Tonic contractions

The lower esophageal sphincter is a manometrically-defined zone of the distal esophagus with an elevated basal resting pressure. The sphincter is normally in a tonic, contracted state, preventing the reflux of gastric material from the stomach. It relaxes on swallowing to permit the free passage of food into the stomach. 

Sympathetic and parasympathetic nerves innervate the penis. In the flaccid state, OC2-adrenergic receptors mediate tonic contraction of the arterial and corporal smooth muscles. This maintains high penile arterial resistance and a balance exists between blood flow into and out of the corpora. With sexual stimulation, nerve impulses from the brain travel down the spinal cord to the thoracolumbar ganglia.3 A decrease in sympathetic tone and an increase in parasympathetic activity then occurs, causing a net increase in blood flow into the erectile tissue. Erections may also occur as a result of a sacral nerve reflex arc while patients are sleeping (nocturnal erections). 

Gastrointestinal sphincters are formed where the circular layer of smooth muscle is thickened. Sphincters occur at several points along the tract. Their function is to limit the movement of food materials from one region to another. For example, the pyloric sphincter found between the stomach and duodenum of the small intestine plays an important role in limiting the rate of gastric emptying. Sphincters undergo tonic contractions that may be sustained for minutes or hours. 

GTC seizures may be preceded by premonitory symptoms (i.e., an aura). A tonic-clonic seizure that is preceded by an aura is likely a partial seizure that is secondarily generalized. Tonic-clonic seizures begin with a short tonic contraction of muscles followed by a period of rigidity. The patient may lose sphincter control, bite the tongue, or become cyanotic. The episode may be followed by unconsciousness, and frequently the patient goes into a deep sleep. 

Fig. 4.2. Effects of triphenylethylene SERMs on spontaneous and depolarization-induced contractions in visceral smooth muscle. Tamoxifen (a) and ethylbromide tamoxifen (EBTx, b) rapidly and reversibly inhibit spontaneous peristaltic activity in duodenal muscle. Both compounds also inhibit depolarization-induced tonic contraction of uterine muscle (c). The inhibition of L-type voltage-dependent calcium channels underlies the relaxing effects illustrated here. Drugs concentrations were 10 xM in all cases. %RA percent of activity related to maximal activity...

The main function of vascular smooth muscle is to distribute blood flow through selective vasoconstriction and vasomotion. The latter is clearly associated with oscillations in [Ca2+]j, but it was long thought that tonic contraction was initiated by SR Ca2+ release and maintained by a steady state elevation of [Ca2+] dependent on influx. However, confocal microscopy of intact blood vessels has... 

Lee CH, Poburko D, SahotaP, Sandhu J, Ruehlmann DO, van Breemen C 2001 The mechanism of phenylephrine-mediated [Ca2+] oscillations underlying tonic contraction in the rabbit inferior vena cava. J Physiol 534 641-650... 

Wier We don t find an effect of APB on high K+ contraction if phentolamine is present. With respect to your mechanism of tonic contraction, which you indicated was dependent on Ca2+ influx, in the mesenteric small artery that we study, which develops a tonic contraction, this isn t accompanied by tonic elevation of Ca2+, but rather by these asynchronous Ca2+ waves that we have already seen. Nevertheless, when we add up all these Ca2+ indicator signals we get something that looks like a steady elevated level of Ca2+. We would say that in that tissue the dependence on Ca2+ influx is to keep the SR going, to keep generating these waves. Is this relevant to your tissue ... 

Results obtained in this way were helpful, but of limited value. The analyses told us whether or not the bile was supersaturated with cholesterol, but did not tell us whether the abnormality was due to too much cholesterol, too few bile acids, too few phospholipids or to some combined defect. The next step, therefore, was to measure the hour-by-hour bile lipid-secretion rates using marker-corrected perfusion techniques. These assume that, in response to the perfusion stimulus (such as an intra-duodenal amino acid mixture), the gallbladder remains tonically contracted throughout and steady-state conditions ensue. 

