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C Kordon

Publications and source records attributed to C Kordon.

At least 37 records · Page 2Linked to original sources
PubMed1995

Modulation by somatostatin of glutamate sensitivity during development of mouse hypothalamic neurons in vitro.

Glutamate sensitivity development and interactions of somatostatin (SRIF) with AMPA/Kainate receptor-mediated glutamate responses were studied in dissociated hypothalamic neurons from 16-day-old mouse embryos grown in vitro. Only 18% of functionally innervated cells could be found at 6-9 DIV whereas the percentage of innervated neurons progressively increased thereafter to reach 100% at 19-22 DIV. The glutamate sensitivity, estimated from glutamate-induced peak inward current, was very low at 6-9 DIV, sharply increased at 11-14 DIV and developed at a low increase rate thereafter. SRIF either unaffected glutamate peak current (27% of the cells), or significantly decreased (50%) or increased it (23%). Pertussis Toxin pretreatment abolished the SRIF-induced decrease of the glutamate response without affecting the excitatory effect. The number of glutamate responsive neurons inhibited by SRIF increased with time in culture whereas that of neurons responding to SRIF by an increased glutamate response was not statistically modified by functional innervation. The present data suggest that increased glutamate sensitivity coincides with the onset of functional synaptogenesis in mouse hypothalamic neurons in culture. SRIF can modulate glutamate sensitivity of hypothalamic neurons with either synergistic or antagonistic effects. Since glutamate has been shown to stimulate SRIF synthesis and secretion from hypothalamic neurons, the reverse capacity of SRIF to modulate the glutamate response suggests that both transmitters exhibit complex reciprocal interactions.

Animals↗
PubMed1995

Characterization of [hydroxyproline9]luteinizing hormone-releasing hormone and its smallest precursor forms in immortalized luteinizing hormone-releasing hormone-secreting neurons (GT1-7), and evaluation of their mode of action on pituitary cells.

[Hydroxyproline9]luteinizing hormone-releasing hormone ([Hyp9]LHRH), an endogenous hydroxylated post-translational product of the LHRH sequence, has been isolated from mammalian hypothalamus. Using the LHRH-hypothalamic cell line (GT1-7) of fetal origin, we attempted to define the substrates available for the hydroxylation process during LHRH synthesis and to characterize immunologically the [Hyp9]LHRH and pro-[Hyp9]LHRH forms with anti-LHRH antibodies of different specificities after separation by HPLC. Their biological activity and mode of action were evaluated and compared to that of LHRH and LHRH intermediate precursors in normal pituitary cells and in a gonanodotrope cell line alpha T3-1. immunoreactivity was progressively increased in cells and media during cell culture. [Hyp9]LHRH and its two smallest precursor forms ([Hyp9]LHRH-(Gly11) and -(11-13)) were detected in cells and in media. They were simultaneously detected with the homologous LHRH molecular forms indicating that the hydroxylation occurs early in the processing of pro-LHRH. [Hyp9]LHRH-like molecules were more abundant than LHRH forms in media. This predominant release may thus represent a physiological process occurring during fetal life. Free acid forms of both decapeptides were detected only in cells. Furthermore, the results obtained suggest that conversion of Gln1 in pyroGlu1 occurs before or during processing into the hydroxylated or non-hydroxylated LHRH intermediate (11-13)-precursors. The biosynthetic pathway is thus common for both decapeptides and it is not altered by the hydroxylation process. LHRH and [Hyp9]LHRH shared the same receptor for their biological activity, as assessed by measuring luteinizing hormone release and activation of phospholipase C and A2. [Hyp9]LHRH was, however, less potent than LHRH.

Amino Acid Sequence↗
PubMed1995

Molecular pharmacology of somatostatin receptors.

