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Biomedical subjects

B del Castillo

Publications and source records attributed to B del Castillo.

12 recordsLinked to original sources
PubMed1998

Age-related weakening of baroreflex-mediated sympathetic activity in spontaneously hypertensive rats in response to blood pressure reduction.

Nicardipine, a dihydropyridine type calcium channel blocker, was infused into 4-, 6-, and 23-wk-old spontaneously hypertensive (SH) and age-matched normotensive Wistar-Kyoto (WKY) rats (under sodium thiobutabarbital anesthesia and ventilation, n = 4) through the left femoral vein, resulting in the reduction of blood pressure. In each rat, mean arterial blood pressure, heart rate, and the concentration of plasma catecholamines (CAs), norepinephrine (NE), and epinephrine (E) were concomitantly determined, and the correlations between these three variables were studied. During the infusion of nicardipine, the plasma concentration of CAs was measured with an automatic detection system in blood samples collected from the right femoral artery of each rat. The reduction in blood pressure induced by nicardipine brought about an increase in plasma CA levels. The blood pressure correlated well with the logarithm of plasma NE or E concentration according to the formula Y= -alpha log (X) + m (Y, blood pressure; X, concentration of plasma NE or E; a, slope; and m, intercept). The slopes (as) of 6-wk-old and 23-wk-old SH rats were significantly greater than those of aged-matched WKY rats, meaning that the increment in plasma CAs in response to a decrease in blood pressure was smaller in SH than in WKY rats of similar ages. However, no significant differences were found between the as of 4-wk-old SH and WKY rats. We conclude that the increment in the baroreflex-mediated sympathetic activity in response to a drop in blood pressure induced by nicardipine is similar or greater in prehypertensive SH than in normotensive WKY 4-wk-old rats, while the increment becomes smaller in SH rats with the onset of hypertension (6-wk-old rats), and is much less in fully hypertensive adult (23-wk-old) SH rats than in age-matched WKY rats. On the basis of these findings and previous data obtained by neurography, we conclude that plasma CAs can be used to evaluate baroreflex-mediated sympathetic activity countering the blood pressure reduction caused by calcium antagonists.

Aging↗
PubMed1996

Analytical applications of retinoid-cyclodextrin inclusion complexes. 1. Characterization of a retinal-beta-cyclodextrin complex.

In studies in these laboratories on the supramolecular chemistry of the retinoids, it has been recently confirmed that inclusion of these substances within the cavity of cyclodextrins protects their excited states, thus improving their photochemical stability. In the present paper, the isolation is described of a crystalline stable complex between retinal and beta-cyclodextrin, which has been characterized by means of several techniques including atomic force microscopy (AFM). The complex shows distinct spectroscopic differences from both retinal and beta-cyclodextrin. Thus, it absorbs at lambda(max) = 380 nm in water whereas retinal is insoluble; it shows room-temperature luminescence, which retinal does not; finally, it give 1H-NMR and 13C-NMR spectra in d6-DMSO with clear differences in chemical shifts with respect to those of beta-cyclodextrin. Besides these studies in solution, the behaviour of the complex in the solid state has been compared with that of physical mixtures of retinal and beta-cyclodextrin. IR spectroscopy shows clear differences, particularly a shift in the retinal carbonyl absorption (1644-1672 cm-1). AFM studies reveal the existence of aggregates; X-ray diffractometry also supports the formation of a cyclodextrin-retinal complex.

Cyclodextrins↗
PubMed1996

Differentiating inclusion complexes from host molecules by tapping-mode atomic force microscopy.

Tapping-mode atomic force microscopy imaging under different cantilever vibration amplitudes has been used to differentiate the host beta-cyclodextrin nanotubes from retinal/beta-cyclodextrin inclusion complex nanotubes. It was observed that both compounds were deformed differently by the applied probe force because of their different local rigidity. This change in the elasticity properties can be explained as a consequence of the inclusion process. This method shows that tapping-mode atomic force microscopy is an useful tool to map soft sample elasticity properties and to distinguish inclusion complexes from their host molecules on the basis of their different mechanical response.

Biophysical Phenomena↗
PubMed1996

Use of micellar media for the fluorimetric determination of ellipticine in aqueous solutions.

