Involvement of nitric oxide in hyporeactivity of rat mesenteric vascular bed during endotoxic shock: effect of dexamethasone and endothelin-I

The present study was carried out on mesenteric vascular bed from LPS-injected rats in order to investigate the cause of hyporesponsiveness in resistance blood vessels, during septic shock syndrome. The involvement of L-Arg/NO pathway was evaluated by administration of L-Arg, which produced a decrease in perfusion pressure in LPS-treated rats, whereas it was ineffective in control rats. Furthermore, DEX-pretreatment in endotoxaemic rats significantly reduced the vasorelaxation by L-Arg, whereas it was ineffective to reverse vascular hyporeactivity occurring in septic shock. In order to evaluate whether hyporesponsiveness could be due to defects in contraction mechanisms, we tested the effect of ET-I. This peptide was able to markedly enhance the contractile response to NA in LPS-treated rats. Our findings suggest that vascular hyporesponsiveness during septic shock may depend on both activation of the L-Arg/NO pathway and alterations in post-receptor mechanisms involving calcium handling.

Postnatal developmental changes of receptor responsiveness in rat mesenteric vascular bed

1. The response to perivascular nervous stimulation (PNS) and the responsiveness to receptor agonists, in different stages of neurogenesis, on rat mesenteric vascular bed (MVB), was investigated. Rats of different age groups (5-7, 9-11, 14-16, 20-22 days) were tested, using 60-day-old rats as controls. 2. In the 5-7 days age group, the response to PNS was resistant to TTX treatment (1 x 10(-6) M). The TTX inhibition increased with age and became almost complete in 60-day-old rats. 3. In the 1st week of postnatal life (pre-innervation period), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) produced contraction, whereas isoprenaline (ISO) and dopamine (DA) caused relaxation. During the 1st and 2nd week, pD2 values of NA and ISO were significantly higher than in adult control rats. No significant difference in pD2 values of 5-HT and DA was observed during postnatal development. 4. At 5-7 days, the relaxation by acetylcholine (ACh), typical of adult age, was absent and ACh evoked only contractile responses. The relaxant effect by ACh appeared at 9-11 days, increased with age and, by the end of the 2nd week, did not differ from that of the adult group. 5. These results provide evidence that responsiveness of all tested receptors in the MVB is already present in the pre-innervation period (1st week). Adrenergic receptor responsiveness is higher at birth and decreases by the end of the 3rd week of postnatal life, when connections between the central nervous system and effector organs are established. Only muscular muscarinic receptors, responsible for ACh-induced contraction, are functional in the 1st week, while endothelial muscarinic receptors, responsible for ACh-induced relaxation, become gradually responsive later in postnatal life.

Intestinal absorption of bile acids in the rabbit: different transport rates in jejunum and ileum

BACKGROUND & AIMS

A direct comparison of jejunal and ileal absorption rates of bile acids has not been reported. The aim of this study was to compare the relative transport rates of different bile acids in the jejunum and ileum.

METHODS

Jejunal and ileal rabbit intestinal segments were separately perfused with bile acid solutions, and dose-response curves were obtained for taurocholate, ursodeoxycholate, chenodeoxycholate, deoxycholate, and their glycoconjugates. Membrane fluidity and bile acid transport were assessed in brush border membrane vesicles.

RESULTS

Taurocholate showed active transport in the ileum and no transport in the jejunum. Unconjugated bile acids showed passive diffusion in the two tracts, whereas glycoconjugated bile acids showed both components of transport in the ileum and passive diffusion in the jejunum (lower in the latter). A higher membrane fluidity and lower cholesterol-to-phospholipid ratio were found in the jejunum. Ursodeoxycholate reduced bile acid uptake into membrane vesicles from both ileum and jejunum.

CONCLUSIONS

Active transport is limited to the ileum. Passive diffusion is higher through a less fluid membrane with a higher cholesterol-to-phospholipid ratio in the ileum than in the jejunum. Ursodeoxycholate inhibition may be at the level of a facilitated, sodium-independent diffusion in the jejunum.

Species differences in hepatic bile acid uptake: comparative evaluation of taurocholate and tauroursodeoxycholate extraction in rat and rabbit

Dose-response curves for taurocholate and tauroursodeoxycholate were performed in rat and rabbit livers to get more insight into species differences in the hepatic bile acid uptake. The bile acids showed saturation kinetics in both animals, the Vmax in rat being higher than in rabbit and the Km being lower in the rat than in the rabbit for both the bile acids, with no significant difference in the hepatic cells morphometric parameters. Therefore, it is possible that differences in the kinetic parameters are related to the number and, to a lesser extent, to the affinity of the transporters on the sinusoidal plasma membranes.

