Substance P in human essential hypertension.

Substance P (SP) plays an important role in central nervous and peripheral blood pressure regulation. Its effects include modulating influence on the adrenergic system and inhibition of stress-induced plasma noradrenaline increase in animal studies. In patients with essential hypertension (n = 45, WHO stages 1 and 2) the SP-like immunoreactivity (SPLIR) was found significantly (p less than 0.01) lower (1.36 +/- 0.23 pg/100 microliters) than in 24 normotensive subjects (4.54 +/- 0.72 pg/100 microliters). Furthermore, the influence of a mental stress test on SPLIR was investigated in patients with essential hypertension (n = 11, WHO stage 1) and compared with nine normotensive subjects. Whereas in normotensive subjects plasma SP increased under a standardized mental arithmetic test (4.03 +/- 0.48 to 4.74 +/- 0.56 pg/100 microliters), in hypertensive patients a decrease of SP from lower baseline levels (2.85 +/- 0.54 to 2.57 +/- 0.54 pg/100 microliters) was demonstrated. The significantly different changes of plasma SP in normotensive and hypertensive subjects under mental stress conditions had the opposite direction in comparison with the adrenergic reaction [higher and prolonged increase of plasma noradrenaline (NA) in the hypertensive group]. Under antihypertensive drug treatment with prazosin (4.5 mg/day, n = 10) or with captopril (450 mg/day, n = 10) an increase of plasma SP was registered. The results support the participation of SP in the pathogenesis of human hypertension and in therapeutic mechanisms. Lower plasma levels and decreased responsiveness of SP possibly represent the enhanced stress sensitivity in primary hypertension.