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Abstract

Micropuncture and microperfusion experiments were performed at the exposed pancreas of rabbits. In the free-flow samples Cl⁻ concentration was determined, while in the stopped flow microperfusion samples the dilution of a plasma sample injected into the duct lumen was determined by measuring the change of Cl⁻ and labeled inulin concentrations. Following results were obtained: 1. Within 3–6 min a plasma sample injected into interlobar ducts of unstimulated glands increased in volume by a factor of 1.15 by the admixture of secreted fluid. The corresponding Cl⁻ concentration in the secreted fluid was in the mean 107 meq/l. After secretin stimulation the volume increased 2.33 fold and the mean Cl⁻ concentration of the secreted fluid was 52 meq/l. 2. A higher Cl⁻ concentration was measured along the entire duct under free-flow conditions during winter than during sommer. In each of both experimental series the Cl⁻ concentration decreased along the entire duct system when the gland was stimulated, but increased in the unstimulated gland. 3. The Cl⁻ concentration in samples obtained from the acini (probably from the centroacinar and adjacent intralobular duct) remained unchanged after secretin stimulation, while it decreased in the mean by 17 meq/l after pancreozymin stimulation. 4. Transtubular potential differences in all duct segments ranged between 2 and 6 mV (lumen negative).
From the results in can be concluded that bicarbonate and water are secreted within the entire duct system. The Cl⁻ concentration in the secreted fluid decreases and the HCO₃⁻ and Cl⁻ occurs in the ducts at small flow rates. Secretin does not change HCO₃⁻ concentration in the duct segments near the acini but that of more distal duct segments. A different, season dependent factor, influences the level of the Cl⁻ and HCO₃⁻ concentrations of the pancreas. Measurements of potential differences support the hypothesis that ductular secretion consists of an active HCO₃⁻ transport in addition to active Na+ transport postulated by others.