Effects of oestrogen replacement therapy on pattern reversal visual evokedpotentials

As a result of a regression in the ovarian functions, oestrogen level in ci rculation during the menopause drops to 1/50 of its value in the normal rep roductive cycle. Excitatory oestrogen increases the sensitivity of the cent ral nervous system to catecholamines by changing the opening frequency of v oltage-related L-type calcium channels and augmenting the effect of glutama te; in addition it inhibits the formation of gamma-amino butyric acid (GABA ) by the inhibition of glutamate decarboxylase enzyme. It is argued that oe strogen increases transmission in the optic pathways and that oestrogen is responsible for the shorter latency values and higher amplitudes of visual evoked potentials in women. We recorded the monocular pattern reversal visu al evoked potentials (PRVEP) of both eyes of 54 post-menopausal women befor e treatment and of 30 of them after replacement therapy with Tibolon, and o f 24 women receiving placebo treatment. The explicit values of P-100 latenc y of right and left eyes before treatment were 98.8 +/- 3.5 and 99.0 +/- 3. 3 ms, respectively. The explicit values of P-100 latency of right and left eyes after placebo treatment were 98.6 +/- 3.7 and 98.8 +/- 4.0, respective ly. The explicit values of P-100 latency of right and left eyes after repla cement treatment were 94.6 +/- 3.7 and 94.8 +/- 4.0, respectively. We found a statistically significant decrease in the mean PRVEP latencies and a sta tistically significant increase in mean amplitudes after replacement treatm ent (P < 0.001) compared with those before treatment and those after placeb o treatment, We attributed the changes in PRVEP values after replacement tr eatment to the action of Tibolon, which acted as a natural sex steroid and speeded the visual transmission time via the widespread receptors in the ce ntral nervous system. It is concluded that PRVEP is an objective electrophy siological assessment method in evaluating the efficiency of hormone replac ement therapy in post-menopausal women.