The effect of pregnancy and lactation on the development of experimental heart lesions.

The authors studed the effect of pregnancy and lactation on the resistance of myocardium against damage. Lesions of the heart were induced by isoprenaline in vivo. The extent of lesions was evaluated macroscopically and quantitatively according to the increased accumulation of 203HCl2 in the damaged heart tissue. In vitro, the damage of the isolated right ventricle was induced by anoxia and the resistance of heart tissue was evaluated according to the recovery of contractility. During the first week after delivery, the extent of isoprenaline-induced heart lesions was increased in nursing mothers as compared with virgin females of the same age. The mortality did not change significantly. Restitution of contractility of the right ventricle in vitro and anoxia was lower than in virgin females. In nursing mothers 35 days after delivery, the mortality and the extent of heart lesions induced by isoprenaline was significantly reduced as compared with virgin females. Furthermore, the resistance to anoxia of their isolated right ventricle was higher than that of virgin females. The reduced effect of isoprenaline lasted for several months after devlivery. The mortality and the extent of isoprenaline-induced heart lesions were not reduced significantly 35 days after delivery in non-lactating mothers, which were deprived of their young.