Somatostatin was discovered for its ability to inhibit growth hormone (GH) secretion. Later, it was found to be widely distributed in other brain regions, in which it fulfills a neuromodulatory role, and in several organs of the gastrointestinal tract where it can act as a paracrine factor or as a true circulating factor. In mammals, two molecules of 14 (somatostatin 14) and 28 (somatostatin 28) amino acids are the only biologically active members of the family. They originate from a single gene which gives rise to a single propeptide alternately cleaved in different tissues. In 1992, a major breakthrough in our understanding of somatostatin functions was made with the cloning of five different receptor genes (sstr1 to sstr5) which belong to the seven transmembrane domain receptor family. Their closer relatives are opioid receptors. In first approximation, the tissular expression of the sstrs matches quite well with the distribution of somatostatin binding sites in the "classical" targets of the peptide ie brain, pituitary pancreatic islets and adrenals. The pharmacology of GH inhibition is very close to sstr2 binding but other actions of somatostatins have not yet been attributed clearly to a single receptor subtype. All clinically relevant agonists tested so far (octreotide, lanreotide and vapreotide) are selective of sstr2 being less potent on sstr3 and inactive for sstr1 and sstr4. Surprisingly, rat sstr5 displays nanomolar affinities for octreotide and vapreotide while these agonists are only active at much higher concentrations on human sstr5. All five receptors can be more or less efficiently coupled to inhibition of adenylate cyclase activity in transfected cell systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Differential sites of action of 8OHDPAT, a 5HT1A agonist, on ACTH and PRL secretion in the rat.

We recently obtained evidence that activation of the 5HT1A subtype receptor enhances both plasma ACTH and prolactin (PRL) concentrations in rats. In order to explore the possible neuroanatomical structures involved in this interaction, we examined ACTH and PRL responses to intracerebral infusions of the 5HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8OHDPAT). In addition we also tested in vitro effects of 8OHDPAT added to the perifusion medium of pituitary cells or of hypothalamic slices on hormone or neurotransmitter release, respectively. The ACTH response to 8OHDPAT (0.1 mg/kg) was decreased after depletion of endogenous 5HT stores by p-chlorophenylalanine (PCPA) treatment. In contrast, the PRL response was markedly increased under that condition. Infusion of 8OHDPAT (1 microgram/microliter/15 min) into the dorsal raphe nucleus induced a slow elevation of ACTH release but was ineffective on PRL secretion while infusion of 8OHDPAT into the PVN induced a moderate elevation of both ACTH and PRL. After bilateral destruction of the PVN, PRL response to 8OHDPAT (0.1 and 0.25 mg/kg) was markedly potentiated. In contrast, PVN-lesioned animals showed a blunted ACTH response to 8OHdPAT. Basal or CRF-stimulated ACTH secretion rates from perifused dispersed adenohypophyseal cells were not affected by 8OHDPAT but the 5HT1A agonist induced a very slight and transient inhibition of PRL release. 8OHDPAT antagonized, in a dose-dependent manner, the K(+)-induced release of 3H-DA previously taken up in neurons of mediobasal hypothalamic slices. This data suggests that major sites of 5HT1A interaction in PRL and ACTH regulation are located within the CNS and not in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1995

Molecular and pharmacological characterization of somatostatin receptor subtypes in adrenal, extraadrenal, and malignant pheochromocytomas.

SRIH receptors were quantified by radioautography in 33 pheochromocytomas and 5 normal adrenals. Binding was evenly distributed over the tumors, whereas it was more intense in adrenal medulla than cortex. Binding levels were significantly higher in tumoral than in normal tissue, but did not differ among tumors. At 100 nmol/L, SRIH-14 and octreotide (or BIM23014 in cross-linking experiments to a 57-kilodalton component) comparably displaced SRIH binding, BIM23042 and BIM23052 were less potent, and BIM23056 was inefficient. In increasing doses, the rank order of potency was SRIH-14 > SRIH-28 > octreotide > BIM23052 >> BIM23042 >> > BIM23056. All five species of SRIH receptor (SSTR1-5) messenger ribonucleic acids (mRNAs) were measurable in pheochromocytomas and normal adrenals, SSTR2 and SSTR4 mRNA were the most expressed moieties. The proportion of SSTR5 mRNA species was higher in normal adrenals (21%) than in pheochromocytomas (6%). In the presence of guanylylimidodiphosphate, SRIH binding was reduced by 83%. However, SRIH did not alter basal or forskolin-stimulated adenylyl cyclase activity. Taken together, these pharmacological and molecular data indicate that SRIH binding on pheochromocytomas depends on a mixed population of receptors, mainly of the SSTR2 and SSTR4 subtypes, efficiently coupled to G proteins, but not to adenylyl cyclase inhibition.

