Effects of P5, a novel oxazolo(3,2-a)pyridine derivative with a long-acting antihypertensive activity, on different agonist-mediated pressor responses in pithed rats

1. An oxazolo(3,2-a)pyridine derivative P5, described chemically as (+/-)-ethyl-7-(3-nitrophenyl)-5,8a-dimethyl-6-methoxycarbonyl-2,3,8,8a-tetrahydro-7H-oxazolo[3,2-a]pyridin-8-carboxylate, is a novel compound that has been synthesized as a possible antihypertensive prodrug of the 1,4-dihydropyridine type. Its antihypertensive activity was described in a previous study by the authors (Morán, Martin, Velasco, Martin, San Roman, Caballero, Puebla, Medarde & San Feliciano, 1997). 2. The aim of this work was to establish in vivo, the possible mechanisms participating in this antihypertensive action. Accordingly, we examined the effect of P5 on the pressor responses induced in pithed rats by noradrenaline (an alpha1-, alpha2- and beta-adrenoceptor agonist), xylazine (an alpha2-adrenoceptor agonist), methoxamine (an alpha1-adrenoceptor agonist), angiotensin I, angiotensin II, L-NAME (a nitric oxide synthase inhibitor) and BayK 8644 (a calcium channel agonist) and compared them with those of nifedipine, used as the reference drug. 3 Intravenous (i.v.) administration of P5 (2.5-10 mg kg(-1)) inhibited the pressor responses to noradrenaline (1 microg kg(-1)), xylazine (80 microg kg(-1)), angiotensin I (0.5 microg kg(-1)), angiotensin II (0.5 microg kg(-1)), BayK 8644 (30 microg kg(-1)) and L-NAME (10 mg kg(-1)). Nifedipine (10 microg kg(-1), i.v.) reduced the pressor responses to all these agonists and also to methoxamine (2 microg kg(-1)). 4. However, P5 was more effective than nifedipine in inhibiting these responses and its inhibitory effect lasted longer. Intravenous infusion of calcium gluconate (1 ml kg(-1) min(-1)) reversed the reduction in the pressor responses as a result of nifedipine. The effects of P5 were only reversed at 2-3 h after administration. 5 These results suggest that P5 has a strong capacity to inhibit the pressor responses to several agonists after its i.v. administration and that such effects are related to its potent antihypertensive activity.

Idle time in the washing and iron concentration in leachate removed: two basic parameters in the desulphurization of coal in a packed column

Column biodesulphurization of coal is at the experimental stage and is influenced by many variables including temperature, pH, particle size, concentration of iron in solution, among others. Idle time in the washing process and the concentration of dissolved iron in the purged leachate are two variables with a definite effect on the yield of the desulphurization system. In the laboratory, several trials were run with columns packed with coal for different idle times: 1, 2, 3, 5, 6 and 7 days, and for different concentrations of iron in the purged leachate: 500 to 4,000 mg/l. The optimal values for the two variables; that is, those allowing for the highest desulphurization yields, were idle times of 3 and 5 days, which give an elimination of 56% and 49% of pyritic sulphur, respectively, and 3,000 mg/l of iron concentration in the purged leachate, giving a decrease in pyritic sulphur in coal of 57%.

Characterization of mechanisms involved in presynaptic inhibition of sympathetic pressor effects induced by some 5-HT1 receptor antagonists

1. In a previous study, we showed that the presynaptic inhibitory action of 5-hydroxytryptamine receptor agonists on sympathetic pressor effects obtained in the pithed rats were mainly mediated by activation of 5-HT1A and 5-HT1D receptor subtypes. At the time, we observed that some 5-HT1 receptors antagonists - WAY 100,635 and NAN-190 (both 5-HT1A receptor antagonists), methiothepin (a 5-HT1,2,5,6,7 receptor antagonist) and spiperone (a 5-HT1,2 receptor antagonist) - reduced per se the pressor effects obtained by electrical stimulation. The aim of the present work was to investigate the mechanism participating in this inhibitory effect. 2. The inhibition induced by WAY 100,635 (1000 microg kg-1, i.v.) was blocked after i.v. treatment with idazoxan, an alpha2-adrenoceptor antagonist (300 and 1000 microg kg-1) and was not modified after i.v. treatment with propranolol, a beta-adrenoceptor antagonist (1000 microg kg-1) and sulpiride, a D2 receptor antagonist (1000 microg kg-1). The inhibition induced by spiperone (500 microg kg-1 i.v.) was significantly blocked by sulpiride (1000 microg kg-1) and was not modified by idazoxan or propranolol. 3. Sulpiride (1000 microg kg-1) partially blocked the inhibition induced by methiothepin (50 microg kg-1 i.v.). Only pretreatment with idazoxan (300 microg kg-1) modified the inhibition induced by NAN-190 (100 microg kg-1 i.v.), such inhibition increasing after intravenous administration of idazoxan. 4. All the antagonists used in our experiments failed to inhibit the pressor responses elicited by i.v. noradrenaline administration. 5. The above results suggest that the inhibitory effects of these 5-HT1 receptor antagonists are presynaptic in nature, but not related to the blockade of 5-HT1 receptors subtypes. The simultaneous activation or inhibition of other receptor systems could explain the inhibition produced by each 5-HT1 receptor antagonist studied.

