EFFECT OF CHANGING BODY-TEMPERATURE ON THE VENTILATORY AND METABOLIC RESPONSES OF LEAN AND OBESE ZUCKER RATS

We measured body temperature (T-b) and ventilatory and metabolic varia bles in lean (n = 8) and obese (n = 8) Zucker rats. Measurements were made while rats breathed air, 4% CO2, and 10% O-2. Under control condi tions, T-b in obese rats was always less than that of their lean count erparts. Obese rats adopted a more rapid, shallow breathing pattern th an lean rats in air and had a lower ventilation rate in 4% CO2. Respir ation in 10% O-2 was similar for the two groups. Metabolic variables d id not differ between lean and obese rats whatever the gas breathed. W hen lean rats were cooled to match T-b in control obese rats with an i mplanted abdominal heat exchanger, they increased ventilation and meta bolism in air; there was no effect of cooling on responses to 4% CO2, and ventilation increased while metabolism decreased in 10% O-2. When obese rats were warmed to match Tb in control lean rats, trends in ven tilation and metabolism resulted in a tendency toward hyperventilation in air and 4% CO2, but not in 10% O-2. Taken overall, matching T-b in lean and obese rats accentuated differences in respiratory and metabo lic variables between the two groups. We conclude that differences in respiration between lean and obese Zucker rats are not due to the diff erence in T-b.