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F J Lopez

Publications and source records attributed to F J Lopez.

11 recordsLinked to original sources
PubMed2001

A high-resolution radiation hybrid map of the human genome draft sequence.

We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases.

Algorithms↗
PubMed2000

Use of solid-phase microextraction for the quantitative determination of herbicides in soil and water samples.

An in-depth study of SPME optimization and application has been made, considering not only aqueous (surface water and groundwater samples) but also the more complex soil samples. Seven herbicides widely used in the area of study have been selected including five triazine herbicides (atrazine, simazine, terbumeton, terbuthylazine, terbutryn), molinate, and bromacil. linearity range was between 0.1 and 10 ng/mL and the repeatability below 10% when applying the optimized SPME procedure to water samples. Reproducibility was found to be lower than 20% at the 1 ng/mL level, and the limits of determination in environmental water samples using GC/MS (SIM mode) were well below 0.1 ng/mL (values ranging from 10 to 60 ng/L). Extraction of selected herbicides from soil was carried out by microwave-assisted solvent extraction using methanol in screw-capped vials, leading to recoveries over 80% in spiked soil samples at the 5-200 ng/g level. SPME application over methanolic soil extracts required a 10-fold dilution with distilled water. The recommended procedure was found to be fully applicable for quantitative determination of selected herbicides in soils containing low organic matter content with coefficients of variation below or around 10% and limits of determination ranging from 1 to 10 ng/g. Both procedures were applied to real-world surface water and soil samples where several pesticides were detected including atrazine, simazine, terbuthylazine, and molinate.

Herbicides↗
PubMed1999

Estrogen activity and novel tissue selectivity of delta8,9-dehydroestrone sulfate in postmenopausal women.

Recent basic and clinical advances have consolidated the concept of tissue-selective estrogens, i.e. molecules that express different degrees of partial agonist, full agonist or antagonist activity in different tissues or cells. Delta8,9-Dehydroestrone sulfate (delta8,9-DHES) is a conjugated estrogen and a component of conjugated equine estrogens (CEE). It is metabolized in the human in at least a 1:1 ratio to its 17beta form, 17beta-delta8,9-DHES. To evaluate its activity in different clinical and biochemical parameters, a clinical research study was conducted with delta8,9-DHES and estrone sulfate as a comparator in postmenopausal women. Delta8,9-DHES was given orally at a daily dose of 0.125 mg for 12 weeks in a group of 10 women. Two additional groups of women received either estrone sulfate alone (1.25 mg/day) or the combination of delta8,9-DHES and estrone sulfate at the previously specified doses. A significant and consistent suppression of hot flushes (number, severity, and total score) was observed with delta8,9-DHES, reaching more than 95% suppression in all parameters of vasomotor symptoms. This level of activity was equal to that obtained with the much higher dose of estrone sulfate, and it was sustained for the duration of the treatment period (12 weeks). Measurements of a bone resorption marker, i.e. urinary excretion of N-telopeptide, demonstrated that delta8,9-DHES at 8 weeks produced a degree of suppression (40%) similar to that observed with the higher dose of estrone sulfate. Gonadotropin secretion (FSH and LH) was significantly suppressed in women receiving delta8,9-DHES, similar to that observed with estrone sulfate alone or with the combination of the two. Other parameters, such as total cholesterol, low density lipoprotein cholesterol and high density lipoprotein cholesterol were not modified significantly, whereas serum globulins (sex hormone-binding globulin and corticosteroid-binding globulin) showed only marginal increases after delta8,9-DHES administration. Taken together with preclinical data, it is found that delta8,9-DHES is an active estrogen with a distinct pharmacological profile that results in significant clinical activity in vasomotor, neuroendocrine (gonadotropin and PRL) and bone preservation parameters, whereas displaying little or no efficacy, at the dose tested, on other peripheral parameters normally affected by estrogens. Collectively, this information supports the concept that delta8,9-DHES is an integral component of CEE, with distinct tissue selectivity contributing to the CEE's overall clinical activity, and places this estrogen as a distinct member of a novel class of centrally active molecules with unique peripheral tissue selectivity.

Adult↗
PubMed1999

Pharmacological characterization of soluble human FSH receptor extracellular domain: facilitated secretion by coexpression with FSH.

