Respiratory muscle blood flow during exercise: Effects of sex and ovarian cycle.

Sex and ovarian cycle have been speculated to modify respiratory muscle blood flow control during exercise, but the findings are inconclusive. We tested the hypotheses that females would have higher respiratory muscle blood flow and vascular conductance (VC) compared with males during exercise and that this difference would be accentuated in proestrus vs. ovariectomized (OVA) females. Mean arterial pressure (carotid artery catheter) and respiratory muscle blood flow (radiolabeled microspheres) were measured during moderate-intensity (24 m/min, 10% grade) exercise in male ( n = 9), female ( n = 9), and OVA female ( n = 7) rats and near-maximal (60 m/min, 5% grade) exercise in male ( n = 5) and female ( n = 7) rats. At rest, diaphragm, intercostal, and transversus abdominis blood flow were not different ( P = 0.33) among groups. During moderate-intensity exercise, diaphragm (M: 124 ± 16; F: 140 ± 14; OVA: 140 ± 20 ml·min-1 ·100 g-1 ), intercostal (M: 33 ± 5; F: 34 ± 5; OVA: 30 ± 5 ml·min-1 ·100 g-1 ), and transversus abdominis blood flow (M: 24 ± 4; F: 35 ± 7; OVA: 35 ± 9 ml·min-1 ·100 g-1 ) significantly increased in all groups compared with rest but were not different ( P = 0.12) among groups. From rest to moderate-intensity exercise, diaphragm ( P < 0.03) and transversus abdominis ( P < 0.04) VC increased in all groups, whereas intercostal VC increased only for males and females ( P = 0.01). No differences ( P > 0.13) existed in VC among groups. During near-maximal exercise, diaphragm (M: 304 ± 62; F: 283 ± 17 ml·min-1 ·100 g-1 ), intercostal (M: 29 ± 8; F: 40 ± 6 ml·min-1 ·100 g-1 ), and transversus abdominis (M: 85 ± 14; F: 86 ± 9 ml·min-1 ·100 g-1 ) blood flow and VC were not different ( P > 0.27) between males and females. These data demonstrate that respiratory muscle blood flow and vascular conductance at rest and during exercise are not affected by sex or ovarian cycle in rats. NEW & NOTEWORTHY It has been proposed that sex and ovarian cycle modulate respiratory muscle blood flow control during exercise. We demonstrate herein that neither sex nor ovarian cycle influences respiratory muscle blood flow or vascular conductance at rest or during exercise in rats.