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M Pullen

Publications and source records attributed to M Pullen.

At least 55 records · Page 3Linked to original sources
PubMed1993

Sex difference in the antidiuretic activity of vasopressin in the rat.

A possible gender difference in the antidiuretic activity of vasopressin was studied in male and female Sprague-Dawley rats. Infusion of vasopressin (3-100 pg.kg-1.min) into conscious, chronically instrumented water-loaded rats resulted in a dose-dependent antidiuresis in both male and female rats. Male rats, however, were more than three times more sensitive to vasopressin than female rats. Thus the effective doses of vasopressin (pg.kg-1.min-1) to decrease urine flow to 30 microliters.min-1.100 g-1 (18 +/- 5 in males; 58 +/- 12 in females), to increase urine osmolality to 600 mosmol/kgH2O (35 +/- 5 in males; 119 +/- 15 in females), and to decrease free water clearance to 30 microliters.min-1.100 g-1 (8 +/- 3 in males; 28 +/- 7 in females) were significantly (P < 0.05) lower in males. Furthermore, in vitro studies in papillary collecting duct cells demonstrated a significantly higher density of vasopressin V2 receptors and a greater ability of vasopressin to stimulate adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in males than in females. Vasopressin V2-receptor density (maximum binding) was 359 +/- 47 and 238 +/- 22 fmol/mg in male and female rats, respectively (P < 0.05). There was no difference in apparent dissociation constants (Kd). Vasopressin resulted in a dose-dependent increase in cAMP accumulation in papillary collecting duct cells, and at the highest concentration of vasopressin used (10(-8) M) cAMP increased from 44 +/- 10 to 182 +/- 51 fmol/micrograms protein in males and from 30 +/- 4 to 91 +/- 18 fmol/micrograms protein in females (P < 0.05). (ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Endothelin inhibits vasopressin action in rat inner medullary collecting duct via the ETB receptor.

We characterized the endothelin (ET) receptor subtype responsible for the inhibition of vasopressin (AVP)-induced increases in osmotic water permeability (Pf) and cAMP accumulation in rat inner medullary collecting ducts (IMCD). ET-1 (10 nM) produced a rapid and transient decrease in AVP-stimulated Pf from 1241 +/- 112 to 224 +/- 38 microns/sec. At the same concentration (10 nM), the selective ETB receptor agonist sarafotoxin 6c (S6c) produced the same degree of inhibition with a time course identical to that of ET-1. Exposure of IMCDs to the ETA-selective antagonist BQ123 (100 nM) had no effect on ET-1-induced inhibition of AVP-dependent Pf. In suspensions of IMCD cells, ET-1, ET-3 or S6c produced concentration-dependent inhibition of AVP-stimulated cAMP accumulation to the same extent and with similar potencies (IC50 = 10-30 nM). BQ123 (1 nM to 10 microM) had no effect on ET-1-induced inhibition of AVP-stimulated cAMP formation. Saturation binding experiments with radiolabeled ET-1 and the selective ETB agonist IRL1620 and competition binding studies with selective ETA and ETB receptor ligands demonstrated that > or = 80% of the ET-1 binding sites in IMCD membranes were of the ETB subtype. Therefore, results from functional, biochemical and binding studies suggest that the ETB receptor is the ET receptor subtype that inhibits AVP action in the rat IMCD.

Animals↗
PubMed1993

Novel endothelin receptors in the follicular membranes of Xenopus laevis oocytes mediate calcium responses by signal transduction through gap junctions.

