Substance P-like immunoreactivity in plasma and adrenal medulla of rats with spontaneous hypertension and WKY rats under acute stress.

The substance P-like immunoreactivity (SPLIR) of plasma and adrenal medulla from spontaneously hypertensive (SHR) and normotensive WKY rats was measured by a sensitive and highly specific radioimmunoassay for substance P (SP). With increasing age the level of substance P in the adrenal medulla decreased, whereas the SP content of the plasma remained constant in both groups. The SPLIR in plasma of SHR was significantly lower than in normotensive WKY rats. After acute stress the SPLIR, especially of the adrenal medulla of WKY rats, increases, and decreases in SHR. The reason for this different behaviour is discussed and it is assumed that hyperreactions in the sympathetic system may be responsible.