Plasma Endothelin-1 is Increased in the Recovery from Acute Leg Heating in Older Adults

Blood pressure is reduced in older adults following exposure to acute leg heating, but mechanisms mediating this hypotensive response are unknown. We tested the hypothesis that plasma endothelin-1, a potent vasoconstrictor, would be attenuated concurrently with blood pressure in older adults following acute leg heating. Thirteen young and ten older adults were exposed to 45 minutes of leg heating. Plasma endothelin-1 concentrations were measured immediately prior to and 30 minutes into recovery from heating. Mean arterial blood pressure was well maintained in young adults (pre-heat, 86±6 mmHg vs. recovery, 88±7 mmHg; P = 0.4), but was markedly reduced in older adults (pre-heat, 101±7 mmHg vs. recovery, 94±6 mmHg; P < 0.05). Systemic vascular conductance did not differ from pre-heat (69±3 ml min-1 mmHg-1) to recovery (70±3 ml min-1 mmHg-1; P = 0.7) in young adults, whereas conductance was increased in older adults (pre-heat, 55±6 ml min-1 mmHg-1 vs. recovery, 62±5 ml min-1 mmHg-1; P = 0.07). Plasma endothelin-1 was increased in both groups following leg heating (young adults, [delta]0.23±0.42 pg ml-1; older adults [delta]0.20±0.43 pg ml-1; P< 0.05). Despite increased plasma endothelin-1, blood pressure was reduced in parallel with an increase in systemic vascular conductance which suggests that endothelin-1-mediated vasoconstriction may be altered following leg heating in older adults. Alternatively, increased endothelin-1 may be preventing a further deleterious reduction in blood pressure by restraining the increase in systemic vascular conductance.