Glutamergic transmission and cardiovascular apparatus in normotensive rats

The cardiovascular effects induced by L-glutamic acid (G) on the cardiovascular apparatus of normotensive ethyl urethane-anaesthetized rats have been evaluated. (a) When administered i.v. (1 to 100 mg/kg) G induced a transitory and dose-dependent increase of arterial pressure (AP) with very moderate sinus bradycardia. It was antagonized by L-glutamic acid diethyl ester (GDEE, 0.1 to 100 mg/kg i.v.). (b) The intracerebroventricular (i.c.v.) administration of G (third ventricle, right lateral ventricle, posterior hypothalamus and striatum) at a dose of 0.1 to 10 mg/an induced a transitory and dose-dependent increase of AP, abolished by i.c.v. GDEE (1 to 10 mcg/an). (c) G hypertension was reduced by several procedures, i.e. catecholamine depletion, alpha 1, alpha 1 and alpha 2 or beta adrenergic blocks, alpha 2 central adrenergic stimulation, Ca2+ transmembrane or gangliary block, surrenectomy, and spinal transection at C7. (d) Atropine, bilateral vagotomy and sinus carotidal denervation increased G hypertension. (e) Therefore the bradycardia does seem to be due to a reflex-mediated effect via sinus carotid and aortic baroreceptors. (f) These data show that glutamergic transmission also participates through a central mechanism in the regulation of cardiovascular function in rats, via an increase in central sympathetic efferent activity.