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Biomedical subjects

G Thibault

Publications and source records attributed to G Thibault.

At least 199 records · Page 11Linked to original sources
PubMed1986

Platelet binding sites for atrial natriuretic factor in humans. Characterization and effects of sodium intake.

Platelets bear receptors for vasoactive peptides such as angiotensin II and vasopressin. The presence of binding sites for another vasoactive peptide, atrial natriuretic factor, was therefore investigated in human platelets. 125I-labeled synthetic atrial natriuretic factor bound specifically to human platelets. Steady-state and kinetic experiments demonstrated the existence of one class of high-affinity low-capacity binding sites for atrial natriuretic factor in platelets with a dissociation constant of 30 pM. The order of potency of atrial natriuretic factor fragments showed that the structural requirements of the high-affinity binding site detected were similar to those of receptors for atrial natriuretic factor in rat blood vessels and adrenal zona glomerulosa. To study the regulation of these binding sites by sodium, normal young men were subjected successively in random order to a low-sodium (40 mmol per day) and high-sodium (300 mmol per day) diet for 4 days. Binding of atrial natriuretic factor to platelets was higher with the low-sodium diet (10.3 +/- 1.0 sites per cell) than with the high-sodium diet (7.1 +/- 0.7 sites per cell). In conclusion, human platelets bear binding sites for atrial natriuretic factor, the density of which may be modulated by sodium intake. The platelet is a useful model for investigating atrial natriuretic factor receptors in different physiopathological conditions in humans.

Adult↗
PubMed1986

Effect of chronic infusion of atrial natriuretic factor on plasma and urinary aldosterone, plasma renin activity, blood pressure and sodium excretion in 2-K, 1-C hypertensive rats.

Conscious two-kidney, one-clip (2-K, 1-C) hypertensive rats and their normotensive sham-operated controls were infused during 13 days with synthetic ANF (Arg 101 - Tyr 126) at 35 pmol/hr/rat by means of osmotic minipumps connected to the jugular vein. The initial blood pressure of 186 +/- 6 mmHg maximally decreased to 118 +/- 7 mmHg at day 5 and slowly rose afterwards without reaching basal values. A concomitant drop in pressure natriuresis and diuresis was observed. No changes were observed in ANF-infused sham-operated rats. Urinary aldosterone excretion declined in ANF-treated rats from a basal value of 63.38 +/- 21.04 micrograms/24 hr to 13.36 +/- 3.78 micrograms/24 hr the last infusion day. No change in urinary aldosterone was observed in either non-infused 2-K, 1-C or ANF-infused sham-operated rats. Plasma aldosterone was significantly higher only in non-treated 2-K, 1-C rats. Renal aldosterone clearance was significantly lower in ANF-infused 2-K, 1-C rats than in the other experimental groups. Plasma renin activity (PRA) was lower in treated (3.92 +/- 2.26 AI ng/ml/hr) than in non-treated (9.08 +/- 2.32 AI ng/ml/hr) hypertensive rats, and not different from ANF-infused or non-infused sham-operated rats. No differences in body weight between infused and non-infused rats, or hematocrit between any group were observed. Atrial immunoreactive ANF was not different in any group. These results demonstrate that chronic administration of ANF not only reduces blood pressure and PRA in 2-K, 1-C hypertensive rats but also plasma and urinary aldosterone. Whether the latter is a direct inhibitory effect or secondary to the normalization of PRA is not known. The hypotensive response may be due to a direct effect on vascular smooth muscle but a role of renin cannot be excluded. Because blood pressure returned toward basal values during the last days of the observation period, the possibility of a tachyphylactic effect of ANF on vascular smooth muscle cannot be excluded.

Aldosterone↗
PubMed1986

Identification of the released form of atrial natriuretic factor by the perfused rat heart.

