Submitted on March 16, 2004
Accepted on June 9, 2004
Fructose Feeding and Intermittent Hypoxia Affect Ventilatory Responsiveness to Hypoxia and Hypercapnia in Rats
Evelyn H Schlenker1*, Shi Yijiang1, Joni Wipf1, Douglas S Martin1, and Curtis K Kost, Jr.1
1 Basic Biomedical Sciences, University of South Dakota School of Medicine, Vermillion, SD, USA
* To whom correspondence should be addressed. E-mail: eschlenk{at}usd.edu.
We hypothesized that in male rats 10% fructose in drinking water would depress ventilatory responsiveness to acute hypoxia (10% O2 in N2) and hypercapnia (5% CO2 in O2) that would be depressed further by exposure to intermittent hypoxia. Ventilation in air and in response to acute hypoxia and hypercapnia were evaluated in ten rats prior to fructose feeding (FF), during 6 weeks of FF and after FF was removed for 2 weeks. During FF, 5 rats were exposed to intermittent air and 5 to intermittent hypoxia for 13 days. Six rats given tap water acted as control and were exposed to intermittent air and subsequently intermittent hypoxia. In FF rats, plasma insulin levels increased 3 fold in the rats exposed to intermittent hypoxia, and during washout returned to levels observed in rats exposed to intermittent air. During FF, ventilatory (VE) responsiveness to acute hypoxia was depressed due to decreased tidal volume (VT) responsiveness. During washout, ventilation decreased due to decreased VT and frequency of breathing, and the ventilatory responsiveness to hypoxia in intermittent hypoxia rats did not recover. In all rats the ventilatory responses to hypercapnia were decreased during FF and recovered after washout due to an increased VT responsiveness. In control group, hypoxic responsiveness was not depressed after intermittent hypoxia and augmented after washout. Thus FF attenuated the VE responsiveness of conscious rats to hypoxia and hypercapnia. Intermittent hypoxia interacted with FF to increase insulin levels and depress ventilatory responses to acute hypoxia that remained depressed during washout.
