Endogenous opioid analgesia in hemorrhagic shock.
BACKGROUND
Hemorrhagic shock produces an immediate activation of the autonomic nervous system and endogenous opioid pathways. Our studies have demonstrated that endogenous opioid activation aggravates the hemodynamic and inflammatory responses to shock. However, it is unclear whether endogenous opioid activation is triggered by noxious stimuli and furthermore whether it produces analgesia.


METHODS
Experiments were conducted in chronically catheterized, conscious, unrestrained, nonheparinized, male, Sprague-Dawley rats subjected to fixed pressure hemorrhage. Blood samples were obtained for determinations of circulating beta-endorphin and substance P. Analgesia was measured using the tail-flick response to a noxious stimulus before and during hemorrhage. The contribution of sensory neurons to eliciting the neuroendocrine, opioid, and inflammatory responses to hemorrhage was investigated in capsaicin-treated animals.


RESULTS
Hemorrhagic shock produced marked naltrexone-sensitive analgesia without significant modulation of substance P. Peripheral sensory denervation did not alter the hemodynamic, neuroendocrine, or inflammatory responses to shock.


CONCLUSIONS
Endogenous opioid activation during shock produces analgesia. Sensory neuron activation appears to have limited effect on shock-induced hemodynamic and proinflammatory responses. Furthermore, these results suggest that the activation of neuroendocrine and opioid pathways during shock is not likely to be a response to noxious stimuli.
Molina
Patricia E
PE
Department of Physiology, Louisiana State University Health Sciences Center, New Orleans 70112, USA. pmolin@lsuhsc.edu
D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000818:Animals; D002211:Capsaicin / Q000627:therapeutic use; D004195:Disease Models, Animal; D005440:Fluid Therapy; D006439:Hemodynamics / Q000187:drug effects; D008297:Male; D018847:Opioid Peptides / Q000627:therapeutic use*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012151:Resuscitation; D012679:Sense Organs / Q000187:drug effects; D012771:Shock, Hemorrhagic / Q000628:therapy*; D013997:Time Factors
D000701:Analgesics, Opioid; D018847:Opioid Peptides; D002211:Capsaicin