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Biomedical subjects

R Alvarez

Publications and source records attributed to R Alvarez.

At least 127 records · Page 7Linked to original sources
PubMed1996

Postpulse effects on blink reflex responses.

The technique of paired stimulation is routinely used in many laboratories in the assessment of the excitability recovery curve of the blink reflex. Other effects, such as prepulse inhibition or classical conditioning, can also be investigated with repeated presentation of pairs of time-locked stimuli. Regularly repeated presentations of an unpleasant stimulus may give rise to a transient excitability enhancement in neural structures in the reflex circuit. We have investigated whether such a transient shift in excitability can be demonstrated before the actual stimulus is applied. In 10 normal volunteers, we regularly alternated series of 5 trials containing an auditory tone of mild intensity with series of the same auditory tone followed by a relatively strong supraorbital nerve electrical stimulus. We calculated the habituation percentage of the orbicularis oculi responses to the auditory stimulus within a series and compared the results obtained in series containing the auditory tone alone with those from series containing the auditory tone followed by the electrical stimulus. Habituation was significantly less with paired stimulation than with the auditory tone alone, the mean area of the response to the 3rd trial in percentage of that to the first trial being 34.0 +/- 16.4% for paired stimuli, and 20.3 +/- 14.1% for auditory stimulus alone (P = 0.008). This effect, induced by the presence of an impending electrical stimulus on the response to a preceding stimulus, is defined as a postpulse effect in contradistinction to the prepulse effects induced by a weak stimulus on the response to a subsequent startle-eliciting stimulus. When a paradigm with a stimulus pair is used in human subjects, the possibility of effects occurring in both temporal directions should be taken into account. Blink reflex responses to a given stimulus may exhibit excitability changes induced by a preceding or by an impending stimulus.

Acoustic Stimulation↗
PubMed1996

Chromosome aberrations in human spermatozoa treated with Ca2+ ionophore A23187.

Incorporation of A23187 ionophore into the human-hamster fertilization system clearly improves the ability of human spermatozoa to penetrate zona-free hamster oocytes. Thus, an increasing number of laboratories working in human sperm cytogenetics have substituted classical incubation with Biggers-Whitten-Whittingham (BWW) medium plus human serum albumin (HSA) by pretreatment of spermatozoa with calcium ionophore A23187 which directly induces the acrosome reaction in spermatozoa. However, there have been no formal studies on the effects of this ionophore pretreatment. To determine whether calcium ionophore could affect the cytogenetic characteristics of human spermatozoa we compared A23187-treated spermatozoa with controls (only incubated with BWW + HSA) by analysing a total of 447 sperm chromosome complements from two normal donors. Our results show that there are no statistical differences in the frequency and the types of human sperm chromosomal abnormalities between the two methods of sperm treatment. Thus, ionophore A23187 seems not to affect the cytogenetic characteristics of human spermatozoa, and the results of laboratories using either sperm capacitation in BWW + HSA or acrosome reaction by calcium ionophore can be compared.

Acrosome↗
PubMed1996

Aortic thrombosis in a neonate with hereditary antithrombin III deficiency: successful outcome with thrombolytic and replacement treatment.

We report the case of a newborn male who presented an aortic thrombosis during the neonatal period and was subsequently diagnosed as having antithrombin III (AT III) hereditary deficiency type I. This hypercoagulable condition is known to predispose young adults to venous thrombosis, but in our patient the primary thrombotic incident affected the arterial vessels within the first few days of life. Combined treatment with thrombolytic agents and AT III concentrates recovered aortic permeability, suggesting that the use of AT III may be beneficial for the treatment of thrombotic complications during the first few days of life.

Angiography, Digital Subtraction↗
PubMed1996

Transforming growth factor-beta modulation of the alpha 1(IV) collagen gene in murine proximal tubular cells.

