Hypertensive Responses to Orthostatic and Inverse-Orthostatic Stimuli Measured by Cardiovascular Telemetry

摘要

The organism is exposed to diverse orthostatic stimuli that may induce acute and chronic adaptive responses. The effects of various orthostatic stimuli on cardiovascular adaptive responses were investigated in conscious rats. Arterial blood pressure and heart rate were measured by cardiovascular telemetry. Hypertension was induced via inhibition of the NO-synthase. Orthostatic and inverse-orthostatic challenges were induced by 45° head-up (HUT) or head-down (HDT) tilt positions in tubular cages. Experimental protocols included (i.) 5 min duration repeated 3 times with 5-min pauses each "R", or (ii.) sustained tilting for 120 min "S". In normotensive rats, horizontal control blood pressure was R115.4 ± 1.4/S113.7 ± 1.6 mmHg (mean±SEM) and heart rate R386.4 ± 7.0/S377.9 ± 8.8 BPM. HUT increased blood pressure by R< ±1 (n.s.)/S4.6 mmHg (p<0.05). HDT also resulted in a blood pressure increase by R6.2 (p<0.05)/S14.4 mmHg (p <0.05). In NO-deprived hypertension horizontal control hemo-dynamic parameters were R138.4 ± 2.6/S140.3±2.7 mmHg and R342.1±12.0/S346.0 ±8.3 BPM, respectively. HUT and HDT resulted in similar blood pressure changes as seen in normotensives. The sustained hypertensive response was prevented by prazosin (10 mg/kg p.o.). Our data demonstrate that both normotensive and hypertensive conscious rats exhibit hypertensive responses to sustained orthostatic or inverse-orthostatic gravitational stimuli and its mechanism is probably an increased sympathetic outflow. These blood pressure changes may play an important role in cardiovascular adaptation to orthostatic challenges.