Pinealectomy causes glucose intolerance and decreases adipose cell responsiveness to insulin in rats

Although the pineal gland influences several physiological systems, only a few studies have investigated its role in the intermediary metabolism. In t he present study, male Wistar rats, pinealectomized or sham-operated 6 wk b efore the experiment, were submitted to both intravenous glucose tolerance tests (IVGTT) and insulin binding as well as glucose transport assays in is olated adipocytes. The insulin receptor tyrosine kinase activity was assess ed in liver and muscle. The insulin secretory response during the IVGTT was impaired, particularly in the afternoon, and the glucose transport respons iveness was 33% lower in pinealectomized rats. However, no difference was o bserved in the insulin receptor number of adipocytes between groups as well as in insulin-stimulated tyrosine kinase activity, indicating that the ini tial steps in the insulin signaling were well conserved. Conversely, a 40% reduction in adipose tissue GLUT-4 content was detected. In conclusion, pin ealectomy is responsible for both impaired insulin secretion and action, em phasizing the influence of the pineal gland on glucose metabolism.