We have examined the expression of the alpha 1(IV) collagen gene in murine proximal tubular cells (MCT) to better understand how it is regulated in parenchymal cells. Transcriptional activity was examined using luciferase reporters driven by the alpha 1(IV) promoter and varying lengths of 5'-flanking sequences. The minimal bidirectional promoter showed low intrinsic activity in MCT cells, but addition of upstream sequences increased luciferase expression. Maximal activity resided within the first 1,200 bp upstream. A minigene construct was generated by placing a portion of the alpha 1(IV) first intron downstream from the promoter region. The intronic sequences significantly decreased activity of the promoter in MCT cells and 3T3 fibroblasts but greatly enhanced expression in murine parietal yolk sac (PYS) endodermal cells. Addition of transforming growth factor-beta (TGF-beta) to MCT cultures elevated the levels of secreted type IV collagen. Treatment of either transiently or stably transfected MCT cells with TGF-beta produced an increase in the levels of expression of all of the reporters tested. These data support the hypothesis that cell-specific regulation of alpha 1(IV) collagen is dependent upon downstream sequences, which act to decrease the expression of type IV collagen in tubular epithelium. The activity of the alpha 1(IV) collagen gene in proximal tubular cells is increased by TGF-beta, which acts on the domain(s) embedded within the intergenic bidirectional promoter.

3T3 Cells↗
PubMed1996

Analysis of radiation-induced micronuclei in two-cell human-hamster embryos using telomeric and centromeric FISH probes.

Simultaneous, fluorescent in situ hybridization using a centromeric human alpha satellite DNA probe and a telomeric DNA probe was used to analyze the chromosome content of micronuclei induced in two-cell human-hamster embryos by in vitro gamma-ray irradiation of human spermatozoa. In unirradiated samples, about 26% of micronuclei were centromere positive, indicating that both structural chromosome aberrations and numerical changes are involved in the spontaneous production of micronuclei. After exposure of spermatozoa to radiation, a significant increase in the number of micronuclei was found. About 77% of induced micronuclei contained only telomeric signals suggesting that they originated from acentric fragments. However, both centromere-positive and centromere-negative micronuclei increased with radiation dose. These results are consistent with the well known clastogenic effect of ionizing radiation and with its weak aneugenic effect.

Animals↗
PubMed1996

Cholinergic modulation of spontaneous hypothalamic-pituitary-adrenal activity and its circadian variation in man.

Controversy still exists regarding the role of cholinergic pathways in the regulation of the hypothalamic-pituitary-adrenal axis in man. We studied the effects of the administration of placebo, pyridostigmine (PD); 120 mg, orally), and the combination of PD and pirenzepine (PZP; 100 mg, orally) on ACTH, cortisol, and GH secretion at 0730 and 2230 h in seven normal males. PD induced a clear decrease in ACTH levels at both times of the day compared to treatment with placebo, producing higher suppression in the nocturnal period (34.4 +/- 5.8% vs. 21.8 +/- 10.7%). The combination PD and PZP prevented the inhibitory action of PD on ACTH secretion in the morning, but not in the evening, when ACTH values showed a decrease similar to that seen after giving PD alone (38.1 +/- 5.6% vs. 34.4 +/- 5.8%, respectively). Cortisol values declined only when the association PD plus PZP was given in the evening. GH levels had a significant increase after PD administration in the morning (4.1 +/- 1.2 ng/mL) and in the evening (10.2 +/- 1.6 ng/mL), confirming that cholinergic stimulation was taking place, whereas the addition of PZP to PD induced a significant attenuation of these responses. It is concluded that cholinergic pathways have a inhibitory role in ACTH secretion in man. M1 muscarinic receptors seem to be involved in the diurnal inhibition of PD, whereas our observations are consistent with the mediation of another type of cholinergic receptors as an explanation for the nocturnal effect of PD on ACTH secretion. PD did not alter the circadian variation in the hypothalamic-pituitary-adrenal axis, whereas the association of PD and PZP increased the differences between diurnal and nocturnal ACTH values, suggesting a modulatory effect of the cholinergic system on the circadian rhythm of ACTH secretion.

Adrenocorticotropic Hormone↗
PubMed1995

Synthesis and anti-HIV activity of [AZT]-[TSAO-T] and [AZT]-[HEPT] dimers as potential multifunctional inhibitors of HIV-1 reverse transcriptase.

