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M Waelbroeck

Publications and source records attributed to M Waelbroeck.

144 records · Page 8Linked to original sources
PubMed1982

Rat cardiac muscarinic receptors. II. Influence of thyroid status and cardiac hypertrophy.

The effects of the thyroid state and of aortic stenosis on muscarinic cholinergic binding sites in heart membranes were compared (with proper controls) by simultaneously determining total and high-affinity binding sites and estimating low-affinity binding sites by difference. Hyper- and hypothyroidism induced decreased and increased concentration of high-affinity agonist binding sites, respectively, supporting the hypothesis that these sites were directly regulated by thyroid hormones. This was not the case for low-affinity binding sites, as they decreased in number in both hyper- and hypothyroidism. In hyperthyroid rats, this decreased number of low-affinity binding sites could be due to the rapidly developing cardiac hypertrophy. Indeed, cardiac hypertrophy provoked by aortic stenosis led also to a decreased concentration of low-affinity binding sites without affecting the concentration of high-affinity binding sites.

Animals↗
PubMed1982

Rat cardiac muscarinic receptors. I. Effects of guanine nucleotides on high- and low-affinity binding sites.

The binding properties of muscarinic cholinergic binding sites were investigated in rat cardiac membranes, using the labeled agonist [3H] oxotremorine-M ([3H]Oxo-M) and the labeled antagonist L-[benzilic-4,4'-3H]quinuclidinyl benzilate (L-[3H]QNB). The binding of both tracers was inhibited stereospecifically by dexetimide and levitimide. [3H]Oxo-M labeled only high-affinity agonist binding sites, whereas L-[3H]QNB bound to high- and low-affinity agonist binding sites with equal affinity. Agonists were unable to induce "negative cooperativity" interactions by increasing the dissociation of labeled agonist or antagonist. Guanine nucleotides decreased markedly the affinity of high- and low-affinity binding sites for agonists, without affecting their affinity for antagonists. In the presence of a maximally effective concentration of GTP, all muscarinic receptors showed the same low affinity for agonists. Among these agonists, carbamylcholine and oxotremorine (but not pilocarpine) displayed a lower affinity for both classes of binding sites in the presence of GTP.

Animals↗
PubMed1981

Presence of vasoactive intestinal peptide receptors coupled to adenylate cyclase in rat lung membranes.

(1) The binding of 125I-labelled vasoactive intestinal peptide (VIP) to a particulate fraction from rat lung was rapid, temperature dependent, saturable and specific. This process was also reversible and 125I-labelled VIP dissociation was accelerated by guanine triphosphate nucleotides. The curves describing the inhibition of tracer binding by peptides of the VIP-secretin family suggested the presence of at least two classes of VIP receptor: a "high-affinity' type with decreasing affinity for VIP in the order: VIP = [Val5]secretin greater than [Ala4, Val5]secretin; and a "low-affinity type' with decreasing affinity for VIP in the order: VIP greater than [Val5]secretin greater than [Ala4, Val5]secretin = secretin greater than [Ala4]secretin. (2) VIP and related peptides stimulated the adenylate cyclase activity of the same lung membrane preparation more efficiently than beta-adrenergic agonists and prostaglandins E1 and E2. The dose-effect curves of stimulation of adenylate cyclase by VIP and parent peptides were also compatible with the existence of two classes of VIP receptor, the relative peptide potencies being identical with their ability to compete with 125I-labelled VIP for binding.

Adenylyl Cyclases↗
PubMed1981

Binding of vasoactive intestinal peptide and its stimulation of adenylate cyclase through two classes of receptors in rat liver membranes. Effects of 12 secretin analogues and 2 secretin fragments.

1. Vasoactive intestinal peptide (VIP) receptors were identified in crude rat hepatic membranes by 125I-labelled VIP binding and by the ability of VIP to stimulate adenylate cyclase activity. The specificity of these receptors was evaluated by the capacity of secretin, synthetic secretin analogues, and secretin fragments to inhibit 125I-labelled VIP binding and to stimulate adenylate cyclase. 2. The results were compatible with the existence of two classes of VIP binding sites that could be distinguished according to their affinity for VIP and their specificity. High-affinity sites were more specific for VIP as secretin was 175 times less potent than VIP for recognition of these sites while being only 33 times less potent than VIP for recognition of low-affinity sites. 3. Secretin analogues, monosubstituted in position 2, 3, 4 or 6 were less potent than secretin for adenylate cyclase stimulation as well as for the recognition of the two classes of receptors. [Val5]secretin was more potent than secretin and appeared definitely more VIP-like than secretin; [Ala4, Val5] and [D-Ala4,Val5]secretin were equipotent to secretin. 4. The fragment secretin (7-27) was unable to recognize VIP receptors and to stimulate adenylate cyclase. The substituted fragment [Gln9,Asn15]secretin (5-27) recognized these receptors with weak potency but could not activate the enzyme.

