Weight loss after bariatric surgery was thought to be solely due to the malabsorption and restriction produced by the procedure itself. In recent times the contribution of the altered levels of gut hormones post surgery is being increasingly recognised.   These hormonal changes might be related to the alterations in gut motility in the short and long term, as well as due to changes in weight over time. Secretory changes in some hormones may be secondary to alteration in others and distinguishing these will be a challenging task.

A question that is posed on identification of any hormonal abnormality related to obesity is whether it is the cause or effect of obesity. Reversibility of the abnormalities with weight loss usually would lead one to assume that the hormonal disturbance was likely to be secondary to weight gain rather than the cause of it, although it still does not answer whether the effect of obesity was direct or indirect through other hormones.

GLP-1

 GLP-1 levels rise post bypass surgery to normal levels.  Int J Obes Relat Metab Disord. 1997 May;21(5):387-92  .or even higher than normal levels compared to control lean and obese patients.  Ann Surg. 2006 Jan;243(1):108-14.  This might at least partly be related to the effect of the surgery itself altering the bowel motility with rapid presentation of ingested food to the distal intestines with resultant increased GLP-1 response from L cells in the ileum.  Ann Surg. 1990 Jun;211(6):763-70;    Obes Surg. 2005 Apr;15(4):459-61.  since gastric banding procedures do not seem to produce rise in GLP-1.   Ann Surg. 2006 Jan;243(1):108-14.    In keeping with this hypothesis, experiments in rats using ileal transposition into the jejunum (to make a distal part of the gut more proximal) resulted in increased synthesis and release of GLP-1.  Am J Physiol Endocrinol Metab. 2005 Feb;288(2):E447-53.  

Peptide YY

Peptide YY is a hormone secreted from the lower parts of the gut.  Stimulation of the lower parts of the gut would result in greater PYY release. This in fact seems to be the case as shown by ileal transposition into the jejunum (to make a distal part of the gut more proximal) in rats which resulted in increased synthesis and release of Peptide YY. Am J Physiol Endocrinol Metab. 2005 Feb;288(2):E447-53   Rapid entry of nutrients into the distal parts of the intestines as following gastric bypass surgery would thus be expected to stimulate earlier release and higher levels of Peptide YY. Roux-en-Y gastric bypass (RYGBP) has been shown to increase PYY release post meals by up to 3 times higher than in controls. J Clin Endocrinol Metab. 2005 Jan;90(1):359-65.   ;  an effect that was not demonstrable in patients undergoing gastric banding.  Ann Surg. 2006 Jan;243(1):108-14.

Ghrelin

Ghrelin is a stomach derived hormone with orexigenic properties, and is thought to play a role in short term +/- long term meal regulation. Ghrelin levels tend to rise with most modalities inducing weight loss, very likely as a compensatory response to maintain weight. Gastric surgery involving stomach resections do not seem to be associated with a subsequent Ghrelin rise    J Clin Endocrinol Metab. 2005 Jan;90(1):359-65    Ann Surg. 2006 Jan;243(1):108-14.  This lack of Ghrelin rise was thought to facilitate the weight loss post Roux-En-Y bypass as opposed to other modalities of weight loss which are associated with a rise in Ghrelin and appetite.   Not all studies have been in keeping with the hypothesis of  fundic resection contributing to low Ghrelin levels.  J Clin Endocrinol Metab. 2003 Apr;88(4):1594-602.  The need for post-gastric feedback to stimulate Ghrelin release as shown by pyloric cuff studies  Endocrinology. 2003 Jul;144(7):2765-7.  or using direct intraduodenal infusates suggests that other factors may be at play in determining the changes in Ghrelin secretion post surgery.  Read further on Ghrelin and gut surgery at this site

Adipokines and Bariatric Surgery

Leptin

Leptin levels are unchanged or decrease following laparoscopic adjustable gastric banding, gastric bypass and Biliopancreatic diversion. Obes Surg. 2005 May;15(5):692-9.    In one study, Leptin levels in decreased from 73.9 +/- 8.7 to 16.9 +/- 10.2 ng/ml. The fall in Leptin levels correlated strongly with the drop in BMI, with the weight loss accounting for up to 66% of the Leptin variation post surgery. Obes Surg. 2001 Dec;11(6):693-8.   Insulin levels were not strongly correlated with Leptin changes on multivariate regression analysis.

Adiponectin

Pre-operative Adiponectin levels have been demonstrated to be highly predictive of weight loss.  J Clin Endocrinol Metab. 2003 Apr;88(4):1594-602   Adiponectin levels increase  post bariatric surgery, and is a good predictor of improvement in insulin sensitivity. 

ASP (acyl stimulation Protein)

ASP, an adipocyte derived factor produced from complements, has an important role in determining triglyceride storage. ASP levels fall post-bariatric surgery    J Clin Endocrinol Metab. 2003 Apr;88(4):1594-602   and may have implications on further fat (triglyceride) deposition in adipocytes, as well as weight loss through lipolysis. The drop in ASP levels seem to predict a decrease in Apo B levels. 

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    This page was last updated on: 07/03/2007

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