Isoproterenol pharmacological properties

PHARMACOLOGICAL PROPERTIES The pharmacological actions of NE and Epi have been extensively compared in vivo and in vitro (Table 10-2). They are approximately equipotent in stimulating /3j receptors they differ mainly in their effectiveness in stimulating a and receptors. NE is a potent a agonist and has relatively little action on fi receptors however, it is somewhat less potent than Epi on the a receptors of most organs. Isoproterenol stimulates all /3 receptors but not a receptors. Eigure 10-2 compares the cardiovascular effects of infusions of NE, Epi, and isoproterenol. 

The cardiovascular effects of racemic dobutamine are a composite of the pharmacological properties of the (—) and (-V) stereoisomers. Dobutamine has relatively more prominent inotropic than chronotropic effects, compared to isoproterenol. This useful selectivity may arise because peripheral resistance is relatively unchanged due to a counterbalancing ofa receptor-mediated vasoconstriction and receptor-mediated vasodilation. Alternatively, cardiac receptors may contribute to the inotropic effect. At equivalent inotropic doses, dobutamine enfumces automatic-ity of the sinus node to a lesser extent than does isoproterenol however, enhancement of AV and intraventricular conduction is similar for both drugs. 

Albuterol (ventoun, proventil, others) is a selective P2 agonist with pharmacological properties and therapeutic indications similar to those of terbutaline. It is administered by inhalation or orally for the symptomatic relief of bronchospasm. When administered by inhalation, terbutaline produces significant bronchodilation within 15 minutes effects persist for 3-4 hours. Cardiovascular effects of albuterol are considerably weaker than those of isoproterenol that produce comparable bronchodilation when administered by inhalation. Oral albuterol may delay preterm labor. Rare CNS and respiratory side effects are sometimes observed. 

I. Pharmacology. Isoproterenol is a catecholamine-like drug that stimulates beta-adrenergic receptors (beta-1 and -2). Pharmacologic properties include positive inotropic and chronotropic cardiac effects, periphery vasodilation, and bron-chodilation. Isoproterenol is not absorbed orally and shows variable and erratic absorption from sublingual and rectal sites. The effects of the drug are rapidly terminated by tissue uptake and metabolism effects persist only a few minutes after intravenous injection. 

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