Primary In Vivo Oscillations of Metabolism in the Pancreas

Abstract

The role of metabolism in the generation of plasma insulin oscillations was investigated by simultaneous in vivo recordings of oxygen tension (pO2) in the endocrine and exocrine pancreas and portal blood insulin concentrations in the anesthetized rat. At the start of the experiment, the blood glucose concentration of seven rats was 6.2 ± 0.1 mmol/l and the arterial blood pressure was 116 ± 5 mmHg. These values did not differ from those obtained at the end of the experiment. Islet pO2 was measured by impaling superficially located islets with a miniaturized Clark electrode. The pO2 measurements revealed slow (0.21 ± 0.03 min−1) with superimposed rapid (3.1 ± 0.3 min−1) oscillations. The average pO2 was 39 ± 5 mmHg. Simultaneous recordings of pO2 in the exocrine pancreas were significantly lower (16 ± 6 mmHg), but showed a slow and a rapid oscillatory activity with similar frequencies as seen in the endocrine pancreas. Corresponding measurements of portal insulin concentrations revealed insulin oscillations at a frequency of 0.22 ± 0.02 min−1. The results are the first in vivo recordings of an oscillatory islet parameter with a frequency corresponding to that of plasma insulin oscillations; they support a primary role of metabolic oscillations in the induction of plasma insulin oscillations.