[Morphometric and histochemical studies of the masticatory muscles in growing white rats following ligation of the right common carotid artery].

White Wistar rats served for examinations to the masticatory muscles after ligature of the a. carotis communis dextra on the 42nd d after birth. Gravimetric determinations of the dry substance of the muscles were performed in a total of 229 animals. In 65 animals casts of the vessels in synthetic resin (Kallocryl M) were made and the inside diameters of the blood vessels of the corresponding vascular regions measured. Histological, histochemical and muscle-fibre-morphometric observations of the masticatory muscles were made in 10 animals. Due to processes of adaption the a. carotis communis sinistra with an enlarged cross-section supplied the head with an increased blood volume. However, the anatomical and physiologic conditions of the collateral blood vessels conveying blood to the right side of the head prevented the entry of same share of blood into that side. Obviously there is a causal connection between this circumstance and the reduction in the dry substance of the right-side masticatory muscles. Histologic investigations revealed an increase in the capillaries by 10 percent in the animals operated on. The reduction in the diameters of the muscle fibres on the right side of the head was accompanied by a change in the normal combination of fibre types. 2 out of 5 animals which had been operated on showed a fairly homogeneous distribution of the fibre types in the masticatory muscles. Fibres of type 2 tended to be more vulnerable than fibres of type 1. Pathogenetically, the reduction in the dry substance of muscles and the reduction in the diameters of the muscle fibres are caused by nutritive disturbances in connection with restricted circulation. The neuronal-trophic sphere and the mechanism which is responsible for the differentiation of the muscle-fibre types seem to be affected as well. The myokinetic synapses are not affected.