The Effects of various experimental models of hypertension on visual evoked potentials

ABSTRACT In literature, even though there are many informations about the complications of hypertension, informations of concerning its influence on visual evoked potentials (VEPs) are rare. In the previous studies it was pointed out that hypertension induces changes on VEPs. However, it has not yet been clearified which models of hypertension are more effective on VEP changes. In our study aiming to highlight this subject 60 rats has been used to. The rats were divided into 6 groups as; control, sham, DOCA, 2K- 1C, 1K-1C and L-NAME. In DOCA group after a right nephrectomy, the rats were treated twice weekly with deoxycorticosterone acetate (DOCA),which was administered subcutaneously (15 mg/kg) and %1 NaCl added to their drinking water. In 2K-1C group, a silver clip (0.2 mm) was placed on the left renal artery, however in 1K-1C group, the right kidney was removed and a silver clip with a 0.2 mm gap was placed on the left renal artery. N-omega-nitro-L-arginine-methyl ester (L-NAME) was injected intraperitoneally at a dose of 50mg/kg/day (75 days) to the animals of L- NAME group to induce hypertension via a non-selective inhibition of NOS. At the end of experimental period (10 weeks), visual evoked potentials (VEPs) were recorded from animals. Subsequently, brain and retina tissues of the animals were removed for the measurement of biochemical parameters. Blood pressure of the hypertensive animals (DOCA, 2K-1C, 1K-1C, L-NAME) was significantly increased, compared with the control and sham. However, there was no significant difference in blood pressure among the hypertensive groups. Plasma renin levels, increased in 2K-1C and L-NAME groups v.s. control, whereas decreased in DOCA group; but no changes was observed in 1K-1C group. Brain TBARS levels were increased significantly in all hypertensive groups with respect to the control. Compared with the other hypertensive groups, brain TBARS levels of DOCA group were found to be much more increased. Retina TBARS levels were found to be significantly increased in DOCA, 1K-1C and L-NAME groups, but there was no significant change in the 2K-1C group. Brain nitrite level was found to be increased in DOCA, whereas decreased in 2K-1C, 1K-1C and L-NAME groups compared with the control. On the other hand, with respect to the control rats, retina nitrite levels were decreased in 2K-1C, 1K-1C and L-NAME groups, but no significant alteration was observed in DOCA group. Pi, Nı, P2, N2 and P3 components of VEPs were found to be prolonged in the hypertensive groups compared with the control and sham. Pi and P3 latencies of the L-NAME rats were delayed much more with respect to the other hypertensive animals. Results obtained from amplitudes indicates that, P1N1 and NiP2 amplitudes of DOC A group were increased. Whereas, in L-NAME group the amplitud of P1N1 increased and the amplitud of P2N2 decreased.