Toxicity bioassays in core sediments from the Bay of Santander, northern Spain

The use of Vibrio fischeri as luminescence bacteria is particularly effective in evaluating contaminated sediment. In this study, the ecotoxicity of five core sediments from the Bay of Santander, northern Spain, utilising V. fischeri as marine bacterium, was carried out. Different toxicity assay procedures were applied in order to study the influence of the mobility and bioavailability of the pollutants. Basic Solid Phase Test (BSPT) in whole sediment and acute toxicity test, using pore water and three leaching test procedures as liquid extracts, were applied. In addition, the study of the influence of the pH value on the toxicity results of the leaching tests was conducted. The obtained results show toxicity units (TU50) values in BSPT test ranging from 0.42 to 39.06 with a decrease with depth as general trend and TU50 values from 0.010 to 0.389 in the liquid extracts, where TU50 is calculated as the inverse of EC50 (%). The obtained data show the historical toxicity trends of the Bay of Santander and provides a technical database for the management of contaminated sediments. Moreover, these results showed evidence that each sediment test procedure provided independent and complementary ecotoxicological responses useful for a sediment classification. In order to analyse the correlations between chemical parameters (both organic and inorganic) and the toxicity results, the self-organising map (SOM) neural network and regression equations were applied. Satisfactory correlations (R=0.93) between chemical concentrations of sum of five heavy metals and 16 PAHs and BSPT toxicity were obtained.

Inhibition by reproterol of cAMP PDE in intact mastocytoma P-815 cells

In vitro studies in rat mastocytes and human monocytes suggested that reproterol (a selective beta(2)-adrenoceptor agonist with a theophylline moiety) exerts anti-inflammatory actions through inhibition of cyclic AMP (cAMP) PDE activity. Thus, reproterol was tested for its ability to inhibit cAMP PDE in cultured mouse mastocytoma P-815 cells. cAMP PDE activity was measured in intact cells by spectrofluorometry using the fluorescent substrate 2'-O-anthraniloyl cAMP. Reproterol was more potent than theophylline to inhibit cAMP PDE (pIC(50)=4.28+/-0.25 vs. 3.16+/-0.05). This contrasted with disrupted cells, where the PDE inhibitory potency of reproterol was low (pIC(50)=2.85+/-0.03) and similar to that of theophylline (pIC(50)=2.66+/-0.19). No cAMP PDE inhibition was found with other beta(2)-agonists tested (fenoterol, salbutamol, salmeterol and formoterol). Finally, the selective PDE inhibitors calmidazolium (100 nM), milrinone (5 microM) and rolipram (50 microM) inhibited cAMP PDE activity by approximately 20, 30 and 25% respectively. In conclusion, reproterol potently and non-specifically inhibited intracellular cAMP phosphodiesterases in intact mastocytoma cells. This can explain the previously reported beta(2)-adrenoceptor-independent anti-inflammatory actions of reproterol in vitro. Further studies are required to define the anti-inflammatory potential of reproterol in asthma.

[Role of nitric oxide in the NKCC2 hyperactivity of Dahl "salt-sensitive" rats]

