Involvement of central beta-adrenoceptors in the tachycardia induced by water immersion stress in rats

The purpose of the present study was to investigate whether central beta-ad renoceptors are involved in stress-induced cardiovascular responses in rats . Using a biotelemetry system, blood pressure and heart rate were measured at rest and during stress induced by immersion in 1 cm-deep water. Intracer ebroventricular (i.c.v.) injections of a nonselective beta-adrenoceptor ant agonist, DL-propranolol (5 or 50 mu g). significantly and dose dependently attenuated the tachycardia induced by water immersion stress (drug-induced reduction of tachycardia at 5 min after the start of stress: 61.4 +/- 13.2% for 5 mu g, 72.5 +/- 8.2% for 50 mu g). The same doses of D-propranolol ha d no effect on the resting heart rate. Injection (i.c.v.) of a lower dose ( 5 mu g) Of D-propranolol-which has a lower potency as a beta-adrenoceptor a ntagonist than DL-propranolol, but a similar local anesthetic, membrane-sta bilizing activity-did not attenuate the stress-induced tachycardia, althoug h a higher dose (50 mu g) did. Intravenous administration of DL-propranolol (5 or 50 mu g) significantly attenuated the stress-induced tachycardia (dr ug-induced reduction of tachycardia at 5 min after the start of stress: 20. 0 +/- 7.5% for 5 mu g, 42.4 +/- 3.4% for 50 mu g) However, the attenuation was much smaller than in the i.c.v. Dr-propranolol-injected group. The i.c. v. injection of the 50 mu g dose of DL-propranolol significantly augmented both the resting blood pressure and the presser response to water immersion stress, whereas the lower dose (5 mu g) had no effect. The i.c.v. injectio n of 50 mu g D-propranolol also augmented, although not significantly, the resting blood pressure and the presser response to stress. These results su ggest that central beta-adrenoceptors are involved in the tachycardia induc ed by water immersion stress in rats. (C) 2000 Elsevier Science Inc. All ri ghts reserved.