3-Iodobenzylguanidine↗
PubMed1995

Differential expression of somatostatin receptors by quantitative PCR in the rat brain.

Five subtypes of somatostatin receptors (sst) have recently been cloned and reported to be expressed in rat brain. However, conventional mRNA measurement techniques do not allow to accurately compare the levels of expression of the 5 sst. Thus, we established a quantitative reverse transcriptase polymerase chain reaction method for the 5 sst. A cRNA internal standard was constructed by inserting in msst1 plasmid sequences corresponding to specific sense primers for amplification of each sst. Using a common reverse primer, a unique primer pair by receptor amplifies both wild type and standard RNAs with the same efficiency. The technique was validated by evaluating sst mRNAs in 3 brain structures in which different somatostatin receptor binding levels were previously reported. While the absolute level of expression is similar between regions, sst3 is the major subtype in cerebellum, sst1 predominates in spinal cord and sst4 and sst2 are equally expressed in the hypothalamus.

Animals↗
PubMed1995

Effect of essential fatty acid deficiency on membrane fatty acid content and growth hormone stimulation of rat pituitaries during postnatal development.

Fatty acid composition of anterior pituitary cell membranes of rats deprived of essential fatty acids (EFA) and of rats receiving a standard diet was determined during postnatal development and in adults. Pregnant rats were fed an EFA-deficient diet and the offspring were fed the same diet after weaning. In parallel, effects of the diet on growth and on growth hormone (GH) responsiveness to GHRH stimulation were determined in control animals. Membrane content of arachidonic acid (20:4n-6) and of its elongation product adrenic acid (22:4n-6) increased regularly from day 2 to day 12 after birth. EFA-deficiency resulted on day 2 in increased oleic acid and in substitution of arachidonic and adrenic acids by corresponding elongation-desaturation products of oleic acid: eicosatrienoic (20:3n-9) and docosatrienoic (22:3n-9) acids. At the age of 24 days, n-9 series fatty acid reached the same level as in adult animals. Two-day-old EFA-deficient rats paradoxically exhibited a higher level of 20:4n-6 as compared to control rats. EFA-deficiency also decreased growth rate and GH pituitary responses to GHRH during the prepubertal period. These results suggest that changes in the lipid structure and in pituitary secretion properties elicited by EFA-deficiency depend upon the stage of development.

Animals↗
PubMed1994

Angiotensin II effects on second messengers involved in prolactin secretion are mediated by AT1 receptor in anterior pituitary cells.

The two forms of angiotensin II (Ang II) receptors, AT1 and AT2 subtypes, have been demonstrated in many other cells beside the anterior pituitary cells. Attempting to investigate the subtype(s) of Ang II receptors implicated in the multiple transduction mechanisms involved in Ang II stimulation of prolactin (PRL) release by lactotropes, we studied the effect of selective nonpeptidergic Ang II antagonists on the PRL release, adenylate cyclase (AC), and phospholipase C activities. In intact cells, the AT1 antagonist DuP753 blocked Ang II-induced PRL release, reversed in a dose dependent manner Ang II-evoked inositol phosphates production, and inhibited completely the PLC and protein kinase C (PKC) dependent cAMP accumulation induced by Ang II. In membrane preparations, the Ang II receptors were negatively coupled to AC. The AT1 antagonist blocked in a dose dependent manner the inhibitory effect of Ang II on cAMP production. In intact cells, the negative coupling of Ang II receptor with AC was observed only when PKC was down regulated by long term 12-O-tetradecanolylphorbol-13-acetate pretreatment. Ang II was able to inhibit vasoactive intestinal peptide-induced cAMP accumulation, a response which was also prevented by DuP753. The different coupling of Ang II receptor described above implicated only the AT1 type receptor since the AT2 antagonists (PD123177 and PD123319) were ineffective at any doses tested (10(-8) to 10(-5) M). The obtained results indicate that the regulation of PRL secretion involves the AT1 receptor subtype and that this receptor might be coupled to multiple effectors.

