Studies on an isolated innervated preparation of guinea-pig trachea

An isolated preparation of the guinea-pig trachea with intact parasympathetic and sympathetic innervation has been devised. Responses to nerve stimulation were recorded as increases or decreases in intraluminal pressure from the fluid-filled trachea. The preparation maintained a positive resting intraluminal pressure of 3-4 cmH2O. This was unaffected by atropine, hexamethonium or propranolol. Brief pressor responses, which could be completely blocked by atropine or hexamethonium, were obtained by applying short trains of stimuli to the cervical segment of the right vagus. The amplitude of responses was frequency-dependent up to a maximum at 40 Hz. Depressor responses, more delayed and prolonged than the pressor responses and blocked by propranolol but not by hexamethonium, were obtained by stimulation of the right cervical sympathetic trunk or stellate ganglion in 70% of preparations. Dual pressor-depressor responses were observed in the remaining 30% of preparations. The pressor component was blocked by atropine, the depressor component by propranolol. In the presence of atropine and propranolol, sustained sympathetic stimulation sometimes evoked a small, delayed pressor response which was blocked by phentolamine. Under the same conditions, transmural stimulation produced a depressor response evidently due to non-adrenergic, non-cholinergic nerves. Spontaneous activity was observed in some preparations under normal conditions, but could always be evoked by hypoxia. Responses to sympathetic stimulation were reduced both by hypoxia and during periods of spontaneous activity. 8 The principal advantage of this preparation is that it permits both excitatory and inhibitory responses to be elicited by stimulation of vagal and sympathetic nerves separately in the isolated trachea in the absence of agonist and antagonist drugs.