,Adrenoceptor Agonists,definition,Drugs that mimic the actions of epinephrine or norepinephrine Sympathomimetic drugs,Classification,Depend on the affinity for different groups of receptor -adrenoceptor agonists -adrenoceptor agonists , -adrenoceptor agonists,Chemistry,Parent compound: phenylethylamine Change the affinity for or receptors Change pharmacokinetics properties,Chemistry and pharmacokinetics,Substitutions On the terminal amino group: increase receptors activity On the benzene ring: increase bioavailability and prolongs the duration of action; increase the distribution of molecule to CNS On the alpha or beta carbons: block oxidation by MAO,-adrenoceptor agonists,Norepinephrine Metaraminol 1 -adrenoceptor agonists: phenylephrine and methoxamine,Norepinephrine,Potent effect of receptor Relative little effect on 1 receptor Little effect on 2 receptor,Pharmacological Effects,Blood vessels: constrict (skin vessels, renal vessels); coronary artery dilate Heart: pacemaker activity, conduction velocity, and intrinsic contractility increase. HR decrease by a reflex response.,Pharmacological Effects,Blood pressure: systolic pressure increase at low concentration; at high concentration both systolic and diastolic pressure increase,pharmacokinetics,i.v. drip. Be uptake and metabolized quickly,Therapeutic Uses,neurogenic shock, cardiogenic shock Hypotension hemorrhage of upper digestive tract,Adverse reaction,Avascular necrosis Acute renal failure Contraindication: hypertension, atherosclerosis, cardiopathy,Metaraminol,excite -R replace the NA in vesicles，increase NA release from vesicles directly More stable to MAO, prolong the action Acute tolerance,Pharmacological Effects,similar to NA in its action, but less potent increase systolic and diastolic blood pressure its major therapeutic use is in the treatment of hypotensive state,Phenylephrine, Methoxamine,1-R agonists similar to those of NA, but less potent and has a longer duration of action vasoconstriction, increase arterial pressure, and reflex bradycardia,Clinical Uses,hypotension state; supraventricular paraxosmal pupil mydriasis,、-R agonist,Adrenaline Dopamine ephedrine,Adrenaline,At low concentration , effects predominate; at high concentration , effects predominate. 2-R are more sensitive to Adr than the -R.,pharmacokinetics,Adr- absorption is poor with oral administration can be given iv or im,Pharmacological Effects,Heart a direct effect on 1-R ; increase in heart rate , and increase cardiac output; a propensity toward arrhythmias coronary artery dilate,Pharmacological Effects,Blood vessel Constrict (skin vessels, renal vessels) Dilate: vessels in skeletal muscle , hepatic vessels coronary blood flow,Pharmacological Effects,blood pressure At low concentration: systolic pressure increase At high concentration: both systolic and diastolic pressure increase,Pharmacological Effects,Smooth muscle: Bronchiolar smooth muscle relaxes blood vessel constrict Block the release of histamine,Pharmacological Effects,Metabolic effects increase in glucoses and lactate production via glycogenolysis inhibition of insulin secretion (-R) increase in free fatty acid and oxygen consumption .,Therapeutic Uses,cardiac arrest acute or severe hypersensitivity reaction , it is primary treatment for anaphylactic shock , asthma prolong the duration of local anesthesia,Adverse Effects,Palpitation, BP Hypertension, diabetes mellitus, hyperthyroidism,Dopamine,activate 、1 and dopa-receptor Be metabolized by MAO and COMT quickly No effect on CNS,Dopamine,heart: positive inotropic effect on the myocardium, increase cardiac output blood vessels At low or intermediate concentration: act on D1 receptor, dilate At high concentration : act on -receptor, constrict,Pharmacological Effects,Kidney At low or intermediate concentration: reduce arterial resistance in the mesentery and kidney At high concentration: cause vasoconstriction with consequent reduction in renal function,Clinical uses,Shock Acute renal failure Adverse reaction: arrhythmia, reduction in renal function,Ephedrine,absorbed when taken orally resistant to COMT and MAO, so that its action is prolonged CNS effects may occur: such as insomnia, nervousness, nausea and agitation Acute tolerance,pharmacological Effects,increase cardiac output, increase blood pressure Relax smooth muscle CNS: excitement,Clinical Uses,bronchial asthma nasal decongestant hypotension without crisis Adverse reactions: CNS,-R agonist,1 and 2-R agonist Isoprenaline: lower selectivity to both 1 and 2-R, little effect on -R,pharmacological Effects,heart: positive inotropic effect ,increase the heart rate and conduction, cardiac output increase blood vessels : reduction of peripheral vascular resistance in skeletal muscle, renal and mesenteric vascular beds;,pharmacological Effects,blood pressure: diastolic blood pressure falls , systolic blood pressure may increase Relax both bronchial and gastrointestinal smooth