Renal Vascular Resistance Does Not Differ Between Younger Men and Women

Abstract

PurposeThe incidence of acute kidney injury is nearly two‐fold higher risk in men compared to women. A common cause of acute kidney injury is supply‐demand mismatch that is characterized by the presence of a comparatively low renal oxygen supply (i.e., blood flow) relative to tissue oxygen demand. Thus, it is possible that the control of renal blood flow differs between men and women. For instance, the vasodilator actions of estrogen may protect against excessive renal vasoconstriction or more readily promote renal vasodilation in pre‐menopausal women compared to men. However, whether renal vascular control, a function of both vasoconstrictor and vasodilator capacities, differs between men and women is unknown. Therefore, this study tested the hypotheses that (1) renal vasoconstriction during a sympathetic stimulus (i.e., the cold pressor test, CPT) will be greater in young healthy men compared to young healthy women, and (2) renal vasodilation following an oral protein load will be greater in women compared to men.MethodsHealthy, men (n=13, age 26 ± 3 years) and eumenorrheic women (n=12, age 23 ± 3 years, 4 ± 1 day of menstrual cycle) completed a 2‐min CPT after one hour of supine rest to assess renal vasoconstriction. A whey protein shake (1.2 g of protein/kg of body weight) was ingested 1‐h post‐CPT to assess renal vasodilation. Blood pressure (Penaz method) was measured continually. Renal segmental artery blood velocity (BV, Doppler ultrasound) was measured before and during the CPT (1‐ and 2‐min), and pre‐protein and 75‐ and 150‐min post‐protein. Segmental artery vascular resistance (VR) was calculated as mean arterial pressure (MAP) divided by segmental BV. Data are presented as mean ± SD.ResultsMAP increased in both men and women from pre‐CPT to 2 min (p<0.001), and the magnitude of increase did not differ between men (peak: +25 ± 13 mmHg) and women (peak: +23 ± 9 mmHg, p=0.667). Peak reductions in segmental BV (men: ‐1.3 ± 3.2 cm/s, women: ‐3.7 ± 2.9 cm/s, p=0.065) and increases in segmental VR (men: +1.5 ± 1.0 mmHg/cm/s, women: +2.1 ± 1.0 mmHg/cm/s, p=0.155) during the CPT did not differ between men and women. MAP did not differ between men and women pre‐protein or at 75‐min post‐protein (p>0.586) but was higher in men at 150‐min post‐protein (86 ± 7 mmHg vs. 78 ± 8 mmHg, p=0.042). Peak increases in segmental BV following protein ingestion were greater in women (+5.3 ± 2.2 cm/s) compared to men (+2.7 ± 2.4 cm/s, p=0.009). Similarly, peak reductions in segmental VR were greater in women (‐1.1 ± 0.6 mmHg/cm/s) compared to men (‐0.6 ± 0.6 mmHg/cm/s, p=0.030) following protein ingestion.ConclusionRenal vasoconstrictor responses to sympathetic stimulation do not appear to differ between healthy men and women. However, women displayed greater renal vasodilatory responses to an oral protein load. Therefore, renal vascular control differs between healthy men and women tested in the early follicular phase of the menstrual cycle. These findings may provide mechanistic insights in support of observations that acute kidney injury incidence differs between men and women.