Pancreatic islet blood flow in conscious rats during hyperglycemia and hypoglycemia

Abstract

Anesthesia affects general hemodynamics and regulation of organ perfusion. We used colored microspheres to measure pancreatic islet blood flow in conscious rats at two time points, during either hyperglycemia or hypoglycemia. This method, using black and green microspheres, was validated by comparison with previous microsphere experiments and by lack of effect of a nonmetabolizable glucose analog, 3-O-methylglucose, on islet perfusion. Basal and glucose-stimulated islet blood flow levels were similar in pentobarbital sodium-anesthetized and conscious rats. However, the basal distribution of pancreatic blood flow was altered by anesthesia (fractional islet blood flow 5.8 +/- 0.4% in conscious rats, 7.9 +/- 0.8% in pentobarbital-anesthetized rats, P < 0.05). Insulin-induced hypoglycemia significantly increased whole pancreatic blood flow in conscious rats, whereas islet blood flow remained unchanged and fractional islet blood flow was decreased (5.8 +/- 0.5% in the basal state, 4.2 +/- 0.4% during hypoglycemia, P < 0.001). Methylatropine pretreatment significantly increased islet blood flow during hypoglycemia by 181%. This result suggests that prevention of hypoglycemia-induced increase in islet perfusion may be mediated, at least in part, by a cholinergic, vagal muscarinic mechanism.

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

“…This is in contrast to previous studies, also using the microsphere technique, where either an increased [14] or an unchanged [15] islet blood flow was recorded. The reasons for the discrepancy between these studies are not known.…”

“…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].…”

“…Such low islet blood flow values have previously only been recorded in very young animals [16,33,34]. Another group [15] used an elegant technique with repeated injections of microspheres in conscious rats and showed no influence of insulin-induced hypoglycaemia on islet blood flow. The differences in the results on islet blood flow could therefore be explained by the use of anaesthesia or lack thereof.…”

“…In an early study to induce hypoglycaemia, exogenous administration of insulin increased islet blood flow [14], whereas a more recent study found no effects on islet blood perfusion [15]. Tolbutamide in doses inducing hypoglycaemia has increased islet blood flow [16], whereas mild hypoglycaemia induced by starvation decreased islet blood perfusion [2].…”

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

“…paired analysis of measurements and a reduction of the number of animals needed. In a recent study, repeated injections of differently coloured 10 m-microspheres were found to give reproducible islet blood flow measurements in awake rats (11). The present study evaluated this finding in anaesthetised rats and whether such experiments are restricted to the use of 10 m microspheres or also applicable for 15 m microspheres.…”