Mp. Vicente et Maa. Deartinano, DEMONSTRATION OF THE ALPHA-VASOCONSTRICTION-LOWERING EFFECT OF CALCIUM IN THE PITHED RAT, Journal of vascular research, 30(5), 1993, pp. 303-308
Citations number
34
Categorie Soggetti
Hematology,"Medicine, General & Internal",Physiology
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 alpha1- and alpha2-adrenoceptor stimu
lation 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 alpha1-adrenoceptor agoni
st methoxamine (10-3,000 mug/kg) and the pressor effect of the selecti
ve alpha2-adrenoceptor agonist B-HT 920 (1-1,000 mug/kg) in control ra
ts (1.24 +/- 0.01 mmol/l ionic plasma calcium) and rats treated intrap
eritoneally 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 pre
ssor effect of B-HT 920 was also significantly reduced when the increa
se in calcium levels was more marked. We have also shown that the admi
nistration of CaCl2 (8.8 mg Ca/100 g b.w. i.p.) did not alter the basa
l arterial blood pressure in the pithed rat; however, it caused an imp
ortant decrease in blood pressure when administered 20 min after begin
ning an infusion of methoxamine (50 mug/min i.v.). The results indicat
ed that the blood-pressure-lowering effect of acute calcium administra
tion is at least in part due to peripheral mechanisms which include a
reduction in the pressor responses caused by the alpha1 and alpha2 vas
cular receptor stimulation.