SYMPATHETIC VASCULAR CONTROL OF THE LARYNGEO-TRACHEAL, BRONCHIAL AND PULMONARY CIRCULATION IN THE PIG - EVIDENCE FOR NONADRENERGIC MECHANISMS INVOLVING NEUROPEPTIDE-Y

Neuropeptide Y (NPY) and noradrenaline (NA) are co-stored in sympathet ic perivascular nerves of the airway mucosa and lung. The superior lar yngeal, bronchial and pulmonary vascular responses were therefore stud ied in anaesthetized pigs after systemic injections of NPY and NA and after stimulation (2 or 10 Hz, 15 V, 5 ms) of the cranial and caudal p ortions of the cervical sympathetic trunk or the stellate ganglia. NPY and NA increased vascular resistance, suggesting vasoconstriction in all three vascular beds. Stimulation of the cervical sympathetic trunk in the cranial direction caused clear-cut vasoconstriction and a decr ease in the superficial blood flow in the laryngeal and tracheal circu lation supplied by the superior laryngeal artery. This vascular respon se may be related to release of NA at 2 Hz and possibly also NPY at 10 Hz, since a remaining vasoconstrictor response at 10 Hz was present i n reserpinized preganglionically transected pigs when tissue content o f NA but not NPY was depleted. The decrease in superficial blood flow in the tracheal mucosa on sympathetic stimulation was absent after res erpine, however. Stimulation of the cervical sympathetic trunk in caud al direction provoked vasoconstriction in the bronchial and pulmonary vascular beds in control pigs. The basal tone of these two vascular be ds was not influenced on electrical stimulation after reserpine pretre atment, however, suggesting involvement of NA and possibly also NPY, w hich were both depleted by reserpine. Electrical stimulation of the st ellate ganglia also evoked reserpine-sensitive vasoconstriction in bot h the bronchial and pulmonary vascular beds. The left stellate ganglio n dominated the vasomotor response in the bronchial circulation, where as the right side mainly influenced the pulmonary circulation and the heart.