Functional similarities of hepatic cystic and biliary epithelium: studies of fluid constituents and in vivo secretion in response to secretin.

Hepatic cysts are a frequent manifestation of autosomal dominant polycystic kidney disease, but little is known about their functional characteristics. The goals of our study were to define the composition of hepatic cyst fluid and to determine whether hepatic cysts secrete in response to intravenously administered secretin. We percutaneously punctured five hepatic cysts and one proximal renal cyst from six subjects with autosomal dominant polycystic kidney disease and one solitary hepatic cyst from a subject without autosomal dominant polycystic kidney disease. Most fluids had an electrolyte composition similar to serum. Fluid from all hepatic cysts had glutamyltranspeptidase concentrations above those found in serum [( cyst]/[serum] = 4.93 +/- 5.92), contained secretory component (the epithelial receptor for polymeric IgA) and had glucose concentrations less than 15 mg/dl. Fluid from both hepatic and renal cysts of subjects with autosomal dominant polycystic kidney disease, but not from the subject with the solitary hepatic cyst, demonstrated extensive changes in the electrophoretic mobility of several serum proteins. Initial intracystic pressures ranged from 16 to 40 cm H2O, were reduced 57% to 97% after aspiration of a portion of cyst fluid and were held constant during the secretion study. Within 8 min of the intravenous administration of secretin, secretion of fluid increased in two of three hepatic cysts and in the renal cyst. The electrolyte composition of cyst fluids was not altered by secretin. These data suggest that hepatic cystic epithelium has functional characteristics of biliary epithelium and that secretion by both hepatic and renal cysts may be hormonally regulated.

Ultrastructure and function of cysts from human adult polycystic kidneys.

Twenty cysts from five patients with adult polycystic kidney disease were evaluated morphologically by electron microscopy and functionally by cyst fluid chemical analysis in order to correlate the structure with the function of the cyst wall. Thirteen proximal cysts, as defined by cyst fluid/serum sodium ratios of 0.8 to 1.2, were lined by epithelial cells with open or short closed apical junctions that appeared permeable to lanthanum. In contrast, seven distal cysts, as defined by cyst fluid/serum sodium ratios of less than 0.4, were lined by epithelial cells with long closed apical junctions that appeared impermeable to lanthanum. Cell organelles showed no distinction between proximal and distal cysts. Cyst basement membranes appeared abnormal, but there was no consistent pattern. The fluid of proximal cysts contained lower creatinine, potassium, and hydrogen ion, and higher chloride concentrations than did the distal cysts. These studies provide morphologic and chemical evidence consistent with te view that cysts originate from nephrons. Moreover, the maintenance of the epithelial lining and transmembrane solute gradients over many years extending up to and beyond the development of renal insufficiency suggests that the cysts function as nephronsthrughout the life of the patient.

Fluid turnover in renal cysts.

Cystic puncture was performed percutaneously in 18 patients with solitary renal cysts and in 22 with multiple, congenital renal cysts. With the aid of tritiated water it was possible to estimate the fluid turnover in the cysts and compare it with their volume, pressure and potassium and creatinine levels. Fluid turnover was rapid in all the renal cysts. Two to five hours after i.v. injection of tritium, the tritium concentration in cystic fluid averaged 88% of the concentration in plasma fluid in patients with polycystic kidneys and 73 percent in patients with solitary cysts. Fluid turnover was more rapid in small than in large cysts, but there was no such difference between cysts with high and low pressure. It is possible that the fluid turnover was slightly faster in cysts with high potassium and creatinine levels than in those with low levels. The results show that the fluid turnover in a renal cyst of 10 ml is considerable--probably more than 100 ml/24 hours. This indicates that fluid inflow to the cyst comes mainly from cells in the cyst wall and not from a single glomerule. Fluid probably leaves the cyst actively via cells in the cyst wall, since the fluid turnover does not increase with high cyst pressure. The fluid turnover is probably secondary to the active solute transportation, which is performed by the cyst cells. This means that these cells have a tubular cell-like function and should respond to pharmacotherapy.