Inhibition of the Effect of High Glucose on the Expression of Smad in Human Peritoneal Mesothelial Cells

Objective

As high glucose (HG) concentration in peritoneal dialysis (PD) solution is thought to contribute to peritoneal fibrosis, and angiotensin II receptor blockers (ARBs) may have a key role in preventing fibrosis as they may inhibit the TGF- ß1–Smad pathway, the aims of this in vitro study were to investigate 1) if HG affects the expression of Smad in human peritoneal mesothelial cells (HPMCs) and 2) if ARB (losartan) can inhibit this effect.

Methods

HPMCs, obtained from non-renal patients undergoing elective abdominal surgery, were stimulated by HG solutions with different concentrations (1.5%, 2.5%, 4.25%) of dextrose and mannitol, and by solutions containing combination with dextrose and losartan. The supernatant was assayed for TGF- ß1 by ELISA and cells were collected for the analysis of Smad family by RT-PCR and Western Blot.

Results

1) HG up-regulated the expression of Smad2 on both gene and protein levels, especially in 2.5% and 4.25% dextrose groups (P&0.05), and also stimulated the expression of Smad4 in 4.25% dextrose group. However, the expression of Smad3 was not affected. 2) High osmolality as such (using mannitol) did not affect the TGF-ß1-Smad signaling pathway. 3) Losartan inhibited the expression of Smad2 on the gene level but not on the protein level. 4) HG up-regulated the level of TGF- ß1 with increasing dextrose concentration, while losartan partially inhibited this effect of HG on releasing of TGF-ß1.

Conclusion

A high glucose solution up-regulated the expression of Smad2 and Smad4, suggesting that the TGF- ß1-Smad pathway could be involved in the fibrosis of the peritoneum during PD. As losartan inhibited the expression of Smad2 on the gene level and reduced the concentration of TGF- ß1 in our study, the results of this in vitro study suggest that the use of angiotensin II receptor blockers might represent a possible way to prevent and treat peritoneal fibrosis in PD patients. However, further studies in vivo are needed to confirm this hypothesis.

Improving diet recipe and cooking methods attenuates hyperphosphatemia in patients undergoing peritoneal dialysis

BACKGROUND AND AIMS

Hyperphosphatemia is an independent predictor for cardiovascular and all-cause mortality in patients undergoing peritoneal dialysis (PD). The study aimed to investigate the effect of dietary intervention on reducing serum phosphate concentration in hyperphosphatemic PD patients.

METHODS AND RESULTS

In this single-center clinical trial, 97 prevalent PD patients with serum phosphate concentration ≥ 1.6 mmol/l were allocated to the intervention (n = 48) or control (n = 49) group and followed up for 1 year. In addition to phosphate binder (calcium carbonate) therapy, patients in the intervention group were intensively educated to reduce phosphate-rich food intake and improve cooking methods. While stable in the control group (1.97 ± 0.20 to 1.94 ± 0.35 mmol/l, p > 0.05), the serum phosphate concentration decreased significantly in the intervention group (1.98 ± 0.28 to 1.65 ± 0.33 mmol/l, p = 0.015) concurrently with the drop in dietary phosphate intake (13.03 ± 3.39 to 10.82 ± 3.00 mg/kg ideal body weight/day, p = 0.001). Moreover, after 6 months of intervention, fewer patients needed to use calcium carbonate (from 64.6% to 41.5%, p = 0.029) and the medicine dose reduced significantly (from 2.25 (0, 3.94) to 0 (0, 1.50) g/day, p < 0.001).

CONCLUSIONS

Our data indicated that intensive dietary intervention of reducing phosphate-rich food intake and improving cooking methods attenuated hyperphosphatemia in PD patients. It suggests that regular assessment of dietary phosphate intake and modification of diet recipe and cooking methods are essential for hyperphosphatemia treatment in PD patients in addition to phosphate binder therapy.

