Degenerative changes in masseter muscle following injection of lidocaine: a histochemical study

Local Anesthetics Inhibit Ca-ATPase in Masticatory Muscles

Local anesthetics have myotoxic effects and inhibit Ca-ATPase activity and Ca transport in skeletal muscles. Such effects have not been fully elucidated in masticatory muscles. We tested the hypothesis that local anesthetics increase myoplasmic calcium in masticatory muscles by inhibiting Ca-ATPase at a concentration similar to that of dental cartridges. The effects of lidocaine and bupivacaine on Ca-ATPase from rabbit masseter and medial pterygoid muscles were tested with radioisotopic and colorimetric methods. Bupivacaine had an action similar to that of lidocaine on Ca-ATPase activity, but less effect on calcium transport. The pre-exposure of the membranes to the anesthetics enhanced the Ca-ATPase activity in the absence of calcium ionophore, supporting their permeabilizing effect. The results demonstrate that amide-type anesthetics do not inhibit calcium binding, but do reduce calcium transport and enzyme phosphorylation by ATP, and suggest that the myoplasmic calcium increase induced by lidocaine and bupivacaine might promote masticatory muscle contraction and eventual rigidity.

Skeletal muscle as a paradigm for regenerative biology and medicine

Tissue development and regeneration share common features, since modules of regulatory pathways and transcription factors that are crucial for prenatal development are redeployed for tissue reconstruction after trauma. Regenerative medicine has therefore gained important insights through the study of developmental and regenerative biology. Moreover, diverse experimental models have been used to investigate the regeneration process in different tissues and organs. Paradoxically, little is known regarding the relative contribution of stem cells with respect to the supporting tissue during tissue regeneration. Particular attention will be given to mouse models using distinct injury paradigms to investigate the regenerative biology of skeletal muscle. An understanding of the response of stem and parenchymal cells is crucial for the development of clinical strategies to combat the normal decline in tissue performance during aging or its reconstitution after trauma and during disease. This review addresses these issues, focusing on muscle regeneration and how different factors, including genes, cells and the environment, impinge on this process.

Muscle regeneration in amphibians and mammals: passing the torch

Skeletal muscle in both amphibians and mammals possesses a high regenerative capacity. In amphibians, a muscle can regenerate in two distinct ways: as a tissue component of an entire regenerating limb (epimorphic regeneration) or as an isolated entity (tissue regeneration). In the absence of epimorphic regenerative ability, mammals can regenerate muscles only by the tissue mode. This review focuses principally on the regeneration of entire muscles and covers what is known and what remains to be elucidated about fundamental mechanisms underlying muscle regeneration at this level.

Recovery of jaw muscle function following injection of a myotoxic agent (lidocaine-epinephrine)

Intramuscular injection of 2% lidocaine hydrochloride with epinephrine (1:100,000) bilaterally into the masseter muscles of growing rats resulted in a 30% to 40% decrease in maximal stimulated bite force at 3 days following injection. By 6 days postinjection, bite force had begun to increase, but significant differences from control bite force levels were still present 15 days postinjection. By 25 days postinjection, recovery to control values was complete. These data are consistent with previously documented fiber destruction and subsequent regeneration following exposure to this and other local anesthetic agents. It is suggested that local myotoxic effects produced by the administration of such drugs may result in a transient functional deficit in the injected muscle(s) that may persist for up to 2 weeks.

Mechanism of epinephrine enhancement of lidocaine-induced skeletal muscle necrosis

Epinephrine significantly increases lidocaine-induced skeletal muscle necrosis, even in low concentrations that elicit no damage by themselves. Inasmuch as isoproterenol had no influence on lidocaine myotoxicity, a direct effect of epinephrine on muscle fibers is unlikely. Two vasoconstrictors with dissimilar mechanisms of action, phenylephrine and felypressin, duplicated the potentiating effect of epinephrine on fiber destruction in direct relation to their ability to retard lidocaine absorption from the tissue. It is concluded that the augmentation of muscle necrosis caused by epinephrine is largely due to its ability to increase exposure of skeletal muscle to the local anesthetic.