Pivotal role of leptin in insulin effects

The OB protein, also known as leptin, is secreted by adipose tissue, circulates in the blood, probably bound to a family of binding proteins, and acts on central neural networks regulating ingestive behavior and energy balance. The two forms of leptin receptors (long and short forms) have been identified in various peripheral tissues, a fact that makes them possible target sites for a direct action of leptin. It has been shown that the OB protein interferes with insulin secretion from pancreatic islets, reduces insulin-stimulated glucose transport in adipocytes, and increases glucose transport, glycogen synthesis and fatty acid oxidation in skeletal muscle. Under normoglycemic and normoinsulinemic conditions, leptin seems to shift the flux of metabolites from adipose tissue to skeletal muscle. This may function as a peripheral mechanism that helps control body weight and prevents obesity. Data that substantiate this hypothesis are presented in this review

Possible modulatory role of non-activated lymphocytes on insulin secretion

In order to study the probable physiological role of non-activated lymphocytes on islet B-cells, we incubated and perfused rat pancreatic islets in the presence of low (2.8 mM) and high (l6.7 mM) glucose concentrations after pre-exposure for 60 min to rat lymphocytes or to substances secreted by lymphocytes. Insulin secretion and 86Rb+, 45Ca2+ and [3H]-phosphoinositide metabolite fluxes were lower compared to controls when islets were pre-exposed to lymphocytes but were not different when islets were pre-exposed to substances secreted by lymphocytes. These alterations in isotope flux suggest that, when lymphocytes and islets are in contact, closure of potassium channels and a paradoxical effect of glucose load on insulin release occur in the presence of low glucose concentrations. The alterations observed are probably due to a swift and direct action of lymphocyte secretion perhaps induced by a direct contact of islet cells.

Insulin and prostaglandins as signals between tumor and the host immune system

The development of malignant tissue in vivo is partially favored by the immunosuppression that occurs in cancer patients. However, the signals between tumor and immune tissues remain to be identified. We present evidence that prostaglandins may act as one of these signals by a direct action on cells of the immune system, or by inhibition of insulin secretion which in turn suppresses immune function, or both

Effect of the IV administration of non-activated lynphocytes on rat plasma insulin and glucose levels

Althugh several studies have shown the effect of cytokines on islet B cell function, the role of circulating cells in the control of insulin secretion has not been investigated. The effect of lymphocyte administration on plasma glucose and insulin levels was examined in male Wistar albino rats weighing 180-200g. The animals were anesthetized and the jugular vein was cannulated for saline or lymphocyte injection (10**6 cells in 1 ml) and blood collection after 5, 10, 15, 20, 30, 45, and 60 min. A marked increase in plasma insulin levels (180*U/ml as compared to 56*U/ml in the control group, at 20 min) and an unexpected increase (P<0.05) in blood glucose levels (at 60 min only) were observed after lymphocyte administration. Similar experiments undertaken with simultaneous administration of inhibitors of arachidonic acid metabolism, indomethacin and nordihydroguairetic acid at 1 mg/Kg body weight, suggest that this effect of lymphocytes is not mediated by prostaglandins or leukotrienes

A rotating wheel cage for rats allowing free movement, feeding and drinking

A rotating wheel cage for rats which permits voluntary physical axtivity and free access to food and water is decribed. The cyclometer is entirely mechanical and does not requiere an external energy source. The apparatus can be constructed from commercially available, inexpensive components