Response of trypsin-treated brown and white fat cells to hormones. Preferential inhibition of insulin action.

Insulin did not stimulate glucose metabolism or inhibit lipolysis in brown fat cells isolated by digestion of rat interscapular brown adipose tissue with collagenase plus 1 mg of trypsin per ml. Trypsin-treated cells responded normally to catecholamines and to the antilipolytic agent, prostaglandin El. The stimulation of respiration by lipolytic agents and free fatty acids was not affected by trypsin digestion, but the potentiation of octanoate-induced respiration by insulin was abolished. Incubation of white adipose tissue from rats with trypsin plus collagenase abolished the ability of insulin to inhibit lipolysis and stimulate glucose metabolism but did not afIect the antilipolytic action of prostaglandm El. Trypsin-treated white fat cells metabolized less glucose than cells isolated with collagenase alone but had a normal response to lipolytic agents such as theophylline, growth hormone plus dexamethasone, and catecholamines. The failure of trypsintreated cells to respond to insulin was not due to destruction of insulin, because medium containing insulin which had been incubated with trypsin-treated fat cells stimulated the metabolism of glucose by cells isolated with collagenase only. Trypsin treatment abolished the stimulation of white fat cell glucose metabolism seen in the presence of “bound insulin” but not that due to oxytocm. These studies indicate that trypsin treatment selectively inactivates the response of fat cells to insulin and “bound insulin,” but not to oxytocin, prostaglandin E,, or lipolytic agents.