Cardiorespiratory responses to shivering in vagotomized pigeons during normoxia and hypoxia

Thermoregulatory and metabolic responses of Japanese quail to hypoxia

Common responses to hypoxia include decreased body temperature (Tb) and decreased energy metabolism. In this study, the effects of hypoxia and hypercapnia on Tb and metabolic oxygen consumption (VO2) were investigated in Japanese quail (Coturnix japonica). When exposed to hypoxia (15, 13, 11 and 9% O2), Tb decreased only at 11% and 9% O2 compared to normoxia; quail were better able to maintain Tb during acute hypoxia after a one-week acclimation to 10% O2. VO2 also decreased during hypoxia, but at 9% O2 this was partially offset by increased anaerobic metabolism. Tb and VO2 responses to 9% O2 were exaggerated at lower ambient temperature (Ta), reflecting a decreased lower critical temperature during hypoxia. Conversely, hypoxia had little effect on T(b) or VO2 at higher Ta (36 degrees C). We conclude that Japanese quail respond to hypoxia in much the same way as mammals, by reducing both Tb and VO2. No relationship was found between the magnitudes of decreases in Tb and VO2 during 9% O2, however. Since metabolism is the source of heat generation, this suggests that Japanese quail increase thermolysis to reduce Tb. During hypercapnia (3, 6 and 9% CO2), Tb was reduced only at 9% CO2 while VO2 was unchanged.

Hypoxia-induced anapyrexia: implications and putative mediators

Hypoxia elicits an array of compensatory responses in animals ranging from protozoa to mammals. Central among these responses is anapyrexia, the regulated decrease of body temperature. The importance of anapyrexia lies in the fact that it reduces oxygen consumption, increases the affinity of hemoglobin for oxygen, and blunts the energetically costly responses to hypoxia. The mechanisms of anapyrexia are of intense interest to physiologists. Several substances, among them lactate, adenosine, opioids, and nitric oxide, have been suggested as putative mediators of anapyrexia, and most appear to act in the central nervous system. Moreover, there is evidence that the drop in body temperature in response to hypoxia, unlike the ventilatory response to hypoxia, does not depend on the activation of peripheral chemoreceptors. The current knowledge of the mechanisms of hypoxia-induced anapyrexia are reviewed.

Noradrenaline-induced hypothermia is suppressed in the vagotomized cold-exposed pigeon

Vagotomized (VX) pigeons studied 2 days after surgery exhibited a significant decrease in cloacal temperature (Tb) and respiratory rate (Rf), and an increase in heart rate (Hf) and metabolic rate (M) at the thermoneutral zone, when compared with sham-operated (SVX) pigeons. The effect of intravenous noradrenaline (NA) on Tb, Rf, Hf and M was examined in SVX and VX-pigeons at 15 degrees C. Following NA administration, the Tb and Rf in the SVX-birds dropped from the preinjection level, but in VX-pigeons, they were not significantly altered. In SVX-pigeons, a total suppression of shivering was apparent following NA-injection, while in the majority of VX-pigeons, shivering was only slightly affected or even increased. The Hf in both SVX- and VX-birds increased following NA-injection. The responses to reserpine were qualitatively similar to NA, although much slower. There were no differences between SVX- and VX-birds with regard to Tb, M and Rf following acetylcholine (ACh) and eserine (Ese) injection. Hf increased after ACh+Ese administration in SVX-pigeons, but in VX-birds, it decreased after an initial surge. Shivering was suppressed for 18-20 min in SVX-birds and 30-50 min in VX-birds. It is suggested that the lack of the hypothermic effect of NA in VX-birds is due to the maintenance of oxygen uptake with unimpaired capacity for shivering.

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.