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R L Hébert

Publications and source records attributed to R L Hébert.

32 records · Page 2Linked to original sources
PubMed1995

Rabbit cortical collecting ducts express a novel prostacyclin receptor.

Prostaglandin E2 (PGE2) inhibits vasopressin-stimulated water conductivity (AVP-Lp) and inhibits Na+ reabsorption in the rabbit cortical collecting duct (CCD). Inhibition of Na+ reabsorption is mediated by increased intracellular calcium ion concentration ([Ca2+]i). Prostacyclin (PGI2) has also been shown to inhibit Na+ reabsorption in the CCD. The present studies were designed to examine the effect of the PGI2 agonist, Iloprost (ILP), on AVP-Lp and [Ca2+ in the isolated perfused rabbit CCD and to determine whether ILP activates different receptors than PGE2. ILP and PGE2 each maximally inhibited AVP-Lp equipotently at 10(-7) M. When CCDs were exposed to PGE2 and ILP simultaneously, or if PGE2 was added in the presence of ILP, inhibition of AVP-Lp was additive. Additivity was not observed if the PGI2 agonist, carbaprostacyclin (c-PGI2), was added with ILP, or if the PGE2 agonist, sulprostone, was added with PGE2, or if ILP was added to CCDs preexposed to PGE2. In fura 2-loaded CCD, ILP and PGE2 added separately increased [Ca2+]i. The response to c-PGI2 could be desensitized by prior exposure to ILP. ILP did not cause desensitization to PGE2, but PGE2 could desensitize the CCD to ILP. We conclude that PGI2 inhibits AVP-Lp by activation of a novel IP3 prostacyclin receptor and increases [Ca2+]i by activation of an IP1 prostacyclin receptor in the rabbit CCD. Functional evidence is presented that PGI2 cannot occupy PGE2 receptors and that PGE2 can occupy but cannot activate PGI2 receptors linked to inhibition of AVP-Lp.

Animals↗
PubMed1994

Cellular signalling of PGE2 and its selective receptor analogue sulprostone in rabbit cortical collecting duct.

We have documented new observations with respect to PGE2 action in the rabbit CCD. (1) PGE2 can inhibit both cAMP and vasopressin-induced water flow, depending on the sequence of PGE2 addition with respect to vasopressin or cAMP. (2) PGE2 inhibition of vasopressin or cAMP-stimulated water flow can be reversed with staurosporine. Thus, PGE2 inhibits vasopressin-stimulated water flow by activation of PKC and (3) PGE2 induces release of calcium from intracellular stores. These results strongly suggest the presence of a PGE2 receptor coupled to PIP2 hydrolysis. PGE2 mediated increases in cytosolic calcium are responsible for the inhibitory action of PGE2 on sodium transport. While stimulation of cAMP production by PGE2 may contribute to the inhibition of sodium transport, it is not required since in the presence of 8-CPTcAMP, PGE2 still decreases sodium transport. The effect of PGE2 on sodium transport is pertussis toxin insensitive and is unlikely to be mediated by an inhibitory G protein. Using PGE2 and one of its selective analogues, sulprostone, we have provided evidence for functionally distinct PGE2 receptors. Separate PGE2 receptor subtypes appear to be coupled to separate transport processes. These receptor subtypes may correspond to the EP1, EP2 and EP3 receptors described earlier in smooth muscle. Thus, an EP2 like receptor stimulates cAMP generation and water reabsorption while an EP1 like receptor increases [Ca++]i and inhibits sodium reabsorption. Finally, an EP3 receptor, equivalently activated by sulprostone and PGE2, may couple to Gi and mediate pertussis toxin sensitive inhibition of vasopressin-stimulated water flow.

Adenylyl Cyclase Inhibitors↗
PubMed1993

Evidence that separate PGE2 receptors modulate water and sodium transport in rabbit cortical collecting duct.

