Effects of chronic oral treatment with imidapril and TCV-116 on the responsiveness to angiotensin II in ventrolateral medulla of SHR

Objective. To examine whether chronic oral treatment with an angiotensin-converting enzyme inhibitor imidapril and an angiotensin II type 1 receptor antagonist TCV-116 would alter the response to angiotensin II in the rostral ventrolateral medulla. Methods. Twelve-week-old spontaneously hypertensive rats (SHR) were treated with imidapril (20 mg/kg per day, n = 7), TCV-I16 (5 mg/kg per day, n = 8) or vehicle (n = 8) for 4 weeks. Wistar-Kyoto rats (WKY) (n = 8) served as normotensive controls. At 16 weeks of age, angiotensin II (100 pmol) was microinjected into the rostral ventrolateral medulla of anaesthetized rats. Results. Blood pressure decreased significantly in the rats treated with either imidapril or TCV-116. Presser responses to angiotensin II microinjected into the rostral ventrolateral medulla were comparable in the untreated SHR, the imidapril-treated SHR and WKY (12 ± 2, 15 ± 4 and 10 ± 1 mmHg, respectively), but were abolished in SHR treated with TCV-116 (0 ± 2 mmHg, P < 0.01). Angiotensin-converting enzyme activity in the brain stem was significantly lower in SHR treated with imidapril (0.70 ± 0.06 nmol/mg per h), but significantly higher in SHR treated with TCV-116 (1.62 ± 0.04 nmol/mg per h) than in the untreated SHR (1.37 ± 0.05 nmol/mg per h). Conclusions. Chronic oral treatment with imidapril and TCV-116 may have divergent influences on the renin-angiotensin system within the brain stem. TCV-116, but not imidapril, abolishes the presser effect of angiotensin II in the rostral ventrolateral medulla.