ABSTRACT
Neuromedin B (NB) and gastrin-releasing peptide (GRP) are bombesin-like peptides, found in the gastrointestinal tube and pancreas, among other tissues. Consistent data proposed that GRP stimulates insulin secretion, acting directly in pancreatic cells or in the release of gastrointestinal hormones that are incretins. However, the role of NB remains unclear. We examined the glucose homeostasis in mice with deletion of NB receptor (NBR-KO). Female NBR-KO exhibited similar fasting basal glucose with lower insulinemia (48.4%) and lower homeostasis model assessment of insulin resistance index (50.5%) than wild type (WT). Additionally, they were more tolerant to oral glucose, demonstrated by a decrease in the area under the glucose curve (18%). In addition, 15 min after an oral glucose load, female and male NBR-KO showed lower insulin serum levels (45.6 and 26.8%, respectively) than WT, even though blood glucose rose to similar levels in both groups. Single injection of NB, one hour before the oral glucose administration, tended to induce higher serum insulin in WT (28.9%, p=0.3), however the same did not occur in NBR-KO. They showed no changes in fasting insulin content in pancreatic islets by immunohistochemistry, however, the fasting serum levels of glucagon-like peptide, a potent incretin, exhibited a strong trend to reduction (40%, p=0.07). Collectively, mice with deletion of NB receptor have lower insulinemia, especially in response to oral glucose, and females also exhibited a better glucose tolerance, suggesting the involvement of NB and its receptor in regulation of insulin secretion induced by incretins, and also, in insulin sensitivity.
Subject(s)
Gene Deletion , Glucose/administration & dosage , Glucose/pharmacology , Insulin/metabolism , Receptors, Bombesin/metabolism , Administration, Oral , Animals , Fasting , Female , Glucagon/metabolism , Glucagon-Like Peptide 1/metabolism , Glucose Tolerance Test , Homeostasis/drug effects , Islets of Langerhans/drug effects , Islets of Langerhans/pathology , Male , Mice, Inbred C57BL , Mice, Knockout , Neurokinin B/administration & dosage , Neurokinin B/analogs & derivatives , Neurokinin B/pharmacology , Receptors, Bombesin/deficiencyABSTRACT
Peptide YY (PYY)3-36 is a gut-derived hormone, with a proposed role in central mediation of postprandial satiety signals, as well as in long-term energy balance. In addition, recently, the ability of the hormone to regulate gonadotropin secretion, acting at pituitary and at hypothalamus has been reported. Here, we examined PYY3-36 effects on thyrotropin (TSH) secretion, both in vitro and in vivo. PYY3-36-incubated rat pituitary glands showed a dose-dependent decrease in TSH release, with 44 and 62% reduction at 10(-8) and 10(-6) M (P < 0.05 and P < 0.001 respectively), and no alteration in TSH response to thyrotropin-releasing hormone. In vivo, PYY3-36 i.p. single injection in the doses of 3 or 30 cg/kg body weight, administered to rats fed ad libitum, was not able to change serum TSH after 15 or 30 min. However, in fasted rats, PYY3-36 at both doses elicited a significant rise (approximately twofold increase, P < 0.05) in serum TSH observed 15 min after the hormone injection. PYY3-36 treatment did not modify significantly serum T4, T3, or leptin. Therefore, in the present paper, we have demonstrated that the gut hormone PYY3-36 acts directly on the pituitary gland to inhibit TSH release, and in the fasting situation, in vivo, when serum PYY3-36 is reduced, the activity of thyroid axis is reduced as well. In such a situation, systemically injected PYY3-36 was able to acutely activate the thyrotrope axis, suggesting a new role for PYY3-36 as a regulator of the hypothalamic-pituitary-thyroid axis.
