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Biomedical subjects

L Senécal

Publications and source records attributed to L Senécal.

11 recordsLinked to original sources
PubMed2002

Phagocytic activity of marine and freshwater bivalves: in vitro exposure of hemocytes to metals (Ag, Cd, Hg and Zn).

We measured non-specific immune function of various bivalves from marine (Cyrtodaria siliqua, Mactromeris polynyma, Mesosdesma arctatum, Mya arenaria, Mya truncata, Mytilus edulis, Serripes groenlandicus, Siliqua costata) and freshwater environments (Dreissena polymorpha and Elliptio complanata). We used flow cytometry to quantify the phagocytosis of fluorescent microspheres by hemocytes exposed in vitro to increasing levels of various metal compounds (AgNO(3), CdCl(2), CH(3)HgCl, HgCl(2) and ZnCl(2)). In some species, low doses of mercury (organic and inorganic) and Zn suggest a hormesis-like stimulation of phagocytic activity. At higher levels of exposure, all metals tested induced a significant dose-related inhibition of hemocyte phagocytosis. The species-specific sensitivity of the assay was determined by comparing the in vitro exposure using the metal concentration inducing a 50% suppression (EC(50)) of the phagocytic activity. Different species expressed different levels of sensitivity. Our results show the variability of the toxic response of different species within a group of similar organisms. It also highlights the need to consider species-species differences in ecotoxicological risk assessment.

Animals↗
PubMed1997

Influence of a transscrotal testosterone propionate administration on the serum level of selected hormones of the hypophyso-gonadal axis.

This study was designed to examine the effect of a percutaneous scrotal administration of testosterone propionate (TP) on selected blood variables, in order to identify a reliable anti-doping probe liable to disclose the illicit use of testosterone. Twelve healthy adult males gave their informed consent for the study. Each morning (8:30) and for 10 consecutive days (D), a placebo (D:1,2,3,...8,9,10) or a testosterone propionate (200mg TP on D:... 4,5,6,7...) scrotal patch was installed. On D2 or D3 (placebo-treated) or D7 (TP-treated), venous blood samples were collected at 5 min intervals from 9:00 until 13:00. Serum LH, FSH, 17alpha-hydroxyprogesterone (17HP), testosterone (T), estradiol (E2) and SHBG contents were analysed by immunoassays. The high sampling frequency revealed that TP was associated with the complete abolition of serum LH pulses. Although statistically significant, TP treatment was not related to explicit changes in serum FSH, E2, T/E2 and T/SHBG. TP-induced effects were most significant on serum LH, T and 17HP and were most clearly illustrated by a bi-dimensional distribution plot of serum values of the latter variables. The expression of a combination of the latter parameters could eventually serve to detect testosterone misusers.

17-alpha-Hydroxyprogesterone↗
PubMed1997

Solution structure of the HIV protease inhibitor acetyl-pepstatin as determined by NMR and molecular modeling.

The structure of acetyl-pepstatin has been investigated in solution by two-dimensional NMR spectroscopy and molecular modeling. The analysis of DQFCOSY, TOCSY and NOESY spectra lead to a full assignment of the -NMR signals both in DMSO-d6 and in TFE-d3:H2O 1:1. Interproton distances, dihedral angles and exchanger regimes of NH or OH protons were derived from ROESY connectivities, coupling constants and temperature dependences of the chemical shifts, respectively. Molecular modeling using the NMR distance and dihedral angle constraints obtained in DMSO-d6 yielded a model showing a well-defined structure for the N-terminal segment Ac-1 to Sta-4, but a flexible structure for the C-terminal segment. The structure was less defined in TFE-d3:H2O 1:1 and 13C T1 measurements are indicative of higher mobility. Comparison of the NMR-determined solution structure of acetyl-pepstatin with its crystal structure when bound to HIV-1 protease shows that the conformation is more extended in the complex as a result of intermolecular interactions.

Carbon Isotopes↗
PubMed1997

Frequent serum sampling in healthy men discloses testosterone peaks exacerbated by testosterone propionate administration.

Interval samplings uncover blood diurnal oscillations for several hormones, highlighting the importance of short time intervals in the disclosure of subtle pulsatile patterns of some peptide hormones, namely LH. In a study designed to develop new probes against steroid misuse, venous blood was sampled at 5-min intervals for 4 hours from 12 eugonadal adult male athletes, 6 receiving transcutaneous administrations of testosterone propionate and 6 placebo subjects. Brief supraphysiologic serum testosterone peaks were disclosed, the amplitude and frequency of these peaks being larger for the treated group. No solid explanation could be given to explain these bursts. Neither the binding/dissociation kinetics of SHBG molecules with and without increased circulating level of dihydrotestosterone, nor brief testosterone-inducing LH bursts, nor increased Leydig cell release could be invoked to explain these peaks. Their occurrence, although relatively rare, could represent a threat and lead to improper treatment.

