Estudo com whey protein em ratos

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Departamento de Planejamento Alimentar e Nutrição, Faculdade de Engenharia de Alimentos, Universidade Estadual de Campinas,  Campinas, SP, Brasil

Laboratório Balanço Hidro-Salino, Núcleo de Medicina e Cirurgia Experimental, Disciplina de Medicina Interna, Departamento de Clínica Médica,  Faculdade de Ciências Médicas, Universidade Estadual de Campinas,

Campinas, SP, Brasil

BHryadzriloialynz eJodu prnroatl eoinf Mafefedcictsa Bl aPn adn Bdi osolodgiuicmal eRxecsreeatriochn i(n2 0S0H5R) 38: 1817-1824

ISSN 0100-879X

Effect of intraperitoneally administered hydrolyzed whey protein on blood  pressure and renal sodium handling  in awake spontaneously hypertensive rats

Abstract

The present study evaluated the acute effect of the intraperitoneal (ip) administration of a whey protein hydrolysate (WPH) on systolic arterial blood pressure (SBP) and renal sodium handling by conscious spontaneously hypertensive rats (SHR). The ip administration of WPH in a volume of 1 ml dose-dependently lowered the SBP in SHR

2 h after administration at doses of 0.5 g/kg (0.15 M NaCl: 188.5 ± 9.3 mmHg vs WPH: 176.6 ± 4.9 mmHg, N = 8, P = 0.001) and 1.0 g/kg (0.15 M NaCl: 188.5 ± 9.3 mmHg vs WPH: 163.8 ± 5.9 mmHg, N = 8, P = 0.0018). Creatinine clearance decreased significantly (P = 0.0084) in the WPH-treated group (326 ± 67 ìL min-1 100 g body weight-1) compared to 0.15 M NaCl-treated (890 ± 26 ìL min-1 100 g body weight-1) and captopril-treated (903 ± 72 ìL min-1 100 g body  weight-1) rats. The ip administration of 1.0 g WPH/kg also decreased  fractional sodium excretion to 0.021 ± 0.019% compared to 0.126 ± 0.041 and 0.66 ± 0.015% in 0.15 M NaCl and captopril-treated rats, respectively (P = 0.033). Similarly, the fractional potassium excretion

in WPH-treated rats (0.25 ± 0.05%) was significantly lower (P = 0.0063) than in control (0.91 ± 0.15%) and captopril-treated rats (1.24 ± 0.30%), respectively. The present study shows a decreased SBP in SHR after the administration of WPH associated with a rise in tubule sodium reabsorption despite an angiotensin I-converting enzyme (ACE)-inhibiting in vitro activity (IC50 = 0.68 mg/mL). The present findings suggest a pathway involving ACE inhibition but measurementsof plasma ACE activity and angiotensin II levels are needed to support this suggestion.

Introduction

Peptides derived from food proteins can regulate physiological functions in the igestive, neural and cardiovascular systems(1-3). A functional food can be defined as a dietary ingredient that affects its host in a targeted manner so as to exert positive effects that may eventually justify certain health claims. The term functional food encompasses  a very broad range of products from foods generated around a particular functional ingredient (e.g., stanol-enriched margarine) to staple, everyday foods enriched with a nutrient not usually present to any great extent (e.g., folic acid enriched bread or breakfast cereals). Peptides derived from  soybean and pork proteins can suppress the increase in serum cholesterol after a meal (4,5), while those derived from casein hydrolysates treated with pepsin promote calcium absorption and are used as functional foods, i.e., they contain ingredients that have health-promoting properties that extend beyond their immediate nutritional value. Peptides with hypotensive activity have been identified in hydrolysates of gelatin, casein, maize endosperm protein, and fish muscle (6-9), and are believed to be useful as functional dietary ingredients for hypertensive patients. This activity is attributable mainly to the inhibition of angiotensin-I-converting enzyme (ACE), which plays a prominent role in the regulation of arterial blood pressure by converting the inactive decapeptide angiotensin I to a strong vasoconstrictor octapeptide, angiotensin II, while at the same time inactivating the vasodilator and natriuretic nonapeptide, bradykinin (10,11).Milk proteins are precursors of peptides  with various biological activities, including opioid activity and immunomodulatory and  antihypertensive actions (12). The antihypertensive effect of these peptides has also been related to the inhibition of ACE (13), and has been studied in spontaneously hypertensive rats (SHR) and humans (14,15). These biologically active peptides are released from milk proteins by enzymatic hydrolysis during gastrointestinal digestion, milk fermentation (16) or hydrolysis in vitro. The most common way to produce bioactive peptides is to release them by limited hydrolysis using pancreatic enzymes, mainly trypsin. However, other enzymes and combinations of proteases have been used to generate bioactive peptides. Several studies have used alcalase to obtain antihypertensive hydrolysates from many protein sources (17-19). This enzyme is an industrial alkaline protease that is very stable in organic solvents and serves as a catalyst for the resolution of N-protected amino acids in aqueous solution and organic solvents, and is used to prepare optically pure peptides.

For many years, dietary interventions as a non-pharmacological approach for treating hypertension have focused on the intake of electrolytes. However, according to Martin (20), manipulation of the dietary protein  content could also be useful in the nonpharmacological treatment of hypertension. However, to the best of our knowledge, no study has investigated the hypotensive and renal effects of protein hydrolysates. In the present study, the in vitro ACE-inhibiting activity of a whey protein hydrolysate (WPH) and its effect on blood pressure, renal function and renal handling of sodium were investigated in conscious SHR.

E.L. Costa
1, A.R. Almeida2,
F.M. Netto
1
and J.A.R. Gontijo2

Correspondence

J.A.R. Gontijo,  Departamento de Clínica Médica, FCM, UNICAMP, Caixa Postal 6111, 13083-970 Campinas, SP - Brasil
Fax: +55-19-3788-8925 - E-mail: gontijo@fcm.unicamp.br
Research supported by CNPq (No.500868/91-3), PRONEX (No. 0134/97), CAPES, and FAPESP (No. 00/12216-8). Received January 30, 2004 Accepted August 11, 2005