Renal NaCl reabsorption is increased in Dahl "salt-sensitive" (DS) rats, due to an increased activity of the Na-K-Cl cotransporter NKCC2. On the other hand, nitric oxide (NO) is an inhibitor of NKCC2 and a deficient nitric oxide synthase (NOS) seems to play an important role in salt-sensitivity of DS rats. Here, we investigated the hypothesis that NKCC2 hyperactivity in DS rats is due to a deficient NOS, via the interactions cyclic GMP (cGMP)/cyclic AMP (cAMP) at the level of the thick ascending Henle's loop (TAL). DS rats DS (males, 250-300 g) and their normotensive controls DR ("salt-resistant") are sacrificed, the kidneys removed and NKCC2 activity is measured in medullary TAL (mTAL) as previously described. Medullary contents of NO are measured with a NitroFlux analyser by heat-reduction of nitrates and nitrites to NO. AMPc levels in mTAL are measured by an EIA immunotest. Neither L-NAME (3 mM), nor L-arginine were able to modify NKCC2 activity in mTAL from DS (pre-hypertensive) or DR rats. Levels of NO in the medullary interstitium and AMPc in mTAL were not significantly different between DS and DR rats. Conversely, in DS rats charged with 2% salt (in the food) during 7 weeks, L-arginine significantly inhibited NKCC2 in DS (35.6 +/- 6.8 vs 25.3 +/- 4.9 nmoles/mg protein/min; p<0.05 non-paired Student's t-test), but not in DR rats. In conclusion, NKCC2 in our mTAL preparation of prehypertensive DS and DR rats is insensitive to L-NAME and L-arginine. This suggests the absence of a functional NOS. NKCC2 hyperactivity of prehypertensive DS is therefore not due to a deficient NOS. This was confirmed by the normal levels of interstitial NO and mTAL cAMP in prehypertensive DS rats. Finally, a salt-load seems to induce NOS expression in mTAL of DS rats. This last observation deserves further investigation.

Rat NKCC2/NKCC1 cotransporter selectivity for loop diuretic drugs

It is generally assumed that bumetanide possesses some selectivity for the renal Na-K-Cl cotransporter NKCC2, although the results are scarce in the literature and comparisons were done with extra-renal NKCC1 at its basal, almost silent state. Here we investigated NKCC2/NKCC1 selectivity of loop diuretic drugs (bumetanide, piretanide and furosemide) as a function of the NKCC1 activated state (NKCC1 was activated by hypertonic media). NKCC2 activity was measured in isolated rat medullary thick ascending limb (mTAL) and NKCC1 in rat thymocytes and erythrocytes. When NKCC2 was compared with NKCC1at its activated state, all three diuretic drugs inhibited NKCC2 and NKCC1 with the same potency (bumetanide pIC50=6.48, 6.48 and 6.47; piretanide pIC50=5.97, 5.99 and 6.29; and furosemide pIC50=5.15, 5.04 and 5.21 for mTAL NKCC2, erythrocyte NKCC1 and thymocyte NKCC1, respectively). Basal NKCC1 exhibited a lower diuretic sensitivity, although with marked differences depending on the diuretic drug and the cell type in consideration and with the notable exception of furosemide in erythrocytes. Molecular modelling showed that bumetanide and piretanide possess four potentially active groups, of which three are shared with furosemide at similar intergroup distances. Of these three common groups, one should not bind to basal NKCC1 in thymocytes. The fourth (phenoxy) group (absent in furosemide) confers higher lipophilicity and should not bind to basal NKCC1 in erythrocytes. In conclusion, loop diuretics had no NKCC2/NKCC1 selectivity, when NKCC1 is measured at its activated state. Basal NKCC1 has a reduced diuretic sensitivity, of very different magnitude depending on the diuretic drug and cell type in consideration.

5-HT3- and 5-HT2C-antagonist properties of cyamemazine: significance for its clinical anxiolytic activity

RATIONALE

Cyamemazine is a neuroleptic compound which possesses anxiolytic properties in humans. On the other hand, 5-HT3- and 5-HT2C-receptors have been implicated in anxiety disorders and a previous binding study has shown that cyamemazine possesses high affinity for both serotonin receptor types.

OBJECTIVE

The present study was undertaken to establish whether cyamemazine antagonizes 5-HT3- and/or 5-HT2C-mediated responses, and whether it compares with reference compounds.

METHODS

Cyamemazine was tested for its ability to antagonize: (i) 5-HT3-dependent contraction of the isolated guinea-pig ileum and bradycardic responses in the rat and (ii) 5-HT2C-dependent phospholipase C (PLC) stimulation in rat brain membranes.

