Role of antidiuretic hormone in the attenuated furosemide response observed during indomethacin administration.

Recently we demonstrated that increased chloride reabsorption in Henle's loop is a major contributor to the blunted furosemide response observed during prostaglandin synthesis inhibition. Because antidiuretic hormone (ADH) modulates chloride reabsorption in the loop and because prostaglandin synthesis inhibition potentiates ADH-mediated water reabsorption, ADH may be necessary for the attenuated furosemide response observed during prostaglandin synthesis inhibition. If such were the case, then prostaglandin synthesis inhibition should have no effect on furosemide's chloruretic response in the absence of ADH. To test this hypothesis, the effect of indomethacin on furosemide chloruresis was determined in homozygous (ADH-deficient) Brattleboro rats and in homozygous Brattleboro rats receiving ADH (2.4 mU/hr) over a short period of time. Furosemide-induced chloruresis was not different (P was not significant) between indomethacin-treated homozygous Brattleboro rats and homozygous Brattleboro rats receiving the indomethacin vehicle (fractional excretion of chloride: 6.28% +/- 1.08% vs. 6.24% +/- 0.98%). However, in ADH-infused Brattleboro rats, furosemide chloruresis was lower in indomethacin-treated rat groups than in vehicle-treated rat groups (fractional excretion of chloride: 3.09% +/- 0.62% vs. 6.61% +/- 0.88%; P less than 0.02) and lower than in indomethacin-treated ADH-deficient Brattleboro rats as well (P less than 0.05). Mean arterial pressure, inulin clearance, and renal blood flow were not different between any groups. Urinary prostaglandin excretion rates were not different between ADH-deficient Brattleboro rats and ADH-treated Brattleboro rats during furosemide administration and were markedly reduced by indomethacin in both circumstances. Thus, ADH is necessary for the blunted furosemide response observed during prostaglandin synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)