Effect of beta-receptor blockade on the development of resistance to trauma in rats.

To study the mechanisms of the development of resistance to trauma, we examined the survival of a tumbling trauma using a Noble-Collip drum (40 rpm) by rats conditioned by sublethal drummings with and without prior administration of propranolol. The drum conditioning that consisted of four consecutive sublethal drummings (200, 350, 500, and 650 revolutions) induced increased resistance to an otherwise lethal drumming (800 revolutions) in rats without pretreatment of propranolol. Rats administered with propranolol 4 mg/kg intraperitoneally (ip) prior to each sublethal drumming showed a mortality of 22% after the lethal drumming which was significantly less than the mortality of 92% in nonconditioned rats pretreated with propranolol. This increased resistance to a lethal trauma in rats conditioned by drummings with concurrent administration of propranolol was confirmed in another lot of rats. These results indicated that prior administration of propranolol 4 mg/kg ip did not inhibit the induction of trauma resistance by repeated sublethal drummings, suggesting the existence of a mechanism unaffected by this dose of propranolol.