Assessment of the effects of endothelin-1 and magnesium sulphate on regional blood flows in conscious rats, by the coloured microsphere reference technique

1 There is evidence to suggest that magnesium (Mg2+) is beneficial in the t reatment of a number of conditions, including pre-eclampsia and acute myoca rdial infarction. The mode of action of Mg?; in these conditions is not cle ar, although the vasodilator properties of Mg2+ are well documented both in vitro and in vivo. 2 Previously, we demonstrated that i.v. infusion of magnesium sulphate (MgS O4) alone, or in the presence of vasoconstrictors, caused increases in flow and conductance in the common carotid, internal carotid and hindquarters v ascular beds, in conscious rats. Therefore, the objective of the present st udy was to investigate the regional and subregional changes in haemodynamic s in response to the vasoconstrictor peptide endothelin-l (ET-1) and MgSO4 in more detail, using the coloured microsphere reference technique. 3 Infusion of ET-1 and MgSO4 had similar effects on heart rate and mean art erial pressure as in our previous study. Infusion of ET-I caused a rise in mean arterial pressure and a fall in heart rate, and infusion of MgSO4 retu rned mean arterial pressure to control levels with no effect on heart rate. 4 The responses to MgSO4 in the presence of ET-1 showed considerable region al heterogeneity with blood flow increasing (e.g. skeletal muscle), decreas ing (e.g. stomach) or not changing (e.g. kidney). Of particular interest wa s the finding that MgSO4 caused increases in flow in the cerebral and coron ary vascular beds. 5 This, and our previous studies, have shown that MgSO4 can reverse vasocon striction in a number of vascular beds, and indicate that this compound may have therapeutic benefit in conditions associated with vasospasm.