Physiological responses of vagotomized pigeons exposed to ambient temperatures gradually reduced from 34°C to 2°C

Abstract

In pigeons subjected to bilateral cervical vagotomy and sham-vagotomy, measurements of heart rate, breathing frequency, cloacal temperature (T c), foot temperature (T f), shivering and metabolic heat production (M) were made during gradual ambient cooling from 34 to 2°C on Day 2 as well as on Day 3 post-surgery. Severe tachycardia was observed in both Day 2 and Day 3 vagotomized (VX) pigeons. Lowering of ambient temperature (T a) below 28°C produced increased heart rate in both Day 2 as well as Day 3 sham-vagotomized (SVX) and VX pigeons, except with Day 3 VX pigeons exposed to T a below 12°C when a reversal of the trend became apparent. Breathing frequency in VX pigeons was lower than that in SVX on both days tested, the difference being greater on Day 2 than on Day 3. On both days, the difference in breathing frequency between VX and SVX pigeons was minimal at T a 30°C and became increasingly greater with T a above or below this point. T c dropped significantly in both VX and SVX pigeons in response to ambient cooling on Days 2 and 3. The Day 2 VX pigeons in general had a lower T c than that in SVX and as T a continued to drop below 28°C, T c in VX pigeons dropped more rapidly than in SVX, showing the maximal difference in T c between the two at T a 2°C. A similar trend was also observed with Day 3 VX pigeons when T a dropped below 22°C, but at T a between 32°C and 24°C, these pigeons showed a trend to have a higher T c than that in SVX. T f in both Day 2 and Day 3 SVX as well as VX pigeons dropped significantly during ambient cooling, and with fall in T a below 20°C, T f in VX pigeons dropped considerably below that in SVX, the magnitude of the difference being greater with increased ambient cooling. It is suggested that norepinephrine (NE) and thyroxine (T 4) are involved in the thermoregulatory process in VX pigeons during changes in T a. Shivering response in SVX pigeons was observed as early as at T a 26°C, while in VX the initial response was observed only at 22°C on both days. VX pigeons showed significantly lower shivering intensity than SVX, the difference between the groups being greater with Day 2 than Day 3 birds. As T a dropped, shivering intensity continued to increase in both the groups, but this increase was substantially slower in VX than in SVX, resulting in an increased difference in the shivering intensity between VX and SVX as T a dropped to the lowest (2°C). Metabolic heat production (M) increased significantly in Day 2 and Day 3 SVX as well as VX pigeons at low T a. In Day 2 VX pigeons, M was lower than in SVX at or below T a 24°C, but no significant difference in M was observed between Day 3 VX and SVX pigeons. Because the effects of vagotomy on M, shivering and breathing frequency were less pronounced on Day 3 than on Day 2, it may be inferred that a transient correctional process toward a steady state might have been underway.