Potassium, magnesium, insulin, glucagon and glucose interrelationships in ruminant hypomagnesemia

Effects of hyperkalemia and hypomagnesemia on insulin, glucagon, potassium (K), magnesium (Mg) and calcium (Ca) were investigated in calves. Glucose clearance studies without and with KCl infusion were conducted in normomagnesemic and hypomagnesemic calves fed adequate or excess K. Following glucose injection, insulin release and glucose clearance constants were greater (P<.001) in hypomagnesemic than in normomagnesemic calves. When KCl was infused, insulin response was greater (P<.001) and glucagon levels increased (P<.001) during the third and fourth hour following glucose injections. Without KCl infusion, K levels dropped (P<.05) during insulin elevations, while drops (P<.05) in Mg occurred in normomagnesemic calves fed excess K. Experiments were also conducted in normomagnesemic and hypo magnesemic calves to determine effects of KCl infusions on glucose, insulin, glucagon, K, Mg and Ca fluxes across the portal-drained visceral, hepatic and hindlimb tissues. Increased (P<.001) arterial K was accompanied by increased arterial insulin and glucagon and decreased arterial glucose. Elevated (P<.001) insulin was associated with increased portal-drained visceral production (P<.01). In hypo magnesemic calves, peripheral insulin was higher (P<.001); however, increased portal-drained visceral production in hypomagnesemic calves was not significant. Increased (P<.001) arterial glucagon was apparently due to decreased (P<.10) hepatic extraction ratio in both groups of calves and concomitant nonsignificant increases in portal-drained visceral production. Peripheral glucagon was lower (P<.001) in hypomagnesemic calves and portal-drained visceral production was lower (P<.10). Drops (P<.001) in peripheral glucose occurred in both groups of calves; however, changes in glucose flux were not significant. Portal-drained visceral K release decreased (P<.05) while hindlimb K removal and extraction ratio increased (P<.001) Tissue fluxes of Ca and Mg were unaffected.