Adenylyl Cyclases↗
PubMed1981

Comparative effects of alpha-methyldopa, propranolol and hydralazine therapy on cardiac adenylate cyclase activity in normal and spontaneously hypertensive rats.

Normotensive (WKY) and spontaneously hypertensive (SHR) male rats were treated orally, one week after weaning and for 9 weeks, with alpha-methyldopa (100 mg/kg per day), propranolol (30 mg/kg per day) or hydralazine (10 mg/kg per day). Untreated WKY and SHR rats served as controls. The development of hypertension in SHR rats were attenuated by treatment but none of the drugs was able to restore the impairment in isoproterenol, secretin and glucagon responsiveness of cardiac adenylate cyclase activity which is characteristic of these animals. In heart membranes from both WKY and SHR rats, alpha-methyldopa treatment increased the number of beta-adrenoceptors by 20-32% and the maximal response of adenylate cyclase activity to isoproterenol and glucagon by 20-34%. By contrast, the beta-blocker propranolol was ineffective on these parameters. The results obtained are consistent with the hypothesis that the change in adenylate cyclase seen in SHR rats is genetic in origin and is not a consequence of hypertension.

Adenylyl Cyclases↗
PubMed1981

Comparison of VIP-secretin receptors in rat and human lung.

The binding of 125I-VIP (Vasoactive Intestinal Peptide) to a crude particulate fraction from a rat lung was reversible and 125-I-VIP dissociation was accelerated by guanine triphosphate nucleotides. The relative potency of VIP and related peptides to compete with 125-VIP for binding was similar to their ability to stimulate adenylate cyclase in the same preparation. Dose-effect curves were compatible with the existence of two classes of VIP-receptors: a high-affinity type with equal affinity for VIP and [Val5] secretin, and a low-affinity type with affinity decreasing in the order VIP greater than [Val5] secretin greater than secretin. The response of a crude particulate adenylate cyclase preparation from human lung was also investigated. The biphasic pattern of adenylate cyclase stimulation by VIP suggested the presence of high- and low-affinity VIP receptors coupled to the enzyme. In addition, the stimulation of adenylate cyclase by secretin and [Val5] secretin was also biphasic, suggesting the coexistence of high- and low-affinity secretin receptors, Secretin (7-27) inhibited completely the secretin-stimulated activity operating through high-affinity secretion receptors, so that these receptors appear to be genuine secretin-preferring receptors.

Adenylyl Cyclases↗
PubMed1981

Guanine nucleotide binding sites, responsible for adenylate cyclase activation and carbamylcholine binding inhibition, show similar properties in rat heart membranes.

1/ In rat heart membranes, muscarinic receptors were shown to interact with guanine nucleotide binding sites closely related, if not identical, to those activating adenylate cyclase. The dose-effect curves of GTP, p[NH]ppG, and GTP gamma S for inhibition of carbamylcholine binding (measured by competition with [3H]QNB) and for adenylate cyclase activation (measured in the presence of isoproterenol) were parallel, at both 25 degrees C and 37 degrees C. 2/ Persistent activation of adenylate cyclase was obtained in heart membranes preincubated with p[NH]ppG or GTP gamma S then washed. The affinity for carbamylcholine was reduced after this pretreatment. The SO.5 of p[NH]ppG and GTP gamma S provoking persistent activation of adenylate cyclase and persistent inhibition of carbamylcholine binding were identical. Persistent inhibition of carbamylcholine binding was not additive with the inhibition observed when fresh nucleotide was added after washing. With p[NH]ppG, SO.5 values were unaffected by washing. With GTP gamma S, the SO.5 value for persistent activation of adenylate cyclase (i.e. after washing) and 330 times higher than that implementing activation (i.e. before washing). A similar change was observed when testing the SO.5 of GTP gamma S inhibition of carbamylcholine binding. This might reflect a partial release of GTP gamma S (but not of p[NH]ppG) from "spare" nucleotide binding sites during the washing period. 3/ Adenylate cyclase activity after maximal persistent activation was not increased when 0.1 mM guanine nucleotide, with or without 10 muM isoproterenol, was added to the incubation medium. In contrast, carbamylcholine binding was further decreased when fresh guanine nucleotide was added to the binding assay. This suggests that the proportion of "spare" nucleotide binding sites capable of activating the adenylate cyclase was higher than that capable to inhibit carbamylcholine binding, or that a second class of nucleotide binding sites (binding p[NH]ppG and GTP gamma S reversibly) was also able to inhibit carbamylcholine binding.

Adenylyl Cyclases↗
PubMed1979

Thermodynamics of the interaction of insulin with its receptor.

