Morphology of the porcine myometrium during parturition

The ultrastructure of the porcine myometrium collected at well-defined stages during parturition was investigated by transmission electron microscopy. The morphology of the parturient myometrium resembled in general that in pregnant and non-pregnant pigs. The diameter of the smooth muscle cells was, however, about twice that of non-pregnant myometrium. Thick myofilaments were numerous. The number of caveolae seemed to be higher in parturient compared with non-pregnant and pregnant cells. Gap junctions occurred richly and were large, while the intrinsic innervation was very scanty. To conclude, the endocrinological changes in the pig taking place just prior to parturition, are translated into morphological changes by stimulating the formation of uterine gap junctions. This provides low-resistance pathways between the muscle cells and activates the myometrium for the delivery process.