Atrial natriuretic factor (ANF), released by the isolated perfused rat heart, was extracted from the perfusates by C18 Sep-Pak cartridges and then isolated by immunoaffinity chromatography and by reverse phase HPLC. About 500 ng of immunoreactive material were so obtained and submitted to amino acid sequencing. The C-terminal Tyr was detected by radiolabelling. Identification of these residues indicated that the primary structure corresponds to ANF (Ser 99-Tyr 126) which is identical to the circulating form in the rat. These results indicate that the ANF released by the atria corresponds to a short peptide. Therefore, its maturation process may therefore take place either intracellularly or during secretion and implicates a tryptic-like cleavage after a single Arg residue in position 98.

Amino Acid Sequence↗
PubMed1986

Atrial natriuretic factor: radioimmunoassay and effects on adrenal and pituitary glands.

A simple and sensitive radioimmunoassay was developed for measurement of immunoreactive atrial natriuretic factor (IR-ANF) in rat and human plasma and in rat atria. The two atria contain about 20 micrograms ANF per rat. The right atrium contained 2.5 times more ANF than did the left. Ether anesthesia and morphine markedly increased IR-ANF in rat plasma. The concentration of IR-ANF in plasma of clinically normal human subjects was 65.3 +/- 2.5 pg/ml. Paroxysmal tachycardia and rapid atrial pacing significantly increased IR-ANF in human plasma. Two- to seven-fold higher concentrations were found in coronary sinus blood than in the peripheral circulation. In the plasma of rats and humans, circulating ANF is probably a small-molecular-weight peptide. ANF acts on the adrenal and the pituitary. ANF inhibits aldosterone secretion from rat zona glomerulosa and steroid secretion by bovine adrenal zona glomerulosa and fasciculata. ANF stimulated the basal secretion of arginine vasopressin (AVP) in vitro and inhibited KCl-stimulated release of AVP.

Adenylyl Cyclase Inhibitors↗
PubMed1986

Some physiopathological aspects of atrial natriuretic factor.

Chronic infusion of atrial natriuretic factor (ANF) decreased blood pressure in two-kidney, one clip (2-K, 1C), spontaneously hypertensive rat (SHR) and one-kidney, one clip (1-K, 1C) models of experimental hypertension in the rat, but produced increased sodium excretion only in the 1-K, 1C model. In ANF-infused 2-K, 1C animals plasma renin activity did not differ from normotensive controls. Atrial content of immunoreactive (ir) ANF was significantly lower in SHR and 1-K, 1C animals. At 40-50 days old, cardiomyopathic hamsters had a higher concentration of plasma irANF and a lower ANF content in the left but not in the right atrium, although the difference in plasma ANF was more obvious once heart failure was well established. At 110-130 and 200-300 days old, the hamster atrial ANF content was not only lower in the left but also in the right atrium. No differences were observed in plasma irANF between normal subjects and either untreated or treated essential hypertensive patients. However, a significantly higher plasma ANF was observed in two groups with secondary hypertension, primary hyperaldosteronism and renovascular hypertension. Bolus injection of ANF into healthy subjects produced a dose-related decrease in blood pressure and an increase in the heart rate and natriuresis.

Adult↗
PubMed1985

Partial characterization and solubilization of receptors for atrial natriuretic factor in rat glomeruli.

Specific receptors for atrial natriuretic factor (ANF) have been identified and solubilized in glomeruli from rat kidney. Radioiodinated synthetic ANF (Arg 101-Tyr 126) bound to a single class of high affinity (Kd 27 +/- 24 pM) sites with a density of 390 +/- 230 fmole/mg protein. The binding was time- and temperature-dependent, saturable and reversible. The ANF-receptor complex was not affected by angiotensin II, ACTH or vasopressin. Solubilization with 10 mM 3-[(3-cholamidopropyl)-dimethylammonio]- 1-propane sulfonate (CHAPS) slightly increased the affinity for ANF (Kd 5.0 +/- 3.3 pM) without affecting the density (250 +/- 110 fmole/mg protein). Similar results were found with 1% Triton X-100. ANF-related peptides interact generally in the same way with non-solubilized and solubilized receptors, indicating a fully preserved specificity of the receptors.

Adrenocorticotropic Hormone↗
PubMed1985

Structure-activity relationships of atrial natriuretic factor (ANF). III. Correlation of receptor affinity with relative potency on aldosterone production in zona glomerulosa cells.

The activity of various fragments of ANF as inhibitors of aldosterone secretion and as competitors of [125I] ANF (Arg101-Tyr126) binding to specific receptors was studied in bovine zona glomerulosa. Shortening or lengthening the N-terminal segment of ANF does not alter its biological activity while minimally altering affinity for its receptor. Removal of the C-terminal to Cys121 or expansion up to Arg128 leads to 1000-fold decrease in receptor affinity and activity. The results indicate the importance of the C-terminal segment of ANF in determining its active conformation.

Adrenal Cortex↗
PubMed1985

Gluco- and mineralocorticoids may regulate the natriuretic effect and the synthesis and release of atrial natriuretic factor by the rat atria in vivo.

Adrenalectomy abolished the acute natriuretic effect of ANF which was partially restored to about 50% by combined therapy with gluco- and mineralocorticoids. It is suggested that the lack of effect of ANF may be due to a decreased renal vascular reactivity to the peptide in adrenalectomized animals. Simultaneous administration of Dexamethasone and Deoxycorticosterone acetate to adrenalectomized rats produced a marked increase in immunoreactive ANF in atrial tissue and plasma. The administration of NaCl to these animals produced a relatively lower concentration of atrial ANF and a further increase in plasma ANF. Our results suggest that glucocorticoids may regulate synthesis and release of ANF by the atria and mineralocorticoids may have a permissive role. Furthermore, the presence of steroids is necessary for the NaCl-stimulated ANF release.

Adrenalectomy↗
PubMed1985

Identification of a biologically active circulating form of rat atrial natriuretic factor.

An atrial natriuretic peptide has been isolated from plasma of morphine treated rats by means of glass beads extraction, immunoaffinity chromatography, and reverse phase HPLC. 1.3 micrograms of immunoreactive material was obtained. The biological activity of this material was found comparable to that of ANF (Arg 101 - Tyr 126) on the inhibition of basal aldosterone secretion by rat adrenal zona glomerulosa cells and the displacement curve of iodinated ANF from ANF receptors in a mesenteric artery preparation. Gas phase amino acid sequencing indicated that it is related to ANF (Ser 99 - Tyr 126). These results suggest that the maturation of ANF may require a tryptic-like cleavage after a single Arg residue.

Adrenal Cortex↗
PubMed1985

ANF (Arg 101--Tyr 126) is the peptide secreted by rat atrial cardiocytes in culture.

The atrial natriuretic factor (ANF) secreted from rat cardiocytes in culture was purified and characterized. The purification procedure involves extraction of ANF by activated Vycor glass, followed by HPLC on C18 mu Bondapak and Vydac columns. The detection of ANF in column eluates was performed by a simple and sensitive radioimmunoassay. The amino acid composition and N-terminal amino acid sequencing appeared to be identical to the Arg 101 - Tyr 126 peptide. The isolated ANF showed biological activity, inhibiting basal and ACTH-stimulating aldosterone secretion from rat zona glomerulosa cells with the same potency as the synthetic peptide.

Adrenal Glands↗
PubMed1985

Effect of different anesthetics on immunoreactive atrial natriuretic factor concentrations in rat plasma.

