AJP - Regulatory, Integrative and Comparative Physiology, Vol 268, Issue 3 723-R730, Copyright © 1995 by American Physiological Society
Role of endogenous central opioid mechanisms in maintenance of body sodium balance
D. R. Kapusta and J. C. Obih
Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans 70112.
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.
