Compensatory Adaptation of Bicarbonate Excretion Following Acute Contralateral Kidney Exclusion in the Dog

Abstract

Changes in the excretion of bicarbonate, sodium and potassium in one kidney after exclusion (complete sudden ligation of renal pedicle) of its partner have been studied in 16 dogs undergoing bicarbonate diuresis. Fluid balance, haematocrit, plasma electrolyte and protein concentrations were maintained constant throughout the experiment. Acute contralateral renal pedicle ligation lead to an immediate increase in bicarbonate as well as water, sodium and potassium excretion by the remaining kidney. The rapid and immediate increase in the fractional and absolute rates of bicarbonate excretion was observed at varying levels of bicarbonate loading, with the greatest response occurring at the highest infusion rate. Sodium, potassium and water excretion also increased in parallel with urinary bicarbonate loss. The increase in bicarbonate exposition, glomerular filtration rate, effective renal plasma flow, aldosterone and vasopressin. In 8 sham-operated animals, no abrupt increase in sodium and bicarbonate excretion occurred despite similar continued infusion of sodium bicarbonate. It was concluded that exclusion of one kidney induces immediate adaptive excretory changes for sodium and bicarbonate in the remaining kidney, and that these changes are not accounted for by any of the known factors normally regulating sodium and bicarbonate excretion.

Role of Hemodynamic Changes in the Increased Cation Excretion after Acute Unilateral Nephrectomy in the Anesthetized Dog

“…For these reasons, it seems logical to interpret the increased cation excretion after uninephrectomy in the present studies as resulting from decreased proximal reabsorption, and increased distal delivery, of filtered sodium bicarbonate, leading to increased distal potassium secretion. Increased cation excretion, chiefly potassium, then results, accompanied presumably by bicarbonate (13). The constancy of Uc1V in these experiments is consistent with this formulation.…”

“…The delivery of significant quantities of relatively nonreabsorbable anions such as bicarbonate and sulfate accelerate potassium secretion and lead to increased UKV. In this regard, earlier studies have shown that contralateral kidney clamping causes an increase in urinary sodium bicarbonate excretion (13,15). For these reasons, it seems logical to interpret the increased cation excretion after uninephrectomy in the present studies as resulting from decreased proximal reabsorption, and increased distal delivery, of filtered sodium bicarbonate, leading to increased distal potassium secretion.…”

“…Previous studies of contralateral kidney clamping in the dog have demonstrated a significant depression of proximal tubular reabsorption without an increase in UNaV, suggesting that increased distal reabsorption occurred to prevent natriuresis (5-7). Studies in volume-expanded animals indicate that natriuresis after acute uninephrectomy is more pronounced (4,13); the present experiments were carried out in hydropenic animals, thereby minimizing the natriuretic consequences of this maneuver. As seen in Fig.…”

Prevention by vagotomy or atropine administration of the hemodynamic changes occurring after acute unilateral nephrectomy in the dog.

“…A vasopressin-mediated increase in cation excretion does not seem likely in the present studies, since similar increments were seen after AUN in intact animals and in dogs given atropine; vasopressin levels should not be affected by the administration of atropine (Schrier and Berl, 1972). In addition, the natriuretic response to AUN has been demonstrated in dogs receiving a constant infusion of ADH (Guignard and Dirks, 1976b). A possible role of other humoral factors in mediating the response has been suggested (Coe et al, 1968;Dirks and Wong, 1978).…”

“…The small increment in electrolyte excretion in the face of a large decrease in proximal reabsorption has been attributed to reabsorption in distal nephron segments of much of the increment in fluid delivered out of the proximal tubule. The predominance of increased UKV also has been interpreted as reflecting enhanced distal tubular Na + :K + exchange resulting from increased distal Na + delivery (Guignard and Dirks, 1976b;Humphreys and Ayus, 1978). The identification of a primarily proximal locus of action is remarkable in view of the renal hemodynamic findings shown in Table 2: AUN in group B dogs was accompanied by increases in filtration fraction and renal vascular resistance, changes generally associated with enhanced proximal reabsorption and decreased electrolyte excretion.…”