Parasympathetic agonist & antagonist

1. Parasympathetic agonist & antagonist Muscarinic agonist cholinomimetics agents Parasympathomimetic agents Same effect of Parasympathic system Muscarinic antagonist or Antimuscarinic drug Parasympatholeticagents Same effect sympathic system examples: Atropine , Scopolamine(hyosine) , Ipratropium , Pirenzepine Effect on each organ or system : A. CNS: Atropine in therapeutic doses has a minimal stimulant effect on CNS and a slower-long lasting sedative = drowsiness effect on the brain Scopolamine has more marked CNS effects producing drowsiness in recommended doses BOTH In HIGHR DOSES: agitation, excitement, hallucination and coma B. Eye Mydriasis= pupil dilation Relaxation of ciliary muscle=Cycloplegia (plegia =paralysis) leads to loss of accommodation(eye can not focus on near objects) u need to see far object so u can run and hide Reduction of lacrimal secretion, dry eyes C. Cardiovascular system Heart: The initial effect is bradycardiafollowed by tachycardia bradycardia= slow heart rate :HOW? blockade of presynaptic M1 muscarinic receptors = Ach leakage Tachycardia= High heart rate: HOW? blockade of M2 receptors on the heart =more Ach will effect the contraction of the heart B.Vs : Inhibition of vasodilation = antagonist block M3 Vasodilation induced by cholinomimetics. *هذي تخلي الأوعية الدمية زي ماهي يعني ما تسوي vasoconstriction D- Respiratory system bronchodilation Antimuscarinic drugs are added to general anesthetics to reduce secretion in the trachea • Examples: • Effect on each organ or system A. CNS: excitatory neurotransmitter in the basal ganglia =increased locomotor activity tremor=الرعشة B. Eye • contraction of the smooth muscle of the iris causing miosis= Pupil constriction • contraction ciliary muscle=accommodation of near vision= like when u read u need to see clearly near words • outflow of aqueous humor into the canal of Schlemn , drains the anterior chamber C. Cardiovascular system Heart: Heart rate (-vechronotropy= slow heart rate), Bradycardia conduction velocity , refractory period B.Vs : BP >HOW? Due to Bradycardia and vasodilation?> Muscarinic agonist attached on M3 receptor on B.Vs causes release of NO(vasodilation agent) that’s will lead to : vasodilation that will lead to drop in BP D- Respiratory system: • Bronchio-spasm = bronchoconstuction • increase secretion

2. Parasympathetic agonist & antagonist continued….. E.sweat glands Sweat gland secretions are blocked by antimuscarinic drugs, > thermoregulation is suppressed leading to increase in body temperature. F. GIT marked reduction in salivary secretion (dry mouth) Gastric secretion is blocked less effectively? > not controlled by parsympathic also there r hormones control Gastric secretion G.GU: Smooth muscle of the uterus is relaxed Inhibition of detrusor muscle(covers the bladder) Bladder wall is relaxed and voiding(micturition) is slower A) neuromuscular blockers : 1- depolarizing NMJ blocking drugs; the depolarizing blockers first depolarize the motor end-plate and then prevent further depolarization. E.g. Succinylcholine 2- non-depolarizing NMJ blocking drugs; compete with acetylcholine for receptors at the neuromuscular junction and clinical relaxation begins when 80–85% of the receptors on the motor end-plate are blocked. tubocurarine B) Ganglion blocking drugs can occur by several mechanisms: By interfering with Ach release By prolonged depolarization due to large dose of stimulation = depolarizing By interfering with postsynaptic action of Ach.= non-depolarizing E. Exocrine gland • Increased their secretion, sweating, lacrimation and salivation F. GIT • GIT motility • secretions mainly salivary(wet mouth) and gastric • peristalsis الحركة الدودية بالأمعاء • Sphincters are relaxed • G.GU: Stimulation of detrusor muscle(covers the bladder) and Relaxation of the trigone and sphincter of the bladder thus promote micturition. A)NMJ • Application of nicotine agonist in NMJ leads to depolarization of the endplate The response vary from fasciculation of independent motor units to a strong contraction of entire motor unit. B)Peripheral nervous system • Activation of nicotinic receptors in the autonomic ganglia result in firing action potential in postganglionic neurons • The action is same on both sympathetic and parasympathetic ganglia Nicotinic agonists agonist & antagonist continued…..