[Effects of continuous pure tone stimulation on blood pressure, plasma norepinephrine and urinary norepinephrine concentration in stroke-prone spontaneously hypertensive rats].

: The present study was undertaken to elucidate the effect of pure tone stimulation on sympathetic nerve activity in stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP were exposed to a pure tone stimulation of 4 KHz at 60 dB SPL tone burst which was interrupted at a frequency of one second and continued for one hour a day for either one 10 day course period or two 10 day course periods. Over a period of 10 days, Group A received one hour-long stimulation daily. Group B received the same type of stimulation for two separate 10 day course periods and Group C did not receive any tone stimulation. Group A and Group C did not show any significant changes in blood pressure, heart rate or body weight. However, an increase in urinary norepinephrine (NE) (p less than 0.02) which returned to pretreatment levels after tone stimulation was observed in Group A. Group B showed a significant increase in blood pressure as compared with Group A (p less than 0.02): the systolic blood pressure of Group B was 233.2 +/- 36.1 mmHg; the systolic blood pressure of the sex-age matched Group A was 193.0 +/- 25.7 mmHg. Group B displayed an increase in plasma NE concentration as compared with Group A (p less than 0.05). These findings demonstrated that the summation of two 10 day course pure tone stimulations produced a larger increase in blood pressure and plasma NE concentration than one 10 day course stimulation. These increase in blood pressure and plasma NE concentration occurred via an increase in sympathetic nerve activity.(ABSTRACT TRUNCATED AT 250 WORDS)