Angiotensin I↗
PubMed1994

Neuropeptide Y enhances LHRH binding to rat gonadotrophs in primary culture.

Incubation of dispersed adenohypophyseal cells from intact male rats with Neuropeptide Y (NPY) or Peptide YY (YY) at 21 degrees C increased maximal 125I LHRHa binding (Bmax) by about 50%. In presence of 10(-7) M NPY, Bmax calculated from saturation isotherm curves was 15.3 +/- 1.9 fmoles x mg-1 proteins, as compared to 10 +/- 1 fmoles x mg-1 in control incubates. The increase was dose dependent with an EC50 of 6.3 +/- 1.8 10(-10) M NPY. Preincubation of the cells with pertussis toxin (PT, 15 ng/ml) for 24 h abolished the effect, suggesting coupling of NPY receptors to G alpha o or G alpha i proteins. NPY 10(-7) M inhibited basal and Forskolin 10(-5) M stimulated intracellular cyclic AMP formation by 31.9 +/- 3.4% and 30.6 +/- 2.3% respectively. Desensitization of protein kinase C by overnight preincubation of the cells with 10(-6) M phorbol ester (PMA) did not interfere with the effect of NPY. In contrast, W7, a calmodulin inhibitor, as well as H7, a protein kinase C inhibitor with a relatively wide spectrum, suppressed the effect of NPY with IC50 of 1.4 +/- 0.6 10(-6) M and 2.2 +/- 0.5 10(-5) M, respectively. Taken together, these results suggest that NPY is able to control unmasking of a cryptic LHRH receptor pool in pituitary cells by a process dependent upon both GTP binding proteins and calmodulin dependent protein kinase.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1994

Somatostatin messenger RNA-containing neurons in Alzheimer's disease: an in situ hybridization study in hippocampus, parahippocampal cortex and frontal cortex.

The level of expression of somatostatin messenger RNA-containing neurons in human brain was visualized and quantified by in situ hybridization with a 35S-labelled oligonucleotide complementary to amino acids 96-111 of the preprosomatostatin complementary DNA sequence. The analysis was carried out in the frontal and parahippocampal cortices and hippocampus of six age- and post mortem delay-matched Alzheimer's disease and control brains. By northern blot analysis, in frontal cortex samples, 18S rRNA degradation was identical in control and Alzheimer brains and somatostatin messenger RNAs migrated as a single band of 1 kb. By in situ hybridization, specificity was demonstrated by abolition of the signal using either an excess of unlabelled antisense probe or using a labelled sense probe. Somatostatin messenger RNA-containing neurons displayed a similar regional and subregional distribution in control subjects and patients with Alzheimer's disease, being more abundant in the frontal cortex, followed by the hippocampus and the parahippocampal cortex. An overall reduction of labelled cell density was observed in patients with Alzheimer's disease (frontal cortex gray matter:--41%; white matter:--66%; hippocampus:--44%; parahippocampal cortex white matter:--40%). Due to a great variation between brains, this decrease only reached significance in the parahippocampal cortex (-59%, P < 0.05). A significantly lower level of expression of somatostatin messenger RNA per somatostatinergic cell was observed in the hippocampus of Alzheimer's disease patients (-47%, P < 0.05), but not in frontal cortex gray (-17%) and white (-36%) matter and parahippocampal cortex gray (-42%) and white (-29%) matter. These data are in accordance with the distribution of somatostatin cells as visualized by immunohistochemistry in human brain. They indicate that the ability of cortical cells to express somatostatin messenger RNA is partially preserved in Alzheimer disease brains and that the decrease in the amount of somatostatin messenger RNA per cell is restricted to the hippocampal formation.

