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S Kapas

Publications and source records attributed to S Kapas.

At least 55 records · Page 3Linked to original sources
PubMed1996

Effect of splanchnic nerve section and compensatory adrenal hypertrophy on rat adrenal neuropeptide content.

The neuropeptides which have been immunolocalised within the adrenal cortex have a role in regulating steroidogenesis and adrenal blood flow, but little is known of the mechanisms which regulate adrenal neuropeptide content. The present studies were designed to investigate the regulation in the rat of three adrenal neuropeptides, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY) and substance P (SP), looking at the effects of splanchnic nerve section and also investigating the effects of unilateral adrenalectomy on the neuropeptide content of the contralateral adrenal following 9 days of compensatory growth. Splanchnic nerve section, followed by a 10-day recovery period, caused a significant increase in immunoreactive NPY (irNPY) and irSP content, but had no effect on irVIP in the capsular/zona glomerulosa portion of the rat adrenal gland. In the inner zone/medullary fraction, however, irVIP was significantly decreased, while irNPY and irSP were unaffected by splanchnic nerve section. Unilateral adrenalectomy had no effect on the contralateral adrenal content of any of the peptides, although the left adrenal gland increased in size by around 60% 9 days after removal of the right adrenal. These data suggest that NPY and SP in the rat adrenal capsule/zona glomerulosa and VIP in the inner zones/medulla, are regulated, directly or indirectly, by splanchnic nerve activity, but that VIP in the outer cortex, and NPY and SP in the inner zones are regulated by another mechanism, which is, at present, unclear. These data do not support a role for VIP, NPY or substance P in the adrenal hypertrophic response to unilateral adrenalectomy in the rat.

Adrenal Glands↗
PubMed1996

Inhibition of endothelin- and phorbol ester-stimulated tyrosine kinase activity by corticotrophin in the rat adrenal zona glomerulosa.

1. The experiments described in this study were carried out to investigate the role of tyrosine kinase in the acute adrenal response to peptide hormone stimulation, and to determine whether the activity of this kinase may be subject to regulation by other intracellular signalling mechanisms in the adrenal zona glomerulosa. 2. Previous studies from this laboratory have shown that angiotensin II stimulates tyrosine kinase activity in the rat adrenal cortex. This study has shown, for the first time, that endothelin-1 also stimulates tyrosine kinase activity in this tissue. 3. Using the specific inhibitor of protein kinase C (PKC) activity, Ro 31-8220, we have shown that stimulation of tyrosine kinase activity, in response to endothelin-1, angiotensin II or the phorbol ester phorbol 12-myristate 13-acetate, is at least partly dependent on increased PKC activity. 4. The data presented also provide further evidence of cross-talk between signalling systems in the adrenal cortex. Corticotrophin and its intracellular second messenger, cyclic AMP, significantly attenuate the increment in tyrosine kinase activity seen in response to each of the effectors used. 5. The results of this study provide important new evidence for the regulation of protein kinases by other intracellular second messenger systems.

Adrenocorticotropic Hormone↗
PubMed1996

Differential effects of endogenous and exogenous nitric oxide on the release of endothelin-1 from the intact perfused rat adrenal gland in situ.

Studies using an inhibitor of nitric oxide (NO) synthesis have suggested that endogenous NO may have a role in regulating endothelin release. We investigated the effect of endogenous and exogenous nitric oxide (NO) on the release of irET-1. L-NAME stimulated, but L-arginine inhibited irET-1 release. Perfusing sodium nitroprusside (SNP), however, did not inhibit irET-1 secretion. CyclicGMP, the second messenger for NO action, was stimulated by SNP but not by L-arginine. These data demonstrate that endogenous NO inhibits of irET-1, in a manner which is independent of cGMP, and suggest that this action may contribute to the vasodilatory effect of NO.

Adrenal Glands↗
PubMed1996

Vasoactive intestinal peptide is a local regulator of adrenocortical function.

