Effects of arginine vasotocin on cardiorespiratory and thermoregulatory responses in the pigeon.

1. The effects of intramuscular injections (10 ng, 100 ng, 1 mu or 10 mu/pigeon) of two preparations of synthetic arginine vasotocin (AVT), deamino-dicarba-arginine vasotocin (ddAVT) and arginine vasotocin diacetate tetrahydrate (AVTdt) on heart rate (HR), breathing frequency (BF), oxygen consumption (VO2), cloacal and foot temperatures (Tc and Tf) and shivering (S) were studied in the pigeon housed in a respiratory flow chamber maintained at a temperature of 22.5 degrees, during a 4 hr post-injection period. 2. In general, with the exception of the lowest dose, AVT-treatment produced hypothermic responses, as was indicated by Tc and Tf. 3. Both ddAVT and AVTdt produced increases in HR and BF when administered in high concentrations (10 micrograms/pigeon), the effect being more potent with AVTdt than ddAVT; with lower doses, the effects were considerably less pronounced. This increase in HR and BF is attributed to a probable compensatory response to the hypothermic effect. 4. With a 10 micrograms dose, ddAVT produced a greater decline in VO2 than AVTdt. Although other doses too evoked a drop in VO2 at certain post-injection time points, the effect was of lesser magnitude. 5. No significant shivering response was elicited, in spite of the drop in Tc. 6. It is suggested that, besides the antidiuretic function of AVT, its hypothermic effect would be of considerable importance in thermal homeostasis during flight in birds.