Aged↗
PubMed1994

Growth hormone-releasing hormone, somatostatin, galanin and beta-endorphin afferents to the hypothalamic periventricular nucleus.

A combined retrograde tracing (wheat germ agglutinin-horseradish peroxidase-gold complex)-immunohistochemical technique was used to identify the origin of growth hormone-releasing hormone (GHRH)-immunoreactive (ir), beta-endorphin-ir, galanin (GAL)-ir and somatostatin (SRIH)-ir terminals in the hypothalamic periventricular nucleus, which contains all the hypophysiotrophic SRIH-ir neurons. Retrogradely labeled cells were mostly observed ipsilaterally in the arcuate, dorsomedial (DMH), suprachiasmatic nuclei and the parvocellular part of the paraventricular nucleus. They were less abundant in the ventromedial and periventricular nuclei and in the lateral hypothalamus. The proportion of retrogradely labeled GHRH cells was greater at the outer rim of the ventromedial nucleus (10%) than in the arcuate nucleus proper (3%). In the arcuate nucleus, 14% of the SRIH-ir cells projected to the periventricular nucleus. Of the GAL-ir cells in the arcuate and the DMH 10% were double-labeled. Scattered retrogradely labeled GAL-ir cells were observed in paraventricular and perifornical nuclei and in the lateral hypothalamus. Of the beta-Endorphin-ir cells in the ventral part of the arcuate nucleus 15% were retrogradely labeled. It is concluded that: (1) There is no major direct connection between the hypophysiotropic GHRH and SRIH neurons, respectively, located in the arcuate and periventricular nucleus. (2) GHRH projections to the periventricular nucleus arise mainly from cells located at the outer rim of the ventromedial nucleus. (3) Intrahypothalamic SRIH projections to the periventricular nucleus arise from arcuate SRIH neurons located along the wall of the third ventricle. (4) GAL neurons from the DMH and the arcuate nucleus innervate to the same extent the periventricular nucleus. (5) beta-Endorphin arcuate neurons strongly innervate the periventricular nucleus.

Animals↗
PubMed1994

Selective patterns of expression of G protein alpha subunits during in vitro development of hypothalamic neurons.

Expression of different alpha subunits of G proteins was studied in hypothalamic primary cultures grown in defined medium and enriched in either neurons or glial (astrocyte) cells. In parallel, the cellular distribution of Gi, Gs, and GoA subunits was visualized by in situ hybridization. Immunoblots using specific antisera and hybridization of mRNAs with specific oligonucleotide probes allowed us to characterize Gs, Gi2, and GoA as major neuronal G proteins in the hypothalamus, whereas the glial cells expressed mostly Gs, Gi2, and GoB forms. Gi was found to be expressed very early and transiently in the culture, whereas expression of Gs and GoA increased regularly with time.

Animals↗
PubMed1994

Epidermal growth factor treatment induces D2 dopamine receptors functionally coupled to delayed outward potassium current (IK) in GH4C1 clonal anterior pituitary cells.

GH4C1 cells, a clonal cell line from a rat pituitary tumor, have been widely used as a model to study the regulation of prolactin secretion. These cells, however, do not express dopamine D2 receptors and are therefore not suitable for exploring mechanisms involved in dopamine inhibition of prolactin secretion. The recent demonstration that epidermal growth factor (EGF) is able to induce functional expression of D2 receptors in GH3 cells, a parental clonal cell line, overcomes this difficulty. We have thus undertaken an electrophysiological study in order to check whether coupling of D2 receptors to K+ channels could be restored in that model. Effects of dopamine on the non-inactivating voltage-dependent outward K+ current (IK) were investigated both in control and in EGF-treated GH4C1 cells. The K+ current was not modified by EGF treatment alone. In control cells, IK measured before and during dopamine application was unchanged. In contrast, dopamine application markedly enhanced the K+ current in cells that had previously been exposed to EGF. The effect was mimicked by the specific D2 receptor agonist bromocriptine and blocked by sulpiride, a D2 receptor antagonist, thus indicating that the effect of dopamine was effectively due to the activation of D2 receptors. These results bring further evidence that EGF-induced D2 receptors in clonal strains from rat pituitary tumors are functional and are coupled to the delayed outward K+ current IK.

