Gastrointestinal tract catecholamines

Pituitary Adenylyl Cyclase-activating Polypeptide (PACAP) is a 38-amino acid peptide (PACAP-38), which is widely expressed in the central nervous system. PACAP is most abundant in the hypothalamus. It is also found in the gastrointestinal tract, the adrenal gland and in testis. Its central nervous system functions are ill-defined. In the periphery, PACAP has been shown to stimulate catecholamine secretion from the adrenal medulla and to regulate secretion from the pancreas. Three G-protein coupled receptors have been shown to respond to PACAP, PAQ (PACAP type I) specifically binds PACAP, VPACi and VPAC2 also bind vasoactive intestinal peptide (VDP). Activation of PACAP receptors results in a Gs-mediated activation of adenylyl cyclase. 

Its most important pharmacological effects are dilation of veins and capillaries, increased permeability of capillaries, increased heart rate, contraction of nonvascular smooth musculature (constriction of bronchi, gastrointestinal tract peristalsis), stimulation of gastric juice secretion, and release of catecholamines from adrenal glands. 

Gastrointestinal tract. Relaxation of GIT smooth muscle can be brought about by both a and (3 stimulant agents. Alpha stimulants especially selective agonists, decrease muscle activity indirectly by presynaptically reducing the release of catecholamines, a -receptors may also decrease salt and water flux into the lumen of the intestine. 

Tobacco smoke includes 4000 chemical species with varying potential which cause adverse effects. Nicotine is stimulating to the autonomic nervous system ganglia and neuromuscular junction. The most prominent effects relate to stimulation of the adrenal medulla, central nervous system (CNS), cardiovascular system (release of catecholamines), gastrointestinal tract (parasympathetic stimulation), salivary and bronchial glands, and the medullary vomiting center. There is subsequent blockade of autonomic ganglia and the neuromuscular junction transmission, inhibition of catecholamine release from the adrenal medulla, and CNS depression. 

A. Toluene and xylene cause generalized central nervous system depression. Like other aromatic hydrocarbons, they may sensitize the myocardium to the arrhythmogenic effects of catecholamines. They are mild mucous membrane irritants affecting the eyes and respiratory and gastrointestinal tracts. 

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