Role of endogenous central opioid mechanisms in maintenance of body sodium balance.
The role of endogenous central opioids in the regulation of renal function was studied in Sprague-Dawley rats. In metabolism studies, changes in sodium balance were examined during normal dietary sodium intake (days 1-7; Na+ of 174 meq/kg) and sodium restriction (days 8-14; Na+ of 4.0 meq/kg). The influence of endogenous central opioids was investigated by repeating the protocol in the same rats during intracerebroventricular infusion of the opioid antagonist naltrexone methylbromide (NMBR). Intracerebroventricular NMBR did not alter sodium balance in rats fed normal sodium chow. In contrast, on low-sodium days 8 and 9, rats exhibited a more negative sodium balance during intracerebroventricular NMBR (day 8; -1,191 +/- 37 mu eq) compared with respective predrug control levels (day 8; -641 +/- 39 mu eq). Subcutaneous NMBR did not alter renal adaptation to sodium restriction. Thus central opioids are not involved in the maintenance of sodium balance during normal sodium intake. However, when dietary sodium is restricted, central opioid pathways are activated as a mechanism to maximally retain sodium.
Kapusta
D R
DR
Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans 70112.
Obih
J C
JC
D000222:Adaptation, Physiological / Q000187:drug effects; D000818:Animals; D007276:Injections, Intraventricular; D007668:Kidney / Q000187:drug effects / Q000502:physiology; D008297:Male; D009271:Naltrexone / Q000008:administration & dosage / Q000031:analogs & derivatives; D009292:Narcotic Antagonists / Q000008:administration & dosage; D009318:Natriuresis / Q000187:drug effects / Q000502:physiology*; D018847:Opioid Peptides / Q000037:antagonists & inhibitors / Q000502:physiology*; D000644:Quaternary Ammonium Compounds; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D012982:Sodium, Dietary / Q000008:administration & dosage; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology
D009292:Narcotic Antagonists; D018847:Opioid Peptides; D000644:Quaternary Ammonium Compounds; D012982:Sodium, Dietary; C032257:methylnaltrexone; D009271:Naltrexone; D012964:Sodium