RESULTS

In isolated guinea-pig ileum, cyamemazine potently and competitively antagonized 5-HT-dependent contractions (pA2 = 7.52 +/- 0.08; n = 5). In this test, cyamemazine was 5-7 times more potent (pIC50 = 6.75 +/- 0.13) than tropisetron (pIC50 = 6.02 +/- 0.04). In rats, cyamemazine i.v. antagonized 5-HT-dependent bradycardic responses with ID50% = 3.2 +/- 1.5 mg/kg (n = 4). Finally, in rat brain membranes cyamemazine antagonized 5-HT2C-dependent PLC stimulation with Ki = 424 nM (mianserin exhibits a Ki = 113 nM).

CONCLUSIONS

Cyamemazine behaves as an antagonist at both 5-HT3- and 5-HT2C-receptors, which compares well with reference compounds. These 5-HT3- and 5-HT2C-antagonistic actions of cyamemazine can be involved, at least in part, in its beneficial therapeutic actions in anxiety disorders.

[Na-K-Cl cotransporters and "salt-sensitive" arterial hypertension]

In the 80s, erythrocyte Na-K-Cl cotransporter of essential hypertensive was reported: (i) decreased in fresh erythrocytes and (ii) increased, following repeated cell washings and incubations. This suggested to us that the manipulation of erythrocytes (from essential hypertensives) was able to dissociate a cotransport inhibitory factor, thus unmasking up-regulation of membrane cotransport units. This working hypothesis was recently confirmed in Dahl salt-sensitive rats (DS). The primary defect of DS rats seems to be hyperactivity of cotransporter Na-K-Cl BSC1 at the thick ascending limb of Henle's loop (TAL). Moreover, oral salt-loading induces an abnormally high increase in the urinary and plasmatic CIF levels of DS rats. The increase in urinary CIF excretion seems to be a compensatory mechanism, able to reduce BSC1 hyperactivity and NaCl reabsorption at the TAL. The increase in plasmatic CIF should inhibit erythrocyte BSC2, thus inducing "up-regulation" of the membrane density of cotransport proteins. Further studies are required to test this model in human with "salt-sensitive" hypertension.

Selective blockade by nicergoline of vascular responses elicited by stimulation of alpha 1A-adrenoceptor subtype in the rat

The alpha 1-adrenergic blocking activity of nicergoline was re-examined in rats, with a particular emphasis on alpha 1-adrenoceptor subtypes. In pithed rats, nicergoline and prazosin infused at a single small dose (0.5 microgram/kg/min i.v.) produced a substantial and identical shift to the right of the control dose pressor response curve to the specific alpha 1-agonist cirazoline (ED50 = 4.0 +/- 0.1, 4.0 +/- 0.1 and 0.9 +/- 0.01 microgram/kg i.v. for nicergoline, prazosin and vehicle respectively). In the isolated perfused mesenteric vascular bed, nicergoline strongly inhibited the pressor responses elicited by cirazoline, with approximately 40-fold higher potency (pA2 = 11.1 +/- 0.3) than prazosin (pA2 = 9.5 +/- 0.3). Conversely, nicergoline was 20-fold less potent than prazosin to antagonize the contractile effects of cirazoline in isolated endothelium-denuded aorta (pA2 = 8.6 +/- 0.2 and 9.9 +/- 0.2 for nicergoline and prazosin respectively). Pretreatment of mesenteric vascular beds with chloroethylclonidine did not significantly modify nicergoline antagonistic potency (pA2 = 10.6 +/- 0.2). Nicergoline displaced [3H]-prazosin bound to rat forebrain membranes pretreated with chloroethylclonidine (pKi = 9.9 +/- 0.2) at concentrations 60-fold lower than in rat liver membranes (pKi = 8.1 +/- 0.2). Finally, of the nicergoline metabolites studied, lumilysergol acted as a modest alpha 1 antagonist (bromonicotinic acid was devoid of alpha 1 antagonist activity). In conclusion, nicergoline is a potent and selective alpha 1A-adrenoceptor subtype antagonist, an alpha 1-adrenoceptor subtype which is mainly represented in resistance arteries.

