ANGIOTENSIN-II ACTIVATES PRESSOR AND DEPRESSOR SITES OF THE PONTOMEDULLA THAT REACT TO GLUTAMATE

1. In cats anaesthetized with a mixture of alpha-chloralose (40 mg/kg) and urethane (400 mg/kg) and in rats anaesthetized with a mixture of alpha-chloralose (60 mg/kg) and urethane (800 mg/kg), changes in syste mic arterial pressure (SAP), heart rate (HR) and sympathetic activitie s of vertebral (VNA) and renal (RNA) nerves were determined following the microinjection of angiotensin II (AngII; 0.16 mmol/L; 58 nL) into the presser and depressor sites of the pontomedulla previously reacted to a microinjection of monosodium L-glutamate (Glu; 0.1 mol/L; 50 nL) . Presser sites included gigantocellular tegmental field (FTG) and dor sal medulla (DM) and rostral ventrolateral medulla (VLM). The depresso r site was the caudal VLM (CVLM), The effects of losartan (1 mmol/L; 5 0 nL), a specific AT(1) receptor non-peptide antagonist for AngII, on responses induced by AngII in the VLM, DM and CVLM were also determine d. 2. In 30% of presser sites in the FTG, 55% in the VLM and 67% in th e DM and in 76% of depressor sites in the CVLM previously exposed to G lu, microinjection of AngII to the same site produced presser or depre ssor responses similar to that of Glu, but smaller in magnitude, parti cularly in the presser VLM, Changes in both VNA and RNA induced by Ang II were also smaller than those induced by Glu, particularly RNA from DM activation. 3. In the dorsal motor nucleus of the vagus, AngII, as Glu, produced marked bradycardia, but again this was smaller in magnit ude than the bradycardia produced by Glu. 4. In rats, in the DM near o r around the nucleus of the solitary tract where Glu increased SAP, mi croinjection of AngII (0.8 mmol/L; 60 nL) produced a depressor respons e, while the microinjection of 1.6 mmol/L (60 nL) AngII produced a pre sser response. 5. Losartan blocked the increases in SAP induced by Ang II in the VLM and DM, Decreases in SAP induced by AngII in the CVLM, h owever, were only slightly decreased by losartan. 6. Our data suggest that a significant portion of presser and depressor sites of the ponto medulla contain neurons responsive to both AngII and Glu. In neurons i n the VLM and DM, AngII produced presser responses that were primarily mediated through ATI receptors, while the depressor actions of AngII in the CVLM were not mediated by AT(1) receptors.