Insulin binding to its cellular receptors is markedly dependent on the temperature. The thermodynamic parameters for the reaction of insulin with the high affinity state of its receptor have been evaluated with equilibrium studies at multiple temperatures between 5 degrees and 37 degrees C. The thermodynamics of the insulin-receptor interaction is not classical. The van't Hoff plot is not linear. Both the enthalpy and entropy changes, due to the formation of the hormone . receptor complex, decrease markedly with temperature, corresponding to a large heat capacity change of -766 cal/(mol deg) at 25 degrees C. The reaction is endothermic and entropically driven at low temperature and exothermic and enthalpically driven at higher temperature. This thermodynamic behavior is suggestive of a hydrophobic reaction and supports Blundell's concept that the loss of non-polar surface residues in the formation of the hormone . receptor complex is an important driving force of the reaction. Alternatively, this nonclassical behavior may indicate that the reaction of insulin with its receptor involves more than one step.

Cell Line↗
PubMed1979

Cholinergic and alpha-adrenergic stimulation of prostaglandin release by dog thyroid in vitro.

Dog thyroid slices released in their incubation medium prostaglandins E2 (PGE2), F2 alpha (PGF2 alpha), 15-keto-13,14-dihydro-F2 alpha, and thromboxane B2 (TxB2), as measured by direct RIA. This release could be inhibited by indomethacin and naproxen, indicating that it corresponded to a neosynthesis. Carbamylcholine (2--100 microns) stimulated the release of PGE2, PGF2 alpha, and TxB2, whereas epinephrine (20 microns to 1 nM) enhanced the release of PGE2 and PGF2 alpha but had no effect on TxB2. These stimulations were inhibited by atropine and dihydroergocryptine, respectively, suggesting that a muscarinic and an alpha-adrenergic receptor were involved. The ionophore A23187 reproduced these stimulations, and the stimulatory effects of carbamylcholine and epinephrine were inhibited in the absence of exogenous Ca++ and after EGTA depletion. Ca++ thus appears as a major regulator of PG production in the thyroid. TSH (0.06--10 MU/ml) and dibutyryl cAMP had no effect on the release of PGE2, PGF2 alpha, or TxB2 by dog thyroid in vitro.

Animals↗
PubMedDate not supplied

Vasoactive intestinal peptide (VIP) and peptide having N-terminal histidine and C-terminal isoleucine amide (PHI) stimulate adenylate cyclase activity in human heart membranes.

The presence of receptors, recognized by Vasoactive Intestinal Peptide (VIP) and Peptide having N-terminal Histidine and C-terminal Isoleucine amide (PHI), was documented in membranes from human right auricle and left ventricular cardiac muscle by the ability of these peptides to stimulate adenylate cyclase. The capacity of VIP and PHI to activate the enzyme was comparable, in auricle as well as ventricle membranes, the affinity of the system being moderately higher for VIP than for PHI. In auricles, dose-effect curves appeared compatible with the coexistence of high-affinity and low-affinity VIP receptors. PHI could not, however, discriminate these subclasses of VIP receptors.

Adenylyl Cyclases↗
PubMedDate not supplied

Effects of HIS1 modifications on the ability of vasoactive intestinal peptide to stimulate adenylate cyclase from rat and human tissues.

The importance of the N-terminal His residue of VIP for stimulating adenylate cyclase was appreciated by estimating the intrinsic activity and EC50 of four VIP analogues on membranes from rat lung, liver, brain, anterior pituitary, and pancreas, and on human heart membranes. In all tissue preparations tested except one, the order of efficacy (and often potency) was: VIP greater than (Ac-His1)VIP greater than (Phe1)VIP = (3-Me-His1)VIP greater than (D-His1)VIP. In rat heart membranes, the order of efficacy was somewhat different: VIP greater than (Ac-His1)VIP = (Phe1)VIP greater than (D-His1)VIP greater than (3-Me-His1)VIP. These data demonstrated the key role of His1 in VIP in activating adenylate cyclase. They suggest that a given VIP analogue might act as full agonist in tightly coupled adenylate cyclase systems (such as those of rat lung and liver membranes) whereas the same analogue could not promote full activity in poorly coupled systems (such as that present in rat brain synaptic membranes).

Adenylyl Cyclases↗
PubMedDate not supplied

Heart receptors for VIP, PHI and secretin are able to activate adenylate cyclase and to mediate inotropic and chronotropic effects. Species variations and physiopathology.