Bile acid structure and intestinal absorption in the animal model

A close structure-activity relationship exists between the transport of bile acids (BA) in the liver and intestine; hepatic and intestinal BA transport can be evaluated and compared by using perfused liver and perfused intestine in the rabbit. The passive intestinal absorption is limited to the unconjugated BA, which occurs throughout the small bowel and colon, and is conditioned by the apical membrane lipid composition. A higher diffusion component is found in the terminal ileum compared to the jejunum, and seems to be related to the higher cholesterol-to-phospholipid ratio of the ileal brush border membranes. The active transport system is well characterized and the brush border membrane receptor, cytosolic BA binding proteins and basolateral anion exchange protein have been identified. Recently, the ileal BA transporter has been cloned from the hamster and human ileum and the main cytosolic BA binding protein was cloned from the rat ileum. In the liver, the active transport predominates on the passive diffusion both for conjugated and unconjugated BA. The maximal transport capacity in the liver is tenfold higher than in the intestine, while the Km values are of the same order of magnitude, i.e. in the millimolar range. Neither system operates at its maximum transport rate with prevalent concentrations of BA in portal blood or luminal content.

Hepatic uptake and intestinal absorption of bile acids in the rabbit

The existence of transporters for bile acids (BA) in liver and intestine has been well documented, but information is still needed as to their respective transport capacity. In the present investigation, we compared the hepatic and intestinal transport rates for BA, using perfused livers and intestines. The livers and intestines were separately perfused and dose-response curves (0.25-10 mM) for tauroursodeoxycholate, taurocholate and taurodeoxycholate were obtained. The intestinal and mesenteric concentration and bile acid pattern were also evaluated in six non-fasting rabbits. Taurocholic, tauroursodeoxycholic and taurodeoxycholic acid ileal absorption showed saturation kinetics in the intestine as in the liver; the maximal uptake velocity for each bile acid in the liver was tenfold higher than the respective maximal transport velocity in the intestine; the Km values obtained in the liver were of the same order of magnitude, i.e. in the millimolar range. Taurocholic, tauroursodeoxycholic and taurodeoxycholic acid transport differences in the liver paralleled those in the intestine. Although the intestine was not homogeneously filled, the bile acid concentration in the ileal content fell into the range of the Km for the three studied bile acids, while the portal blood total bile acid concentration was inferior to the observed Kms of liver uptake. Therefore, both the hepatic and intestinal systems do not operate at their maximal transport rates at the prevailing concentrations in portal blood and luminal content, and the hepatic transport occurs at its highest efficiency (below the Km values) in physiological conditions.

Vasodilatation induced by capsaicin in rat mesenteric vessels is probably independent of nitric oxide synthesis

Vasal relaxation induced by capsaicin was investigated on perfused mesenteric vascular bed prepared from Wistar rats. Bolus infusion of capsaicin, from 3.5 to 16 nmol, elicited a dose-dependent vasal relaxation effect, which was antagonized by pretreatment with 3 x 10(-6) M calcitonin gene-related peptide (CGRP) (8-37), an antagonist of CGRP. In order to test whether NO-release is involved in vasorelaxant response to capsaicin, a preparation of mesenteric vascular bed was perfused and superfused for 1 h by N omega-nitro-L-arginine methyl ester (L-NAME) (3 x 10(-3) M), an NO-synthase inhibitor. Vasodilatation induced by capsaicin remained unchanged, while that induced by acetylcholine, used as control, was significantly reduced. The results indicate that in the mesenteric bed, capsaicin-induced vasodilatation is probably independent of the NO-synthesis mechanism and possibly mediated by CGRP.

Effects of pravastatin treatment on vitamin D metabolites

Hyperlipidemias, and notably hypercholesterolemia, represent important risk factors for atherosclerotic vascular disease. The enzymatic inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase, a selective and specific key enzyme involved in endogenous cholesterol synthesis, cause a significant mean reduction in low-density lipoprotein (LDL) cholesterol, both in familial and nonfamilial hypercholesterolemic forms. It has been hypothesized that these compounds might interfere with vitamin D endogenous synthesis secondarily to their effects on cholesterol. To verify this hypothesis, we studied 14 hypercholesterolemic patients treated as follows: 4 weeks of low-lipid, fiber-rich diet followed by 8 weeks of pravastatin treatment at the oral evening dose of 20 mg/d and by a 1-month washout period. No significant changes in serum calcium, 25-hydroxyvitamin D, and 1,25-dihydroxyvitamin D were noticed; on the contrary, significant (P < 0.01) reductions in total cholesterol and LDL cholesterol and a significant (P < 0.05) increase in high-density lipoprotein cholesterol were observed. After the final 1-month washout period, all values returned to baseline levels. In conclusion, our study confirms the clinical efficacy of pravastatin on lipid fractions and demonstrates the absence of any interference on the circulating levels of the main vitamin D metabolites.

