Multiple α1-adrenergic receptor subtypes support synergistic stimulation of vasopressin and oxytocin release by ATP and phenylephrine

Song Z, Gomes DA, Stevens W, Sladek CD. Multiple alpha(1)-adrenergic receptor subtypes support synergistic stimulation of vasopressin and oxytocin release by ATP and phenylephrine. Am J Physiol Regul Integr Comp Physiol 299: R1529-R1537, 2010. First published September 29, 2010; doi:10.1152/ajpregu.00532.2010.-Simultaneous exposure of explants of the hypothalamo-neurohypophyseal system (HNS) to ATP and the alpha(1)-adrenergic receptor (alpha(1)-R) agonist, phenylephrine (ATP + PE) induces a synergistic stimulation of vasopressin and oxytocin (VP/OT) release that is sustained for hours (23). The current studies confirm that the synergism is dependent upon activation of alpha(1)-R by demonstrating that an alpha(1)-R antagonist prevents the response. The role of the alpha(1)A, B, and D-adrenergic receptor subtypes in the synergistic effect of ATP + PE on intracellular calcium ([Ca2+](i)) in supraoptic nucleus (SON) neurons and VP/OT release from neural lobe was evaluated. The increase in [Ca2+](i) induced by PE in SON predominantly reflects release from intracellular stores and is mediated by activation of the alpha(1)A adrenergic receptor subtype. The alpha(1)A subtype is also required for the sustained elevation in [Ca2+](i) induced by ATP + PE. In contrast, although synergistic stimulation of VP/OT release was eliminated by removal of PE and was blunted by benoxathian, an alpha(1)-R antagonist that is not subtype selective, no single alpha(1)-R subtype selective antagonist prevented sustained stimulation of VP/OT release by ATP + PE. Thus, sustained activation of alpha(1)-R is essential for the synergistic VP and OT response to ATP + PE, but multiple alpha(1)-R subtypes can support the response. Redundancy amongst the alpha(1)-R subunits in supporting this response is consistent with the predicted importance of the response for sustaining the elevated VP release required to prevent cardiovascular collapse during hemorrhage and sepsis.