title: Demonstration of the alpha-vasoconstriction-lowering effect of calcium in the pithed rat.
abstract: The mechanism by which calcium administration causes hypotension still remains to be explained. In this paper we have studied the alteration of the pressor effect caused by alpha 1- and alpha 2-adrenoceptor stimulation in the pithed rat after increasing the calcium plasma levels of the rats with an intraperitoneal administration of CaCl2. We compared the vasoconstrictor effect of the selective alpha 1-adrenoceptor agonist methoxamine (10-3,000 micrograms/kg) and the pressor effect of the selective alpha 2-adrenoceptor agonist B-HT 920 (1-1,000 micrograms/kg) in control rats (1.24 +/- 0.01 mmol/l ionic plasma calcium) and rats treated intraperitoneally with CaCl2 that had 1.89 +/- 0.04 or 3.03 +/- 0.11 mmol/l ionic plasma calcium. The pressor effect of methoxamine was noticeably less after both of the increases in ionic plasma calcium, and the pressor effect of B-HT 920 was also significantly reduced when the increase in calcium levels was more marked. We have also shown that administration of CaCl2 (8.8 mg Ca/100 g b.w. i.p.) did not alter the basal arterial blood pressure in the pitched rat; however, it caused an important decrease in blood pressure when administered 20 min after beginning an infusion of methoxamine (50 micrograms/min i.v.). The results indicated that the blood-pressure-lowering effect of acute calcium administration is at least in part due to peripheral mechanisms which include a reduction in the pressor responses caused by the alpha 1 and alpha 2 vascular receptor stimulation.
authors.affiliation: Departamento de Farmacología, Facultad de Medicina, Universidad Complutense, Madrid, España.
authors.forename: M
authors.initials: M
authors.lastname: Puerro Vicente
authors.forename: M A
authors.initials: MA
authors.lastname: Aleixandre de Artiñano
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002118:Calcium / Q000097:blood / Q000494:pharmacology*; D002122:Calcium Chloride / Q000494:pharmacology; D003655:Decerebrate State; D007274:Injections, Intraperitoneal; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D008729:Methoxamine; D002122:Calcium Chloride; D002118:Calcium