title: Endogenous opiate peptides may limit norepinephrine release during hemorrhage.
abstract: The involvement of the sympathetic nervous system in the cardiovascular response to hemorrhage and subsequent opiate receptor blockade was studied in conscious rabbits. Plasma catecholamines were measured by high-pressure liquid chromatography to indirectly assess sympathetic activity. Arterial blood samples were drawn at four times during the experiment: 1) before hemorrhage; 2) after a 15% blood loss; 3) after mean arterial blood pressure decreased to less than 40 mm Hg; and 4) 2 min after an i.v. injection of naloxone (3 mg/kg) or saline. Rapid removal of 15% of the total blood volume (approximately equal to 8 ml/kg) increased heart rate and plasma norepinephrine. Plasma epinephrine and blood pressure remained at control levels. Further hemorrhage (approximately equal to 16 ml/kg) produced a sudden decrease in blood pressure and a large increase in plasma epinephrine. Plasma norepinephrine was not significantly different from the previous sample. Subsequent injection of naloxone significantly increased plasma norepinephrine and blood pressure compared to the saline-treated group. Plasma epinephrine was similar in the two groups. These studies suggest that naloxone may exert its pressor effect during hemorrhagic hypotension in the conscious rabbit by blocking a naturally occurring, opiate peptide-mediated inhibition of norepinephrine release. The results are consistent with a peptidergic limit on sympathetic activity being responsible for the decrease in blood pressure seen during acute hemorrhage.
mesh_terms: D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004723:Endorphins / Q000502:physiology*; D004837:Epinephrine / Q000097:blood; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D006470:Hemorrhage / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009638:Norepinephrine / Q000097:blood*; D011817:Rabbits; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D004723:Endorphins; D009270:Naloxone; D009638:Norepinephrine; D004837:Epinephrine