Characterization of a soluble LHRH-degrading activity in the rat ventral prostate

Recent evidence supports the hypothesis of a direct action of LHRH at the level of the prostate. Since peptidases able to degrade the hormone are present in several LHRH target structures, it was deemed of interest to investigate whether the prostate of adult normal male rats might possess LHRH degrading activities (LHRH-DA). Through the use of RP-HPLC, it has been observed that LHRH-DA is present in the soluble fraction of the rat ventral prostate homogenate, and is able to hydrolyze synthetic LHRH and to generate fragments 1-3 and 1-5 of the decapeptide. The degradation of [pGlu-3H]LHRH is inhibited by LHRH itself, and affected by several LHRH agonists and antagonists with different kinetics and potencies. TRH, the enkephalin analog [D-Ala2-D-Leu5]enkephalin and rat prolactin do not inhibit the degradation of [pGlu-3H]LHRH by the soluble fraction of prostate homogenate; on the contrary, this is inhibited by graded doses of somatostatin. The prostatic LHRH-DA is also inhibited, in a dose dependent manner, by bacitracin, serine protease inhibitors (diisopropylfluorophosphate and phenylmethansulfonylfluoride), the metal chelating agent EDTA, HgCl2, and dithiothreitol. No inhibitory effect on [pGlu-3H]LHRH hydrolysis was observed after incubation of the prostatic extract in the presence of captopril. The prostatic LHRH-DA seems to be different from that present in other tissues of the rat (e.g., hypothalamus, pituitary, gonads), and to be decreased by castration performed 3 weeks before. These results suggest that (1) an LHRH-DA is found in the soluble fraction of rat prostate homogenate; (2) this enzymatic activity exhibits the characteristics of a metallo- and thiol-dependent neutral endopeptidase; (3) it appears to be different from similar hydrolytic activities found in other tissues; and (4) it is influenced by the hormonal milieu, since castration causes a significant decrease of its activity.

An effective regimen of intranasal salmon calcitonin in early postmenopausal bone loss

In order to devise a convenient and effective therapeutic regimen of intranasal salmon calcitonin (sCT) for the treatment of early postmenopausal bone loss, we studied the effects of a 1-year course of sCT nasal spray on vertebral mineral content (VMC), assessed by dual photon densitometry, and bone turnover in 21 early postmenopausal osteoporotic women. Subjects enrolled in the study had a value above the normal average of at least one index of bone turnover: whole body retention (WBR) of 99mTc-methylene-dichloro-bisphosphonate (99mTc-MDP), serum bone gla protein (BGP), urinary hydroxyproline/creatinine excretion (HOP/Cr). After baseline evaluation, patients were randomized for treatment with either sCT (200 IU every other day) or placebo. Treatment with sCT significantly increased VMC by 2.7 +/- 0.9% at 6 months, and 3.3 +/- 0.8% at 1 year, whereas a progressive decline was observed in the placebo group (-2.6 +/- 0.5%, and -3.5 +/- 0.5% after 6 and 12 months, respectively). These changes were associated with a progressive and significant reduction of all parameters of bone turnover in the sCT-treated patients, whereas no changes were detected in the control group during the study period. The differences between the two groups were significant after 1 year for VMC, BGP, and WBR (P less than 0.05, one-way analysis of variance). Thus, 200 IU intranasal sCT administered on alternate days is adequate to stop the fast bone loss occurring early after the menopause in women with high bone turnover rates. This therapeutical modality represents an important addition to the available pharmacologic spectrum for the prevention and treatment of postmenopausal osteoporosis.

Clinical evaluation of ceftazidime in high risk patients

Ceftazidime was used in 19 patients at high risk owing to severe impairment of natural defense systems. The therapeutic efficacy and adverse reactions produced by cephalosporin, as evaluated on the basis of the results of clinical investigations and laboratory tests, were regarded as positive.

Effects of prednisone and deflazacort on mineral metabolism and parathyroid hormone activity in humans

The effects of two different glucocorticoids, prednisone and deflazacort, (an oxazoline derivative of prednisolone) on bone metabolism were analyzed in 10 patients with disorders that required glucocorticoid therapy. Significant elevations in blood immunoreactive parathyroid hormone, alkaline phosphatase and urinary calcium, phosphate, hydroxyproline and nephrogenous cyclic AMP were observed during prednisone therapy in addition to an increase in the exchangeable calcium pool as estimated by 47Ca-kinetic analyses. In contrast to these changes, deflazacort therapy induced minimal, and in some instances, no changes in these indices. In fact, in studies wherein prednisone therapy was followed by deflazacort alterations in bone metabolism, iPTH, and nephrogenous cAMP observed during prednisone were reversed. The data are consistent with the fact that the skeletal effects of prednisone therapy are mediated, at least in part, by increased parathyroid hormone activity, and that deflazacort is less potent in this regard.