Effects of yeast hydrolysate on neuropeptide Y (NPY) and tryptophan hydroxylase (TPH) immunoreactivity in rats

To investigate the appetite regulation mechanism of low and high molecular weight yeast hydrolysate, neuropeptide Y (NPY) and tryptophan hydroxylase (TPH) expressions were analyzed in the brains on rats using immunohistochemical method; normal diet (control), 0.1 g/kg (BY‐1) or 1.0 g/kg (BY‐2) of yeast hydrolysate below 10 kDa, 0.1 g/kg (AY‐1) or 1.0 g/kg (AY‐2) of yeast hydrolysate of 10–30 kDa. Body weight gain was lower in the BY‐2 (133.0 g) than in the control (150.1 g) ( p < 0.05). Triacylglyceride, total cholesterol, and LDL‐cholesterol levels were lower in the BY‐2 as compared to control, BY‐1 and AY‐2 ( p < 0.05). NPY staining intensities at paraventricular nucleus (PVN) were lower in the BY groups (BY‐1: 96.1, BY‐2: 88.6) as compared to the control (105.6) and AY groups (AY‐1: 110.5, AY‐2: 114.1) ( p < 0.05). NPY expression at lateral hypothalamic area (LHA) was lower in the BY‐2 (92.3) than in the control (98.9) ( p < 0.05). The BY groups (BY‐1: 143.9, BY‐2: 154.6) had higher TPH staining intensities at dorsal raphe (DR) than the AY‐2 (115.9) ( p < 0.05). In conclusion, the results indicate that administering yeast hydrolysate of below 10 kDa to normal diet‐fed rats reduced body weight gain and serum lipids by altering NPY and TPH expressions. Copyright © 2008 John Wiley & Sons, Ltd.