Two strains of rats with opposite genetic propensity for hypertension were tested for: (a) the sensitivity to injections of angiotensin and renin, and (b) the influence of their plasma on the reaction velocity of renin and its substrate in vitro.
Intact hypertension-prone (S) rats on low salt had higher sensitivity to angiotensin and a lower sensitivity to renin than hypertension-resistant (R) rats. High NaCl diet did not change the response of the R rats to these injections, but increased the response to renin and angiotensin in intact S rats. Bilateral nephrectomy caused increased response to renin and a decreased response to angiotensin in the S rats, so that both strains were equivalent after bilateral nephrectomy. In vitro, plasma from intact S rats inhibited the activity of hog renin. Plasma from R rats showed no inhibition. The inhibitor disappeared after bilateral nephrectomy. It was speculated that renin inhibitor may be involved in the development of hypertension by increasing sensitivity to angiotensin and other hypertensinogenic stimuli.