The effect of different conditions of blood withdrawal and use of different anesthetics on immunoreactive atrial natriuretic factor (IR-ANF) concentrations in plasma was studied in rats. The concentration of IR-ANF in plasma from jugular vein of non-anesthetized conscious rats, cannulated either 24 hr before blood withdrawal was 93.9 +/- 17.1 pg/ml (n = 30); and 48 hr: 81.9 +/- 11.5 pg/ml (n = 29). Immobilization stress (4 hr) increased IR-ANF concentration: 248.0 +/- 80.2 pg/ml (n = 5). Anesthesia by morphine, diethyl-ether, chloral hydrate and ketamine chlorhydrate increased IR-ANF concentrations to 2,443.0 +/- 281.2 pg/ml (n = 24), 806.1 +/- 74.6 pg/ml (n = 64), 224.0 +/- 81.4 pg/ml (n = 20), and 195.0 +/- 20.3 pg/ml (n = 51), respectively. IR-ANF in plasma of sodium-pentobarbital and urethane anesthetized rats was 59.2 +/- 6.7 pg/ml (n = 10) and 42.6 +/- 8.1 pg/ml (n = 8), respectively. These changes in IR-ANF evoked by different types of anesthetics and different conditions of blood withdrawal have to be taken into consideration during studies on the physiopathological role of atrial natriuretic factor.

Anesthetics↗
PubMed1985

Immunoreactive atrial natriuretic factor (IR-ANF) in human plasma.

A direct radioimmunoassay for ANF in human plasma was developed. A synthetic alpha-human atrial peptide (Ser 99-Tyr 126) was used for preparation of the iodinated tracer and the standards. The sensitivity of the method is 1.9 pg/ml. Concentration of immunoreactive ANF (IR-ANF) in plasma of 59 clinically normal subjects was 65.3 +/- 2.5 pg/ml (mean +/- SE). In two patients who underwent atrial pacing an increase of about 100 percent in circulating IR-ANF was observed. IR-ANF was extracted from human plasma by Vycor glass and purified by HPLC. The main immunoreactive isolated peak contained a low molecular weight peptide.

Atrial Natriuretic Factor↗
PubMed1985

Changes of regional blood flow induced by atrial natriuretic factor (ANF) in conscious rats.

The effect of synthetic atrial natriuretic factor (ANF 101-126) has been studied on regional blood flow distribution. Microspheres (15 +/- 3 microns), labelled with either 113Sn or 57Co, were injected through an intraventricular cannula into conscious rats while a reference blood sample was withdrawn. Two minutes after the first microspheres injection either ANF or NaCl were injected. Five minutes later, the second microspheres injection was administered, and after two minutes the animals were sacrificed, and several tissues removed and counted. Percent of flow distribution, cardiac output and tissue blood flow were calculated by standard formulas. ANF produced a significant increase in absolute blood flow in lungs, heart, spleen, kidneys and testes. Total renal blood flow and total splanchnic blood flow were also increased in ANF-injected animals. No significant changes were observed in cardiac output. It is suggested that the natriuretic and hypotensive responses to ANF in vivo may be, at least partially, explained by its hemodynamic effects.

Animals↗
PubMed1985

Structure-activity relationships of atrial natriuretic factor (ANF). II. Effect of chain-length modifications on vascular reactivity.

The effect of the length of ANF peptides on the inhibition of the norepinephrine-induced contraction was studied. Starting from the 26 residues ANF (Arg101-Tyr126), shorter N- and/or C-terminal fragments were produced, either by N-terminal chemical cleavage or C-terminal enzymatic digestion of ANF or both respectively. The N-terminal removal of Arg101 did not modify the inhibitory response. Further N-terminal truncation up to des-Arg101-Arg102-Ser103-Ser104 ANF still produced a marked inhibitory effect on norepinephrine. In contrast C-terminal cleavage had a much more pronounced effect. Since des-Tyr126 ANF, des-Arg125-Tyr126 ANF and des-Phe124-Arg125-Tyr126 ANF exhibit much lower activities than the parent ANF. Finally, when the 5 residues C-terminal to Cys121 are removed, the resulting molecule is almost inactive. These data indicate that the C-terminal segment of ANF may modulate the binding of ANF to its receptor(s). Relatively, the N-terminal region seems to be much less important.

Animals↗
PubMed1985

Radioautographic localization of 125I-atrial natriuretic factor (ANF) in rat tissues.

