TIME-COURSE OF CHANGES IN NICARDIPINE EFFECTS ON MICROCIRCULATION IN RETINA AND OPTIC-NERVE HEAD IN LIVING RABBIT EYES

The effects of intravenous administration of a calcium antagonist, nic ardipine, on microcirculation in the retina and optic nerve head (ONH) of rabbit eyes were investigated using a laser speckle microcirculati on analyzer. The rabbit fundus was illuminated by an argon (blue) lase r spot to measure the retina or by a diode laser spot to measure the O NH, and the image speckle was detected by an image sensor. The differe nce between the average of the speckle intensity (I-mean) and the spec kle intensity for successive scannings was calculated, and the ratio o f I-mean to this difference was defined as normalized blur (NB); a qua ntitative index of blood velocity in tissue. The average NE over the f ield measured (0.62 x 0.62 mm in the retina and 0.42 x 0.42 mm in the ONH) was calculated to give NE(av), which was found to show a signific ant correlation with the retinal blood now rate determined using a mic rosphere technique. In Dutch rabbits for measurement in the retina and in albino rabbits for measurement in the ONH (nicardipine group), 0.4 mL/kg of 0.01% nicardipine hydrochloride dissolved in physiological s aline was injected intravenously into anesthetized animals. To serve a s control, other groups of Dutch or albino rabbits were injected with 0.4 mL/kg of physiological saline. Mean femoral arterial blood pressur e (FABP(m)) in the nicardipine group dropped to the minimum at 1 minut e post-injection and this level remained significantly lower than that in the control group up to 15 minutes post-injection. The pulse rate, pH, Pco(2), and Po-2 of arterial blood, body temperature and the intr aocular pressure did not show any significant changes during the exper iment. The NE(av) obtained from the retina in the nicardipine group sh owed a significant transient decrease, probably due to the initial dro p in the FABP(m), followed by a significant increase after the FABP(m) returned to the baseline. The time-course of NE(av) obtained from the ONH in the nicardipine group showed little change. These results sugg est that nicardipine may have considerable potential in the treatment of ocular diseases associated with insufficient retinal blood now. The nicardipine effects observed here deserve to be studied further in hu man eyes.