Inhibitory Effect of Galanin on Adrenaline- and Noradrenaline-Induced Increased Oxytocin Secretion in Rat Neurohypophyseal Cell Cultures

Study of the Potential Endocrine-Disrupting Effects of Phenylurea Compounds on Neurohypophysis Cells In Vitro

Homeostatic disruptor agents, and endocrine disruptor compounds (EDC) specifically, can originate from agricultural and industrial chemicals. If they modify the adaptation of living organisms as direct (e.g., by altering hormone regulation, membrane functions) and/or indirect (e.g., cell transformation mechanisms) factors, they are classified as EDC. We aimed to examine the potential endocrine-disrupting effects of phenylurea herbicides (phenuron, monuron, and diuron) on the oxytocin (OT) and arginine-vasopressin (AVP) release of neurohypophysis cell cultures (NH). In our experiments, monoamine-activated receptor functions of neurohypophyseal cells were used as a model. In vitro NH were prepared by enzymatic (trypsin, collagenase) and mechanical dissociation. In the experimental protocol, the basal levels of OT and AVP were determined as controls. Later, monoamine (epinephrine, norepinephrine, serotonin, histamine, and dopamine) activation (10^-6 M, 30 min) and the effects of phenylurea (10^-6 M, 60 min) alone and in combination (monoamines 10^-6 M, 30 min + phenylureas 10^-6 M, 60 min) with monoamine were studied. OT and AVP hormone contents in the supernatant media were measured by radioimmunoassay. The monoamine-activated receptor functions of neurohypophyseal cells were modified by the applied doses of phenuron, monuron, and diuron. It is concluded that the applied phenylurea herbicides are endocrine disruptor agents, at least in vitro for neurohypophysis function.

Central injection of GALR1 agonist M617 attenuates diabetic rat skeletal muscle insulin resistance through the Akt/AS160/GLUT4 pathway

Insulin resistance of skeletal muscle plays an important role in the pathogenesis of type 2 diabetes. Galanin, a 29/30-amino-acid neuropeptide, plays multiple biological actions, including anti-diabetic effects. Although recent results of our study showed that administration of galanin could mitigate insulin resistance by promoting glucose transporter 4 (GLUT4) expression and translocation in skeletal muscle of rats, there is no literature available regarding to the effect of type 1 of galanin receptors (GALR1) on insulin resistance in skeletal muscle of type 2 diabetic rats. Herein, we intended to survey the central effect of GALR1 agonist M617 on insulin resistance in skeletal muscle and its underlying mechanisms. We found that the intracerebroventricular injection of M617 increased glucose infusion rates in hyperinsulinemic euglycemic clamp tests, but attenuated the plasma insulin and glucose concentrations of diabetic rats. Furthermore, administration of M617 markedly increased GLUT4 mRNA expression and GLUT4 translocation in skeletal muscle of diabetic rats. Last, perfusion of M617 increased phosphorylated Akt and phosphorylated AS160 levels in the skeletal muscle of diabetic rats. In conclusion, central injection of M617 mitigated insulin resistance of skeletal muscle by enhancing GLUT4 translocation from intracellular pools to plasma membranes via the activation of the Akt/AS160/GLUT4 signaling pathway.

Intracerebroventricular administration of galanin antagonist sustains insulin resistance in adipocytes of type 2 diabetic trained rats

The aim of this study is to investigate whether galanin (GAL) central receptors are involved in regulation of insulin resistance. To test it, a GAL antagonist, M35 was intracerebroventricularly administrated in trained type 2 diabetic rats. The euglycemic-hyperinsulinemic clamp test was conducted for an index of glucose infusion rates. The epididymal fat pads were processed for determination of glucose uptake and Glucose Transporter 4 (GLUT4) amounts. The Gal mRNA expression levels in hypothalamus were quantitatively assessed too. We found an inhibitory effect of M35 on glucose uptake into adipocytes, Gal mRNA expression levels in hypothalamus, glucose infusion rates in the clamp test and GLUT4 concentration in plasma membranes and total cell membranes of adipocytes. The ratios of GLUT4 contents of the former to the latter in M35 groups were lower. These results suggest a facilitating role for GAL on GLUT4 translocation and insulin sensitivity via its central receptors in rats.

Galanin receptors and ligands

The neuropeptide galanin was first discovered 30 years ago. Today, the galanin family consists of galanin, galanin-like peptide (GALP), galanin-message associated peptide (GMAP), and alarin and this family has been shown to be involved in a wide variety of biological and pathological functions. The effect is mediated through three GPCR subtypes, GalR1-3. The limited number of specific ligands to the galanin receptor subtypes has hindered the understanding of the individual effects of each receptor subtype. This review aims to summarize the current data of the importance of the galanin receptor subtypes and receptor subtype specific agonists and antagonists and their involvement in different biological and pathological functions.