The Effect Of PACAP On Choroidal Blood Flow Regulation

Abstract

 

Purpose:

 

To investigate the effect of PACAP (PACAP-27) and its antagonist PACAP 6-38 on choroidal blood flow regulation in anesthetized rabbits.

 

Methods:

 

In anesthetized New Zealand white rabbits (n= 9) mean arterial pressure (MAP) and intraocular pressure (IOP) were measured with pressure transducers by direct cannulation of the central ear artery, and the vitreous, respectively. Laser Doppler flowmetry was used to measure choroidal blood flow (ChorBF) and choroidal vascular resistance (ChorR) was calculated. PACAP-27 infusion was administrated intravenously (20ng/kg/min) with an infusionrate of 2mL/h. PACAP 6-38 was given as a bolus in a concentration of 40ng/kg body weight. Ocular perfusion pressure was manipulated mechanically with hydrolic occluders around the large vessels and all variables were recorded continuously.

 

Results:

 

Table 1 shows the baseline changes in response to PACAP-27 and PACAP 6-38 on ChorBF, IOP, MAP, ChorR and PP (perfusion pressure). The increase of ChorBF and decrease of ChorR after PACAP-27 infusion was significant as it was on the increase of IOP. The administration of its antagonist PACAP 6-38 was able to block the effects of IOP, ChorBF and ChorR. In addition to the basline changes choroidal pressure flow relationships were shifted upwards by PACAP-27 indicating vasdilation over a wide range of perfusion pressures. The shift was reversed by PACAP 6-38. The effects on ChorBF as well as on ChorR were statistically significant.

 

Conclusions:

 

PACAP is a high potent vasodilator in the choroidal vasculature. The vasodilatory effect was blocked by the receptor antagonist PACAP 6-38.  

 

Keywords: choroid