The obestatin/ghrelin system as a novel regulatory mechanism of iris muscle contraction.
OBJECTIVE
To evaluate obestatin and ghrelin effects on iris muscle contraction.


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).


CONCLUSIONS
This study suggests that obestatin potentiates the cholinergic contraction of the iris sphincter and relaxes the iris dilator muscles.
Rocha-Sousa
A
A
Laboratory of Physiology, Faculty of Medicine, University of Porto, Portugal. arsousa@med.up.pt
Falcão-Reis
F
F
Leite-Moreira
A F
AF
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D054439:Ghrelin / Q000494:pharmacology*; D007498:Iris / Q000187:drug effects*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D011817:Rabbits
D054439:Ghrelin; D002217:Carbachol; D004837:Epinephrine