The effect of magnesium deficiency on volatile anaesthetic requirement in the rat: the role of central noradrenergic neuronal activity

Volatile anaesthetic, minimum alveolar concentration (MAC, a measure of ana esthetic requirement) increased in a time-dependent manner in rats fed a Mg 2+-deficient diet. MAC values in hypomagnesemic rats were 22-30 per cent gr eater than those in age-matched controls at 12 and 17 days after starting t he diet (p<0.01). Noradrenergic neuronal activity, as assessed from the rat io of the concentration of 3,4-dihydroxyphenylethylene-glycol (DHPG) to tha t of norepinephrine (NE), decreased in the brain stem and cerebrum-cerebell um in hypomagnesemic rats owing to an increase in NE concentration in both regions of the brain (p<0.025). We conclude that prolonged hypomagnesemia. (greater than or equal to 12 days) increases volatile anaesthetic MAC in th e rat. The concomitant decrease in the ratio of DHPG/NE suggests that this increase in MAC cannot be attributed to an increase in noradrenergic neuron al activity in brain.