Rats were injected either with synthetic 125I-Arg 101-Tyr 126 atrial natriuretic factor (ANF) or with 125I-ANF together with an excess of cold Arg 101-Tyr 126 ANF. Binding sites in various tissues were accepted depending on two criteria: displacement of radioactivity by cold ANF and absence of localization of silver grains on putative target cells in the presence of cold ANF. Binding sites were localized on zona glomerulosa cells and on adrenergic and noradrenergic cells of adrenal medulla, on hepatocytes, on the base of mature epithelial cells of villi in the small intestine, on smooth muscle cells of the muscularis layer of the colon and on the base of epithelial cells of the ciliary bodies. In addition, binding sites were localized in the vasculature of kidney, adrenal cortex, lung and liver. Binding sites were particularly numerous on renal glomerular endothelial cells. These results indicate that ANF may have important hemodynamic effects in kidney, lung, liver and adrenal cortex, may regulate water and ion transport in small intestine and ciliary bodies and may have metabolic effects in the liver. The presence of binding sites on the zona glomerulosa is in agreement with the important inhibitory effect of the peptide on aldosterone secretion.

Adrenal Glands↗
PubMed1985

Vascular and adrenal receptors for atrial natriuretic factor in the rat.

Previous studies have shown that atrial natriuretic factor, a powerful vasorelaxant of precontracted vessels, inhibits the secretion of aldosterone stimulated by angiotensin II, adrenocorticotropic hormone, and potassium. We now report the presence of specific binding sites for atrial natriuretic factor in rat blood vessels (mesenteric and renal arteries) and adrenal capsules. Radioiodinated synthetic atrial natriuretic factor bound to a single class of high-affinity (KD = 0.1 nM) low-capacity receptors in a particulate fraction from blood vessels and adrenals. Unrelated peptides did not displace atrial natriuretic factor. Fragments of atrial natriuretic factor displaced the labeled ligand with decreasing potency after cleavage at the N-terminal. The cleavage of the C-terminal tyrosine did not decrease the potency of atrial natriuretic factor, but further cleavage at the C-terminal dramatically reduced the affinity of the resulting peptides. The potency of the atrial natriuretic factor fragments in the radioligand assay was in proportion to their potency to inhibit aldosterone secretion by isolated rat glomerulosa cells. Our results suggest that these binding sites mediate the biological actions of atrial natriuretic factor in blood vessels and the adrenal, and that both receptors have similar specificities.

Adrenal Glands↗
PubMed1985

Localization of immunoreactive synthetic atrial natriuretic factor (ANF) in the heart of various animal species.

The localization of two synthetic fragments of the C-terminal portion of atrial natriuretic factor: Arg 101-Tyr 126 which displays full biological activity and Leu 94-Arg 109 which is completely devoid of biological activity, has been investigated by immunohisto- and immunocytochemical methods in the heart of mammals (rat, mouse, guinea pig, hamster, rabbit, cat, dog, man) and nonmammalian vertebrates toad (Bufo marinus), frog (Rana catesbeiana), fish (Cyprinus carpio, Puntius schwanenfeldi, Cichlosoma biocellatum, Carrasius auratus), snake (Python reticulatus) and hen. Antibodies against the synthetic fragments of ANF were raised in rabbits and used either for immunofluorescence (Coons' technique), immunohistochemistry (unlabeled antibody technique) or immunocytochemistry (protein A-gold technique). Results obtained by immunofluorescence and by the unlabeled antibody technique were similar: antibodies against Arg 101-Tyr 126 ANF allowed visualization of granulated cardiocytes in the atria of all mammals. While the reaction was very strong in rat and mouse, it was less so in the rabbit and very weak in all other species studied including man. Antibodies against Leu 94-Arg 109 ANF produced a reaction only in the rat and mouse. In nonmammalian vertebrates, the reaction was always much stronger in atria than ventricles of all species with both antibodies.

Animals↗