[Adaptation to hypotension may involve the cerebral hemispheres].
Arterial vasodilatation was obtained by a slow injection of nicardipine (0.1 microgram/20 min) to normotensive Long Evans rats. Reflex tachycardia was a consequence of a sympathetic activation as labetalol injected prior to nicardipine prevented the calcium antagonist-induced heart rate changes. The slope of the mean blood pressure (mmHg) - heart period (msec) curve was reproducible after a 75 min interval. This index of baroreflex sensitivity was calculated before and after a transient cerebral ischemia. Hemispheric ischemia was induced by electrocauterization of the vertebral arteries and a transient occlusion of the common carotid arteries for 10 min. Brainstem perfusion was maintained with this protocol. The second dose of nicardipine was injected 15 min after recirculation. The tachycardic response to the vasodilatation was markedly reduced after ischemia (1st slope: 0.48 +/- 0.05 msec/mmHg, 2nd slope: 0.12 +/- 0.05 msec/mmHg, n = 12, p less than 0.001, paired t test). We conclude that nicardipine injection is applicable to the study of baroreflex sensitivity in rats. The impairment of baroreflex sensitivity after a transient hemispheric ischemia could reflect a hemispheric interference with brainstem cardiovascular centres involved in the baroreceptor-heart rate reflex.
D000222:Adaptation, Physiological; D000818:Animals; D001921:Brain / Q000503:physiopathology*; D006339:Heart Rate; D007022:Hypotension / Q000503:physiopathology*; D008297:Male; D051381:Rats; D012018:Reflex / Q000502:physiology
L'adaptation à l'hypotension peut mettre en jeu les hémisphères cérébraux.