng technique, for use with epididymal white adipose tissue (eWAT), and we present it here as a protocol to be reproduced. We also offer surgical solutions for the most common variants of vessel distributions in rats. Using the protocol described here, the perfused adipose tissue is viable and metabolically active, as indicated by the maintenance of tissue ATP levels and adiponectin secretion and by endogenous lipolysis regulation. Moreover, there is a high level of lipoprotein lipase activity in the endothelium of the tissue, which is heparin-releasable. Thus, this method is a useful and reproducible tool that allows the perfusion of eWAT for use in metabolic studies.

Adrenergic neurohumoral influences on circulation and lipolysis 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.