Alpha-1 adrenergic receptor

The α1 -adrenoceptors are Gq/11-Protein-gekoppelte receptors that are activated by the signal substances adrenaline and noradrenaline. They are divided on the basis of their pharmacological properties into four subtypes: alpha1A, α1B, α1D and " α1L ". During the first three subtypes on the genomic level embody separate receptors that " α1L " -adrenoceptor seems only represent a Konformationsvariante of alpha1A subtype.

Occurrence and function

α1 -adrenoceptors are a high density in the central nervous system, in the sympathetically innervated tissues, in the salivary glands, in particular in the cardiovascular system and in the urogenital tract as well as in the liver before. The stimulation of smooth muscle α1 -adrenoceptors in blood vessels ( subtypes A, B and D) leads to vasoconstriction induced by increased blood pressure. A contraction of the organs of the urogenital tract (eg prostate and internal sphincter ) is mediated by smooth muscle α1A/L-Adrenozeptoren and thus results, for example for urinary retention. Their importance in the central nervous system, however, is largely unexplored.

Pharmacology

α1 - adrenoceptor agonists: α1 - adrenoceptor agonists stimulate sympathetic α1 -adrenoceptors. They are systemic or topical (local) used to vasoconstriction:

• Phenylephrine, oxedrine and the prodrug midodrine in the treatment of orthostatic hypotension
• Phenylephrine, oxymetazoline and naphazoline for decongestion of the nasal mucosa or with conjunctivitis

α1 - adrenoceptor antagonists ( subset of alpha blockers): α1 - adrenoceptor antagonists inhibit induced by epinephrine and norepinephrine effects and thus be used therapeutically:

• Prazosin, doxazosin, terazosin, alfuzosin and urapidil for treatment hypertonaler blood pressure disturbances
• Tamsulosin is a selective α1A/L-Antagonist and, since it does not cause Kreislauf-/Blutdruckbeeinflussung and orthostatic problems and dizziness, specifically used for the symptomatic treatment of benign prostatic hyperplasia.

Signal transduction

α1 receptors lead via activation of phospholipase C to form the second messenger inositol trisphosphate (IP3 ) and diacylglycerol (DAG ).

IP3 releases Ca2 release from the endoplasmic reticulum, which binds to calmodulin and troponin et al. DAG influenced via the activation of protein kinase C, the activity of other proteins.