The obestatin/ghrelin system as a novel regulatory mechanism of iris muscle contraction

Abstract

Purpose: To evaluate obestatin and ghrelin effects on iris muscle contraction. Materials and Methods: Obestatin (10(-5) M) or ghrelin (10(-5) M) were tested on two consecutive carbachol-or epinephrine-elicited contractions of iris rabbit sphincter or dilator muscles. Ghrelin and obestatin effects on iris muscles basal tension were also tested, and their effects on iris sphincter EFS-elicited contraction were evaluated. Results: Compared with the first, tension of the second carbachol-induced contraction of the iris sphincter decreased 11.5 +/- 5.5% in the vehicle group, increased 19.0 10.2% in presence of obestatin, and remained unchanged by ghrelin. Epinephrine-induced contractions were not affected by obestatin or ghrelin. EFS-elicited contractions were decreased 9.3 +/- 3.2% by ghrelin. Basal tension of the iris sphincter decreased 21.7 +/- 3.7% in presence of ghrelin (10(-5) M), while that of the dilator decreased 14.1 +/- 5.0% in presence of obestatin (10(-5) M). Conclusion: This study suggests that obestatin potentiates the cholinergic contraction of the iris sphincter and relaxes the iris dilator muscles.