Pancreatic microcirculation in the monkey with special reference to the blood drainage system of Langerhans islets: light and scanning electron microscopic study.

The microcirculation of the pancreas in 20 monkeys (Macaca mulatta) was further studied by scanning electron microscopy (SEM) of vascular corrosion casts and light microscopy (LM) of Chinese ink-injected/cleared tissues. The results revealed that 91% of islets observed received arterial blood from the terminal branches of the intralobular arteries--the afferent arterioles, and 9% received no arterial blood, being entirely supplied by the efferent vessels of the intermediate or large islets. Some islets received blood from the translobular afferent arterioles of the adjacent lobule. Two patterns of islet drainage channels with different features in the monkey were demonstrated in our study. These patterns might be termed as continuous or convergent portal vessels. All islets possessed continuous portal vessels, 7-8 microns in diameter, which ran a short distance (approximately 100 microns) and then drained into the peri-islet acinar region, forming a typical continuous insulo-acinar portal system. About 21% of the islets possessed one or two convergent portal vessels, occasionally more. This was first observed in the monkey. These vessels were relatively long and/or thick and drained into different regions: (1) the acinar region far from the islet in the lobule, forming a convergent insulo-acinar portal system, (2) crossed the interlobular septum into an adjacent lobule where sometimes no islet existed and then drained into the exocrine acinar region, forming a translobar convergent insulo-acinar portal system, (3) drained into an adjacent small islet through the insulo-insular drainage vessels--one part of the drainage system of the islets. Translobular vascular anastomoses observed between the microcirculation of pancreatic lobules in the monkey formed a new arrangement of pancreatic microcirculation-translobular pancreatic microcirculation. The functional and clinical significance of the pancreatic portal circulation and translobular circulation is discussed in this report.