The roles of prostaglandins and calcium accumulation in muscular dystrophy

Effect of ambrein on smooth muscle responses to various agonists

The pharmacological effects of ambrein (isolated from ambergris) on the contractile responses induced by some agonists in smooth muscle preparations were investigated. Ambrein in the concentration range of 10, 50 and 250 microg/ml decreased the spontaneous contraction of the isolated rabbit jejunum, rat uterus and guinea-pig vas deferens. Ambrein-induced antagonism to acetylcholine (Ach) in the guinea-pig ileum was abolished when the concentration of calcium chloride in the Tyrode's solution was increased to 5 mM/l. Furthermore, ambrein did not antagonise nicotine-induced contractions in the isolated rabbit jejunum or serotonin-induced contractions in the isolated guinea-pig ileum and vas deferens or the rat uterus. However, ambrein in the concentration range of 10, 50 and 250 microg/ml antagonised prostaglandins (PGs) E2, D2, F2alpha, and oxytocin-induced contractions in the rat uterus in vitro. Ambrein also antagonised (+/-) noradrenaline and (-) adrenaline-induced contractions in the isolated guinea-pig vas deferens. It is concluded that ambrein-induced non-selective dose-dependent antagonism to the effects of some agonists (Ach, adrenaline, noradrenaline, PGs and oxytocin) in some smooth muscles may be due to the ability of this compound to interfere with the mobilisation of extracellular Ca2+ required for muscular contractions induced by these agonists.

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

The pathogenesis of Duchenne muscular dystrophy: significance of experimental observations

The pathogenesis of Duchenne muscular dystrophy (DMD) remains elusive, but as this is an inherited condition the primary manifestation of the disease is assumed to be in the regulatory control or biosynthesis of a protein. Current hypotheses attribute the pathological state of skeletal muscle in DMD to a defect in the nerve supply, or in the vasculature, or in the muscle itself. However, various tissues other than skeletal muscle are also affected; thus the current view of DMD requires reevaluation. The following possibilities should be considered: That the primary lesion is expressed in one of the major communication systems (nervous, vascular, or endocrine). That the primary lesion is expressed in a specific tissue: a) if in skeletal muscle, alterations in non-muscular tissues must be due to the release of muscle constituents into extracellular fluid; b) if in a non-muscular tissue, this might produce too much (or too little or none) of a constituent normally secreted into the extracellular fluid, or produce a "toxic" agent. That the primary lesion is expressed in a wide variety of tissues: the effect on a particular tissue will depend entirely upon the degree of requirement of the altered protein for function.

Contractile and chemosensitive properties of muscle treated with calcium ionophore A23187. Comparison with dystrophic muscle

Rat diaphragms were treated with calcium ionophore, A23187, for 60 min at 37 degrees C, and twitch, tetanus and their derivatives were studied on the basis of the active state concept. Results were than compared with those of human dystrophic muscle. Like dystrophic muscle, maximum tetanic force and maximum velocity of tetanus development were markedly reduced. Changes in twitch parameters, which tend to appear in an early stage of muscular dystrophy, were not noted after the treatment with this ionophore, except alterations relating to prolongation of the active state. Twitch/tetanus ratio was thus increased, while it was decreased in dystrophic muscle. Isoproterenol-induced change of twitch was normally seen in the A23187-treated muscle, while dystrophic muscle responded to catecholamine in a manner different from control. Therefore, the muscle treated with calcium ionophore is not wholly similar to dystrophic muscle.

Microanalysis and X-ray fluorescence spectrometry of platelets in diseases with elevated muscle calcium

Electron microscopic X-ray microanalysis and X-ray fluorescence spectrometry were done on platelets from patients with Duchenne muscular dystrophy and idiopathic scoliosis (both these conditions are known to be associated with increased intramyofibre calcium). A significant increase in calcium and phosphorus concentrations was found in the dense granules and whole cells of both conditions. The findings suggest that idiopathic scoliosis like Duchenne muscular dystrophy is a multisystem disease with detectable changes in platelets.

Biochemistry of muscle membranes in Duchenne muscular dystrophy

In Duchenne muscular dystrophy, as in other genetic diseases, there must be a biochemical abnormality. This fundamental genetic fault has not been identified, but several indirect lines of evidence suggest that the surface membranes of skeletal muscle are affected. The biochemical evidence implies abnormal egress of soluble enzymes and other proteins from muscle, abnormal permeability, and altered properties of membrane-bound enzymes. As a result of the presumed genetic abnormality, functional properties are altered, and impaired regulation of intracellular calcium content could be responsible for the hallmarks of the disease--progressive weakness and degeneration of muscle. The evidence is by no means conclusive, however, and some of it is contradictory. Technical advances must be made before isolated membranes can be characterized biochemically. Other theories are also being evaluated.