Previously, we reported that combination treatment with rat amylin (100 microg/kg.d) and murine leptin (500 microg/kg.d) elicited greater inhibition of food intake and greater body weight loss in diet-induced obese rats than predicted by the sum of the monotherapy conditions, a finding consistent with amylin-induced restoration of leptin responsiveness. In the present study, a 3 x 4 factorial design was used to formally test for a synergistic interaction, using lower dose ranges of amylin (0, 10, and 50 microg/kg.d) and leptin (0, 5, 25, and 125 microg/kg.d), on food intake and body weight after 4 wk continuous infusion. Response surface methodology analysis revealed significant synergistic anorexigenic (P < 0.05) and body weight-lowering (P < 0.05) effects of amylin/leptin combination treatment, with up to 15% weight loss at doses considerably lower than previously reported. Pair-feeding (PF) experiments demonstrated that reduction of food intake was the predominant mechanism for amylin/leptin-mediated weight loss. However, fat loss was 2-fold greater in amylin/leptin-treated rats than PF controls. Furthermore, amylin/leptin-mediated weight loss was not accompanied by the counterregulatory decrease in energy expenditure and chronic shift toward carbohydrate (rather than fat) utilization observed with PF. Hepatic gene expression analyses revealed that 28 d treatment with amylin/leptin (but not PF) was associated with reduced expression of genes involved in hepatic lipogenesis (Scd1 and Fasn mRNA) and increased expression of genes involved in lipid utilization (Pck1 mRNA). We conclude that amylin/leptin interact synergistically to reduce body weight and adiposity in diet-induced obese rodents through a number of anorexigenic and metabolic effects.

In rodents, weight reduction after peptide YY[3-36] (PYY[3-36]) administration may be due largely to decreased food consumption. Effects on other processes affecting energy balance (energy expenditure, fuel partitioning, gut nutrient uptake) remain poorly understood. We examined whether s.c. infusion of 1 mg/(kg x d) PYY[3-36] (for up to 7 d) increased metabolic rate, fat combustion, and/or fecal energy loss in obese mice fed a high-fat diet. PYY[3-36] transiently reduced food intake (e.g., 25-43% lower at d 2 relative to pretreatment baseline) and decreased body weight (e.g., 9-10% reduction at d 2 vs. baseline) in 3 separate studies. Mass-specific metabolic rate in kJ/(kg x h) in PYY[3-36]-treated mice did not differ from controls. The dark cycle respiratory quotient (RQ) was transiently decreased. On d 2, it was 0.747 +/- 0.008 compared with 0.786 +/- 0.004 for controls (P < 0.001); light cycle RQ was reduced throughout the study in PYY[3-36]-treated mice (0.730 +/- 0.006) compared with controls (0.750 +/- 0.009; P < 0.001). Epididymal fat pad weight in PYY[3-36]-treated mice was approximately 50% lower than in controls (P < 0.01). Fat pad lipolysis ex vivo was not stimulated by PYY[3-36]. PYY[3-36] decreased basal gallbladder emptying in nonobese mice. Fecal energy loss was negligible ( approximately 2% of ingested energy) and did not differ between PYY[3-36]-treated mice and controls. Thus, negative energy balance after PYY[3-36] administration in diet-induced obese mice results from reduced food intake with a relative maintenance of mass-specific energy expenditure. Fat loss and reduced RQ highlight the potential for PYY[3-36] to drive increased mobilization of fat stores to help meet energy requirements in this model.

We have previously shown that combined amylin + leptin agonism elicits synergistic weight loss in diet‐induced obese (DIO) rats. Here, we assessed the comparative efficacy of amylin, leptin, or amylin + leptin in the maintenance of amylin + leptin–mediated weight loss. DIO rats pretreated with the combination of rat amylin (50 µg/kg/day) and murine leptin (125 µg/kg/day) for 4 weeks were subsequently infused with either vehicle, amylin, leptin, or amylin + leptin for an additional 4 weeks. Food intake, body weight, body composition, plasma parameters, and the expression of key metabolic genes in liver and white adipose tissue (WAT) were assessed. Amylin + leptin treatment (weeks 0–4) reduced body weight to 87.5% of baseline. Rats subsequently maintained on vehicle or leptin regained all weight (to 104.2 and 101.2% of baseline, respectively), those maintained on amylin had partial weight regain (97.0%). By contrast, weight loss was largely maintained with continued amylin + leptin treatment (91.4%), associated with a 10% decrease in adiposity. Cumulative food intake (weeks 5–8) was reduced by amylin and amylin + leptin, but not by leptin alone. Amylin + leptin, but not amylin or leptin alone, reduced plasma triglycerides (by 55%), total cholesterol (by 19%), and insulin (by 57%) compared to vehicle. Amylin + leptin also reduced hepatic stearoyl‐CoA desaturase‐1 (Scd1) mRNA, and increased WAT mRNA levels of adiponectin, fatty acid synthase (Fasn), and lipoprotein lipase (Lpl). We conclude that, in DIO rats, maintenance of amylin + leptin–mediated weight loss requires continued treatment with both agonists, and is accompanied by sustained improvements in body composition, and indices of lipid metabolism and insulin sensitivity.

To investigate whether the expression of angiotensinogen (ANG) in rat kidney proximal tubules is stimulated by dexamethasone and isoproterenol, immortalized rat proximal tubular cells (IRPTC) were cultured in a monolayer. Immunoreactive rat ANG (IR-rANG) in the culture medium was measured by a specific radioimmunoassay (RIA) for rANG. This RIA was developed by employing rabbit antiserum against the purified recombinant rat ANG (rANG). The purified rANG from plasma and the iodinated rANG were used as the hormone standard and tracer, respectively. The RIA is specific for rat ANG and it has no cross-reactivity with other pituitary hormone preparations or other rat plasma proteins. The sensitivity of detection of the RIA is approximately 2 ng of rANG. The levels of IR-rANG in the culture media of IRPTC ranged from 2 to 5 ng/ml/24 hr/10(6) cells. The addition of dexamethasone (10(-13) to 10(-5) M) stimulated the expression and secretion of rANG from IRPTC in a dose-dependent manner, whereas the addition of isoproterenol alone had no effect. However, a combination of both dexamethasone and isoproterenol synergistically stimulated the expression and secretion of rANG by IRPTC. The synergistic effect of dexamethasone and isoproterenol was blocked by the presence of RU 486 (a glucocorticoid receptor antagonist) or propranolol (beta-adrenoceptor blocker). These studies suggest that the addition of dexamethasone and isoproterenol acts synergistically to stimulate the expression and secretion of ANG protein in rat proximal tubules in vivo.