Attenuation of the hypercapnic ventilatory response in the Brown Norway (BN) rat occurs prior to postnatal (P) day 26 and does not appear to be influenced by gender

Abstract

Adult (<49 days of age) inbred Brown Norway (BN) rats exhibit a blunted hypercapnic ventilatory response compared to inbred Dahl salt sensitive (SS) and outbred Sprague Dawley (SD) strains (Hodges et al., 2002), despite developing high CO2 sensitivity from post‐natal (P) day P12–14 until at least P20–21 (Davis et al., 2006). Thus, we hypothesized that CO2 sensitivity is attenuated between P30–P49 in the BN, but not the SS rat strain, and that the identification of a time window and/or potential gender difference may provide insights into the cause. The hypercapnic ventilatory response (FICO2=0.07) of male (n=6) and female (n=6) BN, and male SS (n=6) rats was measured with flow‐through plethysmography from P26–47, and expressed as a percentage of room air breathing (VE; % control). VE increased during hypercapnia in both male and female BN rats to (151%) at the earliest age studied (P26–27), and was similar throughout the remainder of the ages studied with one exception. At P30–31 there was a modest increase in the hypercapnic ventilatory response in male BN rats, but it was also highly variable. Additional comparisons to the SS strain await further analysis. We conclude from these data that the apparent attenuation of CO2 sensitivity in BN rats occurs prior to P26, and does not appear to be dependent upon gender. Supported by NIH HL097033.