Vasoactive intestinal peptide and cholinergic neurotransmission in the ciliary muscle

The effects of vasoactive intestinal peptide (VIP) on mechanical activity and electrical stimulation of the bovine ciliary muscle in vitro were compared. The generated contractions were enhanced by application of eserine and were abolished completely in the presence of atropine. VIP (10(-8)-10(-6) M) enhanced the response to electrical stimulation, while the contractile amplitude of the ciliary muscle to exogenous carbachol was not altered significantly by application of 10(-7)-10(-6) M VIP. The exogenous VIP had no direct effect on the muscle. As these data indicate that VIP exerts its stimulant effect, prejunctionally, ie, on the nerve terminals, this peptide probably contributes to the control of accommodation as a modulator of cholinergic neurotransmission between short ciliary nerves and the ciliary muscle.