Factors that trigger<unk>  can be exogenous or endogenous in origin. Ambient temperature is an example of exogenous<unk> . Cutaneous<unk>  will occur because of the body's exposure to the severe cold. Examples of endogenous factors include the autonomic nervous system, circulating hormones, and intrinsic mechanisms inherent to the vasculature itself (also referred to as the myogenic response). Examples Examples include stimulants, amphetamines, and antihistamines. Many are used in medicine to treat hypotension and as topical decongestants. Vasoconstrictors are also used clinically to increase blood pressure or to reduce local blood flow. Vasoconstrictors mixed with local anesthetics are used to increase the duration of local anesthesia by constricting the blood vessels, thereby safely concentrating the anesthetic agent for an extended duration, as well as reducing hemorrhage. The routes of administration vary. They may be both systemic and topical. For example, pseudoephedrine is taken orally and phenylephrine is topically applied to the nasal passages or eyes. Examples include: Vasoconstrictors 25I-NBOMe Amphetamines AMT Antihistamines Caffeine Cocaine DOM Ergometrine LSA LSD Methylphenidate Mephedrone Naphazoline Oxymetazoline Phenylephrine Propylhexedrine Pseudoephedrine Stimulants Tetrahydrozoline hydrochloride (in eye drops) Endogenous<unk>  is a procedure of the body that averts orthostatic hypotension. It is part of a body negative feedback loop in which the body tries to restore homeostasis (maintain constant internal environment). For example,<unk>  is a hypothermic preventative in which the blood vessels constrict and blood must move at a higher pressure to actively prevent a hypoxic reaction. ATP is used as a form of energy to increase this pressure to heat the body. Once homeostasis is restored, the blood pressure and ATP production regulates.<unk>  also occurs in superficial blood vessels of warm-blooded animals when their ambient environment is cold; this process diverts the flow of heated blood to the center of the animal, preventing the loss of heat. Vasoconstrictor Receptor (↑ = opens. ↓ = closes) On vascular smooth muscle cells if not otherwise specified Transduction (↑ = increases. ↓ = decreases) Stretch ↑Stretch-activated ion channels depolarization --> * open VDCCs (primarily) --> ↑intracellular Ca2+ * ↑Voltage-gated Na+ channels --> * more depolarization --> open VDCCs --> ↑intracellular Ca2+ * ↓Na+-Ca2+ exchanger activity --> ↑intracellular Ca2+ ATP (intracellular) ↓ATP-sensitive K+ channel ATP (extracellular) ↑P2X receptor ↑Ca2+ NPY NPY receptor Activation of Gi --> ↓cAMP --> ↓PKA activity --> ↓phosphorylation of MLCK --> ↑MLCK activity --> ↑phosphorylation of MLC (calcium-independent) adrenergic agonists e.g., epinephrine, norepinephrine, and dopamine ↑α1 adrenergic receptor Activation of Gq --> ↑PLC activity --> ↑IP3 and DAG --> activation of IP3 receptor in SR --> ↑intracellular Ca2+ thromboxane ↑thromboxane receptor endothelin ↑endothelin receptor ETA angiotensin II ↑Angiotensin receptor 1 * On smooth muscle cells: Activation of Gq --> ↑PLC activity --> ↑IP3 and DAG --> activation of IP3 receptor in SR --> ↑intracellular Ca2+ * On endothelium: endothelin synthesis open VDCCs --> ↑intracellular Ca2+ Reduced production of nitric oxide Antidiuretic hormone (ADH or Vasopressin) Arginine vasopressin receptor 1 (V1) on smooth muscle cells Activation of Gq --> ↑PLC activity --> ↑IP3 and DAG --> activation of IP3 receptor in SR --> ↑intracellular Ca2+ Arginine vasopressin receptor on endothelium Endothelin production * Products of platelet activation * Endotoxin * Thrombin * insulin * Hypoxia * Low shear stress Various receptors on endothelium Endothelin production
Vasoconstriction
Vasodilation
Osteostimulation
Vasoactivity
Cytostasis
Lymphangiogenesis
Nociception
Vascular recruitment