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1 Department of Medicine, Division of Endocrinology and Metabolism, and 2 Department of Medicine, Division of Nephrology and Hypertension, Georgetown University, Washington, DC 20007
Recent results from our
laboratories indicate that renal escape from AVP-induced antidiuresis
is accompanied by marked downregulation of kidney aquaporin-2 (AQP2)
and AVP V2 receptors. The present studies evaluated the effect of
nitric oxide (NO) and PG synthesis blockade on escape from
antidiuresis. dDAVP-infused rats were water loaded (WL) for 5 days. L-NAME, an NO synthesis inhibitor, or
diclofenac, a cyclooxygenase inhibitor, was infused subcutaneously beginning 1 day before WL. As early as 2 days after WL, urine volume
increased and urine osmolality decreased, indicating the onset of
escape. Endogenous NO synthesis, measured as urinary NO2 + NO3 excretion, was significantly
increased in the WL group compared with the non-WL controls during all
5 days of WL. L-NAME (20 mg · kg
1 · day
1)
markedly decreased urine volume on days 4 and 5 of WL, indicating inhibition of the escape phenomenon. Kidney AQP2
protein was significantly increased by this dose of
L-NAME as well. A lower dose of L-NAME (10 mg · kg
1 · day
1) or
diclofenac (2.5 mg · kg
1 · day
1) did not
significantly affect the escape phenomenon by itself, but the
combination of L-NAME and diclofenac showed a marked
inhibitory effect on the escape phenomenon, which was also accompanied
by a significant increase in kidney AQP2 expression. These results therefore suggest that renal NO and PG both play important roles in
escape from AVP-induced antidiuresis by acting synergistically to
downregulate kidney AQP2 expression.
aquaporin-2
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