Effects of sex hormones on experimental autoimmune myasthenia gravis

To examine whether exacerbation of myasthenia gravis (MG) call be induced b y changes in sex hormone levels we immunized 20 female Lewis rats with torp edo antigen to induce experimental autoimmune MG (EAMG). Ten of the animals underwent surgical ovariectomy prior to the induction of EAMG and 10 serve d as controls. Anti-acetylcholine receptor antibody (AChR-ab) titres and th e 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 naive rats. Three rats in each gr oup 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. I mmune reactivity of peripheral lymphocytes and splenic lymphocytes from all groups and controls was also determined. A comparable number of animals wi th and without ovariectomy developed clinical and electromyographic EAMG. T he extent of decrement on REMG and AChR-ab titres did not change following hormonal replacement, Lymphocyte reactivity was similar for rats with and w ithout ovariectomy. In conclusion, sex hormones do not appear to have an in fluence on the susceptibility to and the severity of MG.