Ergot alkaloids contain lysergic acid (formula in A shows an amide). They act on uterine and vascular muscle. Ergo-metrine particularly stimulates the uterus. It readily induces a tonic contraction of the myometrium (tetanus uteri). This jeopardizes placental blood flow and fetal O2 supply. The semisynthetic derivative methylergometrine is therefore used only after delivery for uterine contractions that are too weak. 

Effects of WSAP on Guinea Pig Ileum. In preliminary experiments with a constant infusion of 5 pg/m1 of WSAP in the physiological saline bath the following were observed A) a slow tonic contraction of the smooth muscle segment resulting in a shift of the base line of approximately 30%, B) a latency period of approximately 10 to 15 minutes before there was any significant... 

Comparison of GT-3 and GT-4. Time dependent assays of the ether extracted GT-3 reported by Miller et al. (16) indicated that it had the same time course of action and irreversible effects as described for GT-4. When the ileal preparation was exposed to 10 ng/ml of GT-3 for 15 minutes a 50% inhibition from control response was observed. Upon contact with the preparation, the toxin caused a slow tonic contraction. Washing the segment with clean saline following the 15 minute exposure period caused a gradual relaxation of the preparation to near the base line levels observed in the control. However, when challenged by agonist at any time following the latency period, and irreversible loss of activity was evident. 

Efferth T, Volm M (1992) Expression of protein kinase C in human renal cell cardnoma cells with inherent resistance to doxorubicin. Anticancer Res 12 2209-2211 Eguchi Y, Srinivasan A, Tomaselli KJ, Shimizu S, Tsujimoto Y (1999) ATP-dependent steps in apoptotic signal transduction. Cancer Res 59 2174-2181 Ek TP, Campbell MD, Deth RC, Gowraganahalli J (1989) Reduction of norepinephrine-induced tonic contraction and phosphoinositide turnover in arteries of spontaneously hypertensive rats. A possible role for protein kinase C. Am J Hy-pertens 2 40-45... 

Rigid, violent muscular contraction with limbs fixed Loss of consciousness sudden sharp tonic contractions of mnscles, falling to ground, followed by clonic convulsive movements often postictal depression and incontinence... 

Incubation in 1-20 iM pyridine for 20 min inhibited norepinephrine-induced phasic and tonic contractions in the thoracic aorta, incubated as aortic rings, as well as the endothelium-denuded aorta of Wistar rats (Hsu Lin-Shiau, 1995). These effects were related to inhibition of the calcium influx normally elicited by norepinephrine. 

Administration of succinylcholine may be associated with the rapid onset of an increase in intraocular pressure (< 60 seconds), peaking at 2-4 minutes, and declining after 5 minutes. The mechanism may involve tonic contraction of myofibrils or transient dilation of ocular choroidal blood vessels. Despite the increase in intraocular pressure, the use of succinylcholine for ophthalmologic operations is not contraindicated unless the anterior chamber is open ("open globe") due to trauma. 

Both the tegument and the sarcolemma appear to contain praziquantel-sensitive sites (Blair et al., 1992). When intact worms are bathed in high magnesium, they exhibit a praziquantel-dependent biphasic muscle contraction instead of the tonic contraction that normally occurs. However, although worms with the tegument removed continue to respond... 

Skeletal muscle spasms are used to describe the increased tension often seen in skeletal muscle after certain musculoskeletal injuries and inflammation (muscle strains, nerve root impingements, etc.) occur.20,96 This tension is involuntary, so the patient is unable to relax the muscle. Spasms differ from spasticity because spasms typically arise from an orthopedic injury to a musculoskeletal structure or peripheral nerve root rather than an injury to the CNS. Likewise, muscle spasms are often a continuous, tonic contraction of specific muscles rather than the velocity-dependent increase in stretch reflex activity commonly associated with spasticity. The exact reasons for muscle spasms are poorly understood. According to some authorities, muscle spasms occur because a vicious cycle is created when the initial injury causes muscular pain and spasm, which increases afferent nociceptive input to the spinal cord, further exciting the alpha motor neuron to cause more spasms, and so on.61,96 Other experts believe that muscle spasms occur because of a complex protective mechanism, whereby muscular contractions are intended to support an injured vertebral structure or peripheral joint.96 Regardless of the exact reason, tonic contraction of the affected muscle is often quite painful because of the buildup of pain-mediating metabolites (e.g., lactate). 