Loss of heterozygosity at 3p23 is correlated with poor survival in patients with colorectal carcinoma

BACKGROUND

Loss of heterozygosity (LOH) of chromosome 3p has been observed commonly in carcinomas of various tumor tissues, including colorectal carcinoma (CRC). Because there is no report analyzing 3p deletions in relation to patient prognosis in CRC, the authors investigated the prognostic value of LOH on 3p in 87 patients with sporadic CRC.

METHODS

DNA samples from tumor and nontumor tissues were amplified by using polymerase chain reaction (PCR) and were analyzed for LOH on 3p using four different polymorphic human dinucleotide repeat DNA markers that map on this chromosome arm. The correlations with prognosis were established by the Kaplan-Meier method, and the Cox proportional hazards model was used to identify which independent factors jointly had a significant influence on patient survival.

RESULTS

Overall, allelic losses were detected in 19.5% of the patients evaluated. Only considering informative tumors, the data indicated that LOH was observed in 17 of 71 (29.4%) informative cases. Results from survival analysis showed a significant correlation between this molecular abnormality and both overall survival and disease free survival (P = 0.02 and P = 0.0005, respectively). The worst prognosis was found for the group of patients with LOH at 3p23: This alteration was an independent prognostic factor according to Cox multivariate analysis.

CONCLUSIONS

This study is the first to demonstrate the prognostic significance of LOH at chromosome arm 3p for patients CRC and may help to identify patients who need an intensive postoperative follow-up protocol.

Mesenteric vasoconstrictor response to 5-hydroxytryptamine in the in situ blood autoperfused rat mesentery: involvement of 5-HT(2B) and/or 5-HT(2C) receptor activation

Using a number of agonist and antagonist compounds, we attempted to characterize the responses and receptors involved in the effects of 5-hydroxytryptamine (5-HT) in the in situ blood perfused rat mesentery. An intra-arterial (i.a.) bolus injection of 5-HT increased mesenteric perfusion pressure in a dose-dependent way but did not change the systemic blood pressure. The selective 5-HT(2) receptor agonists alpha-methyl-5-HT, 1-(3-chlorophenyl)piperazine dihydrochloride (m-CPP) and (+/-)-1-(4-iodo-2, 5-dimethoxyphenyl)-2-aminopropane hydrochloride (DOI), caused a local vasoconstrictor effect in the autoperfused vascular mesenteric bed. Intra-arterial injection of 5-carboxamidotryptamine (5-CT) and 1-(m-chlorophenyl)-biguanide (m-CPBG) did not modify the mesenteric perfusion pressure. The vasoconstrictor effect elicited by 5-HT and alpha-methyl-5-HT was significantly decreased by ritanserin and by a selective 5-HT(2B/2C) receptor antagonist, N-3-pyridinyl-3, 5-dihydro-5-methyl-benzo[1,2-b:4,5-b']dipyrrole-1(2H)-carboxamide hydrochloride (SB 206553), but was not modified by prazosin, propranolol, indomethacin or enalapril pretreatment. Our data suggest that the vasoconstrictor serotonergic response induced in the in situ autoperfused rat mesenteric vascular bed is mainly mediated by activation of 5-HT(2B) and/or 5-HT(2C) receptors.

Antihypertensive activity of substituted 2,3,8,8a-tetrahydro-7H-oxazolo[3,2-a]pyridinedicarboxylate enantiomers

The synthesis and antihypertensive activity of racemates and enantiomers of substituted 2,3,8,8a-tetrahydro-7H-oxazolo[3,2-a]pyridinedicarboxylates have been reported.

