In the spontaneously hypertensive rats obtained by Okamoto and Aoki (the animals develop hypertension within 15 weeks of age in 100percent incidence and increase blood pressure with age), the removal of various endocrine organs and kidneys and the administration of hexamethonium and pentbarbital were performed. Blood pressure and body weight were measured in these animals and the results are as follows.
(1) The removal of anyone of the pituitary, adrenals or thyroid in prehypertensive stage prevents the development of hypertension and the blood pressure persists normotensive.
(2) The removal of anyone of the pituitary, adrenals or thyroid in persistently hypertensive stage lowers the high blood pressure to keep it normotensive.
(3) The administration of methylthiouracil inhibits the development and maintenance of hypertension.
(4) From these results it is presumed that the presence of the pituitary, adrenals and thyroid is necessary for the development and maintenance of hypertension in the spontaneously hypertensive rats. Consequently these three endocrine organs are indispensable organs for hypertension.
(5) Gonadectomy has no effect on the development and maintenance of hypertension.
(6) Unilateral and bilateral nephrectomy accelerate hypertension. It seems that the kidney has no pressor action, but rather works to in-hibit enhancement of hypertension.
(7) The administration of hexamethonium and pentbarbital lowers blood pressure. This fact shows hypertension is related to autonomic nervous control.
(8) In hypertension of less than 35-60 weeks' duration, there is no marked difference in the effect of the removal of endocrine organs and the administration of drugs.