Elapsed time Segmentation Tonic contraction Peristalsis... 

Figure 6.4 Types of intestinal motility patterns. Segmentation, tonic contraction, and peristalsis are the three major types of motility patterns observed in the gut. Each serves a specific function for digestion and processing of luminal contents. From E.B. Chang, M.D.Sitrin and D.D.Black (1996) Gastrointestinal motility and neurophysiology. Gastrointestinal, Hepatobiliary, and Nutritional Physiology, Lippincott-Raven, Philadelphia, pp. 27-51...

Tonic contractions characterize certain regions of the gut that serve as sphincters for dividing the gut into functional segments. 

A healthy 19-year-old woman complained of nausea and vomited 8 hours after taking unknown quantities of MDMA and beer 3 hours later, she suddenly clenched her jaw, had tonic contractions of all four limbs, and collapsed. She was obtunded, with occasional moaning and non-purposeful movements of the limbs. Head CT scan showed mild cerebral edema. Her serum electrolytes, including a sodium of 115 mmol/1 and a corresponding urine osmolality of 522 mosm/kg, suggested SIADH. Despite treatment, the serum sodium concentration 10 hours later was 116 mmol/1, but 18 hours after treatment, it rose to 125 mmol/1. She became progressively more responsive, with normalization of her sodium concentration, and after 48 hours was awake and alert, with a serum sodium concentration of 136 mmol/1. 

The presence of proctolin in the reproductive tract of a variety of insects and the action of this peptide on such tissues has been a current focus for many studies. The visceral muscles of the oviducts of Locusta migratoria. for example, are remarkably sensitive to proctolin (30)- Amounts of the peptide as low as 2 fmol induce a tonic contraction that is dose-dependent up to 200 fmol. A proctolin-like immunoreactive substance was found in the axons of nerves leading to the oviduct as well as in a number of cell bodies in the Vllth abdominal ganglion. Moreover, reverse-phase HPLC of tissue extracts of oviducts, oviducal nerves, and the Vllth abdominal ganglia indicate that the proctolin-like bioactive substance co-elutes with authentic proctolin. The peptide was present in areas of the oviduct that receive extensive innervation while it was ten-fold less in areas that receive little or no innervation. 

Relative mydriasis in bright illumination Absent or poor light reaction Slow (tonic) contraction to prolonged near effort Slow redilation after near effort Vermiform movements of pupillary margin (i.e., sector palsies of iris sphincter)... 

Ergometrine and oxytocin differ in their actions on the uterus. In moderate doses oxytocin produces slow generalised contractions with full relaxation in between ergometrine produces faster contractions superimposed on a tonic contraction. High doses of both substances produce sustained tonic contraction. It will be seen, therefore, that oxytocin is more suited to induction of labour and ergometrine to the prevention and treatment of postpartum haemorrhage, the incidence of which is reduced by its routine prophylactic use (generally i.m.). 

Asterixis, a jerky relaxation of tonically contracted postural muscles, was observed in some patients with structural lesions of the brain or metabolic encephalopathy who were taking levodopa, but not in patients with Parkinson s disease (10). 

A 42-year-old woman with neck pain took 15 g of maqianzi in two doses 7 hours apart (recommended dose 0.3-0.6 g) (2). One hour after she took the second dose she suddenly developed tonic contractions of all her limbs and carpopedal spasm lasting 5 minutes, difficulty in breathing, chest discomfort, and perioral numbness. She complained of muscle pain and tiredness and had hyperventilation and weakness of all four limbs. All her symptoms gradually subsided over the next few hours. 

A healthy 19-year-old woman complained of nausea and vomited 8 hours after taking unknown quantities of MDMA and beer 3 hours later, she suddenly clenched her jaw, had tonic contractions of all four... 

Ca influxes and thus attenuating the acetylcholine-induced tonic contraction. 

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