Search PubMed⌕ Search

Biomedical subjects

G David

Publications and source records attributed to G David.

At least 235 records · Page 13Linked to original sources
PubMed1987

Impaired ability of human spermatozoa to penetrate zona-free hamster oocytes: is a postacrosomal sheath anomaly involved?

We selected 17 infertile men whose sperm ultrastructural study revealed at least 70% of spermatozoa with postacrosomal sheath (PAS) anomalies. Among the other sperm head defects, those affecting the nuclear shape were most frequently encountered and were highly correlated with PAS anomalies (r = +0.71; P less than .01). PAS anomalies were also correlated with chromatin condensation defects (r = +0.67; P less than .01) and acrosome anomalies (r = +0.53; P less than .05). Those spermatozoa were tested for their ability to penetrate zona-free hamster oocytes and were compared to a control sperm population. It was shown that sperm head morphological anomalies impaired the ability of spermatozoa to attach to and penetrate the oocyte. The highest significant and negative correlations were found between the penetration rate and 1) the percentage of spermatozoa with PAS anomalies (r = -0.81; P less than .01) and 2) the percentage of spermatozoa with nuclear shape anomalies (r = -0.66; P less than .01). The effect of PAS anomalies on human fertilization process are discussed.

Acrosome↗
PubMed1987

Comparative clinical pharmacology of [111In]-labeled murine monoclonal antibodies.

Patients with metastatic melanoma received either the murine antimelanoma antibody ZME-018 (20 patients) or antibody 96.5 (26 patients) at doses ranging from 1 to 20 mg and coupled to 2.5 or 5 mCi of [111In]. The pharmacokinetics and tissue disposition of these antibodies were measured at various times after infusion of the radiolabel. The clearance of the [111In]label from plasma closely fit (r2 greater than 0.90) an open, one-compartment mathematical model after administration of antibody 96.5. Clearance of [111In] from plasma after administration of ZME-018 fit a one-compartment model in some patients and a two-compartment model in others. The terminal phase half-lives of 96.5 and ZME-018 antibodies at the 20-mg dose were almost identical (27 +/- 2 h and 29 +/- 5 h, respectively). The half-lives calculated for 96.5 were not dependent upon the total antibody dose; however, with increasing doses of ZME-018 there was a dose-dependent increase in t 1/2 (from 17.8 +/- 2 h at the 2.5-mg dose to 29 +/- 5 h at the 20-mg dose). For 96.5 antibody, the apparent volume of distribution (Vd) approximated the total blood volume (7.8 +/- 0.71) at the 1-mg dose and decreased significantly at the 20-mg dose, suggesting saturation of extravascular antigen sites. In contrast, the Vd calculated for ZME-018 did not appear to be dependent upon the administered dose. Improved imaging occurred with increasing doses of unlabeled 96.5 above 2 mg, a finding not observed with ZME-018. The cumulative urine excretion of [111In] after administration of 96.5 or ZME-018 was 10%-14% of the total dose. These studies show that murine monoclonal antibodies of the same subtype but recognizing different surface antigens can exhibit markedly different in vivo pharmacokinetic behavior, which may partially explain differences in imaging noted with increasing doses of monoclonal antibody.

Antibodies, Monoclonal↗
PubMed1987

Collagen metabolism and basement membrane formation in cultures of mouse mammary epithelial cells. Induction of 'assembly' on fibrillar type I collagen substrata.

Collagen metabolism was compared in cultures of mouse mammary epithelial cells maintained on plastic or fibrillar type I collagen gel substrata. The accumulation of dialysable and non-dialysable [3H]hydroxyproline and the identification of the collagens produced suggest no difference between substrata in the all over rates of collagen synthesis and degradation. The proportion of the [3H]collagen which accumulates in the monolayers of cultures on collagen, however, markedly exceeds that of cultures on plastic. Cultures on collagen deposit a sheet-like layer of extracellular matrix materials on the surface of the collagen fibres. Immunoprecipitation of the labelled extracts, electrophoresis, indirect immunofluorescence and immunoperoxidase techniques reveal the presence of type IV collagen, along with laminin and heparan sulfate proteoglycan in this layer, in excess over the amounts detectable on cells cultured on plastic. Transformed cells on collagen produce and accumulate more [3H]collagen, yet are less effective in basement membrane formation than normal cells, indicating that the accumulation of collagen alone and the effect of interstitial collagen thereupon do not suffice. Thus, exogenous fibrillar collagen appears to enhance, but is not sufficient for proper assembly of collagenous basement membrane components near the basal epithelial cell surface.

Animals↗
PubMed1987

[Genetic problems associated with artificial reproduction using donor gametes: solutions adopted by CECOS (Centres d'Etude et de Conservations du Sperme].

Artificial reproductions using donor sperms or oocytes are increasing. In this way they offer the doctor the chance of preventing genetic handicaps that cannot be obtained by natural reproduction, and that therefore should be used. To deny this medical power is dangerously nihilistic. The use of this power for eugenic or commercial ends can lead to abuses. Therefore a strict medical protocol is proposed: 1) The use should be exclusively therapeutic and should include the genetic reasons for using a donor gamete in reproduction. 2) The objectives should be defined and the methods that can be employed in the prevention of abnormal genetic inheritance. 3) Research should be carried out into the possible iatrogenic effects of these methods of artificial reproduction.

Ethics, Medical↗
PubMed1986

Acetylcholine modulates two types of presynaptic potassium channels in vertebrate motor nerve terminals.

Using external microelectrodes to record local circuit currents from preterminal motor nerve axons, two distinct populations of potassium (K) channels were identified in frog motor nerve terminals: delayed rectifier and calcium-activated K channels. Both are sensitive to the transmitter acetylcholine (ACh) which, when externally applied, blocks them in concentrations in the millimolar range. As this action also is not prevented by nicotinic and muscarinic antagonists, it probably is not mediated by classical cholinergic receptors. This cholinergic sensitivity of presynaptic K channels may account for the hyperexcitability of motor nerve terminals manifested when ACh accumulates in the junctional cleft.

Acetylcholine↗
PubMed1986

Heparan sulfate proteoglycans of human lung fibroblasts. Occurrence of distinct membrane, matrix and secreted forms.

Human lung fibroblasts (HLF) were labeled with 35SO2-4 for 48 h and extracted with a guanidinium chloride buffer. A fