No abstract

During the processing of heshiko, a fermented mackerel product, a rapid increase in peptide content in the extract and a remarkable decrease in the IC 50 (the inhibitor concentration to inhibit 50% of enzyme activity) as an index of the angiotensin I-converting enzyme (ACE) inhibitory activity were observed. Systolic blood pressure (SBP) in spontaneously hypertensive rats (SHR) decreased between 2 and 4 h after single oral administration of heshiko extract at a dose of 10 mg/ kg as a peptide, and SBP recovered its initial level by 8 h. For single doses of extract at three different levels (5, 10 and 50 mg/kg), SBP similarly decreased after between 2 and 4 h. The decreased SBP at 50 mg/kg was almost equal to that at 10 mg/kg, indicating a low dose dependency for heshiko extract. Through successive administration of heshiko extract or its desalted extract at 10 mg/kg for 10 days, SBP decreased 7 days after the start of administration and it recovered its initial level 5 days after stopping administration. During these periods, the change in ACE activity in blood plasma from SHR administered the extract roughly corresponded to that of SBP, suggesting that ACE inhibition was related to a decrease in SBP. For long-term administration of the extract to 5-week-old SHR for 70 days, SBP decreased 28 days after the start of administration. The decreased SBP remained low for 28 days after stopping administration, whereas the decreased ACE activity recovered its initial level. These results suggest that heshiko extract influences not only ACE inhibition, but also other systems that regulate blood pressure.KEY WORDS: angiotensin I-converting enzyme inhibition, antihypertensive effect, fermented mackerel, heshiko, peptide, spontaneously hypertensive rat.

During the processing of mackerel narezushi , the fish body was strongly dehydrated by permeation of salt, the low pH of fish meat, and pressure applied to the fish and rice mixture. In the proximate components, moisture, protein and lipid flowed out from the fish meat into the rice mixture, and sugar permeated from the rice mixture into the fish meat. That the total amount of outflow was larger than that of permeation into the fish is thought to contribute to the decrease in fish body weight during processing. In the extractive components, although the nucleotides completely decomposed, free amino acids and peptides increased remarkably because of the decomposition of proteins in fish meat during processing. Especially, six kinds of free amino acid, Glu, Asp, Gly, Ala, Leu, and Ile, which are thought to be the taste components in marine resources, increased. Organic acid increased remarkably because of the fermentation of rice and permeation into the fish meat. The marked increase of the extractive components is thought to contribute to the umami taste and the sour taste of narezushi .KEY WORDS: extractive component, fermented food, free amino acid, mackerel, narezushi , organic acid, peptide, proximate composition.

Heshiko extract was separated into peptide and amino acid fractions by ion-exchange column chromatography. Heshiko extract and these fractions were administered to rats in a diet enriched with lipid and cholesterol for 30 days. In the heshiko extract group, increase of triglyceride, total cholesterol, and low-density lipoprotein (LDL)-cholesterol levels in plasma and accumulation of total lipids in the liver were suppressed, while amounts of both lipid and cholesterol excreted to feces were increased. Administration of heshiko extract tended to increase fecal bile acids and promoted the activity of cholesterol 7a-hydroxylase, the rate-limiting enzyme in the synthesis of bile acid from cholesterol in the liver. However, activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol synthesis system in the liver, decreased due to regulation by the feedback of lipid transportation from diet to the liver. The same effect was observed in the peptide and free amino acid fraction groups. These data suggest that both excretion of cholesterol and bile acid to feces and promotion of cholesterol 7a-hydroxylase activity are related to the hypocholesterolemic effects of heshiko extract and that both peptides and amino acids contribute to that effect.

Narezushi extract was separated into peptide and nonpeptide fractions by ion-exchange column chromatography. The narezushi extract and fractions were administered to rats in a diet enriched with lipid and cholesterol for 30 days. In the narezushi extract and nonpeptide fraction groups, increases in triglyceride, total cholesterol, and low-density lipoprotein-cholesterol levels in the plasma and accumulation of total lipids and triglyceride in the liver were suppressed, while both lipid and cholesterol fecal excretion were increased. In the peptide fraction group, these effects were also observed, except for the suppressing effect on liver lipid accumulation. Narezushi extract administration tended to increase fecal bile acids and promoted the activity of cholesterol 7a-hydroxylase, the rate-limiting enzyme in the synthesis of bile acid from cholesterol in the liver. However, the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in the cholesterol synthesis system in the liver, decreased due to regulation by the feedback of lipid transportation from diet to the liver. These results suggest that both the increase in cholesterol and bile acid fecal excretion and the promotion of cholesterol 7a-hydroxylase activities are related to the hypocholesterolemic effects of narezushi extract. Amino acids and organic acids, which are abundantly contained in the nonpeptide fraction, seemed to have more intensive hypocholesterolemic effects than peptides existing in the peptide fraction.