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Vol. 282, Issue 1, 101-107, 1997
Department of Pharmacology, New York Medical College, Valhalla, New
York
Depression of GFR and antinatriuresis in response to high chloride has
been linked to a cyclooxygenase (COX)-dependent mechanism involving
thromboxane A2 (TxA2) and prostaglandin
endoperoxide (PGH2), because inhibition of COX prevented
the fall in GFR and antinatriuresis produced by hyperchloremia.
However, hyperchloremia did not increase, but unexpectedly decreased,
renal prostaglandin and TxA2 efflux (). To resolve questions regarding the role of eicosanoids in
mediating the renal functional effects of high chloride (117 mM), by
stimulating either TxA2 synthesis or
TxA2/PGH2 receptors, we compared the ability of
indomethacin to block high-chloride effects in the rat isolated kidney
with that of BMS 180291 and SQ 29548, antagonists of the
TxA2/PGH2 receptor. These antagonists differ in
terms of their selectivity and their capacity to inhibit isoforms of
the TxA2/PGH2 receptor. Indomethacin and SQ
29548 had identical actions, preventing the decrease of GFR and
antinatriuresis evoked by hyperchloremia, e.g., sodium
excretion rate in the SQ 29548 and indomethacin groups increased to
7.2 ± 1.3 and 7.1 ± 1.2 µEq/min, respectively, compared with 2.6 ± 0.7 µEq/min in the control group. In contrast,
neither BMS 180291 nor the TxA2 synthase inhibitors, OKY
046 and CGS 13080, modified the negative effects of high chloride on
GFR or sodium excretion. These results argue against either
TxA2 or PGH2 acting as mediator of the effects
of high chloride on renal function and suggest a product of COX
activity such as a 20-HETE analog of prostaglandin endoperoxide.
Evidence to support this proposal was obtained: 1) Hyperchloremia
increased 20-HETE release from the rat kidney by 2-fold when compared
with low-chloride conditions of renal perfusion. 2) The renal
vasoconstrictor action of 20-HETE was shown to be dependent on COX
activity and to be antagonized by blockade of the
TxA2/PGH2 receptor.
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