Ellipticine is a pyridocarbazole alkaloid with interesting antitumour activity. Use of neutral ellipticine is hampered by its very low water solubility and therefore this compound has been administered as a salt; however, nitrogen quaternization modifies the antitumour properties of ellipticine. Potential alternatives to quaternization include the use of cyclodextrins, and also the use of micellar media. The latter possibility is explored in this work as an analytical tool. The results obtained with model anionic (SDS), cationic (CTAB) and neutral (Brij-35) surfactants are described. Fluorimetric analysis shows that ellipticine solubilizes completely in the presence of all these compounds, as a result of its aromatic, planar structure. The use of micellar media considerably increases the slopes of the calibration curves with improved correlation coefficients (e.g. 0.8904 in water and 0.9982 with SDS). Micellar media also modify proton transfer processes, as a consequence of the apolar environment of the micellar phase. Deprotonation of ellipticine is hampered in SDS because of the relationship between this process and the surface charge of the micelles. Finally, fluorescence quenching in micellar media has been studied, it being found that surfactants provide protection towards this phenomenon.

Antineoplastic Agents↗
PubMed1996

Influence of the presence of trace amounts of metals on the polymorphism of tolbutamide.

The polymorphism phenomenon causes an important problem in the preparation of many pharmaceutical dosage forms, including oral suspensions, tablets, creams and suppositories. In this work the influence of the presence of certain metallic elements (Ca(II), Fe(III), Mn(II), Zn(II), Cd(II), Ni(II) and Co(II)) in trace amounts on the polymorphism of tolbutamide is described. For these studies, known amounts (5-500 ppm) of different cations were added to ethanol-water solutions of the pharmacologically active polymorph A of tolbutamide prior to its crystallization. These cations were chosen as being among those that commonly appear in drug solutions as a consequence of elution from glass containers. IR studies show that the presence of cations prevents the appearance of the polymorph B of the tolbutamide. Thus, the peaks at 2980, 2940, 2890, 905, 851, 816 and 727 cm-1 (polymorph A) appeared but not the ones at 1045 and 847 cm-1 corresponding to polymorph B. Scanning electron microscopy studies reveal that, in the presence of Ca2+, a third kind of crystal different from polymorphs A and B appears. This form of olbutamide cannot be identified with "polymorph III" of Al-Saieq and Rileys [S.S. Al-Saieq and G.S. Riley, Pharm. Acta. Helv., 56 (1981) 125-129] due to their different IR data. Dissolution rate tests and X-ray diffractometry were also employed in this study. All these results showed that divalent cations partially avoid the transformation of polymorph A into polymorph B.

Cadmium↗
PubMed1990

Air-breathing behaviour of the Colombian catfish Eremophilus mutisii (Trichomycteridae, Siluriformes).

Eremophilus mutisii uses the vascularized central portion of its stomach for aerial respiration, and is a frequent but not obligatory air breather. Air ventilation takes place during a rapid dash to the surface with the expiration of old air preceding inspiration. The frequency of air breathing is affected by aquatic O2 concentration. E. mutisii can survive at least 10 days without air breathing in normoxic water but cannot survive without air access in water containing less than 2.0 ppm O2.

Air↗
PubMedDate not supplied

Abscisic acid studied by fluorescent techniques.

Crude analytical abscisic acid (ABA) exhibited fluorescence (lambdaex 340, lambdaem 425 nm). The results demonstrated a relationship between fluorescence response and ABA concentration, in the range of 0.04-0.38 microgram/ml. Chromatographic purification increased the emission signal, and oxidation induced by adding a sulphuric acid: ethanol (1:1) mixture also increased and displaced it (lambdaex 450, lambdaem 495 nm). Using these properties, a fluorimetric method for identification and evaluation of ABA, had been developed, and used for inhibitor recognition in P. pinea seed coats.

Abscisic Acid↗
PubMedDate not supplied

Fluorimetric determination of oenanthotoxin.

Oenanthotoxin as crude yellow crystals was obtained, after the extraction and treatment from Oenanthe crocata L. fresh roots. The fluorescence response of oenanthotoxin solutions undergo changes, depending on the solvent used. Chloroformic solutions of oenanthotoxin showed a maximum fluorescent emission at 425 nm when the exciting wavelength was at 370 nm; in methanol it was displaced (lambda ex 375 nm, lambda em 435 nm), and in benzene showed a lambda em at 450 nm when the lambda ex was 395 nm. There was a linear relationship shown between the oenantotoxin concentration and fluorimetric response while within suitable experimental limits, the minimum concentration detected was 9.02 micrograms/ml. Using these properties, a fluorimetric method has been developed for the identifications and evaluation of oenanthotoxin.

Alkynes↗