Contraction/Contracture

Contraction is a general term that refers to the mechanically activated state of myofibrils which is usually caused by action potentials). Contracture means muscle shortening or tension development, which is not triggered by action potentials), e.g. K+ contracture, and caffeine or halothane contracture. The word is also used for deformity or distortion of fingers, hand or limb, such as Dupuytren s or Volkmann s contracture. 

Hypothyroid myopathy occurs in about 30% of patients with hypothyroidism irrespective of its cause. Muscle pain, cramps, and stiffness may be seen, and are often exacerbated by cold weather. Pseudomyotonic features of delayed muscle contraction and relaxation are common. Myoedema (the mounding phenomenon) is due to the painless, electrically silent contracture produced on direct percussion. Muscle biopsy often shows a predominance of type 1 (slow-twitch) fibers, again analogous to that seen in experimental hypothyroidism (Figure 22). Muscle hypertrophy with weakness and slowness of movement occurs in the Debre-Semelaigne syndrome seen in severely hypothyroid children, and Hoffman s syndrome is a similar condition seen in adults with hypothyroidism, but is also accompanied by painful spasms. 

The caffeine contracture test involves exposing viable muscle fibers to incremental doses of caffeine from 0.5-32 mM, the concentration being increased every four min if no contraction develops. A positive caffeine contracture test is defined as the development of 0.2 g tension at 2 tiM caffeine, or > 7% tension change from baseline with 2 mM caffeine. 

False negative muscle contraction tests are very rare. To date, a negative muscle contraction test rules out MH. A false negative test can be explained by the presence of two types of muscle fibers in a MH susceptible patient the response being dependent on the proportion of the two types of muscle fibers. The K-type designation is used to describe a patient who has a positive joint halothane-caffeine contracture, but a negative separate halothane or caffeine contracture. Whether K-type individuals are MH-susceptible or not is a controversial issue. 

Dupuytren s contracture is a contraction of the palmar fascia that usually affects the fourth and fifth digits.27 It is not specific to cirrhosis and can be seen in repetitive use injuries. 

Blaustein We published a paper a couple of years ago on aortic smooth muscle stimulated with serotonin. Using moderate doses for short periods, which cause modest contraction, we saw no effect on Ca2+ in individual mitochondria. However, a big dose for a longer period causes the muscle to go into contracture, and there is a significant rise in Ca2+ in mitochondria. 

Saeki Y, Shibata T, Shiozawa K. 1981. Excitation-contraction coupling in mammalian cardiac muscle during Ba -induced contracture. Am J Physiol 240 H216-H221. 

Ugur, M., and Turan, B. 2001. Adenosine triphosphate alters the selenite-induced contracture and negative inotropic effect on cardiac muscle contractions. Biol. Trace Elem. Res. 79 235-245. 

Reversible cholinesterase inhibitors find their greatest clinical use in the treatment of open-angle glaucoma. Relief is achieved by enhancing the contraction of the ciliary muscle and the iris sphincter. This contracture pulls the iris off the lens and facilitates fluid movement through the canal of Schlemm. The result is decreased pressure with reduced distortion of the lens and increased movement of aqueous humor out of the anterior chamber of the eye. 

Muscle relaxants are drugs that are administered to relax muscles. They are given to relieve the discomfort of muscle spasm or involuntary muscle contracture and also in cases of surgery to relax muscles and provide easier access for the surgeon. Some nonprescription drugs are available to combat painful contraction of the uterus during a woman s menstrual period. 

Studies on skeletal muscle also support an intracellular site of action of the MDIs. Thus, pr-MDI (10 4m) significantly blocked caffeine-induced contractures of the rat diaphragm both in presence and in absence of extracellular calcium (33). Such caffeine-induced contractures are believed to be mediated by intracellular calcium mobilized from the sarcoplasmic reticulum or other intracellular calcium pool (34). Furthermore, bu-MDI (10 M) depresses activation heat in the frog sartorius muscle upon stimulation (35), indicating a reduction in the quantity of calcium released from the sarcoplasmic reticulum, since activation heat represents the energy liberated in association with calcium mobilization and sequestration in contracting muscle (36,... 

Heparin and desulphated heparin inhibit the contractions of frog-heart, nullify the systolic contracture caused by high calcium concentrations and counteract the effects of potassium chloride and acetylcholine . Heparin also results in rapid recovery after cooling and prolongs survival of the isolated guinea-pig auricle. 

The stiffness of rigor mortis is evidently due to the disappearance of ATP (see Bate-Smith and Bendall, 1947, 1949), and whenever the rapid phase of ATP breakdown (which is the cause of the disappearance of ATP) takes place in conditions (pH > 6) under which actomyosin is capable of contracting at all, rigor is accompanied by contracture. 

Generally, there is no contract between the pharmaceutical company and the patient who is prescribed the product by a doctor. In the UK, it has been held that where a product is prescribed under a National Health Service scheme, it is not prescribed as a result of a contract between pharmaceutical company and patient because legislation exists that requires a pharmacist to supply the product on the production of a valid prescription. For non-prescription, over-the-counter (OTC) products, there is a contract between the retailer and the consumer who purchases the pharmaceutical product, but there is still usually no direct link in contractural terms to the maker of the product. However, it may be that the contract between the manufacturer and the retailer contains an indemnity provision. The indemnity may provide that, in the event of a successful claim for breach of contract being made against the retailer by the customer, the manufacturer will pay the retailer the amount the retailer is ordered to pay in compensation to the customer. 

When bullfrog skeletal muscle hbers previously pretreated with 98.5mg/kg Au+ (as gold sodium thiomalate) were subjected to 2.0 mg Au /kg as NaAuCL, the hbers lost their ability to contract upon electrical stim-ulahon, as was the case for 2.0 mg Au+ /kg alone. However in the presence of thiomalic acid, Au" " did not completely block tetanus tension, even at 10 mg Au+ /kg. Thiomalic acid also inhibited Au" -induced membrane depolarization. In bullfrogs, skeletal muscle hbers spontaneously produced phasic and toihc contractures upon addihon of 5-20 xM Ag+ or more than 50 xM Au+ 9.0 mg... 

The compound sanguinarine had a positive inotropic effect followed by contracture in rat ventricular and atrial strips. Sanguinarine also dose-dependently reduced the rate of spontaneous contractions of isolated right atria (Hu et al. 2005). Positive inotropic effects were also observed in isolated guinea pig atria treated with the compound sanguinarine (Seifen et al. 1979). A dose-dependent response in ventricular refractoriness was observed in anesthetized pigs after vascular infusion of up to 4 mg/kg of the compound sanguinarine (Whittle et al. 1980). 

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