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VIP Stimulation of cAMP Production in Corneal Endothelial Cells in Tissue and Organ Cultures

Purpose. To demonstrate that vasoactive intestinal peptide (VIP), an immunosuppressive factor found in the aqueous humor, is a modulator of the corneal endothelium (CE) stimulating its intracellular cAMP production. Methods. Rabbit CE cells in cell culture and CE cells in cornea cup organ cultures established from bovine and human donor eyes were treated with VIP at varying concentrations (0, 10−11–10−6mol/L) for a constant time (4 minutes) or varying times (1, 3.25, 10, 15 minutes) at a constant concentration (1 × 10−6mol/L). Intracellular cAMP was extracted and its concentrations were determined by radioimmunoassay. Agonists that are known to modulate the intracellular cAMP concentrations of target cells were allowed to react with cultured rabbit CE cells at 1 × 10−6mol/L for 4 minutes. Results. Vasoactive intestinal peptide stimulated the intracellular cAMP production in CE cells in a dose- and time-dependent manner. At concentrations lower than 10−9mol/L, VIP showed little effect. Treatment with 10−8, 10−7, and 10−6mol/L VIP for 4 minutes, however, increased the intracellular cAMP by 5.7-, 12.3-, and 9.5-fold, respectively, compared with the basal level in rabbit CE cell cultures, and by 19.5-, 38.7-, and 23.3-fold, respectively, in CE cells in bovine cornea cups. The effect of VIP was confirmed in two pairs of donor human corneas in which an average of 2.7-fold stimulation by 5 × 10−7mol/L was observed. Treatment of rabbit CE cells with 1 × 10−6mol//L VIP for 1 to 15 minutes elevated the intracellular cAMP level by six- to 69-fold. Among the agonists tested, &agr;-melanocyte-stimulating hormone and glucagon were not effective, whereas l-isoproterenol and prostaglandin E1were capable of stimulating the intracellular cAMP levels in rabbit CE cells. Conclusions. The current study demonstrated that VIP stimulated cAMP production in CE cells, similar to that shown previously in trabecular meshwork and nonpigmented ciliary epithelial cells. Tissues bathed in the aqueous humor are thus responsive to VIP modulation.