Administration, Cutaneous↗
PubMed1995

Structural characterizations of neuropeptide tyrosine (NPY) and its agonist analog [Ahx5-17]NPY by NMR and molecular modeling.

The structures of human NPY and of its centrally truncated agonist analog [Ahx5-17]NPY have been investigated in DMSO-d6 by two-dimensional NMR and by molecular modeling. For both peptides, a complete resonance assignment was achieved and a large number (more than 200) of inter-residue NOE connectivities were observed, including long-range connectivities between the N- and C-terminal ends of the chain. Molecular models were calculated using NOE constraints by distance geometry, simulated annealing and conjugate gradient energy minimization. The results indicate that both peptides are folded in the center of their chain, NPY adopting the hairpin shape, whereas the central portion of [Ahx5-17]NPY is characterized by relatively large loops. In contrast to previous models, practically no alpha-helical structure exists for these peptides under our conditions, but two beta-turns are found in NPY and one in [Ahx5-17]NPY. The proximity of the terminal ends could be the determinant factor for their activity.

Amino Acid Sequence↗
PubMed1989

Face cooling-induced reduction of plasma prolactin response to exercise as part of an integrated response to thermal stress.

This study was designed to verify if the decrease in blood prolactin (PRL) induced by selective face cooling during exercise could be part of a response to specific body thermal stress. Five healthy trained male cyclists presenting a significant plasma PRL elevation to exercise were, on three occasions and at weekly interval, submitted to a submaximal exercise (approx. 65% VO2max) on ergocycle with and without selective face cooling. In absence of face cooling a first trial served to establish reference values for workload, heart rate and plasma PRL levels, the latter increasing markedly (450% of resting values) in these conditions. On a second trial but with workload maintained at reference values (222 +/- 9 W), a significant bradycardia was observed with face cooling; furthermore, plasma PRL response to exercise was significantly reduced (to 31% of original response). On a third trial with face cooling, workload had to be significantly augmented (242 +/- 10 W) to maintain heart rate at reference level (78% HRmax); in addition, plasma PRL response to exercise was almost unchanged compared to the reference-value level. The absence of a significant face cooling-induced decrease in sympathetic tonus, as evaluated through peripheral plasma catecholamines response, does not indicate a role for the autonomic nervous system in the face cooling-induced reduction of both heart rate and PRL responses during exercise. Assay of circulating peripheral beta-endorphins could indicate that the face cooling-induced PRL blunted response does not necessarily involve an opioid mediation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1979

Computer processing of intracardiac electrograms for conduction studies.

Computer techniques developed to process intracardiac signals recorded in dogs are presented. The signals under measurement are the auricular and ventricular monophasic action potentials and the His bundle electrogram. Computerized measurement of significant timing parameters on simultaneous recordings of these signals can assess quite precisely changes in the normal conduction scheme of the heart provoked by different experimental protocols. Increased accuracy is mainly due to the objective way of defining wave onsets and the processing power of the system used. Signal recording, signal acquisition, automatic waveform measurements, interactive process and production of end result graphs by computer are all described.

Action Potentials↗
PubMedDate not supplied

Structure of human calcitonin gene-related peptide (hCGRP) and of its antagonist hCGRP 8-37 as determined by NMR and molecular modeling.

The solution structures of human calcitonin gene-related peptide (hCGRP, 37 residues) and of its antagonistic fragment hCGRP 8-37 have been determined by two-dimensional 1H nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Analysis of the double quantum filtered correlation spectroscopy, total correlation spectroscopy and nuclear Overhauser enhancement spectroscopy spectra led to a complete assignment and to the identification of more than 350 intra- and interresidue connectivities for each peptide. Molecular models were calculated by molecular dynamics and energy minimization using distance constraints. The structure of hCGRP is characterized by a rigid N-terminal disulfide-bonded loop followed by helix segments (Val8-Leu16), a gamma-turn (Ser19-Gly21) and several local hydrogen-bonded patterns. The structure of hCGRP 8-37 is less defined than the structure of hCGRP and no helix structure is present. Molecular models of both peptides are consistent with the NH temperature coefficients and secondary chemical shifts of the alpha-protons. Hydrogen bonding with the disulfide-bonded ring appears to be critical for helix formation, both structural elements being essential for agonistic activity.

Amino Acid Sequence↗