Aa. Romanovsky et al., COLD DEFENSE-MECHANISMS IN VAGOTOMIZED RATS, American journal of physiology. Regulatory, integrative and comparative physiology, 42(2), 1997, pp. 784-789
Subdiaphragmatically vagotomized rats cannot mount a febrile response
to pyrogens and are believed to have severe thermoregulatory deficienc
ies. We addressed the issue of thermoeffector competence of vagotomize
d rats by asking three questions. In Expt. 1 we asked, can vagotomized
rats readily recruit tail skin vasoconstriction in the course of a mo
derate cold exposure? In Expt. 2 the question was, can brown adipose t
issue (BAT) thermogenesis readily be activated in vagotomized rats (e.
g., in response to a tail pinch)? In Expt. 3, we investigated the ques
tion: can vagotomized rats elevate their body temperature in response
to ephedrine (a drug of high hyperthermizing potential) to the same ex
tent as sham-operated controls? Rats were vagotomized or sham operated
and implanted with a catheter into the jugular vein and a thermocoupl
e into the interscapular BAT. To prevent the common complications of v
agotomy, special perioperative care was given. During experiments, col
onic, tail skin, and BAT temperatures (T-c, T-sk, and T-BAT, respectiv
ely) were measured. The vagotomized animals were well nourished and ha
d a body mass (325 +/- 6 g) similar to that of the controls (338 +/- 6
g). In Expt. 1, in response to external cooling (15 degrees C, 1 h),
the vagotomized (n = 30) and sham-operated (n = 31) rats recruited tai
l skin vasoconstriction at close values of both T-c (37.84 +/- 0.08 an
d 37.97 +/- 0.07 degrees C) and T-sk (33.16 +/- 0.17 and 33.18 +/- 0.1
8 degrees C, respectively). In Expt. 2, tail pinch-associated stress i
n vagotomized rats resulted in a sharp rise in the T-BAT - T-c gradien
t by 0.3-1.0 degrees C. In Expt. 3, ephedrine administered intravenous
ly (whether in a 5 or 35 mg/kg dose) evoked similar hyperthermic respo
nses in the vagotomized and sham-operated rats: a moderate (similar to
2.5 degrees C) T-c rise in the low dose and a ''supramaximal'' (simil
ar to 5.0 degrees C) rise in the high dose. In sum, the answer to all
three questions asked is yes. Vagotomized rats, at least when well nou
rished, exhibit no signs of thermoeffector deficiency. It is, therefor
e, not effector incompetence but rather vagal deafferentation per se t
hat can explain the febrile irresponsiveness of vagotomized rats.