Lipostat in the lean rat: evidence for a non-causal relationship between glucocorticoids and leptin levels

Diet induced weight loss accelerates onset of negative alliesthesia in obese women

BACKGROUND

The physiological and behavioral responses to hypocaloric diet are to increase energy intake to defend a steady body weight. We utilized the method of "negative alliesthesia" for measuring the hedonic reponse to sweet stimulus before (Initial session) and 3 months after entering a weight loss program. The negative alliesthesia test is known by physiologists but few clinical data exist. It is based on the observation that repeated pleasant gustatory stimuli turn into unpleasantness in the process of alliesthesia. At first visit participants repeatedly ingested sweet stimuli until they found them unpleasant and rated quantitatively on a linear analogue scale their hedonic experience. This procedure was repeated every 3 min until participants felt displeasure to end the session. The same protocol was followed after three months of following a weight loss diet. Dieting energy intake was from 1400 - 2000 kcal/d for 8 wk. Energy composition was 50% carb:25% prot: 25% lipid. After 8 wk caloric intake increased by 50 kcal/wk, to reach daily intake of 1800 - 2400 kcal/d. Energy composition was 50% carb:22% prot: 27% lipid. We report results on the effect of slow weight loss on negative alliesthesia in ten obese female participants enrolled in a commercial diet program based on Canada's Food Guide (Mincavi).

RESULTS

Results showed that diet lowered the mean BMI (Initial session 36.8 +/- 1.8 vs. 3 mo 34.9 +/- 1.8 kg/m2). At 3 mo the onset of negative alliesthesia, time to abandon experimental session, was shortened (Initial session 33 vs. 3 mo 24 min). The same trend was observed in the time to reach indifference (Initial session 21.9 +/- 3.8 vs. 3 mo 16.2 +/-2.4 min). There was no observed difference in maximum (Initial session +79.5 +/- 11.7; 3 mo +94.5 +/- 9.9 mm) and minimum (Initial session -90.0 +/- 14.4; 3 mo -106 +/- 11.1 mm) hedonic rating.

CONCLUSION

Earlier onset of negative alliesthesia, as seen in our participants, is not consistent with previous hedonic studies that showed delayed or absent negative alliesthesia in participants when below their initial body weight. Therefore, it is hypothesized that the accelerated onset of negative alliesthesia observed in our obese participants after weight loss is suggestive of a lowered body weight set-point. Factors inherent to the weight loss diet studied here, such as mild energetic restriction, lowered palatability, and diet composition, may have played a role in this experimental outcome.

Effects of adrenalectomy on CART expression in the rat arcuate nucleus

In order to test for glucocorticoid regulation of CART in the arcuate nucleus, adrenalectomies (ADX) and hormone replacements (HRs) were carried out in groups of rats. CART mRNA levels were determined by in situ hybridization and CART peptide levels by immunocytochemistry. ADX caused a lowering of CART mRNA and peptides levels in the arcuate and this was reversed by HR. These results indicate a glucocorticoid regulation of CART in the arcuate. The regulation could be direct through an action of glucocorticoid receptors or indirectly through ADX-induced changes in leptin levels. These findings suggest a role for CART in the stress response.

Leptin suppresses food intake and body weight in corticosterone-replaced adrenalectomized rats

Intracerebroventricular (ICV) injections of leptin decrease food intake and body weight while increasing energy expenditure. Some of these effects are reportedly enhanced in bilaterally adrenalectomized (ADX) rats. The purpose of the present experiment was to establish the time course of the suppression in body weight and food intake after an ICV injection of leptin. We wanted to establish the effect of varying doses of corticosterone (CORT) on body weight and food intake suppression by using separate groups of ADX, ADX and corticosterone-treated and sham-operated Sprague-Dawley rats. All rats were implanted with cholesterol pellets that varied in CORT content. During the same surgical session, all rats were fitted with a cannula in the lateral ventricle. After recovering from surgery, each rat was administered a 5- micro g ICV injection of leptin. ADX rats that were treated with CORT replacement lost more (P < 0.05) weight and took longer (P < 0.05) to return to baseline body weight than sham-operated controls. Leptin injection decreased food consumption to a greater extent (P < 0.05) in the ADX groups treated with CORT than in the sham-operated controls. Plasma insulin increased in a dose-dependent manner in the ADX rats as a function of CORT replacement. The higher of the two CORT replacement doses used in this experiment restored circulating CORT to levels observed in sham-operated controls. Contrary to earlier reports, physiological doses of CORT appear to enhance leptin-induced weight loss.