5-Hydroxytryptamine inhibits the tachycardia induced by selective preganglionic sympathetic stimulation in pithed rats

It has been shown in several species that serotonin (5-hydroxytryptamine; 5-HT) is able to inhibit the responses produced by sympathetic stimulation in a wide variety of blood vessels and other organs, including the heart. However, in pithed rats, the analysis of potential sympatho-inhibitory actions of 5-HT is hampered by the fact that 5-HT (given as i.v. bolus injections) produces tachycardia per se. Moreover, most studies have investigated 5-HT-induced sympatho-inhibition at only one frequency of stimulation. Thus, the present study set out to find the experimental conditions to overcome these problems. In this regard, we analyzed the potential ability of 5-HT, administered as i.v. continuous infusions, to inhibit the tachycardia caused by stimulation of the preganglionic (C7-T1) sympathetic outflow in pithed rats. Sympathetic cardiostimulation (0.01-3 Hz) resulted in frequency-dependent increases in heart rate; these responses were potentiated after desipramine (50 microg/kg, i.v.). During continuous infusions of 5-HT (3.1-10 microg/kg.min, i.v.), but not saline, the sympathetically-induced tachycardia was dose-dependently inhibited in both control and desipramine-pretreated rats. This inhibitory effect of 5-HT was significantly more pronounced at lower frequencies of stimulation. In contrast, the above infusions of 5-HT did not inhibit the tachycardia induced by i.v. bolus injections of noradrenaline in both control and desipramine-pretreated rats. Taken together, the above findings confirm that 5-HT induces inhibition of the sympathetic chronotropic outflow in the rat by acting at receptors located prejunctionally, without evoking tachycardia, over a wide range of stimulation frequencies.

Characterization of prejunctional 5-HT1 receptors that mediate the inhibition of pressor effects elicited by sympathetic stimulation in the pithed rat

1. A study was made of the effects of 5-carboxamidotryptamine (5-CT) on pressor responses induced in vivo by electrical stimulation of the sympathetic outflow from the spinal cord of pithed rats. All animals had been pretreated with atropine. Sympathetic stimulation (0.1, 0.5, 1 and 5 Hz) resulted in frequency-dependent increases in blood pressure. Intravenous infusion of 5-CT at doses of 0.01, 0.1 and 1 mg kg(-1) min(-1) reduced the pressor effects obtained by electrical stimulation. The inhibitory effect of 5-CT was significantly more pronounced at lower frequencies of stimulation. In the present study we characterized the pharmacological profile of the receptors mediating the above inhibitory effect of 5-CT. 2. The inhibition induced by 0.01 microg kg(-1) min(-1) of 5-CT on sympathetically-induced pressor responses was partially blocked after i.v. treatment with methiothepin (10 microg kg(-1)), WAY-100,635 (100 microg kg(-1)) or GR127935T (250 microg kg(-1)), but was not affected by cyanopindolol (100 microg kg(-1)). 3. The selective 5-HT1A receptor agonist 8-OH-DPAT and the selective 5-HT(1B/1D) receptor agonists sumatriptan and L-694,247 inhibited the pressor response, whereas the 5-HT1B receptor agonists CGS-12066B and CP-93,129 and the 5-HT2C receptor agonist m-CPP did not modify the pressor sympathetic responses. 4. The selective 5-HT1A receptor antagonist WAY-100,635 (100 microg kg(-1)) blocked the inhibition induced by 8-OH-DPAT and the selective 5-HT(1B/1D) receptor antagonist GR127935T (250 microg kg(-1)) abolished the inhibition induced either by L-694,247 or sumatriptan. 5. None of the 5-HT receptor agonists used in our experiments modified the pressor responses induced by exogenous noradrenaline (NA). 6. These results suggest that the presynaptic inhibitory action of 5-CT on the electrically-induced pressor response is mediated by both r-5-HT1D and 5-HT1A receptors.

Renal vasoconstrictor response to 5-hydroxytryptamine in the in situ autoperfused rat kidney: involvement of angiotensin II and the 5-HT2 receptor activation

Using a number of agonist and antagonist compounds, we attempted to characterize the responses and receptors involved in the effects of 5-hydroxytryptamine (5-HT) in the in situ autoperfused rat kidney. An intra-arterial (i.a.) bolus injection of 5-HT (0.0125 to 0.1 microg/kg) increased renal perfusion pressure in a dose-dependent way but did not change the systemic blood pressure. The 5-HT2 receptor agonist, (1-(3-chlorophenyl) piperazine), m-CPP, caused a local vasoconstrictor effect in the autoperfused rat kidney. An intra-arterial injection of 5-carboxamidotryptamine, 5-CT and 1-(m-chlorophenyl)-biguanide (m-CPBG) did not modify the renal perfusion pressure. The vasoconstrictor effect elicited by 5-HT and m-CPP was significantly decreased by ritanserin, enalapril and losartan but was not modified by prazosin, propranolol or indomethacin pretreatment. Our data suggest that the vasoconstrictor serotonergic response induced in the in situ autoperfused rat kidney is mediated through angiotensin II activation by a local 5-HT2 receptor mechanism.

