Effects of semotiadil, a novel calcium antagonist, on the retina and opticnerve head circulation

The effects of semotiadil, a novel benzothiazine calcium antagonist, on the retinal and optic nerve head (ONH) tissue circulation were evaluated using the noninvasive laser speckle method. In urethane-anesthetized Dutch or al bino rabbits, before and up to 90 min following intravenous injection of 40 0 mu g/kg semotiadil fumarate (semotiadil group) or vehicle (control group) , normalized blur value, a quantitative index of tissue blood velocity, in the retina (NBretina) or ONH (NBonh), was serially obtained with monitoring intraocular pressure (IOP) and systemic parameters: arterial pressure, pul se rate, arterial blood gas, and body temperature. There were no significan t differences in IOP and the systemic parameters except arterial pressure b etween semotiadil and control groups during the experiments. Arterial press ure showed an acute and transient drop during the first 5 min after semotia dil administration. The time courses of the normalized blur value were sign ificantly different between semotiadil and control groups in the retina (P = 0.0001, repeated measures two-way ANOVA), but not in the ONH (P = 0.6724) . Changes in NBretina from the baseline in the semotiadil group was signifi cantly greater than those in the control group 50 min or later after the ad ministration (P < 0.0500, Mann-Whitney test). NBonh showed no significant d ifferences between the two groups except during the first few min when arte rial pressure acutely decreased in the semotiadil group. In conclusion, int ravenously injected semotiadil increased the tissue blood velocity in the r etina, but not in the ONH. This vascular selectivity in the ocular neural t issues differs from those of other calcium antagonists, such as nicardipine .