Other Autonomic Neurotransmitters/Cotransmitters

• ATP

  • ATP and catecholamines are found together in neuronal and adrenal medullary storage granules. ATP is released along with transmitters and, in certain cases, has an important role in synaptic transmission.

• Vasoactive Intestinal Peptide (VIP)

  • Vasoactive intestinal peptide (VIP) is found in association with ACh in autonomic parasympathetic fibers innervating blood vessels and exocrine glands and cholinergic sympathetic fibers innervating sweat glands.

  • VIP may be involved in salivation, tracheal and the GI tract responsiveness to parasympathetic input.

• Neuropeptide Y Family]

  • The neuropeptide Y family includes NPY, pancreatic polypeptide, and peptide YY.

  • NPY in the periphery is associated with sympathetic fibers and assists in maintaining vascular tone.

  • NPY is a potent, long-lasting vasoconstrictor, especially of small vessels

• Purines

  • Purines such as ATP and adenosine may be responsible for apparent non-cholinergic, non-adrenergic autonomic neurotransmission.

• Nitric Oxide

  • Blood vessel endothelium is required for ACh-mediated smooth muscle relaxation.

  • The endothelial cell layer modulates vessel responsiveness to autonomic and hormonal influences.

  • Endothelial cell elaborate endothelium-derived relaxing factor (EDRF, nitric oxide) and a contracting factor.

  • Pharmacological actions of serotonin, histamine, bradykinin, purines, thrombin are mediated to some degree by stimulation of EDRF release.

  • Endothelial-released nitric oxide diffuses into vascular smooth muscle and activates guanylyl cyclase which increases cGMP.

  • Clinically, hypotension associated with endotoxemia may be mediated partially by increased release of nitric oxide. A similar mechanism is proposed for hypotension induced by cytokines.

Category: Pharmacology Notes