Induction treatment of proliferative lupus nephritis with leflunomide combined with prednisone: a prospective multi-centre observational study

To evaluate the efficacy and safety of leflunomide in the treatment of proliferative lupus nephritis, a prospective multi-centre observational study was conducted. Patients with biopsy proven proliferative lupus nephritis were assigned to receive either leflunomide or cyclophosphamide with concomitant prednisone. Leflunomide was given orally with a loading dose of 1 mg/kg/day for 3 days followed by 30 mg/day. Intravenous cyclophosphamide was administered monthly at a dose of 0.5 g/m2 of body-surface area. A total of 110 patients were enrolled, 70 in the leflunomide group and 40 in the cyclophosphamide group. The complete remission rate in the leflunomide group was 21% and partial remission rate 52%, as compared with 18% and 55%, respectively, in the cyclophosphamide group. Renal parameters and systemic lupus erythematosus disease activity index improved significantly and similarly in both groups. Serum creatinine decreased or stabilized in both treatment groups. No significant difference was noted with respect to clinical outcome between groups. Repeat biopsy also showed a significant reduction of active lesions in kidney pathology after 6 months of leflunomide treatment. Major adverse events, similar in both treatment groups, included infection, alopecia and hypertension. Leflunomide, compared with cyclophosphamide, in combination with prednisone was effective in the induction therapy of proliferative lupus nephritis and was generally well-tolerated.

A combination of a PPAR-gamma agonist and an angiotensin II receptor blocker attenuates proinflammatory signaling and stimulates expression of Smad7 in human peritoneal mesothelial cells

BACKGROUND

Human peritoneal mesothelial cells (HPMCs) have been shown to regulate the inflammatory response and the subsequent peritoneal extracellular matrix accumulation (ECM) induced by bio-incompatible peritoneal dialysis solutions. Recently, attention has been given to the possible antiinflammatory effect exhibited by angiotensin receptor blockers (ARB) or PPAR-gamma agonists in several tissues including glomerular. As no data on the potential role of these commonly used drugs in reducing peritoneal fibrosis exist, we examined the in vitro effects of an ARB (losartan) and a PPAR-gamma agonist (rosiglitazone) on inflammatory and profibrotic pathways in cultured HPMCs subjected to high glucose.

METHODS

HPMCs were incubated for 48 hours with 3 different concentrations of glucose: 5 mM (G5), 50 mM (G50) and 100 mM (G100), as well as G50 with either losartan (5 or 10 microM) and/or rosiglitazone (1 or 10 microM). IL-6, IL-8, VEGF and TGF-beta1 in the supernatants were measured by cytokine multiplex assays or ELISA. Smad7, the inhibitor of the TGF/Smad signaling pathway, was measured using immunocytochemistry.

RESULTS

All the measured cytokines increased in proportion to increased concentration of glucose. Unexpectedly, this effect was not inhibited, but rather further enhanced, by rosiglitazone and losartan separately. However, only the combination of the two drugs had an inhibitory effect on TGF- beta1 and IL-6, while the expression of inhibitory Smad7 was increased.

CONCLUSION

We conclude that high glucose exposure stimulates an inflammatory response in HPMCs in a dose-dependent manner. Rosiglitazone and losartan appear to have synergetic effects which could decrease fibrosis by inhibiting inflammation and regulating the TGF/Smad signaling pathway, but further studies are needed to elucidate the complex pathways modulated by these drugs.

DDPH inhibited L-type calcium current and sodium current in single ventricular myocyte of guinea pig

AIM

To investigate the effects of 1-(2, 6-dimethylphenoxy)-2-(3,4-dimethoxyphenyl-ethylamino)propane hydrochloride (DDPH) on L-type calcium current (ICa) and sodium current (INa), and to compare its inhibitory potency with verapamil and mexiletine.

METHODS

Whole-cell patch clamp technique was used to record ICa and INa in a single ventricular myocytes of guinea pig.

