Inhibitory effect of αS1- and αS2-casein hydrolysates on angiotensin I-converting enzyme in human endothelial cells in vitro, rat aortic tissue ex vivo, and renovascular hypertensive rats in vivo.

A great number of milk-derived peptides have been shown to exhibit angiotensin converting enzyme (ACE) inhibitory properties and thus potential utility in the regulation of blood pressure. The present work aimed to investigate the effects of 2 milk trypsin hydrolysates from alpha(S1)- and alpha(S2)-casein (CH1 and CH2, respectively) on ACE activity evaluated in human umbilical vein endothelial cells (HUVEC) in vitro, rat aortic tissues ex vivo, and renovascular hypertensive rat in vivo. Incubation of HUVEC and rat aortic tissues with CH1 or CH2 induced a concentration-dependent inhibition of hydrolysis of the ACE substrate hippuryl-histidyl-leucine (HHL), the hydrolysates being much less potent than perindopril (an ACE inhibitor). However, in contrast to perindopril, CH1 and CH2 failed to modify angiotensin I-induced aortic ring vasoconstriction. The HPLC profiles of rat plasma after intragastric administration were variable among individuals but none of the observed peaks corresponded to peptides comprising CH1 or CH2 or to fragments of these peptides. During 4 wk of cardiovascular monitoring, in hydrolysate-fed renovascular hypertensive rats, systolic blood pressure weakly decreased compared with the control group. However, the CH1-fed hypertensive rats exhibited a decrease of heart rate during the nocturnal period of activity. To conclude, our results show that CH1 and CH2 inhibited ACE activity in HUVEC and rat aortic tissue but failed to antagonize the aortic-constricting effects of the natural agonist angiotensin I. Moreover, we demonstrated that CH1, to a greater extent than CH2, can slightly affect cardiovascular parameters although the ingested bioactive peptides could not be detected in the blood.

Absorption and efficiency of insulin after oral administration of insulin-loaded nanocapsules in diabetic rats.

Poly(isobutylcyanoacrylate) nanocapsules have been shown to decrease the blood glucose level after oral administration to streptozotocin-induced diabetic fasted rats after 2 days [Diabetes 37 (1988) 246]. Yet, the absorption of insulin in the blood of rats has not been characterised. The aim of this work was to evaluate the biological activity of insulin given orally as nanocapsules. Humalog-loaded nanocapsules (50 IU/kg) were administered by gavage to streptozotocin-induced diabetic rats. Thirty minutes to 1 h after oral administration, significant levels of human insulin were detected in rat plasma. However, the concentrations were very heterogenous from one rat to another and no decrease of glycemia could be observed. In addition, parenteral injection of insulin in solution showed that high levels of the protein are necessary to decrease blood glucose concentration in diabetic rats. These concentrations were not reached after oral administration. The same dose of insulin decreased glycemia by 50% in normal rats and by only 25% in diabetics. This suggested that an insulino-resistance was developed by streptozotocin-induced diabetic rats.

Chronic administration of verapamil, ketoconazole and carbamazepine: impact on immunological parameters.

Inhibitors of P-glycoprotein (P-gp) (verapamil) or cytochrome P-450 (ketoconazole) may reduce IL2 production and T lymphocyte proliferation in vitro. We have examined the effects of chronic oral administration of these drugs and of the cytochrome P450 inductor, carbamazepine, on the hematological and immunological parameters of mice. We found no changes after giving the mice 0.12 mg verapamil, 0.85 mg ketoconazole, or 0.514 mg carbamazepine per mouse for 4 weeks (5 days/week). But giving the drugs for an additional 7 weeks at 0.6 mg (verapamil), 4.25 mg (ketoconazole) or 2.57 mg/mouse (carbamazepine), resulted in significant decreases in monocytes in the verapamil treated group (-51%) and in CD4+ cells in the carbamazepine group (-35%). Chronic oral administration of these drugs reduced the lymphocyte counts of mice by 10-18% and their NK counts by 10-16%. These changes could be due to changes in P-gp function in the transport of IL2, with decreases caused by verapamil and ketoconazole.

Effect of chronic renal failure on the expression and function of rat intestinal P-glycoprotein in drug excretion.