Prostaglandin E2 (PGE2) modulates both water and sodium transport in the rabbit cortical collecting duct (CCD). To determine whether these effects are mediated by separate PGE2 receptors, we compared the effects of PGE2 and its analogue sulprostone in the isolated perfused rabbit CCD. PGE2 increased basal water permeability (hydraulic conductivity), whereas sulprostone did not. PGE2 and sulprostone were equipotent inhibitors of water absorption when it was prestimulated by vasopressin. Pertussis toxin completely reversed the inhibitory effect of sulprostone but only partially reversed the inhibitory effect of PGE2. In contrast, a protein kinase C (PKC) inhibitor, staurosporine, partially reversed the inhibitory effect of PGE2 but had no effect on sulprostone. PGE2 also raised intracellular calcium ([Ca2+]i). This effect is coupled to its capacity to inhibit Na+ absorption. Sulprostone was 10-fold less potent than PGE2 both in raising [Ca2+]i or inhibiting sodium transport. The results suggest sulprostone selectively interacts with a PGE2 receptor coupled to pertussis toxin-sensitive inhibition of water permeability. Sulprostone less potently activates a PGE2 receptor coupled to [Ca2+]i, PKC activation, and sodium transport and completely fails to interact with the PGE2 receptor that stimulates water permeability in the collecting duct. These results suggest distinct PGE2 receptors modulate sodium and water transport in the CCD.

Alkaloids↗
PubMed1992

PGE2 inhibits water permeability at a post-cAMP site in rat terminal inner medullary collecting duct.

To assess sites and mechanism of action of prostaglandin E2 (PGE2) on water permeability (PF), we determined PGE2 effects on antidiuretic hormone (ADH)- and adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated PF in rat terminal inner medullary collecting ducts perfused in vitro. PGE2 (10(-7) M) reversibly inhibited ADH-stimulated PF (1.131 +/- 192 to 532 +/- 208 microns/s). In contrast to that observed in rabbit, PGE2 also inhibited an established PF response to the exogenous cAMP analogue 8-p-(chlorophenylthio)-cAMP (696 +/- 107 to 399 +/- 99 microns/s). PGE2 alone had no effect on PF. The protein kinase C inhibitor staurosporine (10(-8) M) blocked PGE2-mediated inhibition of cAMP-stimulated PF. PGE2 caused a rapid spikelike increase in intracellular calcium [( Ca2+]i) followed by a stable elevation above basal values. Only the latter effect was abolished in a zero calcium bath. Neither staurosporine nor cAMP altered the [Ca2+]i response. These studies are the first to demonstrate PGE2-mediated inhibition of an established PF response to cAMP independent of changes in intracellular cAMP. The pattern of [Ca2+]i release and sensitivity to staurosporine suggests that this effect is mediated via signaling through phospholipase C. The results underscore the importance of species differences, axial heterogeneity, and/or in vivo conditioning for functional expression of cellular signaling pathways.

Alkaloids↗
PubMed1992

Endothelin inhibits vasopressin-stimulated water permeability in rat terminal inner medullary collecting duct.

Renal tubule solute and water transport is subject to regulation by numerous factors. To characterize direct effects of the recently discovered peptide endothelin (ET) on renal tubule transport, we determined signaling mechanisms for ET effects on vasopressin (AVP)-stimulated water permeability (PF) in rat terminal inner medullary collecting duct (IMCD) perfused in vitro. ET caused a rapid, dose-dependent, and reversible fall in AVP- but not cyclic AMP-stimulated PF, suggesting that its effect on PF is by inhibition of cyclic AMP accumulation. Indomethacin did not block ET actions, ruling out a role for prostaglandins in its effect. The protein kinase C (PKC) inhibitor calphostin, or pretreatment of perfused tubules with pertussis toxin, blocked ET-mediated inhibition of AVP-stimulated PF. ET caused a transient increase in intracellular calcium ([Ca2+]i) in perfused tubules, an effect unchanged in zero calcium bath or by PT pretreatment. ET effects on PF and [Ca2+]i desensitized rapidly. Inhibition of PF was transient and largely abolished by 20 min ET preexposure, and repeat exposure to ET did not alter [Ca2+]i. In contrast, PGE2-mediated inhibition of AVP-stimulated PF and increase of [Ca2+]i were sustained and unaltered by prior exposure of IMCD to ET. Thus desensitization to ET is homologous. We conclude that ET is a potent inhibitor of AVP-stimulated water permeability in rat terminal IMCD. Signaling pathways for its effects involve both an inhibitory guanine nucleotide-binding protein and phospholipase-mediated activation of PKC. Since ET is synthesized by IMCD cells, this peptide may be an important autocrine modulator of renal epithelial transport.

