Renal vascular control during normothermia and passive heat stress in healthy younger men and women.

We tested the hypothesis that the renal vasoconstrictor and vasodilator responses will be greater in younger women compared to men during passive heat stress. Twenty-five healthy adults [12 women (early follicular phase), 13 men] completed two experimental visits, heat stress or normothermic time-control, assigned in a block-randomized crossover design. During heat stress, core temperature was increased by ~0.8°C in the first hour before commencing a 2-min cold pressor test (CPT). Core temperature remained clamped and at one-hour post-CPT, subjects ingested a whey protein shake (1.2 g of protein/kg body weight), and measurements were taken pre-, 75-, and 150-min post-protein. Segmental artery vascular resistance (VR, Doppler ultrasound) was calculated as segmental artery blood velocity ÷ mean arterial pressure. CPT-induced increases in segmental artery VR did not differ between trials (trial effect: p=0.142) nor between men (heat stress: 1.5 ± 1.0 mmHg/cm/s, normothermia: 1.4 ± 1.0 mmHg/cm/s) and women (heat stress: 1.4 ± 1.2 mmHg/cm/s, normothermia: 2.1 ± 1.1 mmHg/cm/s) (group effect: p=0.429). Reductions in segmental artery VR following oral protein loading did not differ between trials (trial effect: p=0.080) nor between men (heat stress: -0.6 ± 0.8 mmHg/cm/s, normothermia: -0.6 ± 0.6 mmHg/cm/s) and women (heat stress: -0.5 ± 0.5 mmHg/cm/s, normothermia: -1.1 ± 0.6 mmHg/cm/s) (group effect: p=0.204). Renal vasoconstrictor responses to the cold pressor test and vasodilator responses following an oral protein load during heat stress or normothermia do not differ between younger men and younger women in the early follicular phase of the menstrual cycle.