Follicular oocytes from Xenopus laevis display saturable and high affinity endothelin (ET)-1 binding sites. Competition binding experiments using unlabeled ET-1, ET-3, and sarafotoxin 6c indicated that these ET receptors belong to the ETA receptor subtype. However, the ETA receptor-selective antagonist BQ123 [cyclo(D-Trp,D-Asp,L-Pro,D-Val,L-Leu)] failed to inhibit 125I-ET-1 binding to these receptors, suggesting that these receptors belong to a novel subtype of ETA receptors (ETAX) distinct from the human ETA receptors. These endogenous receptors are present in the follicular layer, because defolliculated oocytes did not show any 125I-ET-1 binding. Addition of ET-1 to follicular oocytes led to Ca2+ mobilization, which was reversibly blocked by treatments that uncouple gap junctions, suggesting that these ETAX receptors mediate their response by transferring signals through gap junctions. On the other hand, the expressed human ETA receptor-mediated Ca2+ mobilization was not blocked by inhibitors of gap junctions. In agreement with the binding data, the endogenous ETAX receptor-mediated response was not inhibited by BQ123 even at 100 nM, whereas the expressed human ETA receptor-mediated response was inhibited by 50% at concentrations as low as 10 nM. This further confirms that the amphibian ETAX receptors are different from mammalian ETA receptors. Finally, ET-1 enhanced the rate of progesterone-induced maturation of follicular oocytes, implying the involvement of these endogenous ETAX receptors in an in vivo maturation process.

Amino Acid Sequence↗
PubMed1993

Rat kidney endothelin receptors in ischemia-induced acute renal failure.

The current study was designed to assess the possible changes in kidney endothelin (ET) receptors in a model of ischemia-induced acute renal failure. In unilaterally nephrectomized (right kidney) Sprague-Dawley rats, the left renal artery was occluded for 30 min under pentobarbital anesthesia (40 mg/kg i.p.). Body temperature was maintained at 37 degrees C. Sham-operated rats were used as control. Plasma creatinine levels were measured and ET receptors were quantitated by binding of [125I]ET-1 to membranes prepared from the renal cortex at 0, 2, 5 and 24 hr after reperfusion. There was a time-dependent increase in plasma creatinine levels as well as in [125I]ET-1 binding to cortical membranes at 2, 5 and 24 hr postreperfusion. Saturation binding experiments using [125I]ET-1 and [125I]ET-3 indicated that this increase in binding was due to an increase in affinity without significant change in maximum binding. The affinities were 219, 134, 100, 69 and 80 pM for [125I]ET-1 and 320, 273, 130, 168 and 80 pM for [125I]ET-3 and, for sham, 0, 2, 5 and 24 hr postreperfusion, respectively. These data support the hypothesis of ET involvement in the pathophysiology of acute renal failure in rats.

Acute Kidney Injury↗
PubMed1992

Dexamethasone down-regulates the expression of endothelin receptors in vascular smooth muscle cells.

Steroid hormones have been shown to modulate a number of physiological processes in addition to their potent antiinflammatory effects. Endothelin (ET) is a newly discovered vasoconstrictor that is synthesized and released by endothelial cells and acts on adjacent vascular smooth muscle cells by interacting with specific cell surface receptors. Proinflammatory agents such as thrombin and transforming growth factor beta have been shown to up-regulate ET gene expression in vascular endothelial cells. We wondered whether the anti-inflammatory steroids might have any regulatory effect on the ET receptors present in the vascular smooth muscle cells. Rat vascular smooth muscle cells (A-10 cell line, ATCC.CRL 1476) were used as a model system to study the effects of glucocorticoids on ET receptor expression and function. These cells display high density and high affinity ET receptors that belong to the ETA subtype. Pretreatment of these cells with dexamethasone reduced the number of ET receptors by 50-60% without changing the affinity. Of the steroids tested, dexamethasone was most effective followed by prednisolone and hydrocortisone. Aldosterone, a mineralocorticoid, was 5000-fold less potent than dexamethasone. This effect of dexamethasone was dependent on the time of pretreatment and concentration of the steroid used. This down-regulation of ET receptors was also accompanied by an attenuated response to ET-1 in dexamethasone-pretreated cells. The inhibitory effect of dexamethasone was selective for ET receptors because the vasopressin-mediated response was unaffected. In addition, dexamethasone pretreatment of these cells resulted in 50-60% reduction in the steady-state level of ETA receptor mRNA as revealed by Northern analysis. These results suggest that glucocorticoid pretreatment of smooth muscle cells resulted in the down-regulation of the ETA receptor at the mRNA level.

Animals↗
PubMed1992

Activation of endothelin ETB receptors increases glomerular cGMP via an L-arginine-dependent pathway.

