Effects of sex hormones on experimental autoimmune myasthenia gravis.

To examine whether exacerbation of myasthenia gravis (MG) can be induced by changes in sex hormone levels we immunized 20 female Lewis rats with torpedo antigen to induce experimental autoimmune MG (EAMG). Ten of the animals underwent surgical ovariectomy prior to the induction of EAMG and 10 served as controls. Anti-acetylcholine receptor antibody (AChR-ab) titres and the degree of decrement on repetitive stimulation electromyography (REMG) at 3 Hz were obtained at base line and compared between rats with and without ovariectomy and a second control group of naïve rats. Three rats in each group were then injected with excess oestrogen and progesterone for one week, and three of the remaining rats in each group were given sham injections, and the degree of decrement on REMG and AchR-ab titres were re-evaluated. Immune reactivity of peripheral lymphocytes and splenic lymphocytes from all groups and controls was also determined. A comparable number of animals with and without ovariectomy developed clinical and electromyographic EAMG. The extent of decrement on REMG and AChR-ab titres did not change following hormonal replacement. Lymphocyte reactivity was similar for rats with and without ovariectomy. In conclusion, sex hormones do not appear to have an influence on the susceptibility to and the severity of MG.