RESULTS

(1) DDPH (3 - 300 micromol . L-1) decreased ICa at 0 mV in a concentration-dependent manner with an IC50 value of 28.5 micromol . L-1 (95 % confidence limits: 14.3 - 42.7 micromol . L-1, n = 8 cells from 8 guinea pigs). Verapamil (0.3 - 30 micromol . L-1) reduced ICa with an IC50 value of 1.8 micromol . L-1 (95 % confidence limits: 1.3 - 2.3 micromol . L-1, n = 6 cells from 6 guinea pigs). Mexiletine 100 micromol . L-1 did not affect ICa (n = 5 cells from 5 guinea pigs, P > 0.05). The degree of use-dependent blocking effect of DDPH 30 micromol/L on ICa was 58 % +/- 13 % (n = 5 cells from 5 guinea pigs, P < 0.01) at 1 Hz and 76 % +/- 11 % (n = 5 cells from 5 guinea pigs, P < 0.01) at 3 Hz. (2) DDPH (20 - 320 micromol . L-1) could also block INa in a concentration-dependent manner with an IC50 value of 89.0 micromol . L-1 (95 % confidence limits: 68.7 - 109.3 micromol . L-1, n = 9 cells from 9 guinea pigs). The IC50 value of mexiletine was 32.2 micromol . L-1 (95 % confidence limits: 11.7 - 52.7 micromol . L-1, n = 5 cells from 5 guinea pigs). Verapamil at the concentration of 10 micromol . L-1 did not affect INa (n = 5 cells from 5 guinea pigs, P > 0.05). The blocking effect of DDPH 80 micromol/L on INa was non use-dependent.

CONCLUSION

DPH exhibited inhibitory effects on both ICa and INa, but its inhibitory effect on ICa was weaker than verapamil, and on INa was weaker than mexiletine.

Inhibitory effect of 1-(2, 6-dimethylphenoxy)-2-(3, 4-dimethoxyphenyl-ethylamino) propane hydrochloride on inward rectifier and delayed rectifier K+ currents in guinea pig ventricular myocytes

AIM

To study the effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxyphenyl-ethylamino) propane hydrochloride (DDPH) on action potential (AP), inward rectifier K+ current (IK1), and delayed rectifier K+ current (IK) in isolated guinea pig ventricular myocytes.

METHODS

Whole cell patch-clamp recording techniques.

RESULTS

DDPH 0.1-100 mumol.L-1 decreased 50% duration of action potential (APD50) concentration-dependently. APD50 was shortened from (493 +/- 58) to (262 +/- 38) ms (n = 7 cells from 5 guinea pigs, P < 0.01) by DDPH 10 mumol.L-1. However, 90% duration of action potential (APD90) was increased by DDPH (> 1 mumol.L-1). At high concentration (> 10 mumol.L-1) DDPH decreased resting membrane potential (RP) and amplitude of action potential (APA). DDPH inhibited tail current of IK (IK.tail) concentration-dependently, 46% at 10 mumol.L-1 and 78% at 100 mumol.L-1. EC50 for DDPH inhibiting IK was 13.3 (11.6-16.7) mumol.L-1. DDPH also blocked IK1. DDPH at high concentration (> 10 mumol.L-1) shifted the reverse potential of IK1 positively. All the effects of DDPH were reversible after washout.

CONCLUSION

DDPH blocked both IK1 and IK current in guinea pig ventricular myocytes.

Modulation by muscarinic receptor antagonists on negative chronotropic effects of tetrandrine

AIM

To investigate the influence of selective antagonist for muscarinic (M) receptor subtype on tetrandrine (Tet) reducing heart rate, inhibiting sinoatrial node (SAN) function, and its ionic mechanism.

METHODS

Effects of reducing heart rate of Tet were maintained in isolated right atrium and pithed rats. Modification on action potentials (AP) of SAN cells and L-type calcium current (ICa-L) by Tet were recorded by means of standard microelectrode and patch-clamp whole cell recording techniques.

RESULTS

Tet inhibited spontaneous beating rate of isolated right atrium (EC50, 23.7 mumol.L-1) and reduced heart rates in pithed rats in a concentration-dependent manner (EC50, 18.6 mg.kg-1). Automaticity of SAN was inhibited by Tet. AP upstroke velocity (Vmax), spontaneous depolarization rates in phase 4 (SP4) were decreased and sinus cycle length (SCL) was prolonged when treated with Tet. Tet (30 mumol.L-1) caused a reduction in peak value of ICa-L from (1275 +/- 190) pA to (498 +/- 94) pA in isolated single cardiomyocyte. Atropine and AF-DX 116 (M2 subtype selective antagonist) could attenuate such effects of Tet in a competitive mode.

