Depressor effect of intraventricular administration of calcium on spontaneously hypertensive rats

Abstract The role of central Ca 2+ in the regulation of blood pressure (BP) was investigated in conscious spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). Ten μl of a high Ca 2+ solution (Ca 2+ : 32.6 mM) administered intracerebroventricularly (i.c.v.) decreased the mean arterial pressure (MAP) for more than 20 min in SHR ( n = 7, P n = 6). This depressor response to Ca 2+ i.c.v. was dose-dependent at Ca 2+ concentrations between 16.3 and 65.2 mM. We also investigated the effect of high Ca 2+ i.c.v. in SHR after pretreatment with Ca 2+ channel blockers, diltiazem (60 μg/10 μl) or nisoldipine (4, 8, 16 and 32 μg/10 μl), administered i.c.v., the autonomic ganglion, hexamethonium (50 mg/kg), administered i.v. and α-methyl- p -tyrosine (100 and 400 μg/10 μl) delivered i.c.v. Pretreatment with i.c.v. diltiazem (=8) or nisolipine ( n =5 for 8 μg, n =6 for 4,16,32 μg) abolished and/or blunted the decrease of MAP due to high Ca 2+ . Hexamethonium administered i.v. ( n =6) also canceled the depressor action of i.c.v. Ca 2+ . Pretreatment with 100 μg of i.c.v. α-methyl- p -tyrosine could not prevent the depressor action of i.c.v. Ca 2+ ; however, 400 μg of α-ethyl- p -tyrosine administered i.c.v. abolished the effect of i.c.v. Ca 2+ . Furthermore Ca 2+ channel blockers administered i.c.v. in themselves increased MAP in SHR ( P 2+ is involved in the central regulation of BP in SHR. This effect may be mediated through changes in sympathetic activity.