The erythrocyte Na,K,Cl cotransporter and its circulating inhibitor in Dahl salt-sensitive rats

BACKGROUND

Abnormal Na,K,Cl cotransport is thought to be a pathogenic factor in Dahl salt-sensitive rat models, but the only direct evidence for this is an increased cotransport activity found in erythrocytes from salt-loaded Dahl salt-sensitive rats.

OBJECTIVE

To re-examine erythrocyte cotransport fluxes and a circulating cotransport inhibitory factor (CIF) in inbred Dahl rats maintained on a low (0.2%) salt diet. Cotransport fluxes were investigated both under basal conditions and after stimulation by cell shrinking.

METHODS

Blood was drawn from 12 male Dahl salt-sensitive and 12 Dahl salt-resistant rats of the inbred John Rapp strain. Erythrocyte Na,K,Cl cotransport activity was equated to the bumetanide-sensitive fluxes of sodium, rubidium or lithium. Plasma CIF activity was tested in human erythrocytes.

RESULTS

In Dahl salt-sensitive rats: (1) plasma CIF activity (5.7+/-0.4 units/ml) was modestly higher than in Dahl salt-resistant rats (2.97+/-0.12 units/ml, P < 0.0001), but much lower than that previously found in salt-loaded Dahl salt-sensitive rats (16.1 units/ml), and (2) erythrocytes exhibited a similar bumetanide-sensitive sodium efflux (rate constant 0.056+/-0.008 h(-1)) as in Dahl salt-resistant rats (0.047+/-0.007 h(-1)). Following hypertonic shock, the bumetanide-sensitive rubidium influx reacted more to cell shrinkage in Dahl salt-sensitive than in Dahl salt-resistant erythrocytes (cell volume decrease required to stimulate bumetanide-sensitive rubidium influx by 4000 micromol/l cells per h=-4.04+/-0.36 versus -5.89+/-0.44 fl, respectively; P< 0.01).

CONCLUSIONS

When fed a low-salt diet, Dahl salt-sensitive rats present slightly increased plasma CIF levels and normal erythrocyte cotransport fluxes under basal conditions, but an increased response to a hypertonic shock. Therefore, if there is any primary cotransport abnormality in Dahl salt-sensitive rats, it appears to be restricted to the renal Na,K,Cl cotransporter BSC1 isoform. Alternatively, any such change may be the consequence of abnormal regulation by osmolarity-dependent mechanisms.

Regulation of renal Na-K-Cl cotransporter NKCC2 by humoral natriuretic factors: relevance in hypertension

A furosemide-sensitive Na-K-Cl cotransporter (NKCC2 isoform) accounts for almost all luminal NaCl reabsorption in the thick ascending limb of Henle's loop (TALH). The activity of this transport protein is regulated by humoral factors (CIF: cotransport inhibitory factors). One family of CIF compounds is represented by the urinary phytoestrogens equol and genistein, which inhibit cotransport fluxes at similar concentrations as furosemide. Moreover, they possess similar salidiuretic potency as furosemide in the isolated perfused rat kidney, but are less potent than furosemide in vivo. Thus, dietary phytoestrogens can be responsible, at least in part, for the low blood pressure of vegetarians. A second type of CIF is represented by a circulating and urinary factor which is evoked by salt-loading. This, which is not a "ouabain-like" factor, appears to be a new retropituitary natriuretic compound. Endogenous CIF is increased in hypertensive Dahl salt-sensitive rats, probably as a compensatory mechanism against the enhanced NaCl reabsorption in the TALH, which characterizes this model of hypertension. Finally, chronic excess of circulating CIF inhibits and induces up-regulation of erythrocyte Na-K-Cl cotransporter NKCC1.

