The intestinal lymph fistula model—a novel approach to study ghrelin secretion

Abstract

The orexigenic hormone ghrelin is secreted from the stomach and has been implicated in the regulation of energy and glucose homeostasis. We hypothesized that ghrelin, like other gastrointestinal (GI) hormones, is present in intestinal lymph, and sampling this compartment would provide advantages for studying ghrelin secretion in rodents. Blood and lymph were sampled from catheters in the jugular vein and mesenteric lymph duct before and after intraduodenal (ID) administration of isocaloric Ensure, dextrin, or Liposyn meals or an equal volume of saline in conscious Sprague-Dawley rats. Total ghrelin levels were measured using an established radioimmunoassay. Acyl and des-acyl ghrelin were measured using two-site ELISA. Fasting ghrelin levels in lymph were significantly higher than in plasma (means +/- SE: 3,307.9 +/- 272.9 vs. 2,127.1 +/- 115.0 pg/ml, P = 0.004). Postingestive acyl and des-acyl ghrelin levels were also significantly higher, whereas the ratio of acyl:des-acyl ghrelin was similar in lymph and plasma (0.91 +/- 0.28 vs. 1.20 +/- 0.36, P = 0.76). The principle enzymes responsible for deacylation of ghrelin were lower in lymph than in plasma. Following ID Ensure, maximum ghrelin suppression occurred at 2 h in lymph compared with at 1 h in plasma. The return of suppressed ghrelin levels to baseline was also delayed in lymph. Similarly, dextrin also induced significant suppression of ghrelin (two-way ANOVA: P = 0.02), whereas Liposyn did not (P = 0.32). On the basis of these findings, it appears that intestinal lymph, which includes drainage from the interstitium of the GI mucosa, is enriched in ghrelin. Despite reduced deacylating activity in lymph, there is not a disproportionate amount of acyl ghrelin in this pool. The postprandial dynamics of ghrelin are slower in lymph than plasma, but the magnitude of change is greater. Assessing ghrelin levels in the lymph may be advantageous for studying its secretion and concentrations in the gastric mucosa.

Using the lymphatics to study nutrient absorption and the secretion of gastrointestinal hormones

“…Do other gastrointestinal hormones, such as gastrin, secretin, and xenin, have elevated concentrations in lymph versus plasma? It has been recently shown that the lymphatic concentration of ghrelin is also higher than in plasma [88]. Regarding the mechanisms of nutrient-induced incretin secretion, what is the role of nutrient absorption in regulating incretin release?…”

NIH Mouse Metabolic Phenotyping Centers: the power of centralized phenotyping

“…The consortium has published standard operating procedures for measuring food intake (Ellacott et al 2010) and for performing glucose clamps (Ayala et al 2010). Individual MMPCs have published papers describing methods (Ayala et al 2006; Jandacek et al 2004; Kaiyala and Schwartz 2011; Kaiyala et al 2010; Rottman et al 2007; Shearer et al 2008; Tong et al 2010; Yin et al 2011), standards (Ayala et al 2006; McGuinness et al 2009; Rottman et al 2003), and strain comparisons (Berglund et al 2008; Burgess et al 2005; Qi et al 2005). The Vanderbilt MMPC maintains a comprehensive online laboratory manual for in vivo testing (http://www.mc.vanderbilt.edu/mmpc) and has a video of the surgery and glucose clamp that can be viewed online (Ayala et al 2011).…”