Renal ATPases twenty-four hours after uninephrectomy: the role of IGF-1.

We studied the effect of 24 h of uninephrectomy and somatostatin analogue, an inhibitor of growth hormone secretion, in microdissected nephron segment H-ATPase, H-K ATPase and Na-K ATPase activities. Systemic acid-base status, plasma and tissue electrolytes, and aldosterone levels in the uninephrectomized rats were similar to controls. Uninephrectomy increased fractional sodium, potassium, and bicarbonate excretion (p < 0.05). After 24 h the solitary kidney weighted the same as the single kidney from sham-operated controls. Protein content of the microdissected nephron segments studied enzymatically did not differ from control. Insulin-like growth factor-1 (IGF-1) levels in plasma and kidney were also similar. By contrast, ATPase values in uninephrectomized animals were markedly elevated: H-ATPase was increased by 91 +/- 5% in proximal convoluted tubule (PCT) (p < 0.005), 65 +/- 3% in medullary thick ascending limb of Henle's loop (MTAL) (p < 0.01), 92 +/- 9% in cortical collecting tubule (CCT) (p < 0.005), and 94 +/- 8% in medullary collecting tubule (MCT) (p < 0.005). In these same animals, H-K ATPase activity was also increased: 88 +/- 6% in CCT (p < 0.005) and 92 +/- 5% in MCT (p < 0.005). Uninephrectomy also decreased Na-K ATPase activity in PCT, MTAL and CCT, but enzyme activity in MCT remained unchanged. Somatostatin analogue administration to animals with one kidney had no effect on metabolic parameters or plasma and kidney IGF-1 concentrations nor did it prevent the alterations in renal ATPase activities observed with uninephrectomy done. The analogue alone had no effect in control animals. While the mechanisms responsible for the increase in renal ATPases seen after uninephrectomy are not known, they are independent of aldosterone, potassium, or IGF-1.