Inhibition by (-)-cicletanine of the vascular reactivity to angiotensin II and vasopressin in isolated rat vessels

In pithed rats, the levorotatory (-)-enantiomer of cicletanine reduces the pressor responses to angiotensin II (AII) and also, to a lesser extent, those to arginine-vasopressin (AVP). Here we have attempted to characterize further these inhibitory effects by studies of isolated perfused rat kidney and mesenteric vascular beds. In the isolated rat kidney, (-)-cicletanine behaves as a noncompetitive antagonist of AII- and AVP-receptor stimulation, with Ki values of 9.6 and 208 micromol/L respectively. In the isolated mesenteric vascular bed, (-)-cicletanine antagonized both AII dependent contractions with an inhibitory concentration (IC50) of 54.0 +/- 20.5 micromol/L (n = 6), and AVP dependent contractions with an IC50 of 31.6 +/- 5.0 micromol/L (n = 8). In conclusion, (-)-cicletanine antagonizes AII more effectively in rat kidney than in mesenteric vascular beds. Moreover, in rat kidney vascular beds (-)-cicletanine is more potent in blocking the pressor responses to AII than in blocking those to AVP. A selective blockade of AII induced contractions in kidney vascular beds can be one factor explaining both the greater antagonistic potency of (-)-cicletanine against AII compared with AVP in pithed rats, and the renal protective properties of cicletanine in both hypertensive and aged rats.

Renal and vascular actions of equol in the rat

BACKGROUND

The urinary isoflavonoid equol inhibits membrane Na-K-Cl cotransporters at similar concentrations to those at which furosemide inhibits them, but the significance of this action is not known.

OBJECTIVE

To investigate the potential salidiuretic and vascular actions of equol in the rat.

METHODS

Renal functioning was assessed in vitro in the isolated perfused kidney and in vivo in conscious rats. The vascular contractility of isolated aorta was assessed.

RESULTS

In the isolated perfused kidney equol was concentrated 50- to 70-fold in the urinary fluid, it was 3-4 times less potent than furosemide at increasing diuresis, natriuresis and kaliuresis (the difference was due to its higher protein-binding affinity), and it induced a modest but significant increase in glomerular filtration rate. In vivo, orally administered equol was a modest natriuretic agent, about 8-fold less potent than orally administered furosemide (in molar terms). In isolated aortic rings precontracted by administration of phenylephrine, administration of equol relaxed the contracted aorta at 10-fold lower concentrations (concentration for half-maximal activity 58.9 +/- 16 micromol/l, n = 3) than did furosemide (concentration for half-maximal activity 633 +/- 145 micromol/l, n = 3).

CONCLUSIONS

Equol is a modest natriuretic and vasorelaxant agent in the rat. Further studies are required in order to investigate the potential natriuretic and perhaps hypotensive actions of dietary equol precursors (daidzein).

Celiprolol: agonist and antagonist effects at cardiac beta 1- and vascular beta 2-adrenoceptors determined under in vivo conditions in the rat