The effects of endothelins (ET) on guanosine 3',5'-cyclic monophosphate (cGMP) levels in intact rat glomeruli were examined. ET-3 produced a rapid approximately fivefold increase in cGMP levels with the maximum effect occurring at 1 min. The ET-3-induced increase in cGMP accumulation occurred in the absence and presence of 3-isobutyl-1-methylxanthine. ET-1, ET-2, ET-3, and the structurally related toxin, sarafotoxin S6c, all increased glomerular cGMP levels in a concentration-dependent manner and with similar potencies (EC50 approximately 15-30 nM). The L-arginine analogue, N omega-nitro-L-arginine (L-NNA), reduced basal levels of cGMP and also totally inhibited ET-induced increases in cGMP as did methylene blue, an inhibitor of soluble guanylate cyclase. The effect of L-NNA was attenuated by L-arginine but not by D-arginine. The stimulation of cGMP accumulation by ET-3 was dependent on extracellular Ca2+ and was additive to atriopeptin III but not to acetylcholine. The ETA-selective antagonist, BQ 123, had no effect on ET-3-induced formation of cGMP. Glomerular membranes displayed high-affinity (Kd = 130-150 pM) and high-density (approximately 2.0 pmol/mg) binding sites for 125I-ET-1 and 125I-ET-3. ET-1, ET-3, and sarafotoxin S6c displaced 125I-ET-1 binding to glomerular membranes with similar affinities. BQ 123 had no effect on 125I-ET-1 binding. We conclude that ET increases cGMP levels in glomeruli by stimulating the formation of a nitric oxide-like factor that activates soluble guanylate cyclase. This effect of ET appears to be mediated by activation of ETB receptors and may serve to modulate the contractile effects of ET.

Acetylcholine↗
PubMed1992

Identification of endothelin receptor subtypes in human renal cortex and medulla using subtype-selective ligands.

High affinity and high density endothelin (ET)-binding sites were identified in membranes prepared from human kidney cortex and medulla. Saturation binding experiments performed in membranes prepared from cortex and medulla using [125I]ET-1 and [125I]ET-3 revealed that the proportion of [125I]ET-3-binding sites was 30-35% less than that of [125I]ET-1-binding sites. The apparent dissociation constants and maximum binding for [125I]ET-1 and [125I]ET-3 to membranes from cortex were 91 +/- 5 pM and 165 +/- 10 fmol/mg protein, and 117 +/- 9 pM and 110 +/- 7 fmol/mg protein, respectively, whereas in medulla they were 139 +/- 10 pM and 360 +/- 11 fmol/mg protein, and 142 +/- 11 pM and 245 +/- 15 fmol/mg protein, respectively. In the presence of 10 nM sarafotoxin-6c, which is selective for ETB receptors, [125I]ET-1 binding was decreased by 65-70%, whereas [125I]ET-3 binding was totally abolished, suggesting that 65-70% of [125I]ET-1 binding and 100% of [125I]ET-3 binding was to ETB receptors. This was further confirmed by the use of a cyclic pentapeptide [cyclo(D-Trp,D-Asp,L-Pro, D-Val,L-Leu)] (BQ123), which is selective for ETA receptors. In the presence of 1 microM BQ123, [125I]ET-1 binding was decreased by 25-30%, whereas [125I]ET-3 binding was unaffected, confirming that 30-35% of ET receptors belong to the ETA subtypes, and that [125I]ET-1 bound to both ETA and ETB receptors with the same high affinity, but [125I]ET-3 bound only to ETB receptors with high affinity. These results suggest that human kidney cortex and medulla contain ETA and ETB receptors in a ratio of 30:70, and that sarafotoxin-6c and BQ123 are valuable tools in identifying the subtype of ET receptors in various tissues.

Cell Membrane↗
PubMed1992

Identification of endothelin receptor subtypes in rat kidney cortex using subtype-selective ligands.

