Search PubMed⌕ Search

Biomedical subjects

C Gros

Publications and source records attributed to C Gros.

At least 55 records · Page 3Linked to original sources
PubMed1991

Dopaminergic regulation of enkephalin release.

The effects of dopamine receptor stimulation on enkephalin release were evaluated in vitro and in vivo by measuring the changes in the levels of [Met5]enkephalin (YGGFM) and Tyr-Gly-Gly (YGG), a characteristic extracellular enkephalin metabolite produced under the action of enkephalinase. In rat striatal slices, D1-receptor agonists or antagonists did not modify enkephalin release. By contrast, D2-receptor agonists enhanced the potassium-induced release of YGGFM and YGG without affecting spontaneous release from nondepolarized slices. This response was prevented by the D2-receptor antagonists haloperidol and RIV 2093, the latter compound being more potent, which suggested the involvement of a putative D2-receptor subtype. Acute administration of apomorphine or selective D2-receptor agonists, but not that of a D1-receptor agonist, enhanced the steady-state level of YGG without affecting the YGGFM level in rat striatum. The effect was blocked selectively by D2-receptor antagonists which, administered alone, had no effect. These observations indicate that D2-receptor stimulation in vitro or in vivo facilitates enkephalin release from striatal neurons, but that endogenous dopamine does not exert any tonic influence upon the opioid peptide neuron activity under basal conditions. However, chronic administration of haloperidol resulted in increases in striatal YGGFM and YGG, an effect presumably reflecting a long-term adaptive process.

Animals↗
PubMed1991

Effect of sinorphan, an enkephalinase inhibitor, on plasma atrial natriuretic factor and sodium urinary excretion in cirrhotic patients with ascites.

We examined the acute effects of sinorphan, an inhibitor of enkephalinase, on plasma atrial natriuretic factor (ANF) and urinary sodium excretion in cirrhotic patients with ascites. A single oral dose of sinorphan (100 or 30 mg in 11 and 5 patients, respectively) was administered against placebo according to a double blind cross-over protocol. Basal plasma ANF levels varied over a large range between 2.6-79 pmol/L. Sinorphan, at a dose of 100 mg, inhibited 70% of plasma enkephalinase activity 60 min after ingestion and elicited simultaneously an increase in plasma ANF and cGMP levels 1.8 and 1.5 times basal values, respectively. There was a transient increase in sodium urinary output without a change in creatinine clearance over the initial 2-h period following drug administration. An increase in urinary cGMP was also observed on a longer period of 6 h. Plasma aldosterone decreased significantly, but the lowest concentration was reached 1 h later than the peak of plasma ANF. Mean blood pressure and PRA were unmodified. The effects of 30 mg sinorphan on plasma ANF, cGMP, and aldosterone were also significant, but less marked than those of the higher dose. Therefore, enkephalinase inhibition transiently increases sodium urinary excretion in cirrhotic patients with ascites via a mechanism that is likely to imply reduction of ANF catabolism. These results suggest that ANF could play a role in the control of sodium homeostasis in liver cirrhosis with ascites.

Administration, Oral↗
PubMed1991

Thiorphan-induced natriuresis in volume-expanded rats: roles of endogenous atrial natriuretic factor and kinins.

Thiorphan, a potent inhibitor of enkephalinase (membrane metalloendopeptidase, atriopeptidase, EC 3.4.24.11) enhanced markedly (+214%) and prolonged the rise in plasma atrial natriuretic factor (ANF) immunoreactivity in anesthetized rats submitted to acute extracellular volume expansion obtained through i.v. injection of a Ringer's solution. These changes were accompanied by marked potentiations of the natriuretic and diuretic responses to the ANF-releasing stimulus, whereas kaliuresis was only slightly affected. Thiorphan also enhanced markedly the biphasic rise in urinary cyclic GMP excretion elicited by volume expansion. All these renal responses to volume expansion in thiorphan-treated rats were significantly reduced by pretreatment with anti-ANF antibodies, suggesting an involvement of the endogenous natriuretic hormone protected against degradation. However, pretreatment with antibradykinin antibodies led to qualitatively similar results, suggesting that the endogenous kinin-generating system in kidney may also participate in the responses to endogenous ANF and their potentiation by the peptidase inhibitor.