Follicle-stimulating hormone (FSH) is a member of the glycoprotein hormone family that regulates gametogenesis and steroidogenesis. Glycoprotein hormones signal through a unique class of G-protein-coupled receptors (GPCRs) that have a long extracellular domain (ECD), which is the primary site for hormone binding. The hFSHR-ECD was expressed in insect cells as a C-terminal, epitope-tagged protein resulting in production of soluble active receptor in the intracellular compartment and in the secreted culture medium. Coexpression of hFSHR-ECD with FSHbeta or FSHalpha/beta increased the secretion of the truncated receptor. Pharmacological studies to assess ligand-receptor interactions without the transmembrane domains showed higher affinity values (K(D)S) for [125I]hFSH using mammalian-expressed full-length receptor, secreted hFSHR-ECD, or secreted hFSHR-ECD coexpressed with FSHbeta, whereas the K(D) value for hFSHR-ECD coexpressed with FSHalpha/beta subunits showed lower affinity. Competition of other glycoprotein hormones for secreted hFSHR-ECD coexpressed with FSHbeta or mammalian full-length hFSHR resulted in similar binding profiles, indicating analogous pharmacology. Finally, we have demonstrated that a small molecule, suramin, which has been reported to interact with the mammalian full-length FSHR, competes for the binding of [125I]hFSH by interacting directly at the hFSHR-ECD.

Animals↗
PubMed1998

Solid-phase microextraction for quantitative analysis of organophosphorus pesticides in environmental water samples.

Solid-phase microextraction (SPME) is a relatively new technique that appears as a convenient and efficient extraction method in contrast with more complex techniques used for pesticide residue analysis based on liquid-liquid and solid-phase extraction. This extraction procedure involves the absorption of analytes into a polymeric film coated onto a fine silica fiber directly dipped in the aqueous sample. An SPME procedure for the determination of 12 organophosphorus pesticides in clean environmental water samples at low ng/ml concentration level has been developed by optimising variables involved in extraction and desorption. The absorption equilibrium has been estimated by mathematical treatment of the process using an expression that describes experimental absorption time profiles. The method was evaluated according to the reproducibility, linearity range and limits of detection using two different fiber coatings: 100 microm polydimethylsiloxane and 85 microm polyacrylate. The limits of detection obtained using nitrogen-phosphorus detection ranged between 0.01 and 0.2 ng/ml with relative standard deviations lower than 15% at the 1 ng/ml level. The method showed good linearity between 0.1 and 10 ng/ml with regression coefficients ranging between 0.97 and 0.999. Determination of organophosphorus pesticides in water samples in concentration below 0.1 ng/ml can be easily carried out with this fast, economic and solvent-free SPME procedure.

Adsorption↗
PubMed1997

Induction of promiscuous G protein coupling of the follicle-stimulating hormone (FSH) receptor: a novel mechanism for transducing pleiotropic actions of FSH isoforms.

Under physiological conditions, FSH is secreted into the circulation as a complex mixture of several isoforms that vary in the degree of glycosylation. Although it is well established that the glycosylation of FSH is important for the serum half-life of the hormone and coupling of the receptor to adenylate cyclase, little is known concerning how physiologically occurring glycosylation patterns of this hormone affect receptor signaling. In this study, we have examined the biological activity of deglycosylated human FSH (DeGly-phFSH), recombinant mammalian-expressed hFSH (CHO-hFSH), and insect cell-expressed hFSH (BV-hFSH, alternatively glycosylated) as compared with that of purified human pituitary FSH (phFSH) using a Chinese hamster ovarian cell line stably expressing the hFSH receptor (3D2 cells). Differentially glycosylated forms of FSH did not bind to the FSH receptor in the same manner as phFSH. Although all hormones showed similar potency in competing for [125I]phFSH binding to the hFSH receptor, competition curves for deglycosylated and insect cell-produced FSH were steeper. Similarly, glycosylation of FSH had a profound effect on bioactivity of the hormone. Purified hFSH produced a sigmoidal dose-dependent stimulation in cAMP production, whereas DeGly-phFSH and BV-hFSH induced biphasic (bell-shaped) dose-response curves. BV-hFSH also elicited biphasic effects on steroidogenesis in primary cultures of rat granulosa cells. The cellular response to BV-hFSH was dependent on the degree of receptor-transducer activation. BV-hFSH bioactivity was strictly inhibitory when combined with the ED80 of phFSH. Lower concentrations of phFSH resulted in a gradual shift from inhibition to a biphasic activity in the presence of the ED20 of phFSH. Biphasic responses to BV-hFSH were attributed to activation of different G protein subtypes, since treatment of 3D2 cells with cholera toxin or pertussis toxin differentially blocked the two phases of BV-hFSH bioactivity. These data suggest that alternative glycosylation of FSH leads to a functionally altered form of the hormone. Functionally different hormones appear to convey distinct signals that are transduced by the receptor-transduction system as either stimulatory or inhibitory intracellular events via promiscuous, glycosylation-dependent G protein coupling. Promiscuity in signaling of the FSH receptor, in turn, may represent a potentially novel mechanism for FSH action, whereby the gonad may respond in diverse ways to complex hormonal signals such as those presented by circulating FSH isoforms.