Animals↗
PubMed1991

Prostaglandin E2 inhibits sodium transport in rabbit cortical collecting duct by increasing intracellular calcium.

The mechanism by which prostaglandin E2 (PGE2) inhibits sodium absorption (JNa) in the rabbit cortical collecting duct (CCD) was explored. PGE2 activates at least three signaling mechanisms in the CCD: (a) by itself PGE2 increases cAMP generation (b) PGE2 also inhibits vasopressin-stimulated cAMP accumulation, and (c) PGE2 raises intracellular calcium([Ca++]i). We tested the contribution of these signaling pathways to PGE2's effect on Na+ absorption, measuring 22Na flux (JNa) and [Ca++]i (using fura-2) in microperfused rabbit CCDs. In control studies PGE2 reduced JNa from 28.2 +/- 3.4 to 15.6 +/- 2.6 pmol.mm-1.min-1. Lowering bath calcium from 2.4 to 45 nM did not by itself alter JNa but in this setting PGE2 failed to inhibit JNa (28.6 +/- 5.4 to 38.5 +/- 4.0). In separate tubules, PGE2 raised [Ca++]i in a spike-like fashion followed by a sustained elevation. However, in 45 nM bath Ca++, PGE2 failed to produce a sustained [Ca++]i elevation. While pretreatment of CCDs with pertussis toxin blocked PGE2 inhibition of vasopressin-stimulated water permeability, it did not block the effect of PGE2 on JNa. To see if cAMP generation contributes to the effect of PGE2 on JNa, we tested the effect of exogenous cAMP, (8-chlorophenylthio(CPT)cAMP) on JNa. 0.1 mM 8-CPTcAMP reduced JNa from 35.75 +/- 2.3 to 21.6 +/- 2.2. However, the addition of PGE2 further blunted JNa to 15.9 +/- 1.3. In CCDs pretreated with indomethacin, 8-CPTcAMP did not significantly decrease JNa 33.6 +/- 2.8 vs. 28.4 +/- 2. However, superimposed PGE2 reduced JNa to 19.0 +/- 3.0. We conclude that PGE2 inhibits sodium transport predominantly by increasing intracellular calcium. This action is not mediated by a pertussis toxin-sensitive G protein. Finally, cAMP, through a cyclooxygenase-dependent mechanism, also inhibits CCD JNa and may contribute to the effects of PGE2 on JNa in the rabbit CCD.

Animals↗
PubMed1990

PGE2 inhibits AVP-induced water flow in cortical collecting ducts by protein kinase C activation.

It is well known that prostaglandin E2 (PGE2) both inhibits arginine vasopressin (AVP)-stimulated water permeability (hydraulic conductivity, Lp) in the cortical collecting duct (CCD) or, if administered alone, modestly increases Lp in the CCD. These bifunctional effects on Lp correspond to PGE2's capacity to inhibit AVP-stimulated adenylate cyclase (AC) activity, or to singularly stimulate AC activity in the collecting duct. The present studies suggest that the inhibitory effect of PGE2 on Lp may also be mediated by phosphatidylinositol (PI) hydrolysis. Using in vitro microperfused rabbit CCDs, we show that PGE2 releases Ca from intracellular stores. We also demonstrate that the inhibitory effect of PGE2 on AVP-stimulated Lp in the CCD is significantly reversed by the protein kinase C (PKC) inhibitor, staurosporine (SSP). Although PGE2 does not reduce an established water flow response to 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (8-CPTcAMP), when the sequence of addition is reversed and PGE2 is added first, marked inhibition of 8-CPTcAMP-induced Lp is observed. This provides independent evidence that PGE2 can act through a mechanism separate from modulating AC activity. PGE2 inhibition of 8-CPTcAMP-induced Lp is reversed by SSP pretreatment. Finally, SSP pretreatment also markedly potentiates the capacity of PGE2 itself to increase Lp. We conclude that PGE2 releases Ca from intracellular stores and, by activating PKC, inhibits AVP-induced osmotic water flow. This suggests an important role for PI hydrolysis in mediating PGE2's effects on the CCD.

Alkaloids↗
PubMed1989

Inhibition of platelet-activating factor induced renal hemodynamic and tubular dysfunctions with L-655,240, a new thromboxane-prostaglandin endoperoxide antagonist.

