ROLE OF ADRENERGIC RECEPTORS ON SKELETAL MUSCLE CONTRACTILITY

Abstract

We examined the effects of adrenaline on the contractility ofrat

. diaphragm, diaphragmatic contractility was assessed from changes in simple twitch tension, tetanic tension, contraction time, half relaxation time generated. by direct supramaximal stimuli (100 volts) of the muscle. Aru! also we investigate the role of a and 13-receptors by using both phentolamine as a-blocker (1 microM/50ml) and propranolol as 13-

blocker (1 microM/50ml).

Simple twitch and tetanic contractions are recorded 5 minutes after m vitro addition of adrenaline, then response of muscle contractions to adrenaline is recorded again with prior addition of both and :13-blockers.

We also assessed the contractility of the diaphragm 8 days after single intramuscular injection of corticosteroid (trimethelone acetate 1.5 mg/kg), as well as the response to adrenaline addition.

The results of this study were significant increase in both simple twitch tension and tetanic tension after adrenaline addition without significant changes in both contraction time, half relaxation time. The effect was found to be mediated via 13-adrenergic receptor. And as regards absolute corticosteroid treatment there was significant decrease in tetanic force while twitch characteristics were unaffected with significant increase in both tetanic tension force and simple twitch tension after using adrenaline in corticosteroid treated rats without significant changes in either contraction time or half relaxation time.