Drugs Used to Influence Smooth Muscle Organs

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Bronchodilators. Narrowing of bronchioles raises airway resistance, e.g., in bronchial or bronchitic asthma. Several substances that are employed as bronchodilators are described elsewhere in more detail: ß2-sympathomimetics (p. 84, given by pulmonary, parenteral, or oral route), the methylxanthine theo-phylline (p. 326, given parenterally or orally), as well as the parasympatholytic ipratropium (pp. 104, 107, given by inhalation).

Spasmolytics. N-Butylscopolamine (p. 104) is used for the relief of painful spasms of the biliary or ureteral ducts. Its poor absorption (N.B. quaternary N; absorption rate <10%) necessitates par-enteral administration. Because the therapeutic effect is usually weak, a potent analgesic is given concurrently, e.g., the opioid meperidine. Note that some spasms of intestinal musculature can be effectively relieved by organic nitrates (in biliary colic) or by nifedipine (esoph-ageal hypertension and achalasia).

Myometrial relaxants (Tocolytics). ß2-Sympathomimetics such as fe-noterol or ritodrine, given orally or par-enterally, can prevent premature labor or interrupt labor in progress when dangerous complications necessitate cesar-ean section. Tachycardia is a side effect produced reflexly because of ß2-mediat-ed vasodilation or direct stimulation of cardiac ßi-receptors. Magnesium sulfate, given i.v., is a useful alternative when ß-mimetics are contraindicated, but must be carefully titrated because its nonspecific calcium antagonism leads to blockade of cardiac impulse conduction and of neuromuscular transmission.

Myometrial stimulants. The neu-rohypophyseal hormone oxytocin (p. 242) is given parenterally (or by the nasal or buccal route) before, during, or after labor in order to prompt uterine contractions or to enhance them. Certain prostaglandins or analogues of them (p.

196; F2a: dinoprost; E2: dinoprostone, misoprostol, sulprostone) are capable of inducing rhythmic uterine contractions and cervical relaxation at any time. They are mostly employed as abortifacients (oral or vaginal application of misopros-tol in combination with mifepristone [p. 256]).

Ergot alkaloids are obtained from Secale cornutum (ergot), the sclerotium of a fungus (Claviceps purpurea) parasitizing rye. Consumption of flour from contaminated grain was once the cause of epidemic poisonings (ergotism) characterized by gangrene of the extremities (St. Anthony's fire) and CNS disturbances (hallucinations).

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.

Ergotamine, as well as the ergotox-ine alkaloids (ergocristine, ergocryp-tine, ergocornine), have a predominantly vascular action. Depending on the initial caliber, constriction or dilation may be elicited. The mechanism of action is unclear; a mixed antagonism at a-adrenoceptors and agonism at 5-HT-re-ceptors may be important. Ergotamine is used in the treatment of migraine (p. 322). Its congener, dihydroergotamine, is furthermore employed in orthostatic complaints (p. 314).

Other lysergic acid derivatives are the 5-HT antagonist methysergide, the dopamine agonists bromocriptine, pergolide, and cabergolide (pp. 114, 188), and the hallucinogen lysergic acid di-ethylamide (LSD, p. 240).

Bronchial asthma

Bronchial asthma

Smooth Muscle Spasm
Spasm of smooth muscle

Bronchodilation

Theophylline 0

ß2-Sympathomimetics e.g., fenoterol

Ipratropium

Spasmolysis

N-Butylscopolamine

Scopolamine

Nitrates e.g., nitroglycerin

Secale cornutum (ergot)

Ipratropium

Secale cornutum (ergot)

Tonic contraction of uterus e.g., ergometrine

Fungus:

Claviceps purpurea Secale alkaloids

Inhibition of labor

Sympathomimetics

Induction of labor

Oxytocin

Prostaglandins F2a, E2

Fungus:

Claviceps purpurea Secale alkaloids

Effect on vasomotor tone

Tonic contraction of uterus e.g., ergometrine

Contraindication: before delivery

Indication: postpartum uterine atonia

e.g., ergotamine

Fixation of lumen at intemediate caliber

A. Drugs used to alter smooth muscle function

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Coping with Asthma

Coping with Asthma

If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.

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