CONCLUSION

Negative chronotropic effects of Tet are due to its inhibition of ICa-L. Modification on ICa-L is the major mechanism of M receptor modulating Tet effects.

Effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxyphenylethylamino) propane hydrochloride on heart function, lactate dehydrogenase and its isoenzymes in rats with cardiac hypertrophy

AIM

To investigate the effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxyphenylethylamino) propane hydrochloride (DDPH) on cardiac systolic and diastolic function, lactate dehydrogenase (LDH) activity, and LDH isoenzymes in rats with cardiac hypertrophy.

METHODS

The cardiac hypertrophy of rats was induced by partly occluding abdominal aorta. The rats were given i.g. DDPH for 8 wk 4 wk after operation, and isolated working heart was made.

RESULTS

Eight wk later, in model group, left ventricle systolic pressure (LVSP), LV + dp/dtmax, -dp/dtmax and aorta pressure (AP) decreased by 20.2%, 20.0%, 41.4%, and 13.6%, respectively. Left ventricle ending diastolic pressure (LVEDP) increased by 173.9%. The hemodynamic study showed that flowing liquid of aorta (AF) and coronary (CF) and cardiac output (CO) decreased by 49.4%, 41.2%, and 48.9%, respectively. After the rats were given i.g. DDPH, the all above-mentioned parameters recovered to different degrees. Under condition of cardiac hypertrophy, LDH isoenzymes and subunits changed significantly. Isoenzymes LDH3, LDH4, and LDH5, especially LDH5 increased, LDH1 decreased, subunit M in hypertrophied heart increased 1.69 times than that in normal heart. DDPH could decrease subunit M and increase subunit H.

CONCLUSION

DDPH can increase cardiac function, coronary flow and reverse changes of LDH isoenzymes in rats with cardiac hypertrophy.

[Effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxyphenylethylamino) propane hydrochloride on proliferation of vascular smooth muscle cells and PDGF-B, bFGF, c-sis, c-myc in spontaneously hypertensive rat]

In order to determine the effects of 1-(2, 6-dimethylphenoxy)-2-(3, 4-dimethoxyphenylethylamino) propane hydrochloride(DDPH) on proliferation of vascular smooth muscle cells(VSMC), growth factor PDGF-B, bFGF and expression of oncogene c-sis and c-myc in spontaneously hypertensive rat(SHR), 3H-thymidine(3H-TdR) incorporation, electronic microscopy, immunohistochemistry and in situ hybridization assays were used. The results showed that after DDPH administration (50 mg i.g. q.d. x8 wk to SHR), morphological change of VSMC was antagonized, blood pressure and 3H-TdR incorporation were significantly reduced. Furthermore, DDPH was shown to reverse the enhanced antigen PDGF-B and bFGF and reverse the reduced expression of oncogene c-sis and c-myc in SHR. These results suggest that DDPH may inhibit VSMC proliferation in SHR, which may be relevant to the molecular biological mechanism of growth factors and oncogene control.

[Characterization of outward current in mouse ventricular myocytes]

Depolarization-activated, calcium-independent outward currents (Iout) in enzymatically dispersed mouse ventricular myocytes were characterized by whole-cell recording technique. During brief depolarizations to potentials positive to -50 mV, outward K+ currents in these cells rise rapidly to a peak followed by a slower decay to an apparent plateau. The relative peak to plateau amplitudes in a single cell varied as a function of the holding potential (HP) from which the currents were evoked. Reversal potentials for the peak and plateau components were -64.3 +/- 3.9 mV and -53.3 +/- 2.9 mV, respectively (uncorrected for junction potentials). The outward current decay is well described by double exponential fits, whereas the time course of peak Iout decay following a 500 ms prepulse is best fitted by single exponential function, indicating the presence of two distinct components, IKf and IKs, of the outward currents in mouse ventricular cells. Application of 4-AP were accompanied by a marked attenuation of peak Iout and plateau Iout, indicating that both IKf and IKs display similar sensitivities to 4-AP. The steady state inactivation of IKf is found incomplete within the test potential range (-80 - +30 mV) owing probably to the fact that the APD of mouse myocardium is too short.