Animals↗
PubMed1996

Causal order does not affect cue selection in human associative learning.

Waldmann and Holyoak (1992) presented evidence in support of the claim that cue selection does not emerge in "diagnostic" human learning tasks in which the cues are interpretable as effects and the outcomes as the causes of those effects. Waldmann and Holyoak argued that this evidence presents a major difficulty for associationist theories of learning and instead supports a "causal model" theory. We identify a number of flaws in Waldmann and Holyoak's experimental procedures and report three new experiments designed to test their claim. In Experiment 1, cue selection was observed regardless of causal order and regardless of whether the cues were abstractly or concretely specified. In Experiments 2 and 3, cue selection was again observed when subjects predicted causes from effects. We conclude that our results are consistent with simple associationist theories of learning but contradict Waldmann and Holyoak's causal model theory.

Adult↗
PubMed1990

Colocalization of galanin and luteinizing hormone-releasing hormone in a subset of preoptic hypothalamic neurons: anatomical and functional correlates.

Colocalization of neurotransmitters, including neuropeptides and amines, in the same neuron of certain areas or well-defined nuclei of the central and peripheral nervous systems appears to be the rule rather than the exception. The coexistent neurotransmitters can be coreleased and interact at pre- and postsynaptic levels in a synergistic or antagonistic manner. Galanin is a recently isolated and characterized "gut-brain" peptide. It is colocalized with many neurotransmitters in both the central and the peripheral nervous systems. Among other regions in the central nervous system, galanin is present in neuronal perikarya of the septum and the hypothalamus. The dense accumulation of nerve terminals in the external zone of the median eminence suggests that galanin is an important peptide regulating neuroendocrine functions. Although most galanin and luteinizing hormone-releasing hormone (LHRH) neurons have a distinctly different morphology, a subset of galanin-immunoreactive perikarya in the diagonal band of Broca and the medial preoptic area, near the organum vasculosum of the lamina terminalis, have morphological features similar to those of LHRH neurons. By using double-labeling immunocytochemistry, we have found that in the preoptic region of the male rat brain approximately 15-20% of these "LHRH-like" galanin-immunoreactive neurons are also immunopositive for LHRH. Moreover, in the medial preoptic area and the diagonal band of Broca, some of the single-labeled LHRH cells are surrounded with galanin-immunoreactive nerve terminals, suggesting that LHRH perikarya have synaptic contacts with galanin-immunoreactive terminals. Additional studies indicated that galanin can readily enhance in vitro release of LHRH from nerve terminals in the median eminence. The observations that (i) galanin is coexpressed with LHRH, (ii) galanin seems to innervate LHRH-producing neurons, and (iii) galanin acts as a putative neurotransmitter to enhance the release of LHRH suggest that galanin should be considered an important regulator of LHRH-containing neurons and, therefore, of reproductive functions.

Animals↗
PubMed1990

Galanin stimulates luteinizing hormone-releasing hormone secretion from arcuate nucleus-median eminence fragments in vitro: involvement of an alpha-adrenergic mechanism.

Galanin (GAL), a 29-amino acid peptide originally isolated from porcine intestine, has been shown to be widely distributed not only in the gut, but also in the central nervous system. Several studies have shown that GAL participates in the hypothalamic regulation of PRL, GH, and LH secretion. In this study, we evaluate the effects of rat GAL (rGAL) on LHRH and prostaglandin (PG) E2 release from arcuate nucleus-median eminence fragments in vitro. Fragments were incubated for 30-min periods in Krebs-Ringer bicarbonate buffer containing the different test substances. The addition to the medium of rGAL in concentrations ranging from 5-1000 nM increased the release of both LHRH and PGE2 in a concentration-dependent manner. The ED50 values were approximately 55 and 80 nM for LHRH and PGE2, respectively. rGAL-induced LHRH and PGE2 release were related, as suggested by the finding that the addition to the medium of indomethacin (10 microM), a PG synthesis blocker, completely blocked rGAL-induced LHRH release. In addition, an active catecholaminergic system appears to be necessary for obtaining the stimulatory effect of rGAL. The addition to the medium of the alpha-adrenergic blocker phentolamine or prazosin impaired the ability of rGAL to release both LHRH and PGE2. rGAL-induced stimulation of LHRH and PGE2 release was blocked by phentolamine at doses of 1-10 microM, while prazosin was able to block it at doses as low as 0.1 microM. In summary, rGAL stimulates LHRH and PGE2 release from arcuate nucleus-median eminence fragments in vitro in a dose-dependent fashion. Such an effect is blocked by both indomethacin and alpha-adrenergic blockers, indicating that rGAL-induced stimulation of LHRH secretion is exerted through alpha-adrenergic receptors and requires PGE2 as an intracellular mediator.

Adrenergic alpha-Antagonists↗