title: Mechanisms of the enhanced contractile response to phenylephrine in thoracic aorta isolated from rats with dietary magnesium deficiency.
abstract: The mechanisms underlying the enhanced contractile response to phenylephrine (PE) and increased susceptibility to nifedipine of de-endothelialized thoracic aorta isolated from rats with dietary magnesium deficiency (Mg-deficient rats) were examined by functional and radioligand binding studies. Enhanced PE-induced contractions and increased susceptibility to nifedipine in Mg-deficient rats were not observed in the presence of 10 microM H7. PE significantly decreased the KD value without changing Bmax in the binding of [3H]PN200-110 to de-endothelialized aortic strips. The KD value obtained in the Mg-deficient rats was significantly smaller than that in the controls. Nifedipine displaced the binding of [3H]PN200-110 concentration-dependently, and the pKi value in Mg-deficient rats was significantly larger than that in the controls. A combination of PE and H7 abolished this difference. These results indicate that the modulation of L-type Ca2+ channels via the stimulation of alpha 1-adrenoceptors may be involved in the enhancement of vasoconstriction and increased susceptibility to nifedipine in aortas isolated from Mg-deficient rats. The H7-sensitive mechanisms may play an important role in these phenomena.
authors.affiliation: Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sakaguchi
authors.forename: A
authors.initials: A
authors.lastname: Nishio
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000378:metabolism; D004032:Diet; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000494:pharmacology; D017275:Isradipine / Q000378:metabolism; D008275:Magnesium Deficiency / Q000503:physiopathology*; D008297:Male; D009543:Nifedipine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D007546:Isoquinolines; D010879:Piperazines; D010656:Phenylephrine; D011189:Potassium Chloride; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D009543:Nifedipine; D017275:Isradipine