RENAL ATPASES 24 HOURS AFTER UNINEPHRECTOMY - THE ROLE OF IGF-1

We studied the effect of 24 h of uninephrectomy and somatostatin analo gue, an inhibitor of growth hormone secretion, in microdissected nephr on segment H-ATPase, H-K ATPase and Na-K ATPase activities. Systemic a cid-base status, plasma and tissue electrolytes, and aldosterone level s in the uninephrectomized rats were similar to controls. Uninephrecto my increased fractional sodium, potassium, and bicarbonate excretion ( p<0.05). After 24 h the solitary kidney weighed the same as the single kidney from sham-operated controls. Protein content of the microdisse cted nephron segments studied enzymatically did not differ from contro l. Insulin-like growth factor-1 (IGF-1) levels in plasma and kidney we re also similar. By contrast, ATPase values in uninephrectomized anima ls were markedly elevated: H-ATPase was increased by 91+/-5% in proxim al convoluted tubule (PCT) (p<0.005), 65+/-3% in medullary thick ascen ding limb of Henle's loop (MTAL) (p<0.01), 92+/-9% in cortical collect ing 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). Unin ephrectomy also decreased Na-K ATPase activity in PCT, MTAL and CCT, b ut enzyme activity in MCT remained unchanged. Somatostatin analogue ad ministration to animals with one kidney had no effect on metabolic par ameters or plasma and kidney IGF-1 concentrations nor did it prevent t he 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 un inephrectomy are not known, they are independent of aldosterone, potas sium, or IGF-1.