Antihypertensive effect of peptides obtained from Enterococcus faecalis-fermented milk in rats.

Previous studies have demonstrated that milk fermented with Enterococcus faecalis decreases the systolic blood pressure (SBP) and the diastolic blood pressure (DBP) of spontaneously hypertensive rats. In this study, we evaluated the antihypertensive activity of the following peptide sequences: LHLPLP, LHLPLPL, LVYPFPGPIPNSLPQNIPP, VLGPVRGPFP, and VRGPFPIIV. These peptides isolated from E. faecalis-fermented milk showed in vitro angiotensin I-converting enzyme-inhibitory activity. Because the most potent angiotensin I-converting enzyme-inhibitory sequences were LHLPLP and LVYPFPGPIPNSLPQ-NIPP, we administered different doses of these peptides to spontaneously hypertensive rats. High doses of the remaining sequences were also administered to these animals. Water served as a negative control and captopril as a positive control. All products were administered orally. The SBP and DBP were measured before administration and also at 2, 4, 6, 8, and 24 h after administration. Before administration of the different products, spontaneously hypertensive rats showed SBP and DBP values of 218 +/- 2.5 and 157 +/- 5.9 mmHg, respectively (n = 30). The sequences LHLPLP, LVYPF-PGPIPNSLPQNIPP, VLGPVRGPFP, and VRGPFPIIV caused clear and significant decreases in SBP, DBP, or both in the animals. In particular, the antihypertensive effect could be clearly established when 2 or 3 mg/kg of LHLPLP was administered. These 2 doses of LHLPLP showed similar antihypertensive properties. Four hours after administration of captopril or the highest doses of the different peptides, the decreases in the SBP and the DBP (mmHg) were as follows: captopril (SBP = 52 +/- 5.8, DBP = 38.8 +/- 3.8), 3 mg/kg of LHLPLP (SBP = 25.3 +/- 8.2, DBP = 29.5 +/- 7.6), 6 mg/kg of LVYPFPGPIP-NSLPQNIPP (SBP = 14.9 +/- 3.7, DBP = 8.7 +/- 4.4), 10 mg/kg of LHLPLPL (SBP = 7.7 +/- 4.1, DBP = 9.4 +/- 3.1), 10 mg/kg of VLGPVRGPFP (SBP = 16.2 +/- 5.8, DBP = 21.64 +/- 3.2), and 10 mg/kg of VRGPFPIIV (SBP = 16.05 +/- 2.74, DBP = 9.19 +/- 3.49). The results obtained suggest that the sequences LHLPLP, LVYPFPGPIPNSLPQ-NIPP, VLGPVRGPFP, and VRGPFPIIV could be responsible, at least in part, for the antihypertensive properties described for E. faecalis-fermented milk.

Effect of simulated gastrointestinal digestion on the antihypertensive properties of ACE-inhibitory peptides derived from ovalbumin.

Food-derived bioactive peptides with ACE-inhibitory properties are receiving special attention due to their beneficial effects in the treatment of hypertension. In this work we evaluate the impact of a simulated gastrointestinal digestion on the stability and activity of two bioactive peptides that derive from ovalbumin by enzymatic hydrolysis, YAEERYPIL and RADHPFL. These peptides possess in vitro ACE-inhibitory activity and antihypertensive activity in spontaneously hypertensive rats (SHR). The results showed that YAEERYPIL and RADHPFL were susceptible to proteolytic degradation after incubation with pepsin and a pancreatic extract. In addition, their ACE-inhibitory activity in vitro decreased after the simulated digestion. The antihypertensive activity on SHR of the end products of the gastrointestinal hydrolysis, YAEER, YPI, and RADHP, was evaluated. The fragments YPI and RADHP significantly decreased blood pressure, 2 h after administration, at doses of 2 mg/kg, but they probably did not exert their antihypertensive effect through an ACE-inhibitory mechanism. It is likely that RADHP is also the active end product of the gastrointestinal digestion of the antihypertensive peptides FRADHPFL (ovokinin) and RADHPF (ovokinin 2-7).

Changes in arterial blood pressure in hypertensive rats caused by long-term intake of milk fermented by Enterococcus faecalis CECT 5728.

We have evaluated the changes in arterial blood pressure caused in spontaneously hypertensive rats (SHR) by long-term intake of an Enterococcus faecalis CECT 5728-fermented milk with significant angiotensin-converting enzyme (ACE)-inhibitory activity. After being weaned, male 3-week-old SHR were randomized into five groups. Until the 20th week of life, rats in each group were given one of the following drinking fluids: tap water (negative control 1), a fermented milk without ACE-inhibitory activity (negative control 2), captopril (100 mg/kg) (positive control), the E. faecalis CECT 5728-fermented milk that had significant ACE-inhibitory activity, or Ca-enriched E. faecalis CECT 5728-fermented milk. Animals in the different groups were then given tap water as drinking fluid from the 20th to 25th week of life. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured weekly in the rats, from the 6th to 25th week of life, by the tail-cuff method. A definite decrease in SBP and DBP could be observed in the rats treated with captopril and also in the rats that received the E. faecalis CECT 5728-fermented milks. The greatest antihypertensive effect was observed when the pharmacological treatment was administered. The effect of the Ca-enriched fermented milk was slightly more accentuated and more constant than the effect of the E. faecalis CECT 5728-fermented milk that had not been enriched in Ca. SBP and DBP increased in the treated SHR when the corresponding antihypertensive treatment was removed. Fermentation of milk with E. faecalis CECT 5728 may therefore be a successful strategy to produce a functional food with antihypertensive activity.

A comparison of the effects of TMB-8 and nifedipine on pressor responses to alpha 1- and alpha 2-adrenoceptor agonists in pithed rats.

TMB-8 has been characterized as an inhibitor of the release of Ca2+ from intracellular pools. We have studied the modification of the pressor responses to selective alpha 1-adrenoceptor agonists (methoxamine and phenylephrine), and to selective alpha 2-adrenoceptor agonists (B-HT 920 and B-HT 933) in pithed rats, produced by TMB-8. We have compared this modification with that produced by the calcium antagonist nifedipine. Nifedipine (100 micrograms/kg, 300 micrograms/kg, and 1000 micrograms/kg) inhibited in a dose-dependent manner the pressor responses to the alpha 1- and alpha 2-adrenoceptor agonists, the dose-response curves to the alpha 2-adrenoceptor agonists being shifted further to the right. TMB-8 at a dose of 3000 micrograms/kg did not modify the pressor effects of the alpha 1-adrenoceptor agonists, and neither did it reinforce the inhibition of such responses produced by nifedipine. By contrast, TMB-8 pretreatment (0.03 micrograms/kg, 0.3 micrograms/kg, 3 micrograms/kg, 30 micrograms/kg, 300 micrograms/kg and 3000 micrograms/kg) inhibited the responses to both alpha 2-adrenoceptor agonists, the inhibition being more pronounced with B-HT 920. A similar effect was obtained with 0.03 micrograms/kg TMB-8 and 0.3 microgram/kg TMB-8, particularly in the case of B-HT 920. It was stronger with higher doses, but similar for all doses over 3 micrograms/kg. The inhibition of the pressor responses mediated by the stimulation of alpha 2-adrenoceptors by TMB-8 was less in rats treated with the Ca2+ entry promoter BAY K 8644 (300 micrograms/kg), and could also be reduced by the continuous infusion of CaCl2 (0.25 microgram/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of acute hypocalcemia in rats.

Decreased plasma calcium levels could produce important changes in cellular functions and drug responses. This communication describes the temporal decrease in calcemia that can be obtained in Sprague-Dawley rats after the ip administration of doses of 1 to 16 IU calcitonin. The injections caused significant reductions in calcemia in this strain of rats, but did not alter the behavior or general condition of the dosed animals. The method described permits the establishment of experimental models of hypocalcemic rats that will be very useful for physiological and pharmacological studies.

Effect of TMB-8 on alpha-adrenoceptor agonist and KC1 induced-contractions in isolated rabbit aorta.

1. TMB-8 (10(-6) M-10(-4) M) depresses the contractile effect of the selective alpha 1-adrenoceptor agonists methoxamine and phenylephrine in the isolated rabbit aorta. 2. TMB-8 also depresses contractions evoked by 80 mM KCl in this tissue when used at similar concentrations. 3. The calcium antagonist nifedipine potentiates the inhibitory effect of TMB-8 on the alpha 1-contractions. 4. In preparations mounted in Ca-free solution containing 0.5 mM EGTA, 10(-4) M TMB-8 markedly depressed the contractions caused by both alpha 1-adrenoceptor agonists. 5. The Ca2+ agonist BAY K 8644 (10(-6) M) partially prevented the inhibitory effect of TMB-8 on 80 mM KCl contractions.

Evaluation of different drugs in two models of immediate hypersensitivity.

The effect of the calcium antagonists, verapamil, nicardipine and diltiazem, the two cromones, disodium cromoglycate and SM-857 (11-oxo-11H-pyrido[2,1-b]quinazoline-2-carboxylic acid), and the anthelmintic, diethylcarbamazine citrate, have been compared on the ovalbumin (OA)-induced contraction of the isolated trachea and longitudinal muscle-myenteric plexus (LM-MP) from sensitized guinea-pigs. The calcium antagonists prevented the OA-induced contractions in LM-MP and to a lesser degree the OA-induced contractions in trachea. Similar doses of SM-857 protected both tissues but neither cromoglycate (10(-5)M) nor diethylcarbamazine (10(-5)M) affected these contractions. The OA-induced contraction in trachea had a tonic phase that was not present in the LM-MP response. Only the calcium antagonists succeeded in relaxing this OA tonic component, diltiazem being the more potent. These results unmask different mechanisms of drug action on immediate hypersensitivity and specific sensibilities, depending on the kind of tissue.

Effects of exposure to high potassium concentration on the longitudinal muscle-myenteric plexus preparation from guinea-pig.

The effect of potassium on the longitudinal muscle-myenteric plexus (LM-MP) preparation from guinea-pig was studied. The strips were exposed to elevated K+ (30 mM, 60 mM, 90 mM, 120 mM or 150 mM). A phasic contraction of the LM-MP was caused by 10 mM K+ or 15 mM K+ followed by an increase of the contractile activity probably due to the increase in acetylcholine release. A higher molarity of K+ produces more marked depolarization in the LM-MP and above 22 mM K+ tetanizing effects were observed. We attempted to demonstrate that opiate-like material could be released when the tissue was exposed to more than 30 mM K+ even though several different neurotransmitters could be liberated by elevated K+ molarities.