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-adrenoceptors 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. Intracerebroventricular (i.c.v.) injections of a nonselective beta-adrenoceptor antagonist, DL-propranolol (5 or 50 microg), 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 microg, 72.5 +/- 8.2% for 50 microg). The same doses of DL-propranolol had no effect on the resting heart rate. Injection (i.c.v.) of a lower dose (5 microg) of D-propranolol--which has a lower potency as a beta-adrenoceptor antagonist than DL-propranolol, but a similar local anesthetic, membrane-stabilizing activity--did not attenuate the stress-induced tachycardia, although a higher dose (50 microg) did. Intravenous administration of DL-propranolol (5 or 50 microg) significantly attenuated the stress-induced tachycardia (drug-induced reduction of tachycardia at 5 min after the start of stress: 20.0 +/- 7.5% for 5 microg, 42.4 +/- 3.4% for 50 microg). However, the attenuation was much smaller than in the i.c.v. DL-propranolol-injected group. The i.c.v. injection of the 50 microg dose of DL-propranolol significantly augmented both the resting blood pressure and the pressor response to water immersion stress, whereas the lower dose (5 microg) had no effect. The i.c.v. injection of 50 microg D-propranolol also augmented, although not significantly, the resting blood pressure and the pressor response to stress. These results suggest that central beta-adrenoceptors are involved in the tachycardia induced by water immersion stress in rats.
Tan
N
N
Department of Exercise and Health Science, Faculty of Education, Yamaguchi University, Japan. tan@po.cc.yamaguchi-u.ac.jp
Morimoto
A
A
Morimoto
K
K
Sone
R
R
Nishiyasu
T
T
Watanabe
T
T
Nakamura
S
S
Murakami
N
N
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001143:Arousal / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D007101:Immersion / Q000503:physiopathology; D008297:Male; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*
D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D011433:Propranolol