Flow distribution between the endocrine and exocrine parts of the isolated rat pancreas during perfusion in vitro with different glucose concentrations

Previous studies in our laboratory have indicated that pancreatic islet blood flow is stimulated by glucose. In an attempt to evaluate to what extent intrapancreatic control mechanisms are involved in the glucose modulation of islet blood flow the distribution of flow between the endocrine and exocrine parts of the rat pancreas during perfusion in vitro with different glucose concentrations have now been studied. For this purpose pancreatic glands from 29 rats were perfused at a flow rate of 1.5 ml min‐1 for 95 min with low (2.8 mm) or high (16.7 mm) glucose‐containing media. Maintenance of vascular reactivity of this preparation in spite of a marked exocrine oedema was confirmed by administration to the perfusion medium of adrenaline, which immediately raised the perfusion pressure. Insulin concentrations in the effluent media were measured to correlate rates of insulin release to changes in islet flow and to assess the functional viability of the preparation. In each experiment non‐radioactive microspheres with a diameter of 10 μ were injected into the perfusion medium at one of four time‐points: 15, 30, 35 or 80 min after the beginning of the perfusion. Two of these injections (15 and 80 min) took place during perfusion with the low‐glucose media and the remaining two during perfusion with high‐glucose medium. The microspheres were counted separately in the endocrine and exocrine parts of the pancreas. The results showed that all preparations had a biphasic insulin response to glucose. The distribution of microspheres within the pancreas was found to be homogeneous with approximately 6% of the injected spheres present in the islets irrespective of the glucose concentration in the perfusion medium at the time of the microsphere injection. This corresponds to an islet perfusion of about 90 μ1 min‐1 which is similar to our previous findings in vivo. Moreover, the lack of effect of glucose on the distribution of flow between the endocrine and exocrine parts supports the view that extrapancreatic, rather than local, factors are involved in the regulation of islet blood flow after glucose administration.