Animals↗
PubMed1994

Alpha-1-noradrenergic inhibition of growth hormone secretion is mediated through the paraventricular hypothalamic nucleus in male rats.

In the present work we investigated a possible role of an alpha 1-noradrenergic (NA) pathway involving the hypothalamic paraventricular nucleus (PVN) in the central regulation of growth hormone (GH) release. A week after bilateral electrolytic lesions of the PVN, pulsatile GH-secretory patterns were monitored in unanesthetized, freely moving control or lesioned male rats. While the pulsatility of GH secretion was maintained, the amplitude of the pulses and the area under the curve during an 8-hour sampling period were twice as high in PVN-lesioned than in control rats. Trough levels of GH were similar in the two groups. Inactivation of PVN alpha 1-receptors by local infusion of an alpha 1-NA antagonist, prazosin (50 ng/rat), also induced an increase in GH release. In control animals, intravenous injection of the alpha 1-NA agonist methoxamine (0.02 mg/100 g body weight) elicited a decrease in GH release but was ineffective when administered to PVN-lesioned rats. These data show that alpha 1-NA receptors, mediating GH inhibition, are located in the PVN. In light of the analogous effects observed herein on PVN-lesioned animals and, previously, after locus coeruleus (LC) lesions it is suggested that GH inhibition by the LC is relayed by the PVN via a local alpha 1-receptor population.

Adrenergic alpha-Agonists↗
PubMed1994

Decreased expression of the two D2 dopamine receptor isoforms in bromocriptine-resistant prolactinomas.

Bromocriptine or other dopamine agonists are usually effective for the treatment of prolactin-secreting adenomas. Five to 18% of prolactinomas, however, do not respond to such therapy. We have shown previously that such resistance to bromocriptine correlates with reduced binding to the D2 receptor subtype of dopamine, the major PRL inhibiting factor. In the present work, we demonstrated that reduced binding actually corresponds to decreased expression of the gene coding for the D2 receptor in the pituitary from bromocriptine-resistant patients, as shown by 4-fold lower levels of the corresponding mRNAs compared to those coding for actin. The existence of two D2 receptor isoforms, D2S and D2L generated by alternative splicing, has been described in several tissues, including the pituitary. Both are negatively coupled to adenylyl cyclase and inhibit prolactin secretion, but, in addition, the shortest one (D2S) is more efficiently coupled to phospholipase C. Consequently, we also investigated whether expression of a particular D2 receptor isoform was preferentially affected in resistant adenomas. The proportion of messengers corresponding to the short receptor isoform (D2S) was lower in resistant compared to responsive adenomas: D2S/D2L = 0.74 +/- 0.08 and 1.00 +/- 0.07, respectively. In parallel, much lower levels of D2 receptor mRNAs were found in growth hormone-secreting adenomas, with a D2S/D2L ratio comparable to those of both normal human pituitary and bromocriptine-sensitive prolactinomas (1.05 +/- 0.11). Thus, resistance to bromocriptine therapy seems to involve defects in D2 dopamine receptor expression and possibly in posttranscriptional splicing.

Adenoma↗
PubMed1994

Selective effect of a diet-induced decrease in the arachidonic acid membrane-phospholipid content on in vitro phospholipase C and adenylate cyclase-mediated pituitary response to angiotensin II.

