title: Magnesium-neurohypophyseal hormone interactions in contraction of vascular smooth muscle.
abstract: The contractile responses of helically cut rat aortic strips to neurohypophyseal hormones and synthetic analogues in the presence and absence of 1.2 mM external magnesium ions [Mg++]o was studied. These experiments demonstrate that 1) [Mg++]o potentiates the contractile actions of a variety of neurohypophyseal peptides on vascular smooth muscle. 2) [Mg++]o can alter both the ED50s (i.e., hormone-receptor affinities) and intrinsic activities (or maximum contractile responses) of these molecules on vascular muscle. 3) The amino acid moieties in positions 1, 2, 3, and 8 of the vasopressin molecule interact, differentially, with [Mg++] to produce contraction of vascular muscle. 4) The length of the side chain, and basicity, in position 8 of the vasopressin molecule are probably important in Mg potentiation in mammalian vascular muscle. 5) Interaction of Mg with an aromatic group in position 3 might be critical for potency of vasopressin hormones of mammalian vascular muscle; the ED50 for oxytocin is not shifted to lower concentrations in the presence of [Mg++]o. Collectively, these data suggest that Mg probably acts at more than one site in vascular smooth muscle in the production of neurohypophyseal peptide-activated contractions. In addition, the present findings indicate that the Mg dependence of these peptides on at least one vascular muscle, rat aorta, is a direct function of the rat pressor potency of the molecules.
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001127:Arginine Vasopressin / Q000494:pharmacology; D001665:Binding Sites; D003894:Deamino Arginine Vasopressin / Q000494:pharmacology; D004357:Drug Synergism; D066298:In Vitro Techniques; D007700:Kinetics; D008236:Lypressin / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D010121:Oxytocin / Q000494:pharmacology; D051381:Rats; D011955:Receptors, Drug; D013329:Structure-Activity Relationship; D014666:Vasomotor System / Q000187:drug effects*; D014667:Vasopressins / Q000031:analogs & derivatives / Q000494:pharmacology*
chemical_list: D011955:Receptors, Drug; D014667:Vasopressins; D001127:Arginine Vasopressin; D010121:Oxytocin; D008236:Lypressin; D003894:Deamino Arginine Vasopressin; D008274:Magnesium