S. Kusano et al., DEPRESSOR EFFECT OF INTRAVENTRICULAR ADMINISTRATION OF CALCIUM ON SPONTANEOUSLY HYPERTENSIVE RATS, Brain research, 618(1), 1993, pp. 63-70
The role of central Ca2+ in the regulation of blood pressure (BP) was
investigated in conscious spontaneously hypertensive (SHR) and Wistar-
Kyoto rats (WKY). Ten mul of a high Ca2+ solution (Ca2+: 32.6 mM) admi
nistered intracerebroventricularly (i.c.v.) decreased the mean arteria
l pressure (MAP) for more than 20 min in SHR (n = 7, P < 0.005), while
no change of MAP was observed in the WKY (n = 6). This depressor resp
onse to Ca2+ i.c.v. was dose-dependent at Ca2+ concentrations between
16.3 and 65.2 mM. We also investigated the effect of high Ca2+ i.c.v.
in SHR after pretreatment with Ca2+ channel blockers, diltiazem (60 mu
g/10 mul) or nisoldipine (4, 8, 16 and 32 mug/10 mul), administered i.
c.v., the autonomic ganglion blocker, hexamethonium (50 mg/kg), admini
stered i.v. and alpha-methyl-p-tyrosine (100 and 400 mug/10 mul) deliv
ered i.c.v. Pretreatment with i.c.v. diltiazem (n = 8) or nisoldipine
(n = 5 for 8 mug, n = 6 for 4, 16, 32 mug) abolished and/or blunted th
e decrease of MAP due to high Ca2+. Hexamethonium administered i.v. (n
= 6) also canceled the depressor action of i.c.v. Ca2+. Pretreatment
with 100 mug of i.c.v. alpha-methyl-p-tyrosine could not prevent the d
epressor action of i.c.v. Ca2+; however, 400 mug of alpha-methyl-p-tyr
osine administered i.c.v. abolished the effect of i.c.v. Ca2+. Further
more Ca2+ channel blockers administered i.c.v. in themselves increased
MAP in SHR (P < 0.05). These results suggest that central Ca2+ is inv
olved in the central regulation of BP in SHR. This effect may be media
ted through changes in sympathetic activity.