125I-Endothelin (ET)-1 and 125I-ET-3 displayed specific, saturable, and high affinity binding to membranes prepared from rat kidney cortex. Saturation binding experiments using 125I-ET-1 and 125I-ET-3 revealed that 125I-ET-3 binding sites were 40-50% less abundant than 125I-ET-1 binding sites. The dissociation constants (Kd) and maximum binding (Bmax) for 125I-ET-1 and 125I-ET-3 with these membranes were 218 +/- 23 pM and 275 +/- 20 fmol/mg of protein and 207 +/- 19 pM and 113 +/- 17 fmol/mg of protein, respectively. In the presence of 10 nM sarafotoxin 6c, a selective agonist for ETb receptors, 125I-ET-1 binding was decreased by 45-50% and 125I-ET-3 binding was totally abolished, suggesting that approximately 40-50% of kidney cortex ET receptors are of the ETB subtype and that 125I-ET-1 binds to both ETA and ETB receptors with the same high affinity, whereas 125I-ET-3 binds to only ETB receptors with high affinity. In addition, in the presence of BQ123 [cyclo(D-Trp,D-Asp,L-Pro,D-Val,L-Leu)], a selective antagonist for ETA receptors, 125I-ET-1 binding was decreased by 50%, whereas 125I-ET-3 binding was unaffected. Our results strongly suggest that rat kidney cortex contains ETA and ETB receptors in a 50:50 ratio and that sarafotoxin 6c and BQ123 are valuable tools in identifying the subtypes of ET receptors in various tissues.

Amino Acid Sequence↗
PubMed1991

Increase in renal phorbol ester receptors in rats with cyclosporine A-induced nephrotoxicity.

Treatment of rats with cyclosporine A (50 mg/kg i.p.) for 4 days resulted in the impairment of renal function. Renal membrane and soluble phorbol ester receptor densities were significantly higher in cyclosporine A-treated rats compared to vehicle-treated rats. These data suggest that increased phorbol ester receptor (protein kinase C) may be involved in the increased renal vascular resistance associated with cyclosporine A-induced nephrotoxicity.

Animals↗
PubMed1991

Effect of nifedipine on cyclosporine A-induced nephrotoxicity, urinary endothelin excretion and renal endothelin receptor number.

The aim of the present study was to determine the effect of a calcium channel blocker on renal function, urinary endothelin excretion and endothelin receptor number in rats. Administration of cyclosporine resulted in a significant impairment of renal function when measured by either [14C]inulin or 24 h creatinine clearances. This nephrotoxicity was associated with statistically significant (P less than 0.05) increases in urinary endothelin excretion and renal endothelin receptor number. Treatment with nifedipine attenuated cyclosporine A-induced renal dysfunction and reduced urinary endothelin excretion. The data provide further evidence of a role for endothelin in cyclosporine A-induced nephrotoxicity.

Animals↗
PubMed1991

Identification of endothelin receptors in cultured cerebellar neurons.

We have described the binding of [125I]endothelin-1 (ET-1) to cultured rat cerebellar granule cells. Binding of [125I]ET-1 was specific, saturable, and time-dependent. Scatchard analysis of saturation binding data indicated a single class of high affinity binding site with a KD of 95 pM, and a Bmax of 8110 receptors/cell. Functionally, the binding of ET-1 stimulated phosphatidylinositide (PI) hydrolysis in a dose- and time-dependent fashion. PI turnover was found to be inhibitable by 1 microM phorbol dibutyrate but not by 1 microgram/ml pertussis toxin, suggesting that the ET-1-mediated response is regulated by protein kinase C and a pertussis toxin-insensitive guanine nucleotide (GTP) binding protein.

Animals↗
PubMed1991

Identification of cardiac endothelin binding sites in rats: downregulation of left atrial endothelin binding sites in response to myocardial infarction.

Endothelin-1 (ET-1) is a recently described potent vasoconstrictor peptide. Plasma and myocardial tissue levels of ET-1 are increased following myocardial ischemia, however, the factors which regulate ET-1 binding sites in vivo are not well understood. ET-1 binding sites were measured by Scatchard analysis of [125I]ET-1 binding to membranes of rat myocardium. The highest number of ET-1 binding sites (2,951 fmol/mg protein) were found in right atrial tissue, and followed the rank order of right atrium greater than left atrium (2,157 fmol/mg protein), greater than right ventricle (835 fmol/mg protein), greater than septum (609 fmol/mg protein) = left ventricle (498 fmol/mg protein). Following coronary artery occlusion for 24 h, ET-1 binding sites of left atrium were decreased by 35% (p less than 0.01), without a change in the Kd (i.e., 98 pM). Other regions of the myocardium did not exhibit any change in the number of ET-1 binding sites. Similarly, no change in ET-1 binding sites were observed following coronary artery occlusion for 0.5 h followed by 24 h reperfusion. These data indicate that there exists considerable regional differences in the density of ET-1 binding sites in the myocardium, and that ET-1 sites are selectively reduced in left atrial tissue following myocardial infarction.

