We examined the effect of a new Ca(2+)channel blocker,
lomerizine (KB-2796), and compared it with that of
nilvadipine, on the optic nerve head circulation in conscious rabbits using a
laser speckle method.
Lomerizine (0.03, 0.1 and 0.3 mg kg(-1), i.v.) and
nilvadipine (0.003, 0.01 and 0.03 mg kg(-1), i.v.) each significantly increased the normalized blur values (an index of tissue blood velocity) in the optic nerve head in a dose-dependent manner. Neither
lomerizine nor
nilvadipine caused a significant change in intraocular pressure.
Lomerizine produced no significant change in mean arterial blood pressure, although at 0.3 mg kg(-1), i. v. heart rate was significantly increased 5 min after its administration. In contrast,
nilvadipine significantly decreased mean arterial blood pressure at 5 to 15 min after its administration and increased heart rate at 5-30 min after its administration (both effects being dose-dependent). Our results indicate that while
lomerizine, like
nilvadipine, increased tissue blood velocity in the optic nerve head, it did not affect mean arterial blood pressure at the doses that affected optic nerve head circulation, unlike
nilvadipine. The plasma concentration of
lomerizine (free base) obtained from rabbits at 15 min after administration at a dose of 0. 03 mg kg(-1)i.v., when time there was a significant increase in tissue blood velocity in the optic nerve head, was very similar to plasma concentration with healthy subjects receiving
lomerizine at 10 mg (5 mgx2) day(-1), p.o., a dose that achieved a significant reduction in the frequency and mean duration of
headache attacks but did not affect the blood pressure or heart rate. These results suggest that
lomerizine may be clinically effective in favorably affecting the optic nerve circulation without producing systemic effects such as the
hypotension seen during treatment with other Ca(2+)channel blockers.