Celiprolol is a beta-adrenoceptor antagonist which has desirable ancillary properties since it is relatively cardioselective and can exert direct vasodilator and bronchodilator effects. Here agonist and antagonist effects of celiprolol at cardiac beta 1- and vascular beta 2-adrenoceptors were determined under in vivo conditions in the rat. All experiments were carried out in catecholamine-depleted, pentobarbital anesthetized and vagotomized rats, placed under artificial respiration. I.v. administrations were made via the femoral vein. Blood pressure was measured from the cannulated right carotid artery and heart rate was recorded with a cardiotachometer. Celiprolol (10 micrograms/kg to 1 mg/kg i.v.) produced dose-related increases in heart rate and decreases in mean carotid artery blood pressure which were of longer duration than those mediated by standard agonists of beta 1-(isoprenaline) or beta 2-(salbutamol) adrenoceptors respectively. Although the maximal increase in heart rate by celiprolol (110 +/- 4 beats/min, n = 7) was approximately half that of isoprenaline (198 +/- 1 beats/min, n = 5), isoprenaline acted at doses 200-fold lower than celiprolol. Betaxolol (0.03-0.3 mg/kg i.v.), a beta 1-adrenoceptor antagonist, inhibited strongly and with similar potency the tachycardiac effects of celiprolol (DR10 = 45 micrograms/kg i.v.) as well as isoprenaline (DR10 = 45 micrograms/kg i.v.). On the other hand, the hypotensive effects of celiprolol and salbutamol were antagonized markedly and with similar potency by ICI 118,551, a relatively selective beta 2-adrenoceptor antagonist (DR10 = 15 and 25 micrograms/kg i.v. respectively). In rats pretreated with celiprolol (0.03 to 0.3 mg/kg i.v.), the heart rate dose-response curves to isoprenaline were shifted to the right of those determined in matched groups of vehicle-pretreated animals. In this respect, celiprolol was half as potent as betaxolol in blocking cardiac beta 1-adrenoceptors. Furthermore, celiprolol also antagonized the hypotensive effects of salbutamol, but, in this respect, celiprolol was 90-fold less potent than ICI 118,551. In conclusion, these results clearly indicate that celiprolol has the ability of stimulating and blocking not only cardiac beta 1- but also vascular beta 2-adrenoceptors. The effects on cardiac beta 1-adrenoceptors as well as the agonism of beta 2-adrenoceptors are produced by similar doses of celiprolol. These doses are notably lower than those necessary to block beta 2-adrenoceptors. Thus, this pharmacological profile, which has also been demonstrated in humans, indicates that celiprolol is a modulator of cardiac beta 1-adrenoceptors with vascular beta 2-adrenoceptor agonist properties.

Endogenous inhibitor of Na-K-Cl cotransport system in inbred Dahl rats

Dahl salt-sensitive (DS) rats seem characterized by a ubiquitous increase in Na-K-Cl cotransport activity. Here, an endogenous inhibitor of the Na-K-Cl cotransport system (cotransport inhibitory factor, CIF) was investigated in inbred Dahl salt-sensitive (DS) and salt-resistant (DR) rats. The animals were orally loaded for 10 days with 2% NaCl. Plasma from salt-loaded DS rats inhibited cotransport with a 50% inhibition concentration value (IC50) of 6.4 +/- 0.6% (% plasma concentration, vol/vol) vs. 24.2 +/- 2.2% in DR rats (P < 0.0001). In urine, IC50 for cotransport inhibition was constantly lower in DS before and all during the whole salt-loading period (after 10 days of salt loading, IC50 was 2.59 +/- 0.11% and 6.00 +/- 0.24% in DS and DR rats, respectively; P < 0.0001). After 3 days of salt loading, higher salt appetite in DS rats magnified the differences in urinary CIF excretion. In erythrocytes from DS rats, increased cotransport activity was strongly correlated with urinary CIF excretion (r = 0.967). In conclusion, DS rats present increased plasmatic and urinary CIF levels. This can be a compensatory phenomenon to reduce cotransport hyperactivity and increased NaCl reabsorption at the thick ascending limb of Henle's loop.

Endogenous sodium-potassium-chloride cotransport inhibitor in congestive heart failure

OBJECTIVES

This study sought to evaluate the relation, if any, between fluid overload in congestive heart failure (CHF) and a newly discovered endogenous natriuretic factor acting like loop diuretic drugs: cotransport inhibitory factor (CIF).

BACKGROUND

The humoral mechanisms regulating volume overload in CHF are not fully understood. Therefore, we investigated whether there is a role for CIF in this pathologic condition.

METHODS

Plasma and urinary CIF levels were investigated in 23 patients with chronic CHF and compared with changes in plasma atrial natriuretic peptide (ANP). Twelve patients without CHF served as control subjects.

