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Biomedical subjects

P Robberecht

Publications and source records attributed to P Robberecht.

At least 217 records · Page 12Linked to original sources
PubMed1981

Impairment of hormone-stimulated cardiac adenylate cyclase activity in the genetically obese (fa/fa) Zucker rat.

The age-related development of the capacity of the cardiac adenylate cyclase system to be stimulated with secretin, vasoactive intestinal peptide (VIP), glucagon, the beta-adrenergic agonist isoproterenol, Gpp(NH)p, and NaF was compared in obese (fa/fa) Zucker rats and their lean (FA/?) littermates. The obese (fa/fa) Zucker rats tested developed postweaning obesity associated with marked hypertriglyceridemia, mild hyperglycemia, and hyperinsulinism. At 4 weeks, there was already a 57% reduction in secretin-VIP-stimulated adenylate cyclase activity in fa/fa rats. At 12 weeks, the secretin-VIP-stimulation was reduced by 77%, and glucagon- and isoproterenol-stimulations by 16-21%. At 45 weeks, secretin-VIP-stimulation was reduced by 91%, glucagon- and isoproterenol stimulations by 34-42%, and Gpp(NH)p- and NaF-stimulations by 16-23%. The reductions of isoproterenol-, Gpp(NH)p-, and NaF-stimulations were totally or partially reversed in 30-week old fa/fa animals submitted for 5 weeks to severe food restriction that almost normalized the altered blood parameters. In sharp contrast, food restriction imposed a further decrease in secretin-VIP- and glucagon-stimulated adenylate cyclase activities. This pattern of impaired secretin-VIP-stimulated adenylate cyclase activity appeared limited to cardiac membranes in obese animals as the responses of liver, brain and anterior pituitary adenylate cyclase activities to secretin and/or VIP were unaltered. These results suggest that secretin-VIP receptors coupled to adenylate cyclase were rapidly and specifically altered in the heart of fa/fa Zucker rats.

Adenylyl Cyclases↗
PubMed1981

Characterization of the VIP- and secretin-stimulated adenylate cyclase system from human lung.

The response of a crude particulate adenylate cyclase preparation from surgically removed human lung to guanine nucleotides, sodium fluoride, beta-adrenergic agonists, prostaglandins, vasoactive intestinal peptide (VIP), secretin, and [Val5]secretin was investigated. The enzyme activity increased 5, 10, and 9-fold, respectively, with GTP, Gpp(NH)p, and sodium fluoride. This activity was stimulated (in the presence as well as in the absence of added GTP) by D,L-isoproterenol, L-epinephrine and L-norepinephrine, the relative potency of these agonists being compatible with the existence of beta-adrenoceptors of the beta2 subtype. Prostaglandins E1 and E2, but not PGF1alpha and PGF2alpha, stimulated the enzyme, PGE1 being at least 10 times more potent than PGE2. The biphasic pattern of stimulation of the same adenylate cyclase activity by VIP suggested the presence of high- and low-affinity VIP receptors coupled to the enzyme. This stimulation by VIP was not inhibited by secretin-(7-27). 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) was able to inhibit completely the secretin stimulation acting through high-affinity secretin receptors but exerted no effect on the stimulation operating through low-affinity secretin receptors, which might indicate that the latter receptors were in fact "VIP-preferring receptors". [Val5]secretin was also used to differentiate these peptide receptors, since its properties were more VIP-like than those of secretin.

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↗
PubMed1980

Secretin and VIP-stimulated adenylate cyclase from rat heart. I. General properties and structural requirements for enzyme activation.

Membrane adenylate cyclase from rat heart was activated by the two gut peptides secretin and vasoactive intestinal peptide (VIP), glucagon, and the beta-adrenergic drug isoproterenol, in the presence of guanosine 5'-triphosphate (GTP). With all the stimuli tested, the optimal magnesium concentration was 5 mM, i.e. in excess over the 0.5 mM ATP substrate concentration and 0.01 mM GTP used as cofactor. Under these conditions, half-maximal adenylate cyclase activation with glucagon, secretin, and VIP was achieved at concentrations of 0.5, 0.5 and 1.0 microM, respectively. Data obtained with the secretin (7--27) fragment, a secretin antagonist, indicate that secretin and VIP acted on the same binding sites, which differed from glucagon binding sites. Structural requirements for secretin activation of cardiac adenylate cyclase were evaluated by comparing the potency and efficacy of parent peptides and synthetic analogs. The gastric inhibitory peptide GIP was inactive. When using 13 mono-or bi-substituted analogs, it appeared that amino acids in positions 1, 2, 3, 4 and 6 were of major importance while those in position 5 and 11 played a relatively minor role.

Adenosine Triphosphate↗
PubMed1980

Secretin and VIP-stimulated adenylate cyclase from rat heart. II. Impairment in spontaneous hypertension.

Cardiac adenylate cyclase activity was normal in 3 weeks-old spontaneously hypertensive rats of the Wistar-Okamoto substrain. The hormone-sensitive adenylate cyclase activity was reduced in 10 weeks-old or older animals, and secretin- and VIP-activations were definitely more impaired (by 64% and 69%, respectively) than isoproterenol- and glucagon-activations (17% and 22%, respectively). By contrast, the fluoride- and p[NH]ppG-stimulations of the enzyme were unaffected. These alterations in the adenylate cyclase system coupled to secretin and VIP appeared specific to the heart as the isolated pancreatic acinar cells from spontaneously hypertensive animals responded normally to secretin, as a liver particulate fraction responded normally to secretin and VIP, and both brain synaptic membranes and a particulate fraction of anterior pituitary to VIP.

Adenylyl Cyclases↗
PubMed1979

Effects of alcohols on the actions of VIP and secretin on acinar cells from guinea pig pancreas.

In dispersed acini prepared from guinea pig pancreas, ethanol inhibited the increase in amylase secretion caused by cholecystokinin, carbachol, secretin, or vasoactive intestinal peptide. Ethanol did not alter binding of [125I] vasoactive intestinal peptide to pancreatic acinar cells or the inhibition of binding cause by secretin or vasoactive intestinal peptide. Ethanol potentiated the increase in adenylate cyclase activity and cellular adenosine 3':5'-monophosphate caused by secretin or vasoactive intestinal peptide. This potentiating action was reversible and could also be detected with straight-chain alcohols having fewer than seven carbon atoms. At sufficiently high concentrations, straight-chain alcohols having more than two carbon atoms inhibited the action of secretin or vasoactive intestinal peptide on adenylate cyclase activity, and this and this action was irreversible.

1-Propanol↗