adrenomimetic, is selective for ßr and ß2-adrenocep-tors. Norepinephrine and epinephrine are thus potent vasoconstrictors of vascular beds that contain predominantly a-adrenoceptors, while isoproterenol has little effect in these vessels.
Isoproterenol and epinephrine are potent ß2-adrenoceptor agonists; norepinephrine is a relatively weak ß2-adrenoceptor agonist. Isoproterenol and epinephrine produce vasodilation in skeletal muscle, but norepinephrine does not; rather it produces vasoconstriction through the ^-adrenoceptors. Isoproterenol, epinephrine, and norepinephrine are potent ^-adrenoceptor agonists; thus, all three can stimulate the heart (Table 9.1).
The existence of a ^-adrenoceptor has recently been demonstrated in human adipose tissue along with the ^-adrenoceptor. This observation raises the possibility that eventually therapeutic drugs may selectively alter lipid metabolism and therefore provide therapeutic management of obesity. The (33-receptor and the recently identified subtypes within the a1- and a2-receptor groups (a1A, a1B, etc.) also have not been included in the table, since as yet few therapeutic drugs distinguish among these further subtypes. One exception is tam-sulosin, an antagonist with some selectivity for a1A-receptors in the urinary tract.
Was this article helpful?
This guide will help millions of people understand this condition so that they can take control of their lives and make informed decisions. The ebook covers information on a vast number of different types of neuropathy. In addition, it will be a useful resource for their families, caregivers, and health care providers.