Animals↗
PubMed1990

Inactivation of atrial natriuretic factor in mice in vivo: crucial role of enkephalinase (EC 3.4.24.11).

Atrial natriuretic factor (ANF) is a hormone whose potent hemodynamic and renal actions might be beneficial in several cardiovascular disorders, but whose poor oral absorption and extremely rapid inactivation in vivo have so far prevented its therapeutic use. We have developed simple tests to study the peptidases responsible for the hydrolysis of ANF in mice in vivo and to assess the effects of peptidase inhibitors. In mice injected with 125I-ANF in low amounts the radioactivity present in kidney, a major target organ for the hormone, was analysed by HPLC, precipitation with trichloracetic acid (TCA) and in a membrane binding assay. All three parameters indicated a rapid inactivation of the hormone: 20 s after injection of 125I-ANF the intact hormone represented less than 20% of the total kidney radioactivity. Oral pretreatment with acetorphan, a potent enkephalinase inhibitor resulted in a marked increase in the amount of intact 125I-ANF (6-fold), TCA-precipitated (5-fold) and membrane bound radioactivity (4-fold) in the kidney; the total kidney radioactivity was enhanced by approximately 2-fold. A similar protective effect was observed with other enkephalinase inhibitors, i.e. thiorphan and kelatorphan; the latter was effective at a 10-fold higher dosage. In contrast, a large variety of inhibitors of metallo-, cysteine, serine and aspartic proteinases had no or only marginal effects. Instead, captopril, an angiotensin-converting enzyme inhibitor, reduced the total and TCA-precipitable radioactivity in the kidneys. Aminopeptidase inhibitors, used either alone or in conjunction with acetorphan, displayed significant but limited protective effects. The crucial role of enkephalinase in ANF inactivation in vivo suggests that inhibitors of this peptidase could be used in a novel therapeutic approach to cardiovascular or renal diseases by protecting endogenous ANF.

Administration, Oral↗
PubMed1990

Diuretic and natriuretic responses in rats treated with enkephalinase inhibitors.

Rat atrial natriuretic factor (125I-rANF, 99-128) is hydrolysed by pure enkephalinase (EC 3.4.24.11) in vitro at a rate similar to that of 125I-hANF. Trichloroacetic precipitated radioactivity was significantly elevated in the kidneys of rats pretreated with acetorphan, an enkephalinase inhibitor, and receiving 125I-rANF, indicating that the exogenous hormone was protected against degradation. A single oral administration of acetorphan elicited diuretic and natriuretic effects in conscious normotensive rats and natriuretic effects in spontaneously hypertensive rats, effects which were not accompanied by significant changes in kaliuresis. The diuretic and natriuretic effects were still observed in conscious normotensive rats after three days of repeated administration of the drug. In conscious or anesthetized rats in which volume expansion was elicited by hydroelectrolytic loads, the initial rate of urinary elimination of water and sodium was nearly doubled by treatment with enkephalinase inhibitors. This effect was prevented by coadministration of an ANF antiserum, which suggests that the effect was mediated by endogenous ANF. These various observations suggest that enkephalinase inhibitors protect endogenous ANF from degradation and thereby enhance the typical renal effects of the hormone.

Animals↗
PubMed1990

Stereoselective protection of exogenous and endogenous atrial natriuretic factor by enkephalinase inhibitors in mice and humans.

