Chronic hyperoxia augments the hypoxic ventilatory response in adult rats

Chronic hyperoxia during postnatal development causes long-lasting attenuation of the hypoxic ventilatory response (HVR) in rats, but similar exposures during adulthood do not attenuate the HVR (Ling et al. J Physiol 405: 561-571, 1996). However, the HVR has not been assessed in adult-exposed rats immediately after chronic hyperoxia (i.e., without several months of recovery in room air). This is important since chronic hyperoxia depresses breathing and blunts the HVR in newborn rats, and only some of these effects persist after return to room air. Accordingly, adult rats were studied after 4 and 14 days of exposure to either 60% O2 (Hyperoxia) or 21% O2 (Control). Ventilation was measured by whole-body plethysmography; metabolic O2 consumption and CO2 production were also measured in a subset of rats. Normoxic ventilation was unchanged, but Hyperoxia rats exhibited a slight increase in their acute HVR after both durations of chronic hyperoxia. Overall, minute ventilation was approximately 10% greater in Hyperoxia rats while breathing 12% O2 and 10% O2 than in Control rats; this effect did not differ significantly between female and male rats. The HVR was also enhanced after 4 days of hyperoxia after controlling for metabolic rate, but the results were less clear after 14 days. After the 14-day exposure, the HVR tended to be enhanced when tested at 12% O2 but not at 10% O2. These data demonstrate that chronic hyperoxia has different effects on the control of breathing in neonatal and adult rats when assessed immediately after the exposure. Supported by NIH grant P20 GM-103423 (Maine INBRE). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.