Effects of seasonal availability of sodium and potassium on the adrenal cortical function of a wild population of snowshoe hares, Lepus americanus

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Abstract
Snowshoe hares (Lepus americanus) collected from the Stokes Bay area of the Bruce Peninsula, Ontario appeared to inhabit a markedly Na+-deficient habitat as evidenced by low Na+ concentrations found in vegetation, precipitation, soil and water samples taken from that area. The percentage of the area of adrenal gland occupied by zona glomerulosa tissue was significantly larger in hares collected during breeding season (especially in pregnant females) than in hares collected during the winter. Preliminary studies also showed plasma aldosterone levels to be elevated in breeding females. Both observations are suggestive of an increased need for Na+ conservation and (or) K+ excretion. Plasma Na+ was depressed and plasma K+ elevated in hares collected in the summer compared with winter levels, whereas muscle Na+ and K+ did not show any age-sex or seasonally related changes. Analyses of urine and feces suggested that hares were maximally conserving Na+ while at the same time excreting excess K+.