1. Noradrenaline, adrenaline and α-methylnoradrenaline administration into the nucleus tractus solitarii (NTS) of anaesthetized rats decreased blood pressure and heart rate in a dose-dependent fashion.
2. Bilateral injections were effective in lower doses than unilateral administration. α-Methylnoradrenaline given bilaterally produced hypotension in a dose of 0·08 nmol whereas after unilateral injection a dose of 0·32 nmol was needed to obtain the same degree of hypotension.
3. Electrical stimulation of the NTS caused hypotension and bradycardia. Conversely, bilateral electrolytic lesions or deafferentation of the NTS led to acute hypertension. Chronically such lesions caused neurogenic hypertension.
4. In spontaneously hypertensive rats increased concentrations of noradrenaline, adrenaline and dopamine were measured in the part of the NTS located just caudal to the obex (A2 region).