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Histamine has two basic centres, namely the aliphatic amino group and whichever nitrogen atom of the imidazole ring does not already have a proton. Under physiological conditions, the aliphatic amino group (having a pK a around 9.4) will be protonated, whereas the second nitrogen of the imidazole ring (pK a ≈ 5.8) will not be protonated. [11]
Histidine decarboxylase is the primary biological source of histamine. Histamine is an important biogenic amine that moderates numerous physiologic processes. There are four different histamine receptors, H 1, H 2, H 3, and H 4, [16] each of which carries a different biological significance.
[1] [2] Histamine is a neurotransmitter involved in various physiological processes. There are four main types of histamine receptors: H1, H2, H3, and H4. H1 receptors are linked to allergic responses, H2 to gastric acid regulation, H3 to neurotransmitter release modulation, and H4 to immune system function. There are four known histamine ...
Gymnema sylvestre [1] is a perennial woody vine native to Asia (including the Arabian Peninsula), Africa and Australia. It has been used in Ayurvedic medicine.Common names include gymnema, [2] Australian cowplant, and Periploca of the woods, and the Hindi term gurmar, which means "sugar destroyer".
Hyoscyamine can be extracted from plants of the family Solanaceae, notably Datura stramonium. As hyoscyamine is a direct precursor in the plant biosynthesis of hyoscine, it is produced via the same metabolic pathway. [18] The biosynthesis of hyoscine begins with the decarboxylation of L-ornithine to putrescine by ornithine decarboxylase (EC 4.1 ...
Mouse-models and other research demonstrated that reducing histamine concentration in the H3R causes tics, but adding histamine in the striatum decreases the symptoms. [ 22 ] [ 23 ] [ 24 ] The interaction between histamine (H3-receptor) and dopamine as well as other neurotransmitters is an important underlying mechanism behind the disorder.
The histamine receptor H 2 belongs to the rhodopsin-like family of G protein-coupled receptors. It is an integral membrane protein and stimulates gastric acid secretion. It also regulates gastrointestinal motility and intestinal secretion and is thought to be involved in regulating cell growth and differentiation. [ 6 ]
Histamine also promotes angiogenesis. [6] Antihistamines suppress the histamine-induced wheal response (swelling) and flare response (vasodilation) by blocking the binding of histamine to its receptors or reducing histamine receptor activity on nerves, vascular smooth muscle, glandular cells, endothelium, and mast cells.