Episodic release of insulin by rat pancreas: effects of CNS and state of satiety

This study reports that insulin is secreted in an episodic manner in rats and that the characteristics of its release can be modified by the central nervous system (CNS) and state of satiety. The pancreata of male Sprague-Dawley rats were perfused using the in situ brain-pancreas technique under urethan anesthesia. Episodic insulin release under non-fasted conditions was not altered by the presence or absence of CNS innervation to the pancreas. Under these conditions the interpeak period was 5.9 and 6 min, respectively, and cycle length was 3.7 and 4 min. However, perfusions that were performed following an overnight fast demonstrated that the CNS is capable of modulating episodic insulin release. After fasting, when comparing CNS-ablated with -intact preparations, the period was shortened from 5.2 to 4.1 min (P less than 0.05), and the number of episodes per 90-min perfusion increased from 16.0 to 19.0 (P less than 0.05) when the pancreas was innervated by the CNS. Additionally, the effect of fasting on denervated pancreata resulted in a shortening of the cycle length, which was prevented when the CNS was functional. These results demonstrate that episodic insulin release can be modified by metabolic conditions and are subject to mediation by the CNS.