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In spontaneously hypertensive rats (SHR) and normotensive control rats (NCR) anesthetized with pentobarbital sodium, first the right and then the left splanchnic nerves were cut. After arterial pressure had stabilized at a new lower level following each cut, the peripheral cut end of the nerve was stimulated electrically with a train of square pulses of 10V-5 msec, to determine the frequency needed to restore the level of arterial pressure before the severance (equivalent stimulation frequency, ESF). ESF is assumed to represent the average discharge rate of sympathetic vasoconstrictor fibers in the splanchnic nerve. ESF's were significantly higher in SHR than in NCR, being 3.4±2.5/sec vs. 0.67±1.63 for the right splanchnic nerve and 3.7±1.1/sec vs. 0.86±0.52 for the left splanchnic nerve (each mean with SD, n=9). Thus SHR is characterized by an elevated sympathetic tone. After severance of the right or bilateral splanchnic nerves the difference in arterial pressure between SHR and NCR was no longer significant.
Juro Iriuchijima (Mon,) studied this question.