Abstract: Previously, ß-conglycinin (ß-CON), one of the major components of soy protein (SOY), was shown to decrease body fat mass and serum and liver triglyceride levels, improve insulin sensitivity, and suppress elevated blood pressure in rodents. The findings suggest that ß-CON has multiple physiological functions and can ameliorate metabolic syndrome. To confirm this, we used the spontaneous hypertensive rat (SHR)/NDmcr-cp as an animal model for metabolic syndrome and examined the physiological effects of dietary β-conglycinin. Male rats (6-week-old) were fed the AIN-93G diets containing 20% protein; either casein (CAS), CAS half replaced with SOY or ß-CON for 13 weeks. During the feeding period, tail-cuff blood pressure was measured at week 2, 6, and 10, and fasting glucose level was measured at week 4, 8 and 12. Also, oral glucose tolerance test (OGTT, 2.0g/kg) was performed at week 12. As a result, dietary SOY and even ß-CON compared with CAS significantly suppressed systolic and diastolic blood pressures at week 6 and thereafter. The antihypertensive effect of ß-CON (and SOY) could be partly associated with an increase of plasma adiponectin concentration. Fasting blood glucose level was comparable among the groups, but the results from OGTT suggested that ß-CON and SOY compared with CAS increased blood glucose clearance. After necropsy, plasma insulin concentration decreased in the order of the CAS, SOY and ß-CON groups. Hemoglobin A1c level also decreased in the same order. Although dietary protein did not affect visceral adipose tissue weights, liver triglyceride concentration significantly decreased by feeding the ß-CON diet compared with the CAS and SOY diets. The protein-dependent decrease could due be to a decrease of fatty acid synthesis and an increase of fatty acid ß-oxidation in the liver. The results indicated that ß-CON simultaneously exerted multiple physiological effects in the SHR/NDmcr-cp, and could ameliorate metabolic syndrome.
