Multiple Injections of Coloured Microspheres for Islet Blood Flow Measurements in Anaesthetised Rats: Influence of Microsphere Size

Abstract

We investigated if coloured microspheres could be used for repeated measurements of pancreatic islet blood flow in rats. An initial injection of 1.0-1.5 10 5 microspheres (black colour), with a size of 10 or 15 m, was made into the ascending aorta, while an arterial reference sample was collected from the femoral artery. Twelve min later, 1 ml of saline or 30% D-glucose was injected intravenously. Three min after this injection a second injection of 10-or 15-m microspheres (green colour) was given. The animals were then killed, and the pancreas and adrenals were removed and samples (150-200 mg) were secured from the duodenum, ileum, colon, right kidney and liver. The microsphere contents were determined with the aid of a freeze-thawing technique and blood flow values were calculated. Our results suggest that 10-m microspheres, but not 15-m microspheres, provide reproducible islet and total pancreatic blood flow measurements when repeatedly injected. Values for the blood flow to the intestines, kidney and liver were less sensitive to the size of the microspheres. We conclude that repeated administration of 15-m microspheres induces a high risk for erroneous islet and total pancreatic blood flow measurements, whereas two such measurements can be performed if 10-m microspheres are used.

Hypoglycaemia induces decreased islet blood perfusion mediated by the central nervous system in normal and Type 2 diabetic GK rats

“…However, although the technique used with repeated injection of microspheres enables paired observations, it relies on the basic concept that the distribution of a second microsphere injection is not influenced by the first injection. As recently evaluated [15,35], such influence might not occur in untreated animals, although it critically depends on the embolized mass in the body. Occlusion of too many capillary beds after the first injection causes an erroneous increase in both whole pancreatic and islet blood flow as measured by a second microsphere injection [35].…”

“…As recently evaluated [15,35], such influence might not occur in untreated animals, although it critically depends on the embolized mass in the body. Occlusion of too many capillary beds after the first injection causes an erroneous increase in both whole pancreatic and islet blood flow as measured by a second microsphere injection [35]. It is therefore not certain that a decrease in islet blood flow is easily detectable with the repeated microsphere technique, especially with a rather high dose of microspheres (400 000 in each injection) [15].…”

Superior beta cell proliferation, function and gene expression in a subpopulation of rat islets identified by high blood perfusion

“…their blood perfusion is below the detection limit [10]. Repeated microsphere injections show that, primarily, islets containing microspheres after the first injection also contain microspheres after repeated microsphere injections, indicating that the heterogeneity in blood perfusion remains constant over time [11].…”

“…This suggests that appropriate blood perfusion is essential for islet metabolism and insulin secretion. However, administration of glucose only seems to increase the blood perfusion of those islets that have the highest blood perfusion [10,11]. It is not known whether any functional differences exist between these highly blood-perfused islets and other islets.…”

Glucose-Induced Time-Dependent Potentiation of Insulin Release, but not Islet Blood Perfusion, in Anesthetized Rats

“…Blood flow measurements were performed with a microsphere technique as previously described (18,19) 3 min after the last injection of saline or glucose. Briefly, a total of 2.5 x 10 5 black non-radioactive microspheres (EZ-Trac™; Triton Microspheres, San Diego, CA, USA), with a diameter of either 10 μm were injected during 10 sec via the catheter with its tip in the ascending aorta.…”