Dietary fat stimulates endogenous enkephalin and dynorphin in the paraventricular nucleus: role of circulating triglycerides

Abstract

Chang GQ, Karatayev O, Ahsan R, Gaysinskaya V, Marwil Z, Leibowitz SF. Dietary fat stimulates endogenous enkephalin and dynorphin in the paraventricular nucleus: role of circulating triglycerides. Am J Physiol Endocrinol Metab 292: E561-E570, 2007; doi:10.1152/ajpendo.00087.2006.-The opioid peptides enkephalin (ENK) and dynorphin (DYN), when injected into the hypothalamus, are known to stimulate feeding behavior and preferentially increase the ingestion of a high-fat diet. Studies of another peptide, galanin (GAL), with similar effects on feeding demonstrate that a high-fat diet, in turn, can stimulate the expression of this peptide in the hypothalamus. The present study tested different diets and variable periods of high-vs. low-fat diet consumption to determine whether the opioid peptides respond in a similar manner as GAL. In six experiments, the effects of dietary fat on ENK and DYN were examined in three hypothalamic areas: the paraventricular nucleus (PVN), perifornical hypothalamus (PFH), and arcuate nucleus (ARC). The results demonstrated that the ingestion of a high-fat diet increases gene expression and peptide levels of both ENK and DYN in the hypothalamus. The strongest and most consistent effect is seen in the PVN. In this nucleus, ENK and DYN are increased by 50 -100% after 1 wk, 1 day, 60 min, and even 15 min of high-fat diet consumption. While showing some effect in the PFH, these peptides in the ARC are considerably less responsive, exhibiting no change in response to the briefer periods of diet intake. This effect of dietary fat on PVN opioids can be observed with diets equal in caloric density and palatability and without a change in caloric intake, body weight, fat pad weight, or levels of insulin or leptin. The data reveal a strong and consistent association between these peptides and a rise in circulating levels of triglycerides, supporting a role for these lipids in the fat-induced stimulation of opioid peptides in the PVN, similar to GAL. galanin; opioid peptides; arcuate nucleus; feeding behavior; lipids RECENT EVIDENCE has demonstrated a close relationship between the orexigenic peptide galanin (GAL) and the consumption of a fat-rich diet. When injected into the paraventricular nucleus (PVN), this peptide stimulates feeding behavior in rats, and while having no specific effect on macronutrient preferences, GAL produces its strongest response in animals that prefer fat or are maintained on a fat-rich diet (34,41,65). Moreover, measurements of endogenous GAL reveal a stimulatory effect of acute or chronic high-fat diet consumption on gene expression and peptide levels specifically in the PVN (13,36,52). This supports the existence of a positive feedback loop, whereby a peptide stimulates intake of a diet that, in turn, increases production of this same peptide.The focus of this study is on the endogenous opioid peptides, enkephalin (ENK) and dynorphin (DYN). These peptides, like GAL, are known to increase feeding in a dose-dependent manner, and this response is observed with injection in...

Overconsumption of dietary fat and alcohol: Mechanisms involving lipids and hypothalamic peptides

“…Recent studies of the endogenous opioid peptides in the hypothalamus reveal a similar effect of dietary fat on these peptides as that described for GAL [29,[45][46][47][48]. The ingestion of a highfat diet increases gene expression of both ENK and DYN in the hypothalamus, and the strongest and most consistent effect is seen specifically in the PVN.…”

“…In this nucleus, ENK and DYN are increased by 50-100% after 1 week, 1 day, 60 min and even 15 min of high-fat diet consumption. In the ARC, these peptides are considerably less responsive, exhibiting no change in response to the briefer periods of diet intake [29,45,48,49]. The stimulation by dietary fat of opioid gene expression in the PVN is accompanied by an increase in opioid peptide levels as measured by radioimmunoassay.…”

Mechanisms of the anorexia of aging—a review

“…The endogenous opioid peptides, β-endorphin, enkephalin, and dynorphin, stimulate feeding behavior and preferentially increase the ingestion of a high-fat diet through the κ receptor (Chang et al 2007). As shown by Kavaliers and Hirst, the opiate-stimulated food consumption is reduced in older mice (Kavaliers and Hirst 1985), probably due to an age-related reduction in the number of opioid receptors.…”

Effects of a high-fat meal on postprandial incretin responses, appetite scores and ad libitum energy intake in women with obesity

“…However, the possibility that TG levels after a high-fat meal are causally related to subsequent hyperphagia still require further elucidation. Evidences suggests that circulating TG act physiologically on brain mechanisms, through orexigenic peptides, to stimulate feeding and, in particular, to mediate high-fat-induced hyperphagia (17,27,28). In fact, a lower secretion of GIP, which is a hormone with possible actions in the food intake regulation, were observed in the HTG group.…”

“…Added to this, evidences in animal studies suggests the involvement of the TG, which are markedly elevated after a high-fat meal, in stimulate hypothalamic peptides known to increase feeding (16)(17)(18)(19), and the hyperphagia after a high-fat meal is preceded by a marked increase in circulating TG levels (19).…”