Combination of Insulin with Muscle of the Hypophysectomized

Both excess and deficiency of the hormones of the pituitary gland are known to influence the action of insulin. To demonstrate such effects surviving isolated tissue in vitro as well as the intact animal has been used. For example, an excess of pituitary hormone caused by pituitary hyperfunction or by injection of pituitary preparations in the intact animal results in an increased resistance to insulin (1). Using the rat diaphragm in vitro, Nelson (2) first showed that the prior injection of anterior pituitary extracts occasions a decrease in the effect of insulin on glycogen synthesis. A deficiency of pituitary hormone, on the other hand, brought about by hypophysectomy, causes the intact animal to become highly sensitive to insulin. But attempts to demonstrate this hypersensitivity in vitro, with the rat diaphragm, have been unsuccessful (3-5). To study this problem we made use of the technique (5, 6) previously reported from this laboratory: a hemidiaphragm is equilibrated for 1 minute or less in a solution containing insulin, washed in two changes of medium without insulin, and then equilibrated, still without added insulin, in a glucose solution. Invariably, the insulin-treated hemidiaphragm utilizes more glucose and synthesizes more glycogen than its paired control. We attribute this extra metabolic activity to the presence of insulin which became chemically bound by muscle tissue during the brief preliminary exposure. We found that this combination of insulin is influenced by hormones. In particular, injection of anterior pituitary extract into the intact animal decreased or abolished the subsequent ability of the isolated diaphragm to respond in normal fashion to the short preliminary exposure t,o insulin. More significant is the observation (5) that antecedent treatment of the diaphragm in vitro with crude anterior pituitary extract or partially purified fractions of pituitary protein for short periods rendered the diaphragm refractory to subsequent combinat,ion with insulin. It is