Several immunohistochemical studies have shown that vasoactive intestinal peptide (VIP) is present in nerve terminals supplying the adrenal capsule and zona glomerulosa, but its function in this tissue has been unclear. Using the intact perfused rat adrenal preparation we showed that VIP is a vasodilator in this tissue, and stimulates aldosterone and corticosterone secretion. The effects of VIP are dependent on the tissue preparation used, and we have evidence that the effect on aldosterone secretion is secondary to local catecholamine release. Administration of a low sodium diet greatly enhanced the aldosterone response to VIP stimulation. Receptor binding studies reveal an increase in the number of VIP receptors in zona glomerulosa tissue in the low sodium group. We have also investigated the regulation of adrenal tissue content of VIP. The low sodium diet caused an increase in peptide content, while a high sodium diet had the opposite effect. Splanchnic nerve section, on the other hand, had no effect on zona glomerulosa VIP content. These findings suggest that adrenal VIP has a significant role in the regulation of zona glomerulosa function, particularly in response to altered electrolyte balance.

Adrenal Glands↗
PubMed1996

Actions of adrenomedullin on the rat adrenal cortex.

The actions of adrenomedullin on cAMP and aldosterone secretion have been investigated using an intact rat adrenal capsular preparation incubated in vitro. Adrenomedullin was found to cause a dose-dependent increase in aldosterone secretion, with a parallel increase in cAMP release. The minimum concentration of adrenomedullin required for significant stimulation of aldosterone secretion was 10nmol/l. Adrenomedullin did not affect ACTH-stimulated aldosterone secretion, but significantly inhibited endothelin-1 stimulated aldosterone secretion. We conclude that adrenomedullin is an aldosterone stimulant in the rat adrenal gland, acting through cAMP generation.

Adrenal Cortex↗
PubMed1996

Regulation of adrenal vascular tone: role of endothelin-1 and nitric oxide.

The adrenal gland is a highly vascular organ, with a highly conserved and well-regulated blood supply. This study was designed to determine the roles of the local vascular regulators, nitric oxide (NO) and endothelin-1 (ET-1), in the regulation of adrenal vascular tone. Using the in situ intact perfused rat adrenal preparation it was found that the ETA receptor antagonist, BQ123, caused a significant increase in perfusion medium flow rate, while the ETB antagonist, RES-701-1, had no effect. Administration of the NO synthesis, inhibitor, L-NAME, or perfusing medium lacking the substrate for NO synthesis, resulted in a significant decrease in perfusion medium flow rate through the adrenal gland. These results suggest that endogenous endothelin causes a tonic vasoconstriction in the rat adrenal gland, mediated by the ETA receptor and that endogenous NO exerts a tonic vasodilatory effect on the rat adrenal.

Adrenal Glands↗
PubMed1996

Agonist and receptor binding properties of adrenocorticotropin peptides using the cloned mouse adrenocorticotropin receptor expressed in a stably transfected HeLa cell line.

The cloned mouse ACTH receptor was expressed in stably transfected human HeLa cells that lack an endogenous melanocortin receptor. ACTH[1-39] and several N- and C-terminally truncated analogues of ACTH were studied for their ability to stimulate cAMP generation and to displace bound 125I-ACTH. Only three of the peptides tested, ACTH[1-24], ACTH[1-39], and ACTH[1-17] were found to have agonist activity with EC50 values of 7.5, 57, and 49 x 10(-12) M respectively. Two peptides, ACTH[11-24] and ACTH[7-39], were devoid of agonist activity but had substantial competitive antagonist activity with IC50 values of approximately 10(-9) M. In binding studies, ACTH[1-39] and ACTH[1-24] were able to fully displace bound ligand, and Scatchard analysis indicated a dissociation constant (KD) of 0.84 and 0.94 x 10(-9) M for the two peptides, respectively. ACTH[1-17], ACTH[11-24], and ACTH[7-39] were only capable of displacing 60-70% of bound ligand. A three-site model for the interaction of ACTH and its receptor is proposed on the basis of these findings.

Adrenocorticotropic Hormone↗
PubMed1995

Identification of an orphan receptor gene as a type 1 calcitonin gene-related peptide receptor.