BACKGROUND: In chronic renal failure, the renal excretion of certain drugs is dramatically reduced. To determine whether other routes of drug elimination, such as secretion through the intestinal barrier by intestinal P-glycoprotein can be altered, we compared P-glycoprotein activity, P-glycoprotein protein content, and P-glycoprotein mRNA levels in intestine of control and chronic renal failure rats. METHODS: Chronic renal failure was surgically induced in rats by partial (7/8) nephrectomy. After 5 weeks, intestinal transport of rhodamine 123, a P-glycoprotein substrate, was carried out using an in vitro model of everted gut sacs. P-glycoprotein protein content was quantified by enzyme-linked immunosorbent assay and P-glycoprotein mRNA expression was evaluated by semi-quantitative reverse transcriptase polymerase chain reaction. RESULTS: A decrease of intestinal rhodamine 123 transport was observed in chronic renal failure rats, pointing to an inhibition of P-glycoprotein activity. Transport was inhibited in both sham-operated rats and rats with chronic renal failure by verapamil and cyclosporin A, but relative inhibition vs baseline was less marked in chronic renal failure than in sham-operated rats. In contrast, no significant differences in levels of P-glycoprotein protein or mRNA were observed between the two groups. CONCLUSIONS: Intestinal secretion of rhodamine 123 is mainly mediated by P-glycoprotein. It was reduced in rats with chronic renal failure, reflecting reduced intestinal drug elimination via a decrease in P-glycoprotein transport activity rather than via protein underexpression.

Role of transcellular pathway in ileal Ca2+ absorption: stimulation by low-Ca2+ diet.

The present study was performed to determine the respective involvement of the cellular and paracellular routes in ileal Ca2+ transport. Two groups of rats were either fed a normal Ca2+ diet (1. 0%) or a Ca2+-deficient diet (0.02%) for 14 days. Ileal Ca2+ absorption was determined using both an in situ method of continuous luminal perfusion and an in vitro method (Ussing chamber model). The low-Ca2+ diet stimulated net Ca2+ flux in the ileum twofold, associated with a twofold increase of the mucosal-to-serosal Ca2+ flux in both models. This effect was observed in the absence of concomitant changes in Na+ or water flux in the in situ model or mannitol flux in the in vitro model, excluding the participation of the paracellular pathway in Ca2+ transport. Thus only cellular Ca2+ flux was stimulated. These data suggest that the ileum plays a major role in the adaptation to low dietary Ca2+. Whereas under physiological conditions with usual Ca2+ intakes the transcellular pathway of Ca2+ transport is negligible, it becomes of major importance in the case of Ca2+ deficiency, at least under the present conditions of severe Ca2+ deprivation.

[Stimulation of ileal transport of calcium by sorbitol in in situ perfused loop in rats]. / Stimulation du transport iléal du calcium par le sorbitol en anse perfusée in situ chez le rat.

OBJECTIVES: The aim of this study was to study the effect of sorbitol on sodium, water and calcium fluxes in rat ileum in situ perfused loop. METHODS: Net water, sodium and calcium fluxes, and one-way calcium fluxes were measured in situ in a perfused rat ileal loop in the presence of varying concentrations of sorbital. RESULTS: High concentrations of sorbitol in perfused ileal solution induced a decrease of sodium and water fluxes and a concomitant increase of lumen to mucosa calcium flux associated with an increase of net calcium flux, using a solution containing either 8.0 or 1.25 mM calcium. These effects were independent of absolute initial values of water and sodium fluxes. They were observed in the presence of 25 mM glucose, 10 mM theophyllin or after treatment of rats with dexamethasone. CONCLUSION: These effects of sorbitol on calcium flux are not compatible with a stimulation of paracellular pathway. By contrast, they can be explained by a stimulation of transcellular calcium pathway in ileum associated with the hyperpolarisation of the cells induced by the decrease of luminal sodium concentration necessary in the presence of sorbitol to maintain unchanged osmolarity of perfusate.

Changes in plasma testosterone levels during the peri-hatching period in the chicken.

Blood was obtained by heart puncture from 19-day-old Black Sex link chicken embryos and from Black Sex link chickens at 1.5, 6, or 24 h post-hatching. Plasma testosterone was determined by gas chromatography-mass spectrometry associated with stable isotope dilution. At 19 days the plasma of male and female chick embryos contains measurable amounts of testosterone and levels do not differ between sexes. After hatching plasma testosterone gradually declines from pre-hatch concentrations in males and females, but in all the post-hatch ages studied, plasma testosterone was significantly higher in male than in female chicks. These results indicate that in male chickens, contrary to mammals at birth, there is no surge in plasma testosterone at hatching.

Effect of diet on folates levels and distribution in selected tissues of the rat.

A technique for the extraction, purification and concentration of folates, followed by high performance liquid chromatography assay with fluorometric detection of the three principal derivatives (tetrahydrofolic, 5-methyl-tetrahydrofolic and formyl-tetrahydrofolic acids) has been applied to the determination of tissue folates in rats. The levels found are compared to those of the microbiological assay using Lactobacillus casei. When rats were fed a diet containing 1 mg of folic acid per kg of food, levels in the intestinal mucosae, liver, whole blood and brain were 0.59, 14.87, 0.28 and 0.83 nmol/g of tissue. An exogenous supply of 200 mg of folic acid/kg of food significantly increased folate levels in all tissues studied, except for the brain: 1.51, 28.93, 0.52 and 0.99 nmol/g, respectively in the above four tissues. The separation of the various derivatives and a variable supply of folic acid have enabled the conversions of these metabolites to be studied.