EFFECTS OF PITUITARY ADENYLATE-CYCLASE-ACTIVATING POLYPEPTIDE ON THE DIRECT-CURRENT ELECTRORETINOGRAM OF THE RABBIT EYE

Pituitary adenylate-cyclase-activating polypeptide (PACAP) is a recent ly discovered neuropeptide present in two different forms, PACAP-27 an d PACAP-38. Both peptides stimulate the catalytic enzyme adenylate cyc lase in pituitary cells. This enzyme is important also regarding the f unction of the retinal pigment epithelium (RPE). The purpose of the st udy was to investigate possible influences of PACAP on the rabbit reti na and the RPE as reflected in the direct-current (d.c.) electroretino gram (ERG) and the standing potential of the eye (SP). After unilatera l sector vitrectomy, a continuous intraocular perfusion with a referen ce solution alternated with a test solution was established. The corne al d.c. ERG and the SP were recorded from both eyes with the contralat eral eye as a control. Both PACAP-27 (0.1 and 1 mu M) and PACAP-38 (1 mu M) increased the c-wave amplitude significantly (p = 0.028, p 0.013 and p = 0.024, respectively, n = 4) while neither PACAP-27 (0.1 and 1 mu M, p > 0.05, n = 4) nor PACAP-38 (1 mu M p > 0.05, n = 4) produced any significant effects on the a- and b-wave amplitudes of the d.c. E RG. The SP response to the two substances differed with a significant elevation of the SP level with PACAP-27 (1 mu M p = 0.017, n = 4), whi le PACAP-38 induced a small, nonsignificant SP elevation (1 mu M, p > 0.05, n = 4). Retinal penetrations during PACAP-27 (10 mu M) perfusion showed an increase in transepithelial potential (TEP) c-wave (p = 0.0 03) as well as in slow PIII (p = 0.011, n = 3) amplitude level. The re sults support the presence of PACAP receptors both on the RPE and in t he neural retina.