Biomedical Sciences ETDs

Publication Date

5-10-1977

Abstract

Ever since the first demonstration that the concentration of bicarbonate ion in mammalian pancreatic juice increased and chloride ion concentration decreased with increased secretory rate (Gamble and McIver 1928), investigators have tried to determine what process or processes account for these observations. Because the pancreas has a definite anatomical organization, there is the potential for modification of a primary secretion as fluid flows through the duct system. Three model systems have been suggested for the composition of the final secretion: 1) Anion exchange; 2) Admixture; and 3) Unicellular. Studies have been conducted to test the validity of these model systems but little critical information has been forthcoming which would permit one to distinguish between these plausible alternatives. The problem has been the inability to determine the concentrations of various secretion constituents (H+, HCO3-. C1-) at specific sites in the ductal system. The techniques of renal micropuncture have been adapted and applied to the study of electrolyte secretion in the extralobular ductal system of the in vivo rabbit pancreas. Samples of pancreatic juice collected from ductules were analyzed for chloride ion and compared with simultaneously collected main duct juice. A new glass­membrane pH-microelectrode has been tested for specificity and accuracy in the measurement of H+ in solutions containing sodium, phosphate, bicarbonate and protein, These microelectrodes have been used to measure in situ pH in the pancreas ductal system. A modified version of a pCO2- electrode has been evaluated and used to measure ductal pCO2 values. Bicarbonate ion concentration of ductal fluid was calculated from in situ measurements with pH and pCO2-microelectrodes using the Henderson­Hasselbalch equation. pKa values of carbonic acid in pancreatic juice were calculated and compared to known values in serum. The glass-membrane pH­microelectrode shows no significant sensitivity to sodium, protein, phosphate or bicarbonate nor did these substances induce a change in the sensitivity of the electrode to the hydrogen ion. Evaluation of the in vivo rabbit pancreas preparation revealed that the juice flow rate was equal to or greater than flow rates observed by other investigators. Ductal fluid chloride ion concentration during spontaneous secretion was about 78 mEq/L and did not vary significantly with ductal size. During secretin-stiffiulated secretion this value was decreased to near 58 mEq/L in all ductal sizes. The pH of ductal fluid during spontaneous secretion was near that of plasma in ducts 200 microns or less and near the pH of final juice in larger ducts. After secretin stimulation the pH of ductal fluid was near that of final juice in all ductal sizes. Ductal fluid pCO2 during spontaneous secretion was about 45 mm Hg in ducts 200 microns or less and near 30 mm Hg in all other ductal sizes and in final juice. Secretin stimulation did not significantly change the ductal values but the final juice pCO2 was significantly lower (p< .05). The bicarbonate concentration in ductal fluid was like that of plasma (30 mEq/L) in ducts 100 microns or less and near 60 mEq/L in all other ductal sizes and final juice. Secretin stimulation increased the bicarbonate concentration to near 80 mEq/L in all ductal sizes and final juice. It was concluded that the ducts of the extralobular collecting system play a role in the secretion of bicarbonate. Bicarbonate is added to a primary secretion, whose origin is the intralobular ductal system, as it flows through the extralobular ducts. This addition takes place during spontaneous and secretin stimulated secretion. There is no evidence for chloride-bicarbonate exchange in the large extralobular ducts. These data are consistant with a modified adreixture model.

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Committee Member (Chair)

William Raleigh Galey Jr.

Second Committee Member

Sidney Solomon

Third Committee Member

Kenneth Drake Gardner

Fourth Committee Member

Leon Hurwitz

Fifth Committee Member

Robert Geoffrey Strickland

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