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Evidence for pancreatic pacemaker for insulin oscillations in low-frequency range
1Department of Medicine, Harbor-University of California Los Angeles Medical Center, Torrance 90502.
The American Journal of Physiology
|June 1, 1994
Summary
Researchers identified low-frequency insulin oscillations in vitro, originating from pancreatic islets. This suggests a pancreatic source for these ultradian insulin rhythms, potentially impacting diabetes mellitus.
Area of Science:
- Endocrinology
- Physiology
- Molecular Biology
Background:
- Circulating insulin exhibits high-frequency (5-17 min) and low-frequency (50-150 min) oscillations in vivo.
- Previously, only high-frequency insulin oscillations were observed in vitro, implying a pancreatic origin.
Purpose of the Study:
- To investigate the presence and characteristics of low-frequency insulin oscillations in vitro.
- To determine if pancreatic islets spontaneously generate low-frequency insulin oscillations.
Main Methods:
- Rat islets of Langerhans were perifused for 20 hours under constant glucose conditions (5.5 mM).
- Perifusate was collected at 9.9-minute intervals to measure insulin concentrations.
- Spectral analysis was used to identify oscillation periods and amplitudes.
Main Results:
- Sustained low-frequency insulin oscillations (50-100 min period) were observed in vitro.
- The mean amplitude of these oscillations was 14.2 +/- 4.2 microU/ml, with an amplitude/mean ratio of 64.6 +/- 12%.
- Significant spectral peaks were found at approximately 50 and 100 minutes, and a smaller peak at 24-37 minutes.
Conclusions:
- Pancreatic islets spontaneously generate sustained, low-frequency, ultradian insulin oscillations in vitro.
- These findings support a pancreatic contribution to in vivo low-frequency insulin rhythms.
- This may offer insights into the glucose entrainment escape observed in non-insulin-dependent diabetes mellitus.