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PubMed1991

Beta-1 and beta-2 adrenoceptors mediate smooth muscle relaxation in bovine isolated mesenteric lymphatics.

The relaxant effects of beta adrenoceptor agonists were investigated in isolated bovine mesenteric lymphatics which had been contracted by 5-hydroxytryptamine. Addition of isoproterenol (a nonselective beta agonist), denopamine (a selective beta-1 agonist) and procaterol (a selective beta-2 agonist) caused concentration-dependent relaxations in the lymphatic preparations. There was no significant difference in the relaxant responses to the beta adrenoceptor agonists between the preparations with and without endothelium. Treatment with 10(-7) to 3 x 10(-6) M metoprolol (a selective beta-1 antagonist) shifted the concentration-response curve for denopamine to the right, whereas 10(-9) to 3 x 10(-8) M ICI 118,551 (a selective beta-2 antagonist) did not affect the relaxant response to denopamine. The relaxations of bovine mesenteric lymphatics induced by isoproterenol were suppressed by both metoprolol and ICI 118,551. The procaterol-induced relaxations were inhibited by 10(-9) to 3 x 10(-8) M ICI 118,551 but not by 10(-7) to 3 x 10(-6) M metoprolol. Schild plot analyses showed that the slope and pA2 values for metoprolol against denopamine were 1.10 and 7.59, respectively, and that those for ICI 118,551 against procaterol were 0.91 and 9.96. These results suggest that both beta-1 and beta-2 adrenoceptors are located on the smooth muscle cells in bovine mesenteric lymphatics and that stimulation of either receptor produces a marked relaxation.

Adrenergic beta-Agonists↗
PubMed1983

Reversal of the muscle relaxant effect of diazepam by the specific benzodiazepine antagonist Ro 15-1788: an electromyographic study in morphine model of muscular rigidity in rats.

The effects of the benzodiazepines diazepam and midazolam on the rigidity produced by systemic administration of morphine (15 mg/kg i.p.) were studied in rats. The rigidity was recorded as a tonic activity from the gastrocnemius-soleus muscle of non-anesthetized rats in the electromyogram. Both diazepam (1-5 mg/kg i.p.) and midazolam (2.5 and 5 mg/kg i.p.), when administered 45 min after morphine, temporarily antagonized the muscular rigidity. When the competitive antagonist Ro 15-1788 (ethyl-8-fluoro-5, 6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5a]-[1,4]benzodiazepine-3 -carboxylate) (5 mg/kg i.p.) was administered together with diazepam (5 mg/kg i.p.), it prevented the effect of diazepam, although by itself it did not affect the morphine-induced muscular rigidity. Our results suggest that diazepam, by acting on benzodiazepine receptors, can antagonize the morphine-induced muscular rigidity. The latter phenomenon might serve as a model for some types of muscular rigidity observed in humans.

Animals↗
PubMed1988

Studies of arterial smooth muscle relaxation in younger (16-18 week) and older (28-31 week) spontaneously hypertensive rats.

Both isometric and isotonic relaxation rates have previously been reported to be decreased in caudal arterial and mesenteric resistance arterial smooth muscle from 16- to 21-week-old spontaneously hypertensive rats (SHR) compared with muscle from age-matched normotensive Wistar-Kyoto rats (WKY). An increased maximum velocity of shortening (Vmax) and an increased shortening ability (delta Lmax) have also been reported for arterial smooth muscle from 16- to 21-week-old SHR. It has been suggested that both increased narrowing and prolonged narrowing of arteries contribute to the development of hypertension. However, SHR Vmax is not different from WKY Vmax when studying arterial muscle from older (28- to 31-week-old) rats. Thus increased arterial narrowing ability cannot be a contributing factor to the maintenance of hypertension. In this study the role of relaxation rate in the maintenance of hypertension was examined by comparing the relaxation rates of isometric and isotonic contractions of caudal arterial strips from 16- to 21-week-old SHR (n = 9) and WKY (n = 8) and from 28- to 31-week-old SHR (n = 7) and WKY (n = 5). While relaxation rates were lower for 16- to 21-week-old SHR compared with age-matched WKY preparations for both isometric and isotonic contractions, only isometric relaxation rates were found to be different in 28- to 31-week-old SHR compared with 28- to 31-week-old caudal arterial muscle (p less than 0.05). Vmax tended to normalize from a once-elevated velocity, while isometric relaxation rate remained decreased in SHR with ageing and (or) with progression of the hypertensive condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1980

Effects of nonspecific smooth muscle relaxants on glycogen phosphorylase activity in depolarized taenia caecum of guinea pig.