Animals↗
PubMed1990

Upregulation of renal endothelin receptors in rats with cyclosporine A-induced nephrotoxicity.

Measurement of endothelin receptors by binding assay was performed in rats treated with cyclosporine A (CYA). Cyclosporine A administration at 50 mg/kg i.p. for 4 days resulted in renal function impairment as indicated by a significant increase in serum creatinine concentration (from 0.46 +/- 0.02 to 0.61 +/- 0.03 mg/dl. P less than 0.01) and a significant decrease in 24 h creatinine clearance (from 0.65 +/- 0.04 to 0.41 +/- 0.02 ml/min per 100 g, P less than 0.01). Renal endothelin (ET) receptor density was significantly higher in CYA-treated rats (312 +/- 34 vs. 196 +/- 26 fmol/mg protein, P less than 0.01). These data support the possible involvement for endothelin in the increased renal vascular resistance associated with CYA-induced nephrotoxicity.

Animals↗
PubMed1990

Identification of endothelin receptors in various regions of rat brain.

Endothelins (ET) are a family of 21 amino acid peptides which carry a high degree of hemology. ET-1, originally isolated from porcine endothelium in culture, is an unusually potent vasoconstrictor. Recent studies indicated the presence of ET-1 and ET-3 in the CNS, and autoradiographic evidence supported the presence of specific ET-1 binding sites. The present study aimed to raise evidence in support for the presence of ET-1 and ET-3 receptors in the rat CNS, to establish their spatial distribution, and gain insight on the molecular species which could be associated to ET-1 and ET-3 binding. The data support the presence of specific binding sites for ET-1 and ET-3 and a heterogeneous distribution of these sites in the CNS. The highest densities were found in the cerebellum (greater than 2200 fmol-mg protein) and the lowest in the cerebral cortex (500 fmol/mg protein). Our data also suggest that ET-1 and ET-3 labelled two different proteins of 45 Kd and 37 Kd molecular weight, but no evidence for separate ET-1 and ET-3 receptors could be noted. These data provide further evidence in support for the possible role of ET-1 and ET-3 in neuromodulation/neurotransmission in the CNS.

Animals↗
PubMedDate not supplied

Nutrition in Crohn's disease.

This article discusses ways in which nurses can help to advise patients who have Crohn's disease about their nutritional requirements.

Crohn Disease↗
PubMedDate not supplied

Protein kinase C regulates TNF-alpha production by human monocytes.

Tumor Necrosis Factor alpha (TNF alpha) is a cytokine mediator that is produced primarily by activated monocytes/macrophages in response to endotoxin/lipopolysaccharide (LPS) as well as other stimuli. The second messenger systems that regulate the synthesis and release of TNF alpha are not clearly defined. In the present study, the role of protein kinase C (PKC) in the production of TNF alpha was investigated in human peripheral blood monocytes stimulated with either LPS or zymosan. Two broad spectrum protein kinase inhibitors (staurosporine and K252a) and two PKC specific inhibitors (calphostin C and chelerythrine), were used as probes to delineate the involvement of PKC in the production of TNF alpha. The results indicate that inhibition of PKC diminished LPS- or zymosan- induced TNF alpha production in a concentration-dependent manner. The IC50 values for the inhibition of TNF alpha production were 0.2 nM for staurosporine, and 20 nM for K252a, Calphostin C and chelerythrine. Furthermore, long term PMA treatment of these cells (to abrogate PKC-mediated responses) resulted in a significant reduction of stimuli-induced TNF alpha production. LPS and zymosan also induced an increase in membrane associated PKC activity in human monocytes, which could be inhibited by pretreatment of the cells with calphostin C. Finally, western blot analysis with PKC isoform-specific antibodies demonstrates that the alpha and xi are the predominent isoforms expressed in human monocytes. These data strongly suggest that an initial step in TNF alpha production by human monocytes challenged with physiological stimulants, such as LPS and zymosan, involves a PKC-dependent mechanism.

Enzyme Activation↗