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, nicardipine, on microcirculation in the retina and optic nerve head (ONH) of rabbit eyes were investigated using a laser speckle microcirculation analyzer. The rabbit fundus was illuminated by an argon (blue) laser spot to measure the retina or by a diode laser spot to measure the ONH, and the image speckle was detected by an image sensor. The difference between the average of the speckle intensity (Imean) and the speckle intensity for successive scannings was calculated, and the ratio of Imean to this difference was defined as normalized blur (NB); a quantitative index of blood velocity in tissue. The average NB over the field measured (0.62 x 0.62 mm in the retina and 0.42 x 0.42 mm in the ONH) was calculated to give NBav, which was found to show a significant correlation with the retinal blood flow rate determined using a microsphere 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 saline was injected intravenously into anesthetized animals. To serve as control, other groups of Dutch or albino rabbits were injected with 0.4 mL/kg of physiological saline. Mean femoral arterial blood pressure (FABPm) in the nicardipine group dropped to the minimum at 1 minute post-injection and this level remained significantly lower than that in the control group up to 15 minutes post-injection. The pulse rate, pH, Pco2 and Po2 of arterial blood, body temperature and the intraocular pressure did not show any significant changes during the experiment. The NBav obtained from the retina in the nicardipine group showed a significant transient decrease, probably due to the initial drop in the FABPm, followed by a significant increase after the FABPm returned to the baseline. The time-course of NBav obtained from the ONH in the nicardipine group showed little change. These results suggest that nicardipine may have considerable potential in the treatment of ocular diseases associated with insufficient retinal blood flow. The nicardipine effects observed here deserve to be studied further in human eyes.