M. Ezimokhai et al., PREGNANCY-INDUCED ALTERATIONS OF RELAXATION IN RESPONSE TO MAGNESIUM IN THE RAT AORTA MAY BE DUE TO PLASMA-BORNE AGENTS, Heart and vessels, 10(4), 1995, pp. 197-203
The influence of plasma from pregnant and nonpregnant humans was exami
ned, using magnesium-induced relaxation of precontracted rat aortic ri
ngs. The results showing magnesium-induced relaxation of aortic rings
from pregnant and nonpregnant rats were compared. In rat aortic rings
incubated in plasma from pregnant patients, magnesium was more potent
in relaxing the precontractions induced by potassium chloride than in
relaxing-those induced by phenylephrine. The magnesium-induced relaxat
ion of rings incubated in plasma from normal pregnant subjects was sim
ilar to that in unincubated rings from normal pregnant rats. Neither t
he removal of endothelium nor pretreatment with indomethacin affected
the pattern of responses in the rings. The results suggest that the ef
fects of pregnancy on magnesium-induced relaxation of the rat aorta ma
y be mediated by plasma-borne agents, and the mechanisms by which the
agents alter the relaxation do not involve either the vascular endothe
lium or prostaglandin synthesis.