Calcitonin gene-related peptide (CGRP) is a 37 residue neuropeptide that is distantly related to adrenomedullin. We have recently reported the cloning and expression of an adrenomedullin receptor which is approximately 30% homologous to the canine orphan receptor RDC-1. Therefore we tested the hypothesis that RDC-1 was a CGRP receptor. The RDC-1 gene was expressed in COS-7 cells and showed a dose dependant increase of cAMP in response to CGRP and adrenomedullin (EC50 values of 3 x 10(-9) M and 1 x 10(-7) M respectively) which was inhibited by the CGRP antagonist CGRP[8-37]. There was no cAMP response to amylin or [Cys(acm)2,7]a-hCGRP. Ligand binding studies confirmed high affinity of this receptor for CGRP and CGRP[8-37] with KD values of 9.2 x 10(-9) M and 13.4 x 10(-9) M respectively.

Adrenomedullin↗
PubMed1995

Cloning and expression of cDNA encoding a rat adrenomedullin receptor.

Adrenomedullin is a potent vasodilator peptide that exerts major effects on cardiovascular function. Its actions are mediated through an abundant class of specific binding sites that activate adenylyl cyclase through a G protein-coupled mechanism. We report here the identification of a cDNA clone for the adrenomedullin receptor that was originally isolated as an orphan receptor from rat lung. The cDNA encodes a polypeptide of 395 residues that contains seven transmembrane domains and has a general structural resemblance to other members of the G protein-linked receptor superfamily. When expressed in COS-7 cells, this receptor mediates a cAMP response to adrenomedullin with an EC50 of 7 x 10(-9) M, and binds 125I-adrenomedullin with a KD of 8.2 x 10(-9) M, properties that are consistent with those observed in cardiovascular and other target tissues. The receptor gene is expressed as several mRNA species of which the most prominent is a 1.8-kilobase transcript found in the lung, adrenal, heart, spleen, cerebellum, and other sites. Identification of this receptor cDNA should facilitate further investigation of the cellular actions of adrenomedullin and its regulatory effects in normal and disordered states of cardiovascular function.

Adrenomedullin↗
PubMed1995

Effects of the selective protein kinase C inhibitor Ro 31-7549 on human angiotensin II receptor desensitisation and intracellular calcium release.

The mechanism underlying type I angiotensin II (Ang II) receptor (AT1 receptor) desensitisation is unknown. Structural features suggest it may be a substrate for protein kinase C (PKC). The effects of a selective PKC inhibitor, Ro 31-7549, on receptor desensitisation were investigated in CHO cells expressing the human AT1 receptor. Desensitisation was demonstrated with respect to the calcium response to Ang II in Fura-2-loaded cells. Ro 31-7549 had no effect on desensitisation. However, pretreatment with Ro 31-7549 caused a dose-dependent reduction in calcium release from intracellular stores. PKC may therefore act at a locus distal from the receptor itself.

Angiotensin II↗
PubMed1995

Cloning, characterization and expression of a functional mouse ACTH receptor.

A polymerase chain reaction-generated mouse ACTH-R probe was used to screen a mouse genomic library, and a clone of 13kb containing the entire coding sequence was isolated. The coding sequence shows 84% homology with the human gene at the DNA level and encodes a peptide with 89% homology to the human ACTH-R. This gene is expressed as a major transcript of 1.8kb in the mouse adrenal gland. The gene was expressed in HeLa cells and cAMP production in response to either ACTH or alpha-MSH was measured. cAMP increased in an ACTH dose dependent manner suggesting an EC50 of 7 x 10(-10)M ACTH. alpha-MSH was without effect on this receptor. In conclusion we have cloned a mouse ACTH receptor gene and demonstrated for the first time its expression and functional effect in HeLa cells.

Amino Acid Sequence↗
PubMed1995

Role of tyrosine kinase and protein kinase C in the steroidogenic actions of angiotensin II, alpha-melanocyte-stimulating hormone and corticotropin in the rat adrenal cortex.

