Generation second messengers by prostanoids in the iris-sphincter and ciliary muscles of cows, cats and humans

We have examined the generation of second messengers after stimulation of feline, bovine, human iris-sphincter and ciliary muscles by selected prostaglandins (PGs). The tissues, labeled or unlabeled with ³H-myo-inositol, were stimulated by a range of concentrations of 16, 16-dimethyl PGE₂, 11-deoxy PGE₁, 17-phenyl trinor PGE₂ and PGF_2α. In both tissues of all three species, 16, 16-dimethyl PGE₂ and 11-deoxy PGE₁ stimulated the formation of cyclic AMP. Butaprost, an EP₂ receptor agonist, which was tested only in feline ciliary muscle, generated cyclic AMP. In the feline iris-sphincter and in bovine and feline ciliary muscles, 17-phenyl trinor PGE₂, an EP₁ receptor agonist, significantly increased inositol phosphate turnover. The FP receptor agonist, PGF_2α stimulated inositol phosphate turnover in the bovine, feline, and human iris-sphincter muscles and in human ciliary muscles. Feline and bovine ciliary muscles did not respond to PGF_2α.These results suggest that EP₁ receptors are present in feline iris-sphincter muscle and in bovine and feline ciliary muscles. The EP₂ receptors exist in both tissue. These results also suggest the presence FP receptors in bovine, feline, and human iris-sphincter and in human ciliary muscles. Bovine and feline ciliary muscles do not appear to express FP receptors.