Physiological responses of naloxone-treated pigeons to changes in ambient temperature

1. In pigeons given single intramuscular injection of naloxone, the heart rate (HR), breathing frequency (BF), oxygen consumption (VO₂), cloacal temperature (T_c) and foot temperature (T_f) were monitored during gradual lowering of the ambient temperature (T,) from 34°C to 6° in 6 hr.2. The two doses of naloxone tested (2 mg and 5 mg/kg b.w.) had an inhibitory effect on HR, the effect being greater with the higher dose as well as with the fall in T_a.3. The higher dose showed a tendency to have a stimulatory effect on BF in T_a above 22°C and an inhibitory effect in T_a below 22°C. With the lower dose, BF remained unaltered except in T_a below 12°C during which it showed a trend toward a decrease.4. VO₂ decreased with the higher dose, the extent of decrease being greater with drop in T_a. With the lower dose, VO₂ was not affected at or below T_a 26°C, but showed a trend toward an increase at T_a above 26°.5. The higher dose produced hyperthermia when T_a was below 14°C, whereas with the lower dose, T_c showed no significant change except for a slight drop at T_a 6°C.6. T_fwas not significantly affected by naloxone treatment.7. It is suggested that these effects were caused by the inhibition of endorphine-mediated catecholamine release by naloxone.