High-fat diet increases respiratory frequency and abdominal expiratory motor activity during hypercapnia

Breathing disorders are commonly observed in association with obesity. Here we tested whether high-fat diet (HFD) impairs the chemoreflex ventilatory response. Male Holtzman rats (300-320g) were fed with standard chow diet (SD) or HFD for 12 weeks. Then, tidal volume (V-T), respiratory frequency (f(R)) and pulmonary ventilation (V-E) were determined in conscious rats during basal condition, hypercapnia (7% or 10% CO2) or hypoxia (7% O-2). The mean arterial pressure (MAP), heart rate (HR) and baroreflex sensitivity were also evaluated in conscious rats. A group of anesthetized rats was used for the measurements of the activity of inspiratory (diaphragm) and expiratory (abdominal) muscles under the same gas conditions. Baseline f(R), V-T and V-E were similar between SD and HFD rats. During hypercapnia, the increase of f(R) was exacerbated in conscious HFD rats (60 +/- 3, vs. SD: 47 +/- 3 Delta breaths.min(-1), P < 0.05). In anesthetized rats, hypercapnia strongly increased abdominal muscle activity in HFD group (238 +/- 27, vs. basal condition: 100 +/- 0.3%; P < 0.05), without significant change in SD group (129 +/- 2.1, vs. basal condition: 100 +/- 0.8%; P = 0.34). The ventilatory responses to hypoxia were similar between groups. In conscious HFD rats, MAP and HR were elevated and the baroreflex function was impaired (P < 0.05). These data demonstrated that 12 weeks of HFD exaggerate the ventilatory response activated by hypercapnia. The mechanisms involved in these responses need more in-vestigation in future studies. (AU)