FEBRILE RESPONSIVENESS OF VAGOTOMIZED RATS IS SUPPRESSED EVEN IN THE ABSENCE OF MALNUTRITION

The repeatedly observed attenuation of fever in vagotomized rats has b een accepted as evidence of an essential role of vagal afferents in th e transduction of pyrogenic signals from the periphery to the brain. I f, however, the general condition of a vagotomized animal is poor (the usual case) and accompanied by malnutrition and body mass loss (commo n complications of vagotomy), the febrile responsiveness can be suppre ssed not because of the lack of vagal afferentation, but rather second arily to a malnutrition-associated thermogenic incompetence. In the pr esent study, we addressed this dilemma. Male Wistar rats were subjecte d to subdiaphragmatic vagotomy (or sham surgery) and, 24 days later, c atheterized in the jugular vein. Postsurgically, the rats were closely watched and fed highly palatable food. Their febrile responsiveness [ colonic (T-c) and tail skin (T-sk) temperature responses] to Escherich ia coli lipopolysaccharide (LPS; 1 mu g/kg iv) was tested on day 27 po stvagotomy. To verify the completeness of vagotomy, each rat was food deprived for 24 h and then euthanized; its stomach's evacuatory functi on was assessed by weighing the organ. One month postsurgery, both foo d consumption and body mass of the vagotomized rats (33 +/- 2 g/day an d 313 +/- 4 g, respectively) were similar to the control values (30 +/ - 1 g/day and 315 +/- 8 g). In the sham rats, LPS induced a monophasic T-c rise of 0.5 +/- 0.3 degrees C at 70 min postinjection (peak), pre ceded by a fall in T-sk. Neither this T-sk fall (tail skin vasoconstri ction) nor the resultant fever occurred in the vagotomized rats; at 70 min, T-c change was -0.1 +/- 0.1 degrees C. The gastric mass (4.1 +/- 0.5 g in the vagotomized vs. 1.8 +/- 0.1 g in sham rats) indicated th e effectiveness of vagotomy. In sum, although the vagotomy-associated malnutrition was successfully prevented with special perioperative car e, the vagotomized animals still did not respond to LPS with fever. Ma lnutrition is, therefore, unlikely to constitute the main reason of th e febrile irresponsiveness of vagotomized rats.