Effect of nifedipine on arterial pressure lability of sino-aortic deafferentated rats

Sino-aortic deafferentation (SAD) in rats produces arterial pressure lability (APL) whose mechanisms are not completely understood. In the present study we infused nifedipine (500 micro g kg(-1) min(-1)) for 30 min into sham-operated and acute SAD rats (24 h) and the changes in mean arterial pressure (MAP) and APL were measured during this period by a computerized technique. APL was reported as the standard deviation of the mean of all MAP sampling points. In SAD rats with high basal APL levels (SAD high APL, N = 8) nifedipine produced a significant reduction in MAP (from 116 +/- 5 to 88 +/- 3 mmHg) and APL (from 19.62 +/- 1.46 to 9.51 +/- 0.88 mmHg). while in SAD rats with low basal APL levels (SAD low APL, N = 8) it significantly reduced MAP (from 120 +/- 7 to 95 +/- 6 mmHg) and did not change APL (9.46 +/- 0.69 to 10.93 +/- 1.62). Nifedipine infusion into sham-operated rats (N = 8) produced no significant changes in MAP (105 +/- 3 vs 104 +/- 2 mmHg) or APL (4.17 +/- 0.53 vs 3.99 +/- 0.67 mmHg). Since nifedipine infusion reduced APL only in SAD high APL rats but reduced the MAP in both groups of SAD rats. we conclude that its effect on APL is not related to decreases in MAP. These data suggest that extracellular calcium influx through calcium channels plays an important role in the generation of APL, especially in SAD rats with high APL levels.

The sensitivity of the Bezold-Jarisch reflex is increased in rats with sinoaortic deafferentation

The sensitivity of the Bezold-Jarisch reflex was evaluated by the cardiovascular changes in response to intravenous injection of increasing doses of serotonin (5-hydroxytryptamine) in conscious male Wistar (300-350 g) rats 1 and 15 days after sinoaortic deafferentation. The bradycardia and hypotension induced by serotonin (2, 4, 8, 16 and 32 micrograms, iv) were does dependent in sinoaortic deafferentated as well as in sham-operated rats, but the magnitude of the bradycardiac and depressor response to all doses of serotonin was significantly greater in both groups of sinoaortic deafferentated rats [1 (N = 8) and 15 days (N = 8)] than in sham-operated animals [1 (N = 8) and 15 days (N = 8)], indicating an increased sensitivity of the Bezold-Jarisch reflex. These data suggest that the increased sensitivity of the Bezold-Jarisch reflex may have some functional role in cardiovascular regulation after removal of aortic and carotid baroreceptors