RESULTS

CHF was associated with a highly significant threefold increase in both plasma CIF levels (mean +/- SD 7.10 +/- 3.01 vs. 2.28 +/- 0.92 U/ml, p < 0.0001) and urinary CIF excretion (7,849 +/- 3,600 vs. 2,351 +/- 1,297 U/day, p < 0.0001) with respect to patients without CHF. CIF increased as a function of impairment in left ventricular ejection fraction (r = -0.703, p < 0.0001) and the severity of clinical status. Plasma ANP was also increased in patients with CHF, although to a lesser extent (68%, p = 0.0501) than plasma CIF, and was also significantly correlated with left ventricular ejection fraction (r = -0.552, p = 0.0004).

CONCLUSIONS

Plasma and urinary CIF activities were strongly and very significantly increased in chronic CHF. In addition to ANP, this long-term natriuretic agent may be of potential importance in reducing fluid overload in CHF.

Reduction by (-)-cicletanine of the vascular reactivity to angiotensin II in rats

Cicletanine [particularly the levorotatory (-)enantiomer] inhibits calcium/calmodulin cyclic GMP phosphodiesterase (PDE) in vascular smooth muscle (VSM) and potentiates the vasorelaxant actions of the guanylate cyclase activators sodium nitroprusside (SNP) and atriopeptin II, but the possible interference with vasopressor mechanisms remains to be determined. We tested racemic (+/-) cicletanine for its ability to modify the vascular responses to vasocontractant agents in pithed rats. The most significant results were obtained with angiotensin II (AII). Therefore, the dose of AII that increased the carotid artery blood pressure (BP) 50 mm Hg was twice as high in cicletanine-pretreated (50 mg/kg orally, p.o.) as that in vehicle-pretreated animals (ED50 = 0.48 +/- 0.012 vs. 0.25 +/- 0.007 microgram/kg, p < 0.05). The displacement by cicletanine represented 47.2% of that obtained with losartan (40 micrograms/kg, intravenously, i.v.). Similar results were obtained with (-)-cicletanine (p.o. or i.v.), but not with (+)-cicletanine. In isolated rat aorta, the contraction induced by AII was reduced by (-)-cicletanine in a noncompetitive manner (the percent reduction was independent of the AII concentration). (-)-Cicletanine reduces the vascular reactivity to AII, which plays a key role in several forms of hypertension. These findings are compatible with an action of (-)-cicletanine at any of the numerous steps that couple the occupation of AII receptors to the final contractile response, such as calcium/calmodulin cyclic GMP PDE.

[A new natriuretic factor acting like loop diuretics. Kinetics in normal and hypertensive rats]

We have recently described that urines from salt-loaded rats contain a potent natriuretic factor acting at the Na-K-Cl cotransport system (CIF: "Cotransport Inhibitory Factor"). Here we investigated the kinetics of the urinary CIF excretion which follows an oral salt-load: (i) in normal rats, relative to that of the atrial natriuretic peptide (ANP) and (ii) in an experimental model of salt-dependent genetic hypertension (Dahl's rats). Thus, Wistar rats were orally loaded with 2% NaCl for 8 days. Urinary CIF excretion was measured by testing the inhibitory potency of urines on bumetanide-sensitive lithium efflux in lithium-loaded human erythrocytes. Plasmatic levels of ANP were measured by radioimmunoassay. Plasma ANP rapidly and transiently increased during the first 24 hs of salt-load, decreasing thereafter down to normal levels in 6-8 days. Conversely, CIF slowly increased after 24 hs up to maximal constant levels after 5 days of salt-loading. Dahl salt-sensitive rats exhibited highly significant increases in urinary CIF excretion with respect to salt-resistant rats. In the basal state (before salt-loading) urinary CIF excretion was 101 +/- 13 vs 17.6 +/- 4.5 units/day in salt-sensitive vs. salt-resistant rats (n = 7 for each group, p < 0.001). This difference was maintained after salt loading (3 380 +/- 990 vs. 456 +/- 159 units/day, p < 0.05 at day 5).(ABSTRACT TRUNCATED AT 250 WORDS)