Calcium in rat peripheral nerve during chronic alterations in plasma calcium

The calcium content in desheathed tibial nerve was compared to that in cerebellum in rats fed diets containing either 0.01% (low), 0.67% (control) or 3.0% (high) Ca, for 8 weeks. For changes in concentration of plasma ionized Ca, 48% below and 35% above the control mean, percent change in endoneurial Ca content is linearly related, with a slope of 0.80, to percent change in plasma ionized Ca. A line with a slope of 0.21 describes the relation between percent change in cerebellum Ca and percent change in plasma ionized Ca. Plasma, cerebellum and nerve concentrations of Na, K and Cl were similar in the control compared with the two experimental groups of animals. The concentration of plasma Mg varied 20% below and 17% above the control mean, inversely with plasma Ca, but nerve and cerebellum Mg did not change from control values. The results of this study fail to demonstrate Ca homeostasis in rat peripheral nerve endoneurium during chronic hypo- and hypercalcemia. Endoneurial Mg, however, appears to be regulated.