Attenuated Blood Pressure Responsiveness During Post-Exercise Hypotension

OBJECTIVE: To test the hypotheses that acute treadmill exercise would produce post-exercise hypotension (PEH) and that PEH would be associated with reduced mean arterial pressure (MAP) responsiveness to the alpha 1-adrenergic agonist phenylephrine. METHODS: Arterial and venous catheters were implanted into exercise-trained female Dahl-salt sensitive rats (n = 9) for measurement of pulsatile blood pressure (BP) and heart rate (HR). The changes in BP following ganglionic blockade (hexamethonium/atropine) and the MAP responses to phenylephrine (PE) injections after ganglionic blockade (GB) were examined on separate days in testing cages (control) and following 40 min of treadmill exercise (post-ex). RESULTS: Thirty minutes following graded treadmill exercise (20-40 m/min, 0% grade, 40 min duration) blood pressure was significantly reduced (-9 +/- 1) mmHg compared to control. After exercise, GB produced a 43 +/- 3 mmHg decrease in BP which tended (p = 0.08) to be less than the reduction observed during control studies (51 +/- 2 mmHg). PE-induced increases in BP were significantly lower post-ex than control for each of the dosages tested (0.5, 1.0 and 2.0 micrograms/kg). CONCLUSIONS: These results demonstrate that there is sustained reduction in PE-induced MAP responsiveness which accompanies exercise-induced decreases in blood pressure in the Dahl salt-sensitive rat. Thus, decreased alpha-adrenoceptor responsiveness may contribute to the production of PEH.