[Trigeminal-related peptides and mammalian intraocular muscles]

Effects of substance P (SP) and vasoactive intestinal peptide (VIP) on bovine intraocular muscle tissues were studied, using isolated strips. While SP generally contracted the iris sphincter, exogenous application of SP did relax the iris sphincter muscle when its tone was highly developed. SP had no significant influence on the bovine dilator, and VIP lowered the tone of the iris muscles. The ciliary muscle tone was not altered by these peptides, but the electrically evoked response of the ciliary muscle was enhanced in the presence of VIP. These results suggest possible different roles of these trigeminal nerve-related peptides (SP, SK, VIP) on intraocular muscle tissues.