Fluid secretion by interlobular pancreatic ducts was determined by using video microscopy to measure the rate of swelling of isolated duct segments that had sealed following overnight culture. The aim was to compare the HCO 3 − requirement for secretin-evoked secretion in mouse, rat and guinea-pig pancreas. In mouse and rat ducts, fluid secretion could be evoked by 10 nM secretin and 5 µM forskolin in the absence of extracellular HCO 3 − . In guinea-pig ducts, however, fluid secretion was totally dependent on HCO 3 − . Forskolin-stimulated fluid secretion by mouse and rat ducts in the absence of HCO 3 − was dependent on extracellular Cl − and was completely inhibited by bumetanide (30 µM). It was therefore probably mediated by a basolateral Na + -K + -2Cl − cotransporter. In the presence of HCO 3 − , forskolin-stimulated fluid secretion was reduced ∼40% by bumetanide, ∼50% by inhibitors of basolateral HCO 3 − uptake (3 µM EIPA and 500 µM H 2 DIDS), and was totally abolished by simultaneous application of all three inhibitors. We conclude that the driving force for secretin-evoked fluid secretion by mouse and rat ducts is provided by parallel basolateral mechanisms: Na + -H + exchange and Na + -HCO 3 − cotransport mediating HCO 3 − uptake, and Na + -K + -2Cl − cotransport mediating Cl − uptake. The absence or inactivity of the Cl − uptake pathway in the guinea-pig pancreatic ducts may help to account for the much higher concentrations of HCO 3 − secreted in this species.

The pancreatic pathology in cystic fibrosis (CF) is normally attributed to the failure of ductal fluid secretion resulting from the lack of functional CF transmembrane conductance regulator (CFTR). However, murine models of CF show little or no pancreatic pathology. To resolve this dichotomy we analysed the transport mechanisms involved in fluid and electrolyte secretion by pancreatic ducts isolated from CFTR-null mice. Experiments were performed on cultured interlobular duct segments isolated from the pancreas of the Cftr(tm1Cam) strain of CFTR-null mouse. Fluid secretion to the closed luminal space was measured by video microscopy. The secretory response of ducts isolated from CF mice to cAMP-elevating agonists forskolin and secretin was significantly reduced compared with wild type but not abolished. The Cl(-)- and HCO(3) (-) -dependent components of the ductal secretion were affected equally by the absence of CFTR. The secretory response to carbachol stimulation was unaltered in CF ducts. Loading the ductal cells with the Ca2+ chelator BAPTA completely abolished carbachol-evoked secretion, but did not affect forskolin-evoked secretion in CF or wild-type ducts. We conclude that pancreatic duct cells from CF mice can secrete a significant amount of water and electrolytes by a cAMP-stimulated mechanism that is independent of CFTR and cannot be ascribed to the activation of calcium-activated chloride channels.

Vitamin D analogs exert a preventative effect on experimental diabetes, but whether or not they are able to halt progress of established diabetes is not yet known. Moreover, it is widely accepted that diabetes may induce osteoporosis, but the efficacy of vitamin D on diabetic osteoporosis is not clear. In order to help clarify these issues, we have tested the efficacy of calcitriol streptozotocin-induced diabetes. Streptozotocin (60 mg/Kg body weight) was injected in 3-month-old Wistar rats, randomly distributed into two groups: vehicle (olive oil) treated diabetic rats (D) and diabetic rats treated with 1.25-(OH)2D3 250 mg, three times a week (DT). Control animals (C) were treated with vehicle alone. The experiment lasted 8 weeks. The histology of the pancreata was evaluated. Blood glucose and calcium and phosphate in serum and urine were measured. Finally, bone mineral density (BMD) of tibia and lumbar vertebrae were evaluated. After 8 weeks, diabetes persisted in 85% of the diabetic rats (D group), but in only 45% of vitamin D-treated group (DT). At the end of the experiment, DT animals were separated into two groups, those still remaining diabetic (DT-NR) and reversed animals (DT-R). Moreover, bone loss was observed in diabetic animals (D), whereas BMD of DT-R rats showed similar values to those of controls (C). Our results suggest that 1.25(OH)2D3 improves diabetes and, as such, may recover BMD in streptozotocin-induced diabetic rats.