Reflex cardiovascular responses induced by electrical stimulation of glossopharyngeal nerves in the rat

Reflex cardiovascular responses to electrical stimulation of glossopharyngeal nerves (GPN) were studied in Dial-Urethane anesthetized rats. GPN stimulation at 3 V, 0.3 msec and 50 Hz produced maximal reflex depressor (34 +/- 2 mmHg) and bradycardia (21 +/- 2 beats/min) responses that were altered as follows: pentolinium (0.25 mg/kg, i.a.) blocked approximately 72% and 89% of control values of depressor and bradycardia responses, respectively; tripelennamine (5 mg/kg, i.a.) significantly reduced depressor responses (76%); whereas atropine (0.4 mg/kg i.a.) blocked only bradycardia (85%). Regional blood flow studies showed that GPN stimulation reduced systemic arterial pressure (approximately 25%), and increased iliac artery blood flow (5%), and decreased blood flow through the renal (14%) and superior mesenteric (13%) arteries. Hence, decreases in vascular resistance during GPN stimulation were greater in the hindlimb vascular bed (28%) than in the renal (14%) or the mesenteric vasculatures. In addition, the magnitude of decreases in hindlimb vascular resistance by GPN stimulation was reduced (80%) by pretreatment with tripelennamine, but not by atropine. The results suggest that reductions in arterial blood pressure and hindlimb vascular resistance of the rat in response to GPN stimulation may be mediated via a histaminergic vasodilator mechanism, and that there may be a differential pattern of reflex vascular adjustments of blood flow and vascular resistance among regional vasculatures of the rate.