Cholinoceptor Blocking Drugs

Cholinoceptor Blocking Drugs

Cholinoceptor antagonists, like agonists, are divided into muscarinic and nicotinic subgroups on the basis of their specific receptor affinities. Ganglion blockers and neuromuscular junction blockers make up the antinicotinic drugs.

Five subtypes of muscarinic receptors have been identified, primarily on the basis of data from ligand-binding and cDNA-cloning experiments. A standard terminol-ogy (M₁ through M₅) for these subtypes is now in common use, and evidence—based mostly on selective agonists and antagonists— indicates that functional differences exist between several of these subtypes.

The M₁ receptor subtype is located on central nervous system (CNS) neurons, sympathetic postganglionic cell bodies, and many presynaptic sites. M ₂ receptors are located in the myocar-dium, smooth muscle organs, and some neuronal sites. M₃ recep-tors are most common on effector cell membranes, especially glandular and smooth muscle cells. M₄ and M₅ receptors are less prominent and appear to play a greater role in the CNS than in the periphery.

 CASE STUDY

JH, a 63-year-old architect, complains of urinary symptoms to his family physician. He has hypertension, and during the last 8 years, he has been adequately managed with a thiazide diuretic and an angiotensin-converting enzyme inhibitor. During the same period, JH developed the signs of benign prostatic hypertrophy, which eventually required prostatectomy to relieve symptoms. He now complains that he has an increased urge to urinate as well as urinary fre-quency, and this has disrupted the pattern of his daily life. What do you suspect is the cause of JH’s problem? What information would you gather to confirm your diagnosis? What treatment steps would you initiate?