delapril and Pain

It has been reported that elevation of blood pressure produces a reduction in pain sensitivity. This study was designed to clarify the correlation in spontaneously hypertensive rats (SHR) between fall in blood pressure and pain sensitivity. In seven-weeks-old male SHR, the angiotensin converting inhibitor delapril (10 mg/kg/day) or calcium antagonist nifedipine (3 mg/kg/day) was administered orally every day for 8 weeks. Systolic blood pressure (SBP) pretreatment was significantly higher in the SHR than in normotensive Wistar-Kyoto (WKY) rats and pain sensitivity measured with the hot plate method was significantly lower in the SHR than in the WKY rats. Administration of both drugs produced a significant suppression of elevation of SBP, and produced a significant elevation of pain sensitivity. Furthermore, at 8 weeks after drug administration, urinary norepinephrine (UNE) significantly decreased and plasma beta-endorphin (beta-end) significantly increased. A significant correlation was noted between pain sensitivity and SBP and also between pain sensitivity and UNE. Of these, pain sensitivity was the more closely correlated to degree of change in UNE than to degree of change in SBP. It appears that elevation of pain sensitivity is due to suppression of the sympathetic nervous system by antihypertensive drugs, but not to elevation of beta-end levels. These data suggest that a fall in blood pressure through administration of delapril or nifedipine reverses decrease in pain sensitivity in SHR and that decrease in sympathetic tone plays an important role in the restoration of levels of sensitivity to pain.

Topics: Animals; Blood Pressure; Hypertension; Indans; Male; Nifedipine; Pain; Pain Measurement; Rats; Rats, Inbred SHR; Sensory Thresholds; Sympathetic Nervous System