Administration of adrenomedullin into subfornical organ inhibits Na(+),K(+)-ATPase activity in single proximal renal tubule of rats.
The present study was designed to investigate the effect of administration of adrenomedullin (ADM) into subfornical organ (SFO) on renal tubular Na(+),K(+)-ATPase activity in rats. Rats under anesthesia were injected with ADM 0.1 mL (20 ng/mL) via an implanted cannula into SFO (n=6). Plasma ADM and serum endogenous digitalis-like factor (EDLF) levels were assayed with radioimmunoassay, and urine samples were collected via a canoula intubated in bladder. Urinary sodium concentration was assayed with flame spectrophotometry. Single proximal renal tubule segments were obtained by hand under stereomicroscope and its Na(+),K(+)-ATPase activity was measured by liquid scintillation counting. In addition, single proximal renal tubule segments from normal rats (n=6) were incubated with serum from animals administered with ADM into SFO, and then the Na(+),K(+)-ATPase activity was determined. The results showed that both urinary volume and sodium excretion amounted to the peak value at 30 min after ADM administration, and sustained a significant high level at 60 min (P<0.01). At 30 min after ADM administration, there was a significant increase in serum EDLF and a decrease in Na(+),K(+)-ATPase activity of proximal tubule (P<0.01, respectively), but not in plasma ADM level. Na(+),K(+)-ATPase activity was decreased significantly in single proximal renal tubule segments from normal rats incubated with serum from rats administered with ADM into SFO (P<0.01). These results suggest that the diuretic and natriuretic responses following administration of ADM into SFO are associated with the inhibition of renal tubule Na(+),K(+)-ATPase activity. The inhibition of renal tubule Na(+),K(+)-ATPase activity is related to the increase in the serum level of EDLF.
Gao
Yuan
Y
Department of Physiology, Zunyi Medical College Zhuhai Campus, Zhuhai 519041, China. gy60211@yahoo.com.cn
Li
Xing-Qi
XQ
D053607:Adrenomedullin / Q000494:pharmacology*; D000818:Animals; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000201:enzymology; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013356:Subfornical Organ
D053607:Adrenomedullin; D000254:Sodium-Potassium-Exchanging ATPase