Beta-funaltrexamine blockade of opioid-induced inhibition of somatostatin secretion from rat stomach

Immunomodulatory action of class mu-, delta- and kappa-opioid receptor agonists in mice

Endogenous opioids exert a variety of functions outwith the central nervous system, including modulation of some murine lymphocyte functions. The results of this study indicate that mu-, delta- and kappa-receptor selective agonists are potent in vitro stimulators of mitogen-induced proliferation of murine T-lymphocytes. Moreover, the observed enhancement of mitogen-induced proliferation was reversed by mu-, delta- and kappa-receptor class selective antagonists, beta-funaltrexamine, ICI 174,864 and nor-binaltorphimine, respectively. An additional study has revealed that repeated administration (four injections) of the opioid receptor selective agonists DAGO, DPDPE and U-50488 also enhanced the concanavalin A-induced proliferation of lymphocytes. These results suggest that there are three classes of opioid receptors on T-lymphocytes and that all these receptor classes are involved in the stimulation of concanavalin A-induced proliferation.

Immunologic action of [Met5]enkephalin fragments

The aim of this study was to evaluate the effects of [Met5]enkephalin, des-Met-[Met5]enkephalin, des-Tyr-[Met5]enkephalin, and Tyr-Gly-Gly on natural killer cytotoxic activity and on concanavalin A- and lipopolysaccharide-stimulated proliferation of B and T cells in mice. Single i.p. injections of [Met5]enkephalin, des-Met-[Met5]enkephalin, and Tyr-Gly-Gly increased both natural killer cytotoxicity and proliferation of mitogen-stimulated B and T cells. These effects were inhibited by naloxone pretreatment, which suggests the opioid mechanism of the peptides studied. The rate of lymphocytic proliferation increases not only after single injection of [Met5]enkephalin or its metabolites, but also after 3 or 7 days of treatment. Apart from the functional effects, [Met5]enkephalin, des-Met-[Met5]enkephalin, and Tyr-Gly-Gly increased the percentages of natural killer cells and T cells. The results of this study suggest that the immunomodulatory action of [Met5]enkephalin may be mediated or enhanced by its N-terminal metabolites des-Met-[Met5]enkephalin and Tyr-Gly-Gly.

Regulation of thyroid hormones in the secretion of insulin and gastric inhibitory polypeptide in male rats

The effect of thyroid hormones on glucose-induced secretion of gastric inhibitory polypeptide (GIP) and insulin was studied. Male rats were thyroidectomized (Tx) or sham Tx. Sham Tx rats were injected with either propylthiouracil ([PTU] 20 mg/kg intraperitoneally) or saline for 2 weeks. In addition, thyroid-intact rats were injected intravenously with triiodothyronine ([T3]5 microg/kg) or saline 10 minutes before an oral glucose load (3.2 g/kg). Blood samples were collected from each animal via a jugular catheter at 0, 10, 20, 30,45, 60, and 90 minutes following glucose ingestion. Plasma levels of GIP and insulin were measured by specific radioimmunoassays (RIAs). Thyroidectomy-induced hypothyroidism increased the basal level of plasma GIP, but decreased that of insulin. Insulin levels at 10, 20, and 30 minutes following oral glucose were lower in hypothyroid rats than in euthyroid rats. Conversely, GIP levels at 60 and 90 minutes following glucose ingestion in PTU-induced hypothyroid rats were higher than those in euthyroid rats. Furthermore, glucose-stimulated insulin secretion was unaltered by pretreatment with T3, whereas the glucose-induced increase in plasma GIP was completely abolished by preinjection of T3 in thyroid-intact rats. These results suggest that thyroid functions are involved in the regulation of insulin and GIP secretion in rats.