Activation of angiotensin II type 1 receptors in the median preoptic nucleus induces a diuretic and natriuretic response in rats

Objective

To investigate the effect of activation of angiotensin II (AngII) type 1 (AT1) receptors in the median preoptic nucleus (MnPO) of rats on renal sodium excretion.

Methods

After anesthesia, the rats were injected into the MnPO via an implanted cannula. Urine samples were collected via a bladder cannula, and the urine sodium concentration was assayed with flame spectrophotometry. The serum level of endogenous digitalis-like factor (EDLF) and Na⁺, K⁺-ATPase activity in the renal cortex tissue were assayed respectively with a radioimmunoassay and with an ammonium molybdophosphate-based kit.

Results

Both the urinary volume and the sodium excretion peaked 60 min after AngII was administered into the MnPO. The responses were accompanied by an increase in serum EDLF and a decrease in Na⁺, K⁺-ATPase activity in the renal cortex. The responses of diuresis and natriuresis, as well as an increase in serum EDLF and a decrease in Na⁺, K⁺-ATPase activity in the renal cortex induced by MnPO adminstration with AngII were inhibited by pior treatment with the AngII receptor blocking agent losartan into the MnPO.

Conclusion

These results suggest that activation of AT1 receptors in the MnPO of rat induces diuretic and natriuretic responses. The responses are associated with an increase release of EDLF and with the inhibition of Na⁺,K⁺-ATPase activity in renal cortex tissue.