Ventilatory Responses During Muscular Activity in Normal, Thyroidectomized and Thyroxinized Rats

¹ From the Department of Physiology, State University of New York, Downstate Medical Center, Brooklyn, New York

Ventilation and oxygen consumption of Wistar albino rats under pentobarbital sodium anesthesia were determined by means of a microspirometer at rest and during induced muscular exercise employing a 60-cycle alternating current modulated sinusoidally. The study was carried out in untreated, thyroidectomized and thyroxinized rats. The resting ventilatory equivalent for oxygen (VEo₂) were 21.53 ± 1.25 (mean ± S.E.), 15.42 ± 1.22 and 27.61 ± 1.62, respectively, and were significantly different from one another. The relationship between ventilation (V, ml/min. BTPS) and oxygen consumption (O₂, ml/min. STPD) in these three groups both at rest and during the steady state of exercise was as follows: in normal rats, V = 18.37 O₂ + 24.64; in thyroidectomized rats, V = 19.52 O₂ – 4.49, and in thyroxinized rats, V = 29.96 O₂ – 2.1. The slopes of these fitted lines were revealed to be different in position, with that of normal rats placed between that of thyroxinized rats (highest) and that of thyroidectomized rats (lowest). In addition, the line for the thyroxinized rats has a higher slope than the others, which signifies that the rate of change in ventilation as a function of oxygen consumption is greater.