Morphometric measurement of collagen in liver tissue with posthepatitis liver cirrhosis portal hypertension

A correct estimation of the collagen content in cirrhosis liver tissue and analysis of its relation to the degree of liver function injury are important to the clinician in the establishment of the diagnosis in the liver diseases. The author has performed the morphometric measurement of collagen with liver tissue pathological section by using TJTY-300 image analysis system. It was found that the cirrhotic liver tissue's collagen area and collagen average grey degree were notably higher than those in normal men (P < 0.05), average optical density was markedly lower than that in normal men (P < 0.05), integral optical density had no significant difference (P > 0.05) between patients and normal controls, but the integral optical density in cirrhotic liver was 1.21 times that of normal men. It suggests that the collagen content in cirrhotic liver tissue increased obviously, the average density of the increased collagen was lower than that in the normal liver tissue and the density of increased collagen was not homogeneous. Comparison between normal controls and patients with different Child-Pugh liver function grades in liver tissue collagen parameters revealed that the cirrhotic liver's collagen content can, to different degree, directly reflect the function status of cirrhotic liver.

[Immunohistochemical and quantitative morphological studies of duct-acinar dysplasia in the prostate]

A series of 56 cases of prostatic adenocarcinoma and 48 cases of benign prostate hyperplasia were studied with histochemical, immunohistochemical methods and Feulgen-Image Analysis Technique. Duct-acinar dysplasia (DAD) was found in 81.8% of the prostate adenocarcinoma cases collected, but only in 47.9% of the benign hyperplasia cases. The frequency and extent of disruption of basal cell layer increased coincidently with the progressive increase of DAD grading. Intraluminal acid mucin and metachromasia stained with toluidine blue around the acini were identified in DAD. Immunohistochemical staining for prostatic acid phosphatase, cytokeratin, vimentin and UEA-1 receptor changed in DAD cells. The nuclear areas, DNA content and ploidy, mean numbers of AgNOR in DAD cells were higher than those in benign hyperplasia of the prostates and lower than those in adenocarcinomas, which indicates the possession of premalignant behavior of prostatic carcinoma.

[Effects of neferine on heart electromechanical activity in anaesthetized cats]

Neferine, an alkaloid extracted from the green seed embryo of Nelumbo nucifera Gaertn, has been shown to have anti-arrhythmic action. Neferine 1-10 mg/kg iv dose-dependently decreased the monophasic action potential amplitude (MAPA), prolonged the monophasic action potential duration (MAPD). It also decreased LVP, dP/dt, prolonged SCL, and reduced arterial blood pressure in a dose-dependent manner. These effects were similar to those of quinidine, and different from tetrandrine. The latter had an inhibitory effect on LVP and dP/dt, but had no influence on MAPA and MAPD. The results indicate that neferine and quinidine have similar effects on heart electro-mechanical activity.

[Effects of alpha-adrenoceptor agonists on cardiac function and blood pressure in rats]

In rat working hearts, alpha 1-adrenoceptor agonist phenylephrine increased LVP, +/- dP/dtmax, ABF and HR in the presence of propranolol. But alpha 2-adrenoceptor agonist B-HT 920 was ineffective. The changes induced by phenylephrine were antagonized by prazosin. In normotensive pithed rats, iv methoxamine dose-dependently increased LVP, +/- dP/dtmax, LVEDP, SAP and DAP. The changes in haemodynamics elicited by iv methoxamine were also antagonized by pretreatment with prazosin, and were attenuated by nifedipine (1 mg/kg, ia). In these two experiments, the increase in HR developed more slowly. The results suggest that postjunctional alpha 1-adrenoceptors, which exist in rat myocardium, produce a positive inotropic effect, which is possibly dependent on influx of extracellular calcium. Postjunctional alpha 2-adrenoceptors-mediated effects were not found in rat myocardium in our functional studies.