MR-14134, a new benzothiazepine with central hypotensive action

Structural changes introduced into the benzothiazepine molecule have led to a compound, MR-14134 (3-[(3-dimethylamino)propyl]-2,3,4,5- tetrahydro-2[4-methoxyphenyl]-1,5-benzothiazepin-4-one oxalate). We have compared the effects of MR-14134 and diltiazem on blood pressure and heart rate in anaesthetized and pithed rats following intravenous administration as well as in anaesthetized rats after intracerebroventricular administration and on the binding of [3H]clonidine in the rat cerebral cortex. MR-14134 (0.1-5.0 mg/kg, i.v.) produced a dose-dependent hypotensive and bradycardic effect similar in intensity but lasting longer than that of diltiazem. These effects were antagonized by previous administration of yohimbine but not by atropine, propranolol or ICI 118,551. Doses of 1 mg/kg i.v. of MR-14134 did not modify either blood pressure or heart rate in pithed rats and did not affect the hypertensive response elicited by electrical sympathetic stimulation or by exogenous administration of norepinephrine in pithed rats. Intracerebroventricular administration of MR-14134 (60 micrograms/kg) decreased blood pressure and heart rate in rats. This effect was antagonized by yohimbine and prazosin. [3H]Clonidine-binding experiments in the rat cortex showed that neither MR-14134 nor diltiazem have affinity for alpha 2A-adrenoceptors. These results confirmed that MR-14134 has a hypotensive and bradycardic effect in which, unlike diltiazem, the central nervous system is involved. These effects were mediated, at least partly, by alpha 2B-adrenoceptors and I1 imidazoline receptors.

Inhibitory 5-hydroxytryptamine receptors involved in pressor effects obtained by stimulation of sympathetic outflow from spinal cord in pithed rats

1. A study was made of the effects of 5-hydroxytryptamine (5-HT) on pressor response induced in vivo by electrical stimulation of the sympathetic outflow from the spinal cord of pithed rats. All animals had been pretreated with atropine. Intravenous infusion of 5-hydroxytryptamine at doses of 10 and 20 micrograms kg-1 min-1 reduced the pressor effects obtained by electrical stimulation at intervals of 10 min over the 1 h of infusion. 2. This inhibitory action of 5-HT was depressed by cyproheptadine and methiothepin but was not modified by ketanserin or MDL-72222. By contrast, the inhibitory action of 5-HT was lost in pithed rats that had been pretreated with exogenous noradrenaline. 3. The 5-HT1 receptor agonist 5-carboxamidotryptamine (5-CT) caused an inhibition of the pressor response, whereas the 5-HT3 receptor agonist, 1-phenylbiguanide, produced a variable but significant increase in the pressor response. The 5-HT2 receptor agonist, m-CPP, did not modify the pressor sympathetic response. 4. Our results suggest that 5-hydroxytryptamine interferes with sympathetic neurotransmission by inhibiting pressor effects as a result of stimulation of the complete sympathetic outflow, and that this inhibition is mainly through a presynaptic 5-HT1 mechanism.

Pharmacological characterization of 5-HT receptors in parasympathetic innervation of rat heart

A study was made of the effects of 5-hydroxytryptamine (5-HT) on bradycardia induced in vivo by electrical stimulation of the vagus nerves in pithed rats pretreated with atenolol. 5-HT significantly decreased vagally induced, but not acetylcholine-induced, bradycardia. The first effect was blocked by methiothepin, ketanserin or methiothepin with ketanserin. When 5-HT1 and 5-HT2 receptors were blocked, 5-HT produced an increase in vagally induced bradycardia. Both the inhibition and the potentiation were blocked by simultaneous pretreatment with methiothepin, ketanserin and MDL-72222. The 5-HT2 receptor agonist m-CPP (1-(3-chlorophenyl) piperazine dihydrochloride) caused an inhibition of vagally induced bradycardia whereas the 5-HT3 receptor agonist m-CPBG (1-(m-chlorophenyl)biguanide hydrochloride) produced a significant increase. The data suggest the presence of presynaptic and/or ganglionic 5-HT2 receptors in parasympathetic innervation of the rat heart, stimulation of which inhibits the release of acetylcholine. The presence of 5-HT3 receptors is also suggested, stimulation of which induces the release of acetylcholine.

