Ornipresín CAS:3397-23-7

Ornipresín je syntetický derivát vazopresínu (arginín-8-vazopresín) v ktorej je ornitín nahradený arginínom v 8 pozíciu. Zásaditosť aminokyselinového zvyšku v polohe 8 molekuly vazopresínu určuje jeho presorický a antidiuretický účinok. Ornitín, sú menej zásadité a aminokyseliny s krátkym reťazcom, znižuje väzbu ornipresínu na receptory v distálnom tubule nefrónu bez narušenia jeho väzby na receptory hladkého svalstva ciev, ktoré sprostredkúvajú vazokonstrikciu. Teda, ornipressin has minimal antidiuretic activity whilst maintaining equipotent vasoconstrictor activity as the natural hormone, vasopressin.

Ornipressin, which has a high affinity for V_1A receptory , activates Gs proteins, which stimulate phospholipase C and result in a breakdown of membrane lipids to inositol triphosphate (IP₃) and diacylglycerol (DAG); IP₃ releases calcium from the endoplasmic reticulum, thus increasing cytosolic calcium, while DAG activates protein kinase C which phosphorylates cellular proteins. This cascade of biochemical reactions leads to sustained vasoconstriction. Avšak, at high concentrations (>0.1 IU mL⁻¹), ornipressin binds to the V₂ receptors when the V_1A receptors are fully saturated. Activation of V₂ receptors results in an increase in cyclic AMP which leads to vasodilatation, a paradoxical effect demonstrated by Fruhstorfer and Heisler.