Hormones histamine

Gastric acid production is regulated by both the autonomic nervous system and several hormones. The parasympathetic nervous system, via the vagus nerve and the hormone gastrin, stimulates the parietal cell to produce gastric acid, acting both directly on parietal cells and indirectly through the stimulation of the secretion of the hormone histamine from ECL cells. Vasoactive intestinal peptides, cholecystokinin and secretin all inhibit acid production. 

There are four amino acids, amongst the 20 that make up proteins, that have an aromatic side-chain, and of these, two have a heteroaromatic side-chain - histidine, with an imidazole, and tryptophan, with an indole. Both of these are amongst the essential amino acids , i.e. they need to be part of the diet since they cannot be biosynthesised by human beings. Decarboxylation of histidine produces the hormone histamine. Proline is the only heterocyclic DNA-coded a-amino acid - it is based on pyrrolidine hydroxyproline is an essential component of collagen, the hbrous structural protein that supports tissues and is the main component of cartilage. 

Only oxazole, of the trio, does not play any part in normal biochemical processes, though there are secondary metabolites (especially from marine organisms) which incorporate thiazole (and oxazole) units - the antibiotic cystothiazole A, from the myxobacterium Cyctobacter fuscus is an example. Imidazole occurs in the essential amino acid histidine histidines within enzymes are intimately involved in catalysis requiring proton transfers. The structurally related hormone, histamine, is a vasodilator and a major factor in allergic reactions such as hay fever. The thiazolium ring is the chemically active centre in the coenzyme derived from thiamin (vitamin B,). 

Bodammer (1967) has recently found that the bronchial action of extremely high doses of AT in guinea-pigs can be entirely suppressed by a combined treatment with tripelennamine and atropine. This seems to indicate that the antihistamine-resistant part of AT-action is mediated by a cholinergic stimulus. AT then appears to be a general liberator of local hormones histamine, catecholamines and acetylcholine. 

Certain amino acids and their derivatives, although not found in proteins, nonetheless are biochemically important. A few of the more notable examples are shown in Figure 4.5. y-Aminobutyric acid, or GABA, is produced by the decarboxylation of glutamic acid and is a potent neurotransmitter. Histamine, which is synthesized by decarboxylation of histidine, and serotonin, which is derived from tryptophan, similarly function as neurotransmitters and regulators. /3-Alanine is found in nature in the peptides carnosine and anserine and is a component of pantothenic acid (a vitamin), which is a part of coenzyme A. Epinephrine (also known as adrenaline), derived from tyrosine, is an important hormone. Penicillamine is a constituent of the penicillin antibiotics. Ornithine, betaine, homocysteine, and homoserine are important metabolic intermediates. Citrulline is the immediate precursor of arginine. 

The release of arachidonate and the synthesis or interconversion of eicosanoids can be initiated by a variety of stimuli, including histamine, hormones such as epinephrine and bradykinin, proteases such as thrombin, and even serum albumin. An important mechanism of arachidonate release and eicosanoid syn-... 

Most GPCRs interact with and activate more than one G-protein subfamily, e.g., with Gs plus Gq/n (histamine H2, parathyroid hormone and calcitonin recqrtors), Gs plus G (luteinising hormone receptor, 32-adrenoceptor) or Gq/11 plus G12/13 (thromboxane A2, angiotensin ATb endothelin ETA receptors). Some receptors show even broader G-protein coupling, e.g., to Gi, Gq/n plus Gi n ( protease-activated receptors, lysophosphatidate and sphingosine-1-phosphate receptors) or even to all four G-protein subfamilies (thyrotropin receptor). This multiple coupling results in multiple signaling via different pathways and in a concerted reaction of the cell to the stimulus. 

Important products derived from amino acids include heme, purines, pyrimidines, hormones, neurotransmitters, and biologically active peptides. In addition, many proteins contain amino acids that have been modified for a specific function such as binding calcium or as intermediates that serve to stabilize proteins—generally structural proteins—by subsequent covalent cross-hnk-ing. The amino acid residues in those proteins serve as precursors for these modified residues. Small peptides or peptide-like molecules not synthesized on ribosomes fulfill specific functions in cells. Histamine plays a central role in many allergic reactions. Neurotransmitters derived from amino acids include y-aminobutyrate, 5-hydroxytryptamine (serotonin), dopamine, norepinephrine, and epinephrine. Many drugs used to treat neurologic and psychiatric conditions affect the metabolism of these neurotransmitters. 

Amino acid receptors Monoamine receptors Lipid receptors Purine receptors Neuropeptide receptors Peptide hormone receptors Chemokine receptors Glycoprotein receptors Protease receptors Metabotropic glutamate and GABAb receptors Adrenoceptors, dopamine and 5-HT receptors, muscarinic and histamine receptors Prostaglandin, thromboxane and PAF receptors Adenosine and ATP (P2Y) receptors Neuropeptide Y, opiate, cholecystokinin VIP, etc. Angiotensin, bradykinin, glucagon, calcitonin, parathyroid, etc. Interleukin-8 TSH, LH/FSH, chorionic gonadotropin, etc. Thrombin... 

Many hormones and other blood-borne substances (including drugs) also alter contractile activity of smooth muscle. Some of the more important substances include epinephrine norepinephrine angiotensin II vasopressin oxytocin and histamine. Locally produced substances that may alter contraction in the tissue in which they are synthesized include nitric oxide prostaglandins leukotrienes carbon dioxide and hydrogen ion. 

Gastrin is a hormone produced by gastric endocrine tissue — specifically, the G cells in the pyloric gland area. It is released into the blood and carried back to the stomach. The major function of gastrin is to enhance acid secretion by directly stimulating parietal cells (HC1) and chief cells (pepsinogen). Gastrin also stimulates the local release of histamine from enterochromaf-fin-like cells in the wall of the stomach. Histamine stimulates parietal cells to release HC1. 

Knigge, U. and Warberg, J. The role of histamine in the neuroendocrine regulation of pituitary hormone secretion. Acta Endocrinol. (Copenh.) 124 609-619,1991. 

Somatostatin (SOM), initially identified by its ability to inhibit the release of growth hormone, is known to have inhibitory effects on a variety of cells [ 109], In mast cells and in basophils, SOM, like NT, has inhibitory as well as stimulatory effects depending on the concentration used. At high concentrations (> 10 8 M), SOM is a powerful stimulus of peritoneal mast-cell secretion (from both normal and athymic rats) and resembles other non-immunologic secretagogues such as compound 48/80, SP and NT in that it triggers a rapid exocytosis that is primarily dependent on cellular Ca [ 110,111], A similar effect is seen in vivo when injected into skin or skin blisters at high concentrations (> 10-8 M), SOM causes a rapid, dose-dependent release of histamine [88, 112] but when used at concentrations lower than those which elicit a secretory... 

Histamine Hr Human cDNA Allergy inflammation, asthma, chronic sinusitis, rhinitis, epilepsy migraine, motion sickness, pain, cancer Smooth muscle contraction, increase in vascular permeability stimulation of hormone release (adrenal medulla), increase in neuronal firing... 

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