We compared the relative potencies of sinorphan and retorphan, the S- and R-enantiomers of acetorphan a potent inhibitor of enkephalinase (EC 3.4.34.11), to inhibit membrane metalloendopeptidase in vivo and to protect exogenous and endogenous ANF after oral administration. In mice, sinorphan was 2-3 fold as potent as retorphan in inhibiting the specific in vivo binding of [3H]acetorphan to kidney enkephalinase. The same potency ratio was found for the enhancement of trichloroacetic acid-precipitated radioactivity in kidneys of mice that had received 125I-ANF, which is used as a test for the protection of the hormone against inactivation in vivo. In nine healthy human volunteers who had received a low oral dosage of sinorphan or retorphan in a double-blind, placebo-controlled, randomized trial, sinorphan was also 2-3 fold more potent than retorphan in inhibiting plasma enkephalinase activity. These effects were accompanied by a related rise in plasma ANF immunoreactivity, which also reflected the difference in the effectiveness of the two compounds. Sinorphan was also more potent than retorphan in enhancing urinary cyclic GMP excretion and sodium excretion in five of these subjects. These data indicate that, in humans as in rodents, enkephalinase plays a crucial role in the inactivation of ANF, its partial inhibition in vivo being accompanied by a significant protection of the exogenous or endogenous hormone as well as by typical ANF-like responses. Thus orally administered sinorphan appears to be a promising compound for therapeutic use in cardiovascular and renal diseases in which ANF has been postulated to exert beneficial effects.

Administration, Oral↗
PubMed1990

Enkephalinase (EC 3.4.24.11) inhibitors: protection of endogenous ANF against inactivation and potential therapeutic applications.

Atrial natriuretic factor (ANF) is a cardiac hormone exerting potent cardiovascular and renal effects but its poor intestinal absorption and rapid inactivation have prevented so far its therapeutic utilisation. However inhibition of endogenous ANF metabolism progressively emerges as a novel therapeutic approach in cardiovascular and renal disorders. The critical role played by enkephalinase (membrane metalloendopeptidase, EC 3.4.24.11) in ANF inactivation was deduced from the effects of inhibitors. These compounds not only protect partially exogenous ANF from hydrolysis by some tissue preparations in vitro but also, in vivo, they increase the half-life of the exogenous hormone in plasma and, even more markedly, its recovery in intact form in kidney, a major target organ. In addition, enkephalinase inhibitors increase by two- to three-fold the circulating level of endogenous ANF, even when the latter is already markedly elevated, such as in patients with chronic heart failure. Finally, enkephalinase inhibitors induce a series of ANF-like responses such as natriuresis, diuresis or increase in cGMP excretion which are attributable to the hormone. These pharmacological observations, as well as preliminary clinical trials, suggest that enkephalinase inhibitors may represent a novel class of therapeutic agents with potential applications in congestive heart failure, essential hypertension and various sodium-retaining states.

Amino Acid Sequence↗
PubMed1990

Degradation of atrial natriuretic factor in mouse blood in vitro and in vivo: role of enkephalinase (EC 3.4.24.11).

The half-life of 125I-ANF (99-126) in mouse blood in vivo, evaluated after HPLC analysis, was approximately 0.5 min. This value was nearly doubled in mice pretreated with sinorphan, an enkephalinase inhibitor. 125I-ANF is also hydrolyzed by mouse blood in vitro but its half-life is much longer and only marginally modified by an enkephalinase inhibitor. Hence, although the peptidase is present in blood plasma and cells, its rate-limiting participation in the clearance of the hormone in vivo does not occur at the blood level.

Animals↗
PubMed1989

Molecular cloning and amino acid sequence of rat kidney aminopeptidase M: a member of a super family of zinc-metallohydrolases.

Using a polyclonal antibody, a partial cDNA clone for rat aminopeptidase M was identified in a lambda gt11 library from rat kidney. A synthetic oligonucleotide probe derived from the sequence of the insert was used to screen a randomly primed lambda gt10 library. This allowed the identification of several overlapping clones encoding the full sequence of the enzyme. The reading frame, 2898 base pairs in length, encodes a 966 amino acid polypeptide. A highly hydrophobic segment, 24 amino acids in length, located close to the aminoterminus, is proposed to serve as the membrane-spanning domain for this membrane-bound enzyme. The sequence includes nine potential N-linked glycosylation sites and one potential sulfation site. In addition, the rat aminopeptidase M sequence contains an eight amino acid consensus sequence believed to serve as the zinc binding domain in a family of zinc-metallohydrolases. Rat aminopeptidase M shows 77% similarity with the recently cloned human enzyme, as well as weaker but significant similarity with aminopeptidase N from E. coli (18%) and with human leukotriene A4 hydrolase (21%).

Amino Acid Sequence↗