Inhibitory effect of alpha-1 adrenoceptor stimulation on cardiac sympathetic neurotransmission in pithed normotensive rats

In the present study we investigated the inhibitory effect of the selective alpha-1 adrenoceptor agonists cirazoline, amidephrine and St 587 on the cardiac sympathetic neurotransmission in pithed normotensive rats. Increases in heart rate were elicited by electrical stimulation of the cardiac sympathetic nerves or by i.v. administration of norepinephrine, isoproterenol or tyramine. Intravenous pretreatment of the animals with cirazoline, amidephrine or St 587 diminished the heart rate response to sympathetic stimulation significantly. However, the tachycardia produced by norepinephrine, isoproterenol or tyramine was also inhibited significantly by the selective alpha-1 adrenoceptor agonists. The selective alpha-1 antagonist prazosin blocked the sympathoinhibitory effect to alpha-1 adrenoceptor stimulation significantly. However, the inhibitory effect of cirazoline and St 587 was not suppressed completely by a maximally effective dose of prazosin. In contrast, the sympathoinhibitory action of amidephrine was antagonized completely by prazosin. However, the selective alpha-2 antagonist rauwolscine also produced a significant, albeit modest, attenuation of the sympathoinhibitory effect to amidephrine. The results of the present study indicate that alpha-1 adrenoceptor agonists, at relatively high doses, inhibit the sympathetic neurotransmission in rat heart. This sympathoinhibitory effect is mediated largely by alpha-1 adrenoceptors which are localized postjunctionally rather than prejunctionally.

A study of the selectivity and potency of rauwolscine, RX 781094 and RS 21361 as antagonists of alpha-1 and alpha-2 adrenoceptors

In a comparative study using various in vivo and in vitro models, the alpha-1/alpha-2 adrenoceptor blocking potencies and selectivities were quantitatively assessed for the purported alpha-2 adrenoceptor selective antagonists rauwolscine, RX 781094 and RS 21361. In pithed normotensive rats, RX 781094 showed direct agonist activity at postjunctional alpha-1 and alpha-2 adrenoceptors and had an indirect tachycardic effect. RS 21361 exhibited but minor actions on diastolic pressure and did not influence heart rate. Rauwolscine, RX 781094 and RS 21361 caused rightward parallel displacements of the log dose-response curve to the increase in diastolic pressure of methoxamine (alpha-1 agonist) and B-HT 920 (alpha-2 agonist) as well as to the B-HT 920-induced reduction in stimulation-evoked tachycardia. Schild plots afforded straight lines with slopes not significantly different from unity. Rauwolscine was more potent than RX 781094 in blocking these alpha-2 adrenoceptors in vivo, whereas both compounds were equipotent at alpha-1 adrenoceptors. RS 21361 possessed moderate in vivo blocking potencies at either subtype. All three antagonists had high blocking selectivity for alpha-2 adrenoceptors in vivo. Rauwolscine was found about 25 times more selective than RX 781094 and 2 times more selective than RS 21361. RX 781094 was approximately 3 times more effective than rauwolscine in antagonizing the centrally mediated alpha-2 adrenoceptor-induced hypotension and sedation of clonidine in rats and mice, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between dilazep and alpha-adrenoceptors

Dilazep, 1,4-bis-[3-(3,4,5-trimethoxybenzoyl-oxy)propyl]perhydro-1,4-diazep ine, is a novel antianginal agent with an unusual chemical structure. The drug is a weak calcium antagonist. In pithed rats dilazep (10-100 mg/kg i.v.) caused a transient hypotensive effect which was accompanied by a strong and persistent reduction in heart rate. Similarly as observed for other, more potent calcium antagonists dilazep (10-100 mg/kg) counteracted the vasoconstriction, evoked by the stimulation of postsynaptic alpha 2-adrenoceptors with the selective agonist B-HT 920. The antagonism proved noncompetitive. The vasoconstriction, induced upon selective stimulation of postsynaptic alpha 1-adrenoceptors with methoxamine, however, was hardly influenced by dilazep. These findings are in accordance with the calcium-antagonistic activity of dilazep, demonstrable at relatively high doses. From radioligand-binding studies it was concluded that dilazep is an extremely weak antagonist of alpha 1-adrenoceptors, whereas it does not possess any measurable affinity towards alpha 2-adrenoceptors. It seems unlikely that the antianginal activity of dilazep can be fully explained by its weak calcium-antagonistic potency. However, the bradycardic effect of dilazep is probably relevant to its antianginal activity.