The role of protein kinases in the steroidogenic actions of alpha-melanocyte-stimulating hormone (alpha-MSH), angiotensin II (AngII) and corticotropin (ACTH) in the rat adrenal zona glomerulosa was examined. Ro31-8220, a potent selective inhibitor of protein kinase C (PKC), inhibited both AngII- and alpha-MSH-stimulated aldosterone secretion but had no effect on aldosterone secretion in response to ACTH. The effect of Ro31-8220 on PKC activity was measured in subcellular fractions. Basal PKC activity was higher in cytosol than in membrane or nuclear fractions. Incubation of the zona glomerulosa with either alpha-MSH or AngII resulted in significant increases in PKC activity in the nuclear and cytosolic fractions and decreases in the membrane fraction. These effects were all inhibited by Ro31-8220. ACTH caused a significant increase in nuclear PKC activity only, and this was inhibited by Ro31-8220 without any significant effect on the steroidogenic response to ACTH, suggesting that PKC translocation in response to ACTH may be involved in another aspect of adrenal cellular function. Tyrosine phosphorylation has not previously been considered to be an important component of the response of adrenocortical cells to peptide hormones. Both AngII and alpha-MSH were found to activate tyrosine kinase, but ACTH had no effect, observations that have not been previously reported. Tyrphostin 23, a specific antagonist of tyrosine kinases, inhibited aldosterone secretion in response to AngII and alpha-MSH, but not ACTH. These data confirm the importance of PKC in the adrenocortical response to AngII and alpha-MSH, and, furthermore, indicate that tyrosine kinase may play a critical role in the steroidogenic actions of AngII and alpha-MSH in the rat adrenal zona glomerulosa.

Adrenocorticotropic Hormone↗
PubMed1995

The relationship between the adrenal tissue renin-angiotensin system, internalization of the type I angiotensin II receptor (AT1) and angiotensin II function in the rat adrenal zona glomerulosa cell.

Many data suggest that the elements of the tissue renin-angiotensin system (RAS) in the adrenal cortex are mostly located in the zona glomerulosa. The relationship of this paracrine/autocrine system with the cellular localization of the angiotensin II (AII) receptor has not bee clarified. Using a specific monoclonal antibody (6313/G2) to the first extracellular domain of the type 1 receptor (AT1), we show here that most of the receptor is internalized in the rat glomerulosa cell. This may result from tonic stimulation by the tissue RAS, and consequent permanent receptor occupancy. When viable glomerulosa cells are incubated with 6313/G2, the receptor is transiently concentrated on the cell surface, and aldosterone output is stimulated. This stimulated output is enhanced by neither threshold nor maximal stimulatory concentrations of AII amide, although the antibody does not inhibit AII binding to the receptor. The antibody directly stimulates inositol trisphosphate (IP3) generation, but, while having no intrinsic action on protein kinase C (PKC) activation, significantly inhibits the PKC response to angiotensin II. The data suggest that although the receptor is mostly internalized, recycling to the plasma membrane is constitutive, or regulated by unknown factors. Retention of the AT1 receptor in the membrane is alone enough to allow sufficient G protein interaction to generate maximal steroidogenic effects, through IP3 generation. PKC activation induced by angiotensin II has no bearing on steroidogenesis in the dispersed glomerulosa cell system.

Adrenal Glands↗
PubMed1995

Action of opioid peptides on the rat adrenal cortex: stimulation of steroid secretion through a specific mu opioid receptor.

While there have been several studies on the actions of opioid peptides on adrenocortical steroidogenesis, the results of these studies have failed to resolve the question as to whether these peptides exert a direct action on the adrenal cortex. The present studies were designed to address this question directly, using collagenase-dispersed rat zona glomerulosa and zonae fasciculata/reticularis cells incubated in vitro. The results obtained clearly show that the opioid peptides tested (beta-endorphin, Leu-enkephalin, Met-enkephalin, and its long-acting analogue, DALA) all exerted a significant stimulatory effect on aldosterone secretion by zona glomerulosa cells and all, except Leu-enkephalin, stimulated corticosterone secretion by inner zone cells. The response was shown to be inhibited by naloxone. There did not appear to be a significant interaction between the effects of ACTH and the opioid peptides on adrenocortical cells. Studies using specific agonists for opioid receptor subtypes (DAMGO, DPDPE and U-50488H, specific for mu, delta and kappa receptors respectively) showed that the effect of opioid peptides on the zona glomerulosa appeared to be mediated exclusively by mu receptors while the response of inner zone cells was mediated by both mu and, to a lesser extent, kappa receptors. Finally, studies on the second messenger systems activated by the opioid peptides and the receptor agonists showed that these peptides act to increase labelling of inositol trisphosphate, and strongly suggest that, in the rat adrenal cortex, both mu and kappa opioid receptors are linked to the activation of phospholipase C.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1995

