Hypothermic responses to infection are inhibited by alpha2-adrenoceptor agonists with possible clinical implications.
BACKGROUND
alpha(2)-Adrenoceptor agonists are currently used as primary sedative agents in high dependency patients who are at high risk of sepsis. Clinical surveillance of such patients relies in part on their ability to mount appropriate responses to infection, in particular thermal responses. Thermoregulatory responses to infection are well studied in the rat and in this species, and humans, infection can induce febrile, hypothermic, or mixed hypothermic and febrile responses. The involvement of noradrenergic systems in thermal responses to infection prompted the hypothesis that ligands that act on adrenoceptors may interfere with the normal thermal responses to infection.


METHODS
In this study on rats, the effect of infusion of the selective alpha(2)-agonist, mivazerol, on hypothermic and plasma corticosterone responses induced by bacterial lipopolysaccharide (LPS) was investigated.


RESULTS
Clinically effective doses of mivazerol (4.8 and 10 microg kg(-1) h(-1)) had no effect on body temperature alone. However, mivazerol significantly inhibited the typical thermoregulatory response to bacterial LPS in a dose-dependent manner. This effect was mimicked by the selective alpha(2)-agonist, UK14304-18 (6 microg kg(-1) h(-1)), and antagonized by the alpha(2)-antagonist, RX811059A (7 microg kg(-1) h(-1)). The alpha(2)-ligands had no effect on basal or LPS-induced corticosterone levels.


CONCLUSIONS
These data suggest that early thermoregulatory responses to infection can be selectively antagonized by ligands that activate alpha(2)-adrenoreceptors. High dependency patients receiving alpha(2)-adrenoceptor agonists may not be capable of mounting a normal thermal response to infecting organisms and clinical monitoring using core temperature to detect infection may therefore be unreliable in these vulnerable patients.
Tolchard
S
S
Department of Anaesthesia, Frenchay Hospital, North Bristol NHS Trust, Frenchay, Bristol, UK. stevetolchard@yahoo.co.uk
Burns
P A
PA
Nutt
D J
DJ
Fitzjohn
S M
SM
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology / Q000627:therapeutic use*; D000818:Animals; D001424:Bacterial Infections / Q000097:blood / Q000150:complications*; D001833:Body Temperature Regulation / Q000187:drug effects; D003345:Corticosterone / Q000097:blood; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000379:methods; D007035:Hypothermia / Q000097:blood / Q000382:microbiology / Q000517:prevention & control*; D007093:Imidazoles / Q000494:pharmacology / Q000627:therapeutic use*; D008024:Ligands; D008070:Lipopolysaccharides; D008297:Male; D051381:Rats; D017208:Rats, Wistar
D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D008024:Ligands; D008070:Lipopolysaccharides; C087969:mivazerol; D003345:Corticosterone