Lack of effect of calcitonin gene-related peptide and amylin on major markers of glucose metabolism in hepatocytes

Effects in liver

Amylin and calcitonin gene-related peptide (CGRP) were each shown to stimulate endogenous glucose production in vivo in rats. Neither peptide had any effect on any of several measures of intermediary carbohydrate metabolism in isolated hepatocytes or isolated perfused liver in rats. The possibility exists that augmentation of endogenous glucose production was secondary to release of lactate from muscle into the plasma, thereby stimulating gluconeogenesis by increasing the availability of substrate. Results from hyperlactemic clamp preparations, which allowed for direct measurement of such an effect, suggested that there were additional mechanisms that accounted for amylin stimulation of endogenous glucose production in rats. There is no evidence that amylin increases endogenous glucose production in humans.

Excitatory non-adrenergic-non-cholinergic neuropeptides: key players in asthma

Professor David de Wied first introduced the term 'neuropeptides' at the end of 1971. Later peptide hormones and their fragments, endogenous opioid (morphine-like) peptides and a large number of other biogenic peptides became classified as neuropeptides. All of these peptides are united by a number of common features including their origin (nervous system and peptide-secreting cells found in various organs such as skin, gut, lungs), biosynthesis, secretion, metabolism, and enormous effectiveness. Neuropeptides are biologically active at extremely low concentrations. The past decade, neuropeptide research has revealed that neuropeptides also participate strongly in immune reactions. The neuro-immune concept has opened up a whole new research area. In the last 20 years, significant advances have been made in investigations of the interaction between immune and nervous systems in chronic inflammatory diseases such as asthma. The goal of this review is to bring together the functional relevance of excitatory non-adrenergic-non-cholinergic (NANC) nerves and the interaction with the immune system in asthma.

Insulin- and glucagon-independent effects of calcitonin gene-related peptide in the conscious dog

Calcitonin gene-related peptide (CGRP) causes vasodilation in many vascular beds, resulting in hypotension and tachycardia. The current studies were conducted in overnight-fasted conscious dogs to determine the effect of different CGRP dosages on carbohydrate metabolism and catecholamine release resulting from hemodynamic changes. During a pancreatic clamp, dogs received intraportal infusions of CGRP at 13, 26, and 52 (n = 3) or 52, 105, and 210 pmol x kg(-1) x min(-1) (n = 4; 60 minutes at each rate). Blood pressure decreased (P < .05) and the heart rate and hepatic blood flow (HBF) increased a maximum of 100% and 30%, respectively (P < .05). For the five CGRP infusion rates, arterial plasma epinephrine increased approximately 1.3-, 2.4-, 7.4-, 12-fold, and eightfold basal, respectively; norepinephrine increased about 2.3-, 3.3-, 4.1-, 4.6-, and 4.8-fold basal, respectively; and cortisol increased about twofold, 3.4-fold, fivefold, sixfold, and 6.2-fold basal, respectively. At CGRP infusion rates of 52 pmol x kg(-1) x min(-1) or higher, increases (P < .05) occurred for plasma glucose, endogenous glucose production (EndoRa), and net hepatic uptake of gluconeogenic substrates (maximum change, 24 mg/dL, 1.3 mg x kg(-1) x min(-1), and 9.9 micromol x kg(-1) x min(-1), respectively). Arterial blood glycerol concentrations increased only a maximum of 30%. At the two highest CGRP infusion rates, glycerol returned to basal concentrations and arterial plasma nonesterified fatty acids (NEFAs) decreased. The increased net hepatic uptake of gluconeogenic substrates during CGRP infusion was sufficient to account for 49% to 58% of the increase in EndoRa. CGRP has no apparent direct effects on hepatic carbohydrate metabolism, but the catecholamines, at levels similar to those observed during CGRP infusion, stimulate hepatic glycogenolysis. Therefore, some factor(s) other than CGRP, probably an increase in circulating catecholamine concentrations, would appear to be responsible for at least 42% to 51% of the increase in EndoRa.