[Suppressing Effect of Isoforskolin and Forskolin on Ocular Hypertension in Rabbits]

Objective: To examine the effects of isoforskolin (isoF) and forskolin (FSK) suspensions administered topically on eyes with ocular hypertension (OHT) and observe the local irritation of the drugs.

Methods: The intraocular pressure (IOP) was measured with pneumotonometer in screened spontaneous or water-loading induced OHT rabbits for evaluation of drug effects, and the irritation indices were recorded as well.

Results: In screened OHT rabbits, isoF significantly lowered IOP from 0.5 to at least 4.5 h after the administration (P < 0.05, paired t-test vs. contralateral control eyes), with the maximum decreases of 0.25% and 1% isoF reaching 8.1 mm Hg and 7.0 mm Hg (1 mm Hg = 0.133 kPa) at about 1.5 h later, respectively. In water-loaded OHT rabbits, both 0.06%, 0.1%, 0.25%, 1% isoF and 1% FSK concentration-dependently suppressed the increments of IOP (P < 0.05 with the exception of 0.06% isoF) induced by water-loading, and the peak effects of the optimal concentration of 0.25% isoF and 1% FSK were 7.1 and 6.9 mm Hg (difference of IOP between bilateral eyes) respectively. The results also indicated that 0.25% isoF or FSK suspension had basically no irritation, but 1% induced slight irritating responses during the experiment.

Conclusion: Both isoF and FSK had suppressing effects on OHT in rabbits with the optimal concentration being 0.25% and 1% respectively; at concentration of 0.25%, topically both drugs had basically no irritation, while 1% of the drugs may induce mild irritating responses.