Effects of papaverine, Aspaminol (an antispasmodic drug), D-600, 2, 4-dinitrophenol and Ca ions on glycogen phosphorylase activity in the KCl-depolarized taenia caecum of guinea pig were tested. External Ca ions dose-dependently activated phosphorylase, indicating that Ca ions, which entered the smooth muscle cells, played an important role in the regulation of phosphorylase activity. Aspaminol, D-600 and removal of Ca ions from bath fluid inhibited phosphorylase activity. Since these treatments relaxed the taenia caecum, the decrease of phosphorylase activity after the treatments may be mainly due to the decrease of energy consumption. Papaverine and 2, 4-dinitrophenol induced an activation of phosphorylase which might be for replenishment of energy stores decreased by them.

Animals↗
PubMed1993

The skeletal muscle relaxant action of Portulaca oleracea: role of potassium ions.

An aqueous extract of the stems and leaves of Portulaca oleracea abolishes the twitch contraction of the directly stimulated rat hemidiaphragm preparation. The effects of the extract mimic qualitatively the action of potassium oxalate--a known constituent of Portulaca oleracea--on the diaphragm. Removal of K+ ions from the methanol extract by passing it through a cation exchange resin reduced the inhibitory effect of the extract. There was a positive correlation between the concentration of K+ ions in the extract and the effects of potassium chloride of similar molarity. It is concluded that the K+ ion content of Portulaca oleracea is at least partly responsible for the relaxant effect observed on the isolated rat diaphragm.

Animals↗
PubMed1996

[Value of monitoring muscle relaxation].

INDICATION: Sensitivity to neuromuscular blocking agents differs between individuals, and residual neuromuscular blockade is a common postoperative problem. Clinical signs such as head lift, hand grip, and inspiratory force are suitable means of showing residual blockade. However, an awake and cooperative patient is needed. Therefore, in clinical practice it is advantageous to use the responses evoked by a nerve stimulator. SITES OF NERVE STIMULATION AND DIFFERING MUSCLE RESPONSE: In clinical anesthesia, the ulnar nerve is the most popular site. The response is evaluated by feeling the contractions of the adductor pollicis muscle. This muscle shows a slow onset of blockade and is highly sensitive to neuromuscular blocking agents. Therefore, the chance of overdosing the patient is decreased and during recovery additional safety is gained, as it can be safely assumed that at the time of normalization of the thumb twitches no residual blockade exists in the diaphragm or larynx. On the other hand, absent twitches of the adductor pollicis using train-of-four stimulation do not preclude intraoperative activity of more resistant muscles such as the diaphragm. RECORDING OF EVOKED RESPONSES AND PATTERNS OF NERVE STIMULATION: In clinical anesthesia, tactile evaluation of the muscle response is the usual method. Mechanomyography (Myograph) with a force transducer is used as the reference standard. This method, as well as the measurement of acceleration (Accelograph, TOF-Guard) and electromyography (Relaxograph) are mainly tools for teaching and research. Different patterns of nerve stimulation are used: during induction, single-twitch stimulation at 1Hz; during profound blockade, post-tetanic count stimulation (PTC); surgical blockade is evaluated using train-of-four stimulation (TOF); and recovery is followed by double-burst stimulation (DBS). Using simple train-of-four stimulation during recovery, a device is needed with a registering capacity to accurately determine a TOF-ratio > 0.7. CONCLUSIONS: Relaxometry allows monitoring of neuromuscular function independently of the patient's cooperation, and should be standard. In the intensive care unit, relaxometry helps to minimize the risk of overdosing. However, muscular weakness can persist despite adequate drug dosage. Relaxometry is only part one of a concept. Intubating and operating conditions are highly dependent on the depth of anesthesia, and the risk of postoperative residual blockade can be minimized by using short or medium action drugs.

Electric Stimulation↗