In an attempt to combine the HIV-inhibitory capacity of 2',3'-dideoxynucleoside (ddN) analogues and non-nucleoside reverse transcriptase (RT) inhibitors (NNRTI), we have designed, synthesized, and evaluated for their anti-HIV activity several dimers of the general formula [ddN]-(CH2)n-[NNRTI]. These dimers combine in their structure a ddN such as AZT and a NNRTI such as TSAO-T and HEPT linked through an appropriate spacer between the N-3 of the thymine base of both compounds. The [TSAO-T]-(CH2)n-[AZT] dimers proved markedly inhibitory to HIV-1. Also, if AZT was replaced by thymidine in the dimer molecules, potent anti-HIV-1 activity was observed. However, although the compounds proved inhibitory to HIV-1, they were less potent inhibitors than the parent compounds from which they were derived. None of the dimers were endowed with anti-HIV-2 activity. In contrast with the TSAO-T monomers, none of the TSAO-T-containing dimers proved markedly cytotoxic to the cells. There was a clear trend toward decreased antiviral potency with lengthening the methylene spacer in the [TSAO-T]-(CH2)n-[AZT] dimers.

Antiviral Agents↗
PubMed1995

A novel regulatory pathway of brown fat thermogenesis. Retinoic acid is a transcriptional activator of the mitochondrial uncoupling protein gene.

The mitochondrial uncoupling protein (UCP) is responsible for the thermogenic function of brown fat, and it is a molecular marker of the brown adipocyte cell type. Retinoic acid (RA) increased UCP mRNA levels severalfold in brown adipocytes differentiated in culture. This induction was independent of adrenergic pathways or protein synthesis. RA stimulated ucp gene expression regardless of the stage of brown adipocyte differentiation. In transient transfection experiments RA induced the expression of chloramphenicol acetyltransferase vectors driven by 4.5 kilobases of the 5'-noncoding region of the rat ucp gene, and co-transfection of expression vectors for RA receptors enhanced the action of RA. Retinoic acid receptor alpha was more effective than retinoid X receptor in promoting RA action, whereas a mixture of the two was the most effective. The RA-responsive region in the ucp gene was located at -2469/-2318 and contains three motifs (between -2357 and -2330) of the consensus half-sites characteristic of retinoic acid response elements. This 27-base pair sequence specifically binds purified retinoic acid receptor alpha as well as related proteins from brown fat nuclei. In conclusion, a novel potential regulatory pathway of brown fat development and thermogenic function has been recognized by identifying RA as a transcriptional activator of the ucp gene.

Adipocytes↗
PubMed1995

Induction of micronuclei in human sperm-hamster egg hybrids at the two-cell stage after in vitro gamma-irradiation of human spermatozoa.

The efficiency of the micronucleus test to assess radiation-induced chromosomal damage in human spermatozoa has been investigated. Micronuclei were scored in human sperm-hamster egg hybrids at the two-cell stage, after exposure of human spermatozoa to in vitro gamma-rays at doses of 0.00, 0.10, 0.25, 0.50, 1.00, 2.00, and 4.00 Gy. The relationship between the yield of micronuclei per two-cell stage as well as the percentage of two-cell stages with micronuclei and the different doses of irradiation were fitted to linear equations. To evaluate whether scoring micronuclei is useful for the quantification of chromosomal damage occurring in human spermatozoa, induced micronuclei at the different doses of sperm irradiation were compared to the induction of breaks and fragments in sperm-derived chromosomes. After interspecific fertilization of zona-free hamster oocytes by irradiated spermatozoa, a total of 699 fertilized eggs at the two-cell stage and a total of 387 sperm-derived complements were analyzed. The incidence of fertilized eggs with micronuclei at the two-cell stage coincided well with the incidence of sperm-derived chromosome breaks and fragments (e.g., 8.9% vs. 6.7% in the 0.25 Gy group and 52.8% vs. 58.6% in the 4.00 Gy group). A similar correlation was found between the number of micronuclei per two-cell stage and the number of breaks and fragments per sperm complement (0.09 vs. 0.07 in the 0.25 Gy group and 0.71 vs. 0.81 in the 4.00 Gy group). The results show that this test system can be used for the quantification of spontaneous or induced chromosomal damage in human spermatozoa.

