Spontaneous hypertension: a humoral component.

A hypertensive factor (HF) has been partially purified from the erythrocytes of spontaneously hypertensive rats. Injection of the factor produces a sustained elevation of the blood pressure of normotensive rats. The blood pressure response following intravenous injection of the factor is characterized by a prolonged period of onset with maximal elevation obtained several days following the beginning of treatment. Subsequently, the elevation of blood pressure is well maintained and may be observed days or weeks following the cessation of treatment. In addition to its pressor effects, the preparation stimulates an increase in the concentration of "lanthanum-resistant" calcium in aortae excised from normotensive or hypertensive rats. In contrast, the efflux of calcium from aortae in the presence of the factor is enhanced suggesting that the factor involved may induce a change in the lability and exchangeability of calcium stores in aortic tissue. Secondarily, the efflux data indicate that the increase in "lanthanum-resistant" calcium noted in aortae exposed to the erythrocyte extract is due to an increase in calcium uptake by the tissue as opposed to a decrease in the extrusion of the ion.