S. Jarkman et al., EFFECTS OF PITUITARY ADENYLATE-CYCLASE-ACTIVATING POLYPEPTIDE ON THE DIRECT-CURRENT ELECTRORETINOGRAM OF THE RABBIT EYE, Ophthalmic research, 30(4), 1998, pp. 199-206
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.