SYMPATHETIC CONTROL OF SKELETAL-MUSCLE FUNCTION - POSSIBLE COOPERATION BETWEEN NORADRENALINE AND NEUROPEPTIDE-Y IN RABBIT JAW MUSCLES

Stimulation of the cervical sympathetic nerve at 10/s increases by 12. 9 +/- 0.7% peak tension of maximal twitches in the directly stimulated jaw muscles and markedly depresses (41.6 +/- 1.3%) the tonic vibratio n reflex (TVR) elicited in the same muscles by vibration of the mandib le. Both effects are not significantly influenced by administration of beta-adrenoceptor antagonists. When both alpha- and beta-adrenergic r eceptors are blocked, sympathetic stimulation induces a very small inc rease in twitch tension (3.8 +/- 0.7%), while no detectable change in the TVR is observed. Close arterial injection of alpha(1)-adrenoceptor agonist phenylephrine mimics the effects induced by sympathetic stimu lation on twitch tension and TVR, dose-dependently. The noradrenaline co-transmitter neuropeptide Y also produces a long-lasting, dose-depen dent increase in the twitch tension which is unaffected by blockade of adrenergic receptors as well as of the neuromuscular junctions. Contr ibution of neuropeptide Y to the sympathetically-induced reduction of the stretch reflex is not clearly demonstrated. These data suggest tha t co-operation between noradrenaline and neuropeptide Y may be effecti ve in determining sympathetic modulation of skeletal muscle function.