A Adrenergic receptor antagonist

The major circulating hormones that influence vascular smooth muscle tone are the catecholamines epinephrine and norepinephrine. These hormones are released from the adrenal medulla in response to sympathetic nervous stimulation. In humans, 80% of catecholamine secretion is epinephrine and 20% is norepinephrine. Stimulation of cy-adrenergic receptors causes vasoconstriction. The selective a,-adrenergic receptor antagonist, prazosin, is effective in management of hypertension because it causes arterial and venous smooth muscle to relax. 

Ono H, Mishima A, Ono S, Fukuda H, Vasko MR (1991) Inhibitory effects of donidine and tizanidine on release of substance P from slices of rat spinal cord and antagonism by a-adrenergic receptor antagonists. Neuropharmacology 30, 585-589... 

Rarely, bladder ontlet obstmction may be caused by a functional obstmction at the level of the bladder neck. Hypertrophy of the smooth mnscle fibers at the level of the bladder neck in men and women may result in obstruction to the flow of nrine. In those patients who fail pharmacologic therapy with a-adrenergic receptor antagonists, endoscopic incision using the cy stoscope is highly effective in treating this very nncommon condition. 

Alkaloid a-adrenergic receptor antagonist. Vasodilator said to be an aphrodisiac. Local anaesthetic about as potent as cocaine. Releases antidiuretic hormone from posterior pituitary. Related to reserpine. 

N.L., Huffman, J.C., 1985. 6,7-Dihydro-5-[[(cir-2-hydroxy-(raiii-3 - phenoxy-cyclopentyl)amino]methyl] - 2 - methy lbenzo[ 6]thiophen-4-(5//)-one a novel a,-adrenergic receptor antagonist and renal vasodilator. J. Med. Chem. 28, 1142-1145. 

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