PATHOLOGY

Detailed explanation-1: -Conclusions: Histamine can produce vasodilation of submucosal arterioles by two distinct mechanisms: activation of vascular H1 receptors resulting in release of nitric oxide from endothelium and activation of H3 receptors on sympathetic nerve terminals resulting in presynaptic inhibition of vasoconstrictor tone.

Detailed explanation-2: -Histamine (HA) is a potent mediator in many physiological processes: it causes vasodilation or vasoconstriction, stimulates heart rate and contractility, and contraction of smooth muscles in the intestine and airways.

Detailed explanation-3: -The H1 histamine receptor plays an important role in allergic response and is widely distributed throughout the peripheral nervous system, particularly the smooth muscle, where its activation causes vasoconstriction.

Detailed explanation-4: -Histamine causes constriction of various smooth muscles with the bronchioles being most sensitive to its effects.

Detailed explanation-5: -Histamine mediates vasodilation during inflammatory and immune responses, as well as following endurance exercise. During exercise, intramuscular histamine concentration increases, and its production, appears related to exercise intensity and duration.