Renal Na-K-ATPase hyperactivity in diabetic Psammomys obesus is related toglomerular hyperfiltration but is insulin-independent

Psammomys obesus, a desert rodent, develops diabetes when displaced from it s natural environment and fed a high energy diet in the laboratory. This st udy was designed to examine variations in renal function in relation to the diabetic state with emphasis on changes in Na-K-ATPase activity. The following groups of Psammomys were studied: (1) Animals fed a saltbush diet; a low energy/high salt diet (natural). (2) Animals fed a low energy/l ow salt diet (laboratory). Both 1 and 2 were normoglycemic and normoinsulin emic and thus served as control. (3) Animals fed a high energy diet (group C) who were hyperglycemic and hyperinsulinemic; this group was divided into two subgroups: C1 presented with glomerular hyperfiltration rate and C2 wi th glomerular hypofiltration rate. (4) Animals fed a high energy diet prese nting with hyperglycemia-hypoinsulinemia (group D). (5) Group D+I, similar to group D but treated with external insulin (2 U/24 h). Groups D and C1, whose glomerular filtration rose above normal by 30% and 7 0% respectively, exhibited metabolic similarity to Type I and Type II diabe tes. In these groups, Na-K-ATPase activity in the cortex increased by 80-10 0% and in the medulla by 180% (P<0(.)001 vs control). In group C2 with redu ced glomerular filtration rate (GFR), Na-K-ATPase activity did not differ f rom control. In group D+I, with normalized glomerular filtration rate, Na-K -ATPase activity was similar to control. There was a linear and significant correlation between GFR and Na-K-ATPase activity both in the cortex and in the medulla. These experiments present a well defined animal model of diabetes mellitus. Variations in glucose and in insulin did not correlate with Na-K-ATPase ac tivity. These results clearly demonstrated that Na-K-ATPase activity in the diabetic Psammomys was determined by glomerular filtration but was indepen dent of plasma glucose or insulin levels.