Thymic and body weight during first syngeneic and allogeneic pregnancy in the rat, and the effects of strain difference.

Two hundred female rats, 91-101 days of age, were used in this investigation which provided data on thymic weight, body weight and where appropriate the number of progeny. The observations began in oestrus phase virgin females from the two highly inbred strains AO (RT1u/AgB2) and DA (RT1a/AgB4), continued at five day intervals throughout syngeneic and allogeneic pregnancy in both strains and were completed in the immediate post-partum period. This experimental protocol permitted sequential observations throughout gestation and allowed syngeneic:allogeneic and interstrain comparisons to be made. The syngeneic:allogeneic comparisons demonstrated significant differences in the body weight response and the number of progeny while the AO:DA comparisons demonstrated significant differences in the thymic weight and body weight responses.