Neuropeptide Y modulates the sensitivity of the rat adrenal cortex to stimulation by ACTH.

Neuropeptide Y (NPY) has been identified in nerves supplying the adrenal cortex of several mammalian species, although its function in this tissue is unknown. The present studies, employing adrenocortical cells prepared by collagenase digestion, have shown that NPY, in the absence of other stimulants, has no effect on steroid secretion by the rat adrenal over a range of peptide concentrations (10(-11) to 10(-6) mol/l). However, in the presence of physiological concentrations of ACTH, which are submaximal for the stimulation of aldosterone secretion, NPY (10(-6) mol/l) significantly enhanced the secretion rate of aldosterone by rat zona glomerulosa cells in response to ACTH. This effect was specific to the rat zona glomerulosa as NPY had no effect on the response to ACTH in rat zona fasciculata cells. The effect of NPY appears to be biphasic, however, as NPY significantly attenuated the steroidogenic response to supramaximal ACTH concentrations: in rat zona glomerulosa cells the aldosterone response to 10(-8) mol ACTH/l was significantly inhibited by NPY. The effect of NPY on the ACTH response appeared to be mediated by changes in the cAMP response. NPY had no effect on the steroidogenic response to potassium ions (K+), but enhanced the response to angiotensin II. NPY (10(-6) mol/l) significantly stimulated inositol 1,4,5-trisphosphate (InsP3) production although this concentration of peptide had no effect on steroid secretion. The effects of NPY on InsP3 production were additive with those of angiotensin II. These results suggest that the role of NPY in the adrenal cortex may be to regulate the sensitivity of the zona glomerulosa to peptide stimulation.

Adenylyl Cyclases↗
PubMed1995

Effects of sodium depletion on the response of rat adrenal zona glomerulosa cells to stimulation by neuropeptides: actions of vasoactive intestinal peptide, enkephalin, substance P, neuropeptide Y and corticotrophin-releasing hormone.

There are several neuropeptides, present in nerves supplying the rat adrenal zona glomerulosa, which have been shown to stimulate aldosterone secretion in the intact perfused rat adrenal preparation. The purpose of the present study was twofold: first, to determine whether these peptides acted directly on adrenocortical cells by examining their effects on collagenase-dispersed rat zona glomerulosa cells, and second, to investigate the likely physiological significance of these actions, by determining whether the responses of zona glomerulosa cells to neuropeptides were changed by prior sodium depletion. Of the peptides tested, neuropeptide Y (NPY) and substance P had only a minor effect on aldosterone secretion, which was not substantially affected by sodium depletion. Corticotrophin-releasing hormone (CRH) had a significant stimulatory effect on aldosterone secretion, but neither the threshold concentration for significant stimulation nor the maximal response to stimulation were altered by prior sodium depletion. Vasoactive intestinal peptide (VIP), on the other hand, had little effect on aldosterone secretion by cells from normal animals, but was a potent stimulus to aldosterone secretion in cells obtained from sodium-depleted animals. The response to the Met-enkephalin analogue, [D-Ala2-Met2]-enkephalinamide (DALA), was also significantly enhanced by prior sodium depletion. Experiments using the angiotensin II receptor blocker, saralasin, were carried out to determine whether the enhanced actions of DALA and VIP seen in sodium depletion may be a result of activation of angiotensin II receptors, known to be increased in sodium depletion. Saralasin did not affect the response to either peptide. These data suggest that all the peptides tested may be able to stimulate aldosterone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