Effect of Xalatan(R) and Cosopt(R) on the vascular tone of quiescent isolated pig ciliary arteries.

BACKGROUND

To investigate whether dilutions of the commercially available Xalatan(R) or Cosopt(R) induce vasoconstrictions in isolated quiescent porcine ciliary arteries.

MATERIAL AND METHODS

Contractions measured with a myograph system (isometric force measurement) were expressed in percent of 100 mM potassium chloride(KCl)-induced contraction (mean +/- standard error). In preliminary experiments, vessels were contracted with 100 mM KCl after previous exposures to different dilutions of Xalatan(R) (1/250 to 1/50) or Cosopt(R) (1/500 to 1/5). In a further series of experiments, vessels were exposed in a cumulative manner to different dilutions of Xalatan(R) or Cosopt(R) (1/50 000 to 1/166).

RESULTS

Contractions induced by 100 mM KCl were not significantly affected by previous exposure to Xalatan(R) or Cosopt(R) at dilutions higher than 1/166 and 1/50, respectively. However, at the lower dilutions tested, 100 mM KCl-induced contractions were significantly (p < 0.001) and markedly inhibited (1/50 Xalatan(R): 22.1 +/- 2.8 %; 1/5 Cosopt(R): 24.8 +/- 4.6 %). In quiescent vessels, diluted (1/50 000 to 1/166) preparations of Xalatan(R) induced, in a dilution-dependent manner, statistically significant (p < 0.05) but, however very small (3.2 +/- 1.0 %) contractions in comparison to Cosopt(R) (- 0.6 +/- 0.2 %).

CONCLUSIONS

Although on the basis of these in vitro experiments no clinical interpretation should be made, at very high dilutions that did not affect KCl-induced contractions, Xalatan(R), but not Cosopt(R), had a very small vasoconstrictive effect in isolated quiescent porcine ciliary arteries. At low dilutions, responses to KCl were inhibited, possibly in relation to an unclear effect of the excipients of Xalatan(R) and Cosopt(R).