Smooth muscle prolongation

PG 15 (R) 15-me—E2me ester inhibitor gastric secretion spasmogen smooth muscle prolonged action active at oral administration... 

As noted in Table 49-3, slow cycling of the crossbridges permits slow prolonged contraction of smooth muscle (eg, in viscera and blood vessels) with less utilization of ATP compared with striated muscle. The ability of smooth muscle to maintain force at reduced velocities of contraction is referred to as the latch state this is an important feamre of smooth muscle, and its precise molecular bases are under smdy. 

Explain why smooth muscle contraction is slow and prolonged... 

Contraction of smooth muscle is significantly slower than that of skeletal muscle. Furthermore, smooth muscle contraction is quite prolonged (3000 msec) compared to that in skeletal muscle (100 msec). The slow onset of contraction as well as its sustained nature is due to the slowness of attachment and detachment of the myosin crossbridges with the actin. Two factors are involved ... 

Within 30 minutes of their administration, 6 -adrenergic drugs often reverse most of the functional deficit in Monday morning byssinotics. As there is no mucous secretion, airway smooth muscle contraction is considered the primary response. Exposure of man to histamine aerosols produces pulmonary function changes similar to those seen after exposure to dust extract. However, exposure to histamine aerosol invariably initiates constriction of smooth muscle more rapidly than exposure to cotton dust ( <15 minutes), and dissipates within minutes, while the acute effects of inhalation of cotton dust and dust extracts lasts for hours. The slowly developing and prolonged effects of dust and extracts suggest that mediators other than histamine are involved. 

Isosorbide Dinitrate Hydralazine (BiDil) [Antianginal, Antihypertensive/Vasodilator, Nitrate] Uses HF in African Amer-icans improve survival functional status, prolong time between hospitalizations Action Relaxes vascular smooth muscle peripheral vasodilator Dose Initially 1 tab tid PO (if not tol ated reduce to 1/2 tab tid), titrate >3-5 d as tolerated Max 2 tabs tid Caution [C, /-] recent MI, syncope, hypovolemia, hypotension, hep impair Contra For children, concomitant use w/ PDE5 inhibitors (sildenafil) Disp Tabs SE HA, dizziness, orthostatic hypotension, sinusitis, GI distress, tach, paresthesia, amblyopia Interactions t Risk of severe hypotension W/ antihypertensives, ASA, CCBs, MAOIs, phenothiazides, sildenafil, tadalafil, vardenafil, EtOH X pressor response Wf i -1- effects W7 NSAIDs EMS Use ASA, antihypertensives and CCBs w/ caution, may t hypotension concurrent Viagra-type drug use can lead to profound hypotension concurrent EtOH use can t effects OD May cause N/V, profound hypotension, skin flushing, HA from ICP, bradycardia, confusion, and circulatory collapse activated charcoal may be effective, epi use is contraindicated... 

Ephedrine increases systolic and diastolic blood pressure heart rate is generally not increased. Contractile force of the heart and cardiac output are both increased. Ephedrine produces bronchial smooth muscle relaxation of prolonged duration when administered orally. Aside from pupillary dilation, ephedrine has little effect on the eye. 

Succinylcholine acts primarily at the skeletal neuromuscular junction and has little effect at autonomic ganglia or at postganglionic cholinergic (muscarinic) junctions. Actions at these sites attributed to succinylcholine may arise from the effects of choline. Succinylcholine has no direct action on the uterus or other smooth muscle structures. It does not enter the CNS and does not cross the placental barrier. It may, however, release histamine from mast cells. Because succinylcholine works by stimulating rather than blocking end plate receptors, anti-AChEs will not reverse muscle paralysis and may actually prolong the block. 

Ox ocin is a nonapeptide which is structurally related to vasopressin. It stimulates rhythmic uterine contractions and is widely used by intravenous infusion of a diluted solution to induce labour and to treat postpartum bleeding. In large doses, it may cause relaxation of vascular smooth muscle causing hypotension in patients with cardiac disease or who are dehydrated. It has water-retaining properties and when given for prolonged periods to patients whose intake is electrolyte-free it causes overhydration and hyponatraemia. This may result in convulsions in the newborn with the risk of cerebral damage. 

Diphenhydramine Competitive antagonism at Hi receptors Reduces or prevents histamine effects on smooth muscle, immune cells also blocks muscarinic and adrenoceptors highly sedative IgE immediate allergies, especially hay fever, urticaria some use as a sedative, antiemetic, and antimotion sickness drug Oral and parenteral t duration 4-6 h Toxicity Sedation when used in hay fever, muscarinic blockade symptoms, orthostatic hypotension Interactions Additive sedation with other sedatives, including alcohol some inhibition of CYP2D6, may prolong action of some 13 blockers... 

Ergotamine Mixed partial agonist effects at 5-HT2 and (X adrenoceptors Causes marked smooth muscle contraction but blocks cx-agonist vasoconstriction Migraine and cluster headache Oral, parenteral duration 12-24 h Toxicity Prolonged vasospasm causing gangrene uterine spasm... 

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