NORADRENALINE-INDUCED HYPOTHERMIA IS SUPPRESSED IN THE VAGOTOMIZED COLD-EXPOSED PIGEON

Vagotomized (VX) pigeons studied 2 days after surgery exhibited a sign ificant decrease in cloacal temperature (T-b) and respiratory rate (R( f)), and an increase in heart rate (H-f) and metabolic rate (M) at the thermoneutral zone, when compared with sham-operated (SVX) pigeons. T he effect of intravenous noradrenaline (NA) on T-b, R(f), H-f and M wa s examined in SVX and VX-pigeons at 15 degrees C. Following NA adminis tration, the T-b and R(f) in the SVX-birds dropped from the preinjecti on level, but in VX-pigeons, they were not significantly altered. In S VX-pigeons, a total suppression of shivering was apparent following NA -injection, while in the majority of VX-pigeons, shivering was only sl ightly affected or even increased. The H-f in both SVX- and VX-birds i ncreased following NA-injection. The responses to reserpine were quali tatively similar to NA, although much slower. There were no difference s between SVX- and VX-birds with regard to T-b, M and R(f) following a cetylcholine (ACh) and eserine (Ese) injection, H-f increased after AC h + Ese administration in SVX-pigeons, but in VX-birds, it decreased a fter an initial surge. Shivering was suppressed for 18-20 min in SVX-b irds and 30-50 min in VX-birds. It is suggested that the lack of the h ypothermic effect of NA in VX-birds is due to the maintenance of oxyge n uptake with unimpaired capacity for shivering.