(1) Recording of electrical activity of the sympathetic (left splanchnic) nerve of the Spontaneously Hypertensive Rat revealed that the peripheral sympathetic tone is remarkably augmented in SHR in comparison with that of the control.
(2) Pithing revealed the important role of the central nervous system in the maintenance of high blood pressure of the Spontaneously Hypertensive Rat.
(3) Transection experiment (cerveau isole and encephale isole) offered the evidence that the pontobulbar portion of brain stem is responsible for the mechanism involved in the tonic maintenance of high blood pressure of the Spontaneously Hypertensive Rat.
It is concluded that the increased sympathetic vasoconstrictor discharge which originates in the lower brain stem constitutes one important factor in the pathogenesis of, or at least, in the maintenance of hypertension in the Spontaneously Hypertensive Rat.