Growth of mesometrial arteries in guinea pigs during pregnancy.

Massive growth was observed in mesometrial arteries supplying the placenta of the guinea pig in the first 60 days of pregnancy. The wet weight of the vessel wall increased 50 times, with an almost constant protein concentration. The DNA content rose 30 times. The length of the arteries increased 3.5 times and there was a 13-fold increase in the cross-sectional area of the wall. The changes in cross-sectional area were most pronounced in the peripheral part of the vessel. The observed changes followed an exponential time course. Histological sections showed proliferation, particularly of connective tissue with collagen fibres, while the synthesis of elastic material was suppressed. After parturition, involution with reduction of internal diameter occurred with a half-time of around five days.