Vasoactive intestinal peptide-stimulated glycoconjugate secretion from conjunctival goblet cells

We have developed an in vitro and in vivo method to determine if VIP-stimulates conjunctival goblet cell secretion in the rat as nerves which contain vasoactive intestinal peptide (VIP) and are most likely parasympathetic are localized around these cells. For the in vitro method, pieces of rat conjunctiva were incubated for 1 hr with no additions or increasing concentrations of VIP (10(-10)-10(-6)M). Goblet cell secretion was measured by determining the amount of Helix pomatia agglutinin (HPA)-detectable glycoconjugates secreted into the medium. HPA-detectable glycoconjugates were assayed using an enzyme-linked lectin assay. For the in vivo method, drops of buffer containing no additions or varying concentrations of VIP (10(-10)-10(-6) M) were placed on the ocular surface of anesthetized rats for 60 min. The rats were killed, the ocular surface chemically fixed, and a button of conjunctiva removed. Mucin-containing goblet cells were stained by Alcian blue-periodic acid Schiff's reagent and the number of cells per 0.16 mm2 was quantified. A decrease in the number of mucin-containing goblet cells indicated an increase in mucous secretion. By immunofluorescent histochemistry, we found that the lectin HPA was localized predominantly in the secretory granules of rat conjunctival goblet cells with little binding present in the remainder of the conjunctiva. Nerves containing VIP surrounded goblet cells labelled with HPA. In pieces of conjuctiva, in vitro VIP (10(-8)-10(-6) M) stimulated HPA-detectable glycoconjugate secretion in a concentration dependent manner. When applied topically to the ocular surface, in vivo VIP AT 10(-8) M stimulated mucous secretion from conjunctival goblet cells. We conclude that VIP is present in nerves around conjunctival goblet cells and stimulates glycoconjugate secretion from these cells.