Young rats were fed on an essential fatty acid (EFA)-deprived diet for 6 weeks after weaning. Their pituitary was removed and adenohypophyseal cells dispersed and maintained in culture. Membrane lipids were analyzed and basal and stimulated levels of hormone secretion were measured after 4-day incubation in a culture medium containing or not 160 microM arachidonic acid 20:4n-6 (AA) in order to obtain EFA-deficient or EFA-restored pituitary cells, respectively. In EFA-deficient cells membrane phosphoglycerides (PGL) were depleted in AA and adrenic acid 22:4n-6; the deficit was overcome by incubation in the presence of AA. Depletion diversely affected PGL classes. AA was highly depleted in choline phosphoglycerides (ChoPG), only moderately depleted in serine and ethanolamine phosphoglycerides (SerPG and EtnPG) and not depleted at all in inositol phosphoglycerides, suggesting preferential preservation of AA in that class of PGL. Restoration of AA by addition of the fatty acid to the culture medium was complete for ChoPG and EtnPG and only partial for SerPG. Depressed levels of AA and adrenic acid in PGL were compensated for by a concomitant increase in 20:3n-9 and 22:3n-9. Growth hormone and prolactin (PRL) secretion was assessed by radioimmunoassay and possible effects of a membrane AA deficit on hormone regulation were tested in cells challenged by either growth hormone-releasing hormone, thyrotropin-releasing hormone, angiotensin II (AII), vasoactive intestinal peptide (VIP) or dopamine. Neither basal nor stimulated growth hormone secretion was different from controls in EFA-deficient cells. PRL modulation by VIP or dopamine was not affected either in EFA-deficient cells. In contrast, the capacity of AII, but not of thyrotropin-releasing hormone, to release PRL was markedly decreased in EFA-deprived cells. It was restored by addition of AA to the incubation medium. Parallel depression of AII-induced inositol phosphates and cAMP accumulation was also observed after EFA deficiency. When tested on membranes, the paradoxical inhibition of adenylate cyclase by AII documented by previous observations was reinforced in EFA-deficient membranes. In contrast, binding of AII was not affected by EFA deficiency. It is concluded that under our experimental conditions EFA deficiency affects selectively coupling of the AII receptor to its effectors without alteration of binding. The effect could involve changes in receptor interactions with coupling proteins.

Adenylyl Cyclases↗
PubMed1993

Vip-induced cross-talk between G-proteins in membranes from rat anterior pituitary cells.

In order to study the activation mechanism of heterotrimeric G-proteins by agonist-liganded receptors, GTP gamma S binding to membranes was measured in rat adenohypophyseal cells after addition of dopamine (DA) or vasoactive intestinal peptide (VIP), which, respectively, inhibit and activate pituitary adenylyl cyclase. G-protein subunit present in anterior pituitary cells was characterized by either ADP-ribosylation catalysed by Bordetella pertussis and cholera toxins or by immunoblot using specific antisera. Binding of GTP gamma S was found to depend upon GTP gamma S and Mg2+ concentrations; it was sensitive to pretreatment of the cells with cholera and Bordetella pertussis toxins (IAP). DA increased binding of the nucleotide. Paradoxically, VIP decreased the rate of GTP gamma S binding; the effect was suppressed by prior treatment of the cells with either cholera toxin or IAP. VIP also increased [33P]ADPribose incorporation in Gi/Go-proteins catalysed by IAP. Forskolin was also able to decrease GTP gamma S binding, thus suggesting that the binding of forskolin with the adenylyl cyclase catalytic unit might activate Gs proteins through an increased interaction between Gs and adenylyl cyclase. Taken together, these results suggest that VIP, as well as forskolin, may both accelerate the activation of Gs and suppress the inhibitory effect of activated Gi/Go-proteins. Interactions between Gs and Gi/Go subunits mediated by beta gamma and/or adenylyl cyclase might thus result in a kinetic coupling of transduction pathways involving distinct G-proteins.

Adenylate Cyclase Toxin↗