Animals↗
PubMed1995

Limited longitudinal sliding of the median nerve in patients with carpal tunnel syndrome.

During normal movements or changes in position of the limbs, nerve structures must accommodate the resulting changes in length of the nerve path. In patients with carpal tunnel syndrome, we monitored electrophysiologically the longitudinal adjustment of the median nerve to positions of extreme flexion and extreme extension of the wrist and elbow, by measuring the differences induced in the latency of the sensory nerve action potential (SNAP) recorded in the forearm and upper arm. In patients, the latency difference was significantly shorter than in normal subjects (0.196 +/- 0.084 ms vs. 0.088 +/- 0.059 ms in the forearm, and 0.485 +/- 0.122 ms vs. 0.129 +/- 0.086 ms in the upper arm). These results indicate that the displacement of the source of the median nerve SNAP with movements of flexion and extension is limited in patients with carpal tunnel syndrome. Such an abnormality may partly underlie the pathophysiology of entrapment syndromes.

Action Potentials↗
PubMed1995

Skeletal malformations induced by the insecticides ZZ-Aphox and Folidol during larval development of Rana perezi.

Tadpoles of Rana perezi were kept for 14 weeks in water containing two sublethal levels of the carbamate insecticide ZZ-Aphox or the organophosphate Folidol. Approximate concentrations of their active ingredients were 0.25 and 1 mg/L. Resulting malformations were studied by skeletal analysis and histological and histochemical investigation of te rear limbs of the tadpoles. The pesticides caused the animals to have malformations of the spinal column (scoliosis) and/or limbs (short and thick long bones with the epiphyses grossly twisted). Histochemical study showed differences in the composition of the connective matrix, and microscopic examination of the long bones indicated alterations in the thickness of the uncalcified bone matrix (osteoid) and the presence of abundant vascularised connective tissue in the region of the periosteum. The results confirmed changes in the composition of the connective tissue matrix as the cause of the defects observed in bone formation which are also discussed in relation to vitamin D absorption and calcium homeostasis.

Abnormalities, Drug-Induced↗
PubMed1995

Elevated intracellular cyclic AMP inhibits chemotaxis in human eosinophils.

Elevated intracellular cyclic AMP is associated with the inhibition of many inflammatory cellular responses. In this study, we examined the effect of cyclic AMP on eosinophil chemotaxis. Eosinophils were isolated from healthy human volunteers using an immunomagnetic method. Eosinophils were treated with agents that elevate intracellular cyclic AMP and evaluated for chemotactic responses to platelet-activating factor (PAF; 10(-6) M) and to complement factor 5a (C5a; 10(-8) M) in microchemotaxis chambers. Forskolin, prostaglandin E1 (PGE1), and a phosphodiesterase (PDE) IV-selective inhibitor inhibited eosinophil chemotactic responses. The mean per cent inhibition of eosinophil chemotaxis in response to PAF by forskolin, PGE1, and the PDE IV-selective inhibitor (10(-5) M) was 16.8 +/- 5.3, 26.6 +/- 9.5, and 35.1 +/- 6.1%, respectively (n = 5). The corresponding values for C5a were 17.5 +/- 7.9, 20.8 +/- 10.7, and 39.5 +/- 5.0%. An exogenous cyclic AMP analogue (dibutyryl cyclic AMP, 10(-3) M) also inhibited eosinophil chemotaxis by 69.4 +/- 12.8 and 66.9 +/- 11.6% in response to PAF and C5a, respectively (n = 5). We conclude that elevated intracellular cyclic AMP inhibits eosinophil chemotaxis.

Alprostadil↗
PubMed1995

Human origin of micronuclei in human x hamster two-cell embryos.

Using fluorescence in situ hybridization techniques with either human or hamster genomic DNA probes, we studied the origin of micronuclei in two-cell hybrid embryos obtained from hamster oocytes and gamma-irradiated human spermatozoa. Our study demonstrates that over 99% of micronuclei hybridize with human DNA probes and not with hamster DNA, revealing their human origin. Thus, the micronucleus test represents a good method to evaluate genetic damage in human germ cells, since it is simpler and faster than sperm chromosome studies.

