Effect of cyclosporin A eyedrops on tear secretion in rabbit

We investigated the tear secretion-stimulating effect of cyclosporin A (CyA) eyedrops in rabbits using Schirmer's method. The following findings were obtained: (1) CyA induced tear secretion in a concentration-dependent manner. CvA in 0.1% concentration showed the strongest effect in accelerating lacrimation, and this effect persisted from 3 to 8 hours after instillation. (2) CyA-induced lacrimation was inhibited by atropine sulfate, a muscarinic blocker. (3) CyA-induced lacrimation was also inhibited in a concentration-dependent manner by (D-Pro2, D-Trp7,9)-Substance P, which is a tachykinin-receptor-selective antagonist. (4) CyA-induced lacrimation was also inhibited by capsaicin, which is a stimulator that releases and depletes neurotransmitters from sensory nerve endings. We conclude from these pharmacological studies that, in the rabbit, CyA-induced tear secretion is mediated by both cholinergic and tachykinergic nerves.