Pressor responsiveness to vasopressin in the rat with DOC-salt hypertension

To further characterize the role of vasopressin in DOC-salt hypertension, four groups of unilaterally nephrectomized rats were studied: control rats given no further treatment, rats treated with DOC and given 1% saline to drink, or rats treated with only DIC or 1% saline had similar pressor responses to exogenous vasopressin and angiotensin II. Within the DOC-salt group, two populations of rats were identified: one with normal pressor responsiveness to vasopressin, and one with markedly enhanced pressor responsiveness to vasopressin. Incidence of enhanced responsiveness increased with duration of treatment. Urinary excretion of vasopressin was elevated in the 1% saline and DOC-salt groups after 1 week of treatment, and in the DOC group after 4 weeks. However, the plasma vasopressin concentration was elevated only in the rats treated with both DOC and saline. It is suggested that vasopressin is essential for the expansion of blood volume in the early stages of DOC-salt hypertension, and functions as a direct pressor agent only in the later stages.