Animals↗
PubMed1995

Determination of the susceptibility in vitro of 54 isolates of Mycobacterium fortuitum against three fluoroquinolones using two methods.

The in vitro susceptibility to ofloxacin, norfloxacin and ciprofloxacin or 54 Mycobacterium fortuitum isolates originating from clinical samples (7) of patients attending the Hospital Universitario de Canarias and Hospital del Tórax, and from environmental (47) sources, were determined. For this, two methods were used: dilution in agar with Middlebrook 7H10 Agar as a base medium culture, and broth microdilution, with Mueller-Hinton Broth without supplement. The different isolates under study revealed a uniform susceptibility by both methods against ciprofloxacin. 100% inhibition was obtained from a Minimum Inhibitory Concentration (MIC) of 0.25 microgram/ml, and 2 micrograms/ml of ciprofloxacin, for broth microdilution and dilution in agar, respectively. For ofloxacin and norfloxacin, all the isolates were inhibited at an MIC of 0.5 microgram/ml, by the broth microdilution method, which contrasted sharply with an MIC of 32 micrograms/ml, in the case of dilution in agar. In this study, we have observed the existence of differences in the in vitro susceptibility of the isolates of M. fortuitum against the three fluoroquinolones assayed, mainly for ofloxacin and norfloxacin, by both methods. We, therefore, consider it necessary to establish a standardized, reproducible assay method, for the study of sensitivity to atypical mycobacteria.

Anti-Infective Agents↗
PubMed1995

Determination of the in vitro susceptibility of 220 Mycobacterium fortuitum isolates to ten antimicrobial agents.

The authors investigated the in vitro susceptibility to antimicrobial agents of 220 Mycobacterium fortuitum isolates originating from clinical samples (14) of patients attending the Hospital Universitario de Canarias and Hospital del Tórax, and from environmental sources (206): 3 from sea water, 10 from the water supply and 193 from sewage. The Minimum Inhibitory Concentration (MIC) was calculated using the broth microdilution method with Mueller-Hinton Broth without supplement. Amikacin was the most efficacious antimicrobial agent against all the isolates of M. fortuitum with an MIC which was considerably lower than its critical concentration. The good results achieved with amikacin in vitro are confirmed by those obtained in vivo, with patients infected with M. fortuitum. No significant difference was found in the efficacy of amikacin and ofloxacin against all the isolates assayed.

Anti-Bacterial Agents↗
PubMed1995

Activation and selective inhibition of a cyclic AMP-specific phosphodiesterase, PDE-4D3.

Prostaglandin E2 produces a transient increase in the intracellular concentration of cAMP in a human promonocytic cell line (U937). The temporal pattern consists of a rapid increase followed by a gradual decline to a new steady state. The decline phase coincides with an increase in the activity of a high affinity form of cAMP phosphodiesterase (PDE). Immunoprecipitation with specific antibodies revealed that the activated enzyme is a variant of PDE-4D. To confirm this observation, three isoforms of human PDE-4 (A, B, and D) were cloned and expressed in Sf9 cells with recombinant baculovirus infection. The activity of only one of the isoforms (PDE-4D3) increased after incubation with the catalytic subunit of protein kinase A and Mg-ATP. Hydrolytic activity of human PDE-4D3 was dependent on Mg2+. Before phosphorylation, the concentration-response curve for Mg2+ was biphasic and ranged from 0.1 to 100 mM. Phosphorylation of PDE-4D3 by protein kinase A produced a monophasic Mg2+ response curve (0.5 Vmax = 0.2 mM). Phosphorylation of PDE-4D3 increased the sensitivity of the enzyme to inhibition by RS-25344 (approximately 100-fold) and RS-33793 (approximately 330-fold). Thus, phosphorylation of PDE-4D3 induces an apparent conformation change that increases maximum velocity and sensitivity to inhibition by some analogues of nitraquazone. These observations provide the basis for a novel pharmacological strategy that targets an activated form of PDE in human leukocytes. Selective PDE-4D3 inhibitors may have useful anti-inflammatory properties with fewer adverse side effects than other PDE-4 inhibitors.

3',5'-Cyclic-AMP Phosphodiesterases↗