1. After a lesion had been made in the anteroventral third ventricle (AV3V), Dahl S rats received daily injections of either pitressin (500 m-units/kg) or vehicle during 10 weeks of high (8%) NaCl diet. Rats with sham lesions served as controls. The blood pressure in sham-lesion rats receiving vehicle was 189 mmHg after 10 weeks of high NaCl diet. Lesion rats given vehicle showed a 60% smaller increase in blood pressure than sham-lesion rats (P < 0.001), the blood pressure averaging 161 mmHg at 10 weeks.
2. Lesion rats given pitressin also showed a smaller increase in blood pressure than sham-lesion rats (P < 0.05), but the final blood pressure averaged 176 mmHg and was significantly higher than that of lesion rats given vehicle (P < 0.025). Pitressin injections corrected the hypernatraemia in lesion rats.
3. In another experiment, the effect of the AV3V lesion on the renal papillary plasma flow (RPPF) in Dahl S rats was studied. Dahl S rats have a lower RPPF than Dahl salt-resistant (R) rats even on a low NaCl intake. The AV3V lesion increased the RPPF by 14% in S rats (P < 0.025).
4. These findings suggest that NaCl-induced hypertension in Dahl S rats requires the integrity of the AV3V region for its full expression, and the ability of the AV3V lesion to attenuate the NaCl-induced hypertension in Dahl S rats is partly related to the attenuation of vasopressin release. Moreover, the AV3V lesion partly corrected one of the characteristic features of Dahl S rats: the reduction in RPPF compared with Dahl R rats on a low NaCl intake.