We have assessed the presence of VIP/PHI/secretin receptors in heart by: (1) testing the ability of the corresponding peptides to activate adenylate cyclase in cardiac membranes from rat, dog, Cynomolgus monkey and man, and (2) examining the ability of the same peptides to exert inotropic and chronotropic effects on heart preparations from rat and Cynomolgus monkey in vitro. Based on their affinity for natural peptides and synthetic analogs, two types of VIP/PHI/secretin receptors were characterized: the relatively nonspecific "secretin/VIP receptor" of rat heart (that is "secretin-preferring" only in that secretin was more efficient than VIP in stimulating adenylate cyclase), and the "VIP/PHI-preferring" receptor of man, monkey and dog heart. Four physiopathological situations affecting secretin/VIP receptors in rat heart were explored: In male rats from the Okamoto strain and the Lyon strain, two strains presenting spontaneous hypertension, heart membranes exhibited a markedly decreased response of adenylate cyclase to secretin/VIP, with lesser alterations in the responses to isoproterenol and glucagon. This impairment developed in parallel with the occurrence of hypertension and was reproduced in normotensive rats submitted to chronic isoproterenol treatment (but not in Goldblatt hypertensive rats). These findings are consistent with a hyperactivity of norepinephrine pathways in spontaneously hypertensive rats, leading to a reduced number of cardiac post-junctional secretin/VIP receptors bound to adenylate cyclase. Heart membranes from genetically obese (fa/fa) Zucker rats also exhibited severely decreased responses to secretin/VIP with lesser alterations in the responses to glucagon and isoproterenol. These anomalies were specific for the heart, and developed in concomitance with obesity. The first anomaly could not be corrected by severe food restriction. Secretin stimulation of heart adenylate cyclase was also selectively altered in streptozotocin-diabetic rats. Thus, two types of diabetic cardiomyopathy were characterized by a severe local alteration of secretin/VIP receptors coupled to adenylate cyclase. Hypothyroidism, provoked in rat by thyroidectomy or propylthiouracil treatment, again induced a marked decrease in secretin-stimulated cardiac adenylate cyclase activity. In rat papillary muscle electrically stimulated in vitro, secretin exerted a positive inotropic effect. This effect was reduced in obese (fa/fa) Zucker rats. In rat right atrium, secretin also exerted a positive chronotropic effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenylyl Cyclases↗
PubMedDate not supplied

Interaction of Gila monster venom with secretin receptors in rat pancreatic membranes.

The stimulatory effect of Gila monster venom on adenylate cyclase activity in rat pancreatic membranes was compared to that of porcine secretin and porcine VIP. The maximal effect exerted by the venom was identical to that of VIP but significantly lower than that of secretin. The effect of Gila monster venom could, however, be attributed to its interaction with secretin receptors rather than with VIP receptors, at variance with its previously described action on guinea pig pancreatic acini. Adenylate cyclase activation by both Gila monster venom and secretin in rat pancreatic membranes was, indeed: (1) dose-dependently inhibited by two secretin fragments secretin-(4-27) and secretin-(7-27), and (2) more severely depressed than VIP stimulation, after pretreating pancreatic membranes with dithiothreitol (DTT).

Adenylyl Cyclases↗
PubMedDate not supplied

Pharmacological characterization of VIP receptors in human lung membranes.

The ability of VIP, PHI, secretin, helodermin, and seven N-terminally D-amino monosubstituted VIP and PHI analogs to occupy (125I)iodo-VIP labeled receptors and to activate adenylate cyclase was tested on human lung membranes purified by the method of Schachter et al. Best fitted Kd, Kact and % of max. values suggested the coexistence, in near equal proportions, of two classes of VIP-preferring binding sites coupled to adenylate cyclase that showed similar decreasing affinity for: VIP greater than (D-Ala4)-VIP greater than (D-Asp3)-VIP = (D-Ser2)-VIP greater than (D-His1)-VIP greater than PHI greater than (D-Phe2)-VIP greater than (D-Phe4)-VIP. (D-Arg2)-VIP was a non-selective agonist. A third receptor type, coupled to adenylate cyclase and showing high affinity for secretin and helodermin but not for VIP, was also detected.

Adult↗
PubMedDate not supplied

VIP and related peptides induce rapid homologous desensitization in the human lymphoma SUP T1 cell line.

Incubation of human SUP T1 lymphoblasts with VIP, helodermin and related peptides induced homologous desensitization within 5 min as indicated by: 1) a secondary decrease in cellular cyclic AMP levels, even in the presence of phosphodiesterase inhibitors, 2) a reduced capacity of cells to bind [125I]helodermin, 3) decreased helodermin stimulation of adenylate cyclase activity in membranes, and 4) unaffected NaF- and Gpp[NH]p-stimulated adenylate cyclase activities. The desensitizing ability of all peptides correlated with their efficacy to occupy cell receptors, except for [D-Phe2]VIP, a partial VIP agonist with low intrinsic activity, that did not desensitize.

1-Methyl-3-isobutylxanthine↗