Effect of bromocriptine on neurogenic vasoconstriction in the isolated autoperfused hindquarters of the rat

The effects of local administration of bromocriptine were studied in the isolated autoperfused hindquarters of the rat, and compared to the actions of apomorphine and pergolide. Local injection of bromocriptine (1 microgram kg-1) (into the hindquarters) did not alter perfusion pressure, but reduced the pressor response to electrical stimulation of the lumbar sympathetic chains at all frequencies used (0.5-10 Hz; 5 ms; 35 V). Bromocriptine (1 microgram kg-1) did not alter the increases in perfusion pressure induced by local administration of noradrenaline. The effects of local administration of apomorphine (1 microgram kg-1) and pergolide (1 microgram kg-1) were similar to that of bromocriptine. The inhibitory effect by bromocriptine, apomorphine and pergolide of the stimulation-evoked pressor responses was completely antagonized by intravenous administration of the dopamine receptor antagonist sulpiride (0.3 mg kg-1) but was not by the alpha 2-adrenoceptor antagonist yohimbine (1 mg kg-1). In this dose, yohimbine antagonized the inhibitory effect of the alpha-adrenoceptor agonist clonidine (1 microgram kg-1). The inhibitory effect of clonidine was not altered by sulpiride but was antagonized by yohimbine. The results indicate that bromocriptine like apomorphine and pergolide inhibit neurally-induced pressor responses in the autoperfused hindquarters of the rat by stimulation of presynaptic dopamine receptors. Stimulation of these receptors leading to a fall in noradrenaline release and consequently of vasomotor tone, might at least in part explain the vasodilatator effects of bromocriptine in the rat.

[Results of the functional tests using calcitonin in patients with chronic diffuse hepatopathy]

A group of ten patients suffering cirrhosis who were treated with 100 U/l of calcitonin was studied with the aim of knowing whether in patients with cirrhosis the calcitonin is able to provoke the usual characteristic biologic modifications on the basis of the knowledge of their hormonal high levels accompanied of oesteopenia. Regarding their baseline determinations, no statistically significant modifications have been observed in calcium, phosphorous, alkaline phosphatase or its thermostable and thermolabile fractions, magnesium, uric acid and creatinine plasma concentrations respectively. This absence of a biological response to calcitonin could be due either to a numeric or functional damage of the hormone receptors or a diminished biodisponibility, although there are facts suggesting a lesser hormone biopotenciality in these patients.

Comparative kinetic studies of Mn2+-activated and fructose-1,6-P-modified Mg2+-activated pyruvate kinase from Concholepas concholepas

Initial velocity and product inhibition studies of Mn2+-activated and FDP-modified Mg2+-activated pyruvate kinase from Concholepas concholepas, were performed. Evidence is presented to show that the Mn2+-enzyme catalyzes an ordered sequential mechanism, with ADP being the first substrate and pyruvate the last product. The results presented are consistent with a random combination of reactants with the FDP-modified Mg2+-activated enzyme and the formation of the dead-end complexes enzyme ADP-ATP and enzyme-PEP-ATP.

Differences between magnesium-activated and manganese-activated pyruvate kinase from the muscle of Concholepas concholepas

In contrast to the Mg2+-activated enzyme, in the presence of Mn2+ pyruvate kinase exhibits hyperbolic kinetics with respect to the substrate phosphoenolpyruvate and is insensitive to fructose 1,6-biphosphate, phenylalanine and alanine. However, with both metal activated species inhibition by excess ADP is observed. In contrast with Mg2+, which affords significant protection against inactivation caused by 5,5'-dithiobis (2-nitrobenzoic acid), the rate of inactivation by this reagent is increased in the presence of Mn2+. Differences in conformational changes induced by combination of pyruvate kinase with Mg2+ or Mn2+ were indicated by u.v. difference spectra.

Thalamic afferents to the motor cortex in the cat. A horseradish peroxidase study

Thalamic projections to the motor cortex have been studied in the cat by injecting small amounts of horseradish peroxidase in different parts of areas 4 and 6. The nuclei which more abundantly project to the motor cortex are the ventral anterior-ventral lateral complex, the ventral medial and the posterior complex. These projections are topographically organized. Other projections arise from the ventral postero-lateral, ventral postero-inferior, central lateral, central medial, medial dorsal, lateral posterior-pulvinar, suprageniculate and centrum medianum-parafascicular nuclei.