Antihypertensive activity and interaction with alpha-adrenoceptors of tibalosine ([1-(2, 3-dihydro-5-benzo-(b)-thienyl)-2-(4-phenyl-butylamino)-1-propanol], CP 804 S) in rat and cat preparations

The antihypertensive and hypotensive effects and the interaction with postjunctional alpha 1- and alpha 2-adrenoceptors of tibalosine were studied in various animal preparations. Tibalosine (CP 804 S, 1-10 mg/kg) elicited dose-dependent reductions in blood pressure upon i.v., oral or i.p. administration in conscious SEHR, in pentobarbitone-anaesthetized, normotensive rats, in chloralose-anaesthetized cats and in vasopressin-supported pithed normotensive rats. These reductions were not influenced by naloxone. Infusion via the vertebral artery of chloralose-anaesthetized cats (1 mg/kg) elicited a modest, centrally mediated reduction of blood pressure, which could be antagonized by yohimbine or naloxone, but not by prazosin. Intracerebroventricular application of tibalosine (3-300 micrograms/kg) to conscious SHR elicited pressor responses. In pithed normotensive rats, tibalosine inhibited the pressor responses to i.v. cirazoline (pA2 = 5.47 +/- 0.17), but not to those by i.v. B-HT 920 Tibalosine selectively displaced [3H]-prazosin from its specific binding site in rat isolated brain membranes. The present study identifies tibalosine as a highly selective alpha 1-adrenoceptor antagonist, 700-1000 times less potent than prazosin. The antihypertensive effect of tibalosine is most likely to be attributed to blockade of alpha 1-adrenoceptors in the peripheral circulation.

Differential inhibition of alpha 2-adrenoceptor-mediated pressor responses by (+)- and (-)-verapamil in pithed rats

The inhibitory effects of (+)- and (-)-verapamil on the hypertensive responses brought about by the alpha 2-adrenoceptor agonist B-HT 920 were investigated in pithed normotensive rats. (-)-Verapamil was found to be about 4 times more potent with respect to depressing alpha 2-pressor responses compared with (+)-verapamil. To rule out the effect of 'unspecific' vasodilatation after the administration of the stereoisomers of verapamil, vasopressin was continuously infused into the carotid artery of pithed rats in a separate series of experiments. In the course of this vasopressin infusion, new inhibitory activities of the stereoisomers of verapamil on alpha 2-adrenoceptor-mediated pressor responses were determined. Under these circumstances, the potency ratio of (-)- vs (+)-verapamil was about 7. With the aid of a radioligand binding assay using [3H]clonidine to identify alpha 2-adrenoceptors, low affinities were measured for the stereoisomers of verapamil. A Ki = 6170 nM for (-)-verapamil and a Ki = 41700 nM for (+)-verapamil were calculated. The results indicate that the interaction between alpha 2-adrenoceptor-mediated pressor responses and calcium entry blockers, such as verapamil, is a stereoselective event.

Hypotensive activity of tetrandrine in rats. Investigation into its mode of action

The influence of tetrandrine on arterial pressure and heart rate of pentobarbitone-anaesthetized and conscious normotensive and hypertensive rats (SH rats, renal hypertensive rats, DOCA-salt hypertensive rats) was investigated. Tetrandrine administered intravenously (i.v.) to these animals caused an acute, long-lasting and dose-dependent decrease in mean arterial pressure. Heart rate was not significantly altered. In pithed rats, tetrandrine injected intraarterially 15 min previously impaired the increase in diastolic pressure induced by i.v. B-HT 920, a highly selective alpha 2-adrenoceptor-stimulating agent, in a dose-dependent manner. In a low dose, a parallel displacement to the right was observed, whereas for higher doses the shift was non-parallel. A high dose of tetrandrine shifted the pressor response curve of the alpha 1-adrenoceptor agonist, methoxamine, only slightly to the right and did not depress the maximal response. Tetrandrine also caused a moderate rightward shift of the vasopressor effect curve of vasopressin applied i.v. Tetrandrine displayed only minor affinities for specific binding sites in rat brain membranes for [3H]-prazosin (alpha 1-adrenoceptors) and for [3H]-clonidine (alpha 2-adrenoceptors). The results obtained suggest that the hypotensive effect of tetrandrine may be related to an impairment of vasoconstrictor tone mediated by vascular postsynaptic alpha 2-adrenoceptors.