The continuous infusion or bolus injection of the platelet-activating factor (PAF) is associated with profound hypotension, marked reductions of renal plasma flow, glomerular filtration, and urinary sodium excretion. All these effects are inhibited by blocking PAF receptors. To examine further the potential mediators of PAF on renal function, we utilized L-655,240 (6 mg/kg, intravenously), a thromboxane-prostaglandin endoperoxide antagonist, to study the systemic and renal response to PAF (0.8 micrograms/kg, intravenously) in the anesthetized dog, using clearance methodology. PAF decreased blood pressure from 115 +/- 7 to 54 +/- 4 mmHg (1 mmHg = 133.3 Pa), renal plasma flow from 105 +/- 6 to 74 +/- 56 mL/min, and glomerular filtration from 43 +/- 3 to 32 +/- 1 mL/min. PAF also reduced urine volume from 1.1 +/- 0.2 to 0.4 +/- 0.1 mL/min, and urinary sodium from 158 +/- 7 to 86 +/- 7 mu equiv./min. L-655,240 alone had no significant effect on blood pressure, renal plasma flow, and filtration rate, at any dose. However, the 6-mg/kg dose resulted in a slight elevation of diuresis, from 1.1 +/- 0.2 to 1.9 +/- 0.1 mL/min, and urinary sodium, from 134 +/- 13 to 212 +/- 19 mu equiv./min. All doses of L-655,240 blocked the effect of PAF on blood pressure. However, the two lower doses of this antagonist (1 and 3 mg/kg) failed to prevent the PAF-induced fall of renal plasma flow and filtration rate, and attenuated the effect on urinary sodium in a dose-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Interaction between prostaglandin E2 and leukotriene D4 on the excretion of electrolytes by the dog kidney in vivo.

Recent experiments indicate that prostaglandin E2 potentiates the vasodilatory properties of leukotrienes in the skin microcirculation. The present experiments were undertaken to study the effect of leukotriene D4 and prostaglandin E2 on renal hemodynamics and urinary electrolytes in the dog. Experiments were performed in three groups of anesthetized Mongrel dogs: the first group was studied under hydropenia, whereas the two remaining groups were studied during water diuresis with (Group 3) or without indomethacin (Group 2). LTD4 (100 ng/min) and PGE2 (3 ug/min) were infused in the left renal artery to minimize systemic effects of these compounds. LTD4 alone failed to influence urinary sodium excretion in all 3 groups. In Group 1, urinary sodium increased from 77 +/- 6 to 393 +/- 74 uEq/min during PGE2, and further increased to 511 +/- 52 uEq/min during LTD4 + PGE2. No change occurred in the contralateral right kidney. In this group, glomerular filtration as well as renal plasma flow were not statistically influenced. In Group 2, the same phenomenon was observed for urinary sodium. The combined infusion of LTD4 + PGE2 increased urinary sodium without significant changes in glomerular filtration and renal plasma flow. Finally, in Group 3, indomethacin was shown to reduce the natriuretic effects of LTD4 and PGE2: during PGE2 alone, urinary sodium increased from 90 +/- 14 to 260 +/- 66 uEq/min, and only rose from 80 +/- 10 to 175 +/- 19 uEq/min during the combined infusion of LTD4 and PGE2. In groups 2 and 3, free water clearance was utilized as an index of sodium chloride reabsorption in the thick ascending limb: this parameter increased from 2.35 +/- 0.25 to 4.70 +/- 0.30 ml/min, while urinary volume was increasing from 3.55 +/- 0.25 to 10.05 +/- 0.65 ml/min, during LTD4 + PGE2. Indomethacin, administered in Group 3, (3 mg/kg/hr) again abolished the effect of combined PGE2 + LTD4. These results indicate a potentiating effect of leukotriene D4 on the PGE2-induced natriuresis in the anesthetized dog. These phenomena occurred in the absence of significant changes in renal hemodynamics, therefore suggesting a direct tubular effect of these arachidonic acid metabolites. Finally, the water diuresis experiments suggest a proximal site of action of PGE2 and LTD4.

Animals↗
PubMed1987

Hemodynamic effects of PAF-acether on the dog kidney.

PAF-Acether (PAF) is a potent vasodilator produced in several organs, including the kidney. In the present study, the effect of intra-femoral PAF (0.78 micrograms/kg) in control dogs (Group 1) or indomethacin (3 mg/kg) treated animals (Group 2) was examined. In Group 1, systemic blood pressure dropped from 108 +/- 8 to 47 +/- 7 mmHg following PAF and hematocrit rose from 42 +/- 2 to 56 +/- 2%. These changes were associated with a reduction in both urine flow, urinary sodium (from 69 +/- 9 to 25 +/- 6 muEq/min), glomerular filtration and renal plasma flow (from 28 +/- 2 to 11 +/- 1 and 52 +/- 5 to 26 +/- 4 ml/min, respectively). All parameters returned to normalcy during the following 50 minutes. In Group 2, the systemic effects of PAF were abolished by indomethacin. However, indomethacin failed to prevent the renal abnormalities which were altered as in Group 1. In additional experiments (Group 3) the influence of BN-52021, a specific antagonist of PAF receptors, was examined. The dose of PAF utilized in this group was 0.78 micrograms/kg, whereas BN-52021 was administered 30 minutes before PAF injections in increasing doses (1.0, 2.5, 5.0 and 25.0 micrograms). This antagonist blocked the effect of PAF on blood pressure and renal parameters in a dose-related manner. Finally, the effect of intrarenal PAF was studied (Group 4: increasing continuous infusions of 2, 5, 10, and 20 ng/kg/min; Group 5: single bolus of 0.15 and 0.30 micrograms/kg). In these two groups, the systemic effects of PAF were abolished as expected. In Group 4, a dose related reduction of urinary sodium was observed during the continuous infusion of PAF. Only at higher doses, was an effect on glomerular filtration and renal plasma flow observed. In Group 5, a marked reduction of urinary sodium (from 110 +/- 15 to 22 +/- 5 muEq/min) occurred while glomerular filtration and renal plasma flow decreased by approximately 50%. These data support a direct influence of PAF on urinary sodium excretion and renal hemodynamics. The peripheral effects of this compound are mediated by vasodilatory prostaglandins, as shown in Group 2. Finally, the actions of this powerful vasodilator on the kidney do not require the intervention of systemic influences, as clearly demonstrated in Groups 4 and 5.

Animals↗
PubMed1985

Potentiating effects of leukotriene B4 and prostaglandin E2 on urinary sodium excretion by the dog kidney.

A synergistic vasodilatation was recently demonstrated with leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) in the cutaneous microcirculation. The present study addresses this question to the renal microcirculation, with respect to its eventual influence on the net transport of sodium, infusing small doses of LTB4 (100 ng/min) and PGE2 (3 ng/min) in the left renal artery, and using the contralateral kidney as control in anesthetized Mongrel dogs. In group 1 (hydropenic animals), LTB4 alone failed to influence natriuresis (UNaV) while PGE2 increased UNaV from 152 +/- 20 to 225 +/- 18 uEq/min. The combined infusion of LTB4 and PGE2 resulted in a marked elevation of natriuresis to 368 +/- 26, 317 +/- 30 and 342 +/- 52 uEq/min. In group 2, water diuresis was induced to examine the eventual site of action of these compounds, and to assess the response of the diluting segment of the nephron. In these dogs, PGE2 was first administered and UNaV rose modestly from 51 +/- 12 to 77 +/- 15 uEq/min. LTB4 again had no significant influence on UNaV, but LTB4 and PGE2 produced a marked increment from 75 +/- 16 to 374 +/- 24 uEq/min. Urine volume, as well as free water clearance, increased from 3.3 +/- 0.2 to 6.5 +/- 0.7 ml/min, and from 2.3 +/- 0.2 to 3.7 +/- 0.4 ml/min, respectively, during LTB4 + PGE2. No significant change occurred in the right control kidney during these manoeuvers. Since renal hemodynamics (glomerular filtration and plasma flow) remained relatively stable in both groups of dogs, it is suggested that the combined infusion of LTB4 and PGE2 exerts a direct influence on the net transport of sodium, probably in the proximal tubule, as inferred by the results obtained in group 2. These two important metabolites of arachidonic acid could be involved in the modulation of renal sodium excretion under normal and/or pathophysiological conditions.

Animals↗