κ‐Opioid‐induced changes in renal water and electrolyte management and endocrine secretion

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Abstract
Subcutaneous injection of the κ‐opioid agonist U50,488 into conscious, saline‐loaded rats was associated with a diuresis, antinatriuresis and antikaliuresis which lasted for up to 3 h. Plasma renin activity and corticosterone levels were elevated but plasma vasopressin (AVP) and aldosterone levels were unaltered in similarly treated rats. U50,488 administration to adrenal demedulated rats was not associated with a diuresis but produced an antinatriuresis, though sodium excretion rates were higher in demedullated than in sham‐operated animals. Plasma AVP and corticosterone levels were not affected by demedulation or subsequent U50,488 treatment. Sham‐operated, U50,488‐treated rats showed the expected increase in plasma corticosterone levels. U50,488 administration resulted in an antidiuresis and an antinatriuresis in AVP‐deficient Brattleboro DI rats. When coupled with fasting stress U50,488 administration resulted in similar but attenuated renal responses compared with those observed in unfasted rats. Basal plasma corticosterone levels were elevated in fasted animals and were further increased by U50,488. Both water and electrolyte handling by the kidney are altered by U50,488. The diuretic effects of U50,488 were reversed by adrenal demedullation and in the absence of endogenous AVP, but the antinatriuretic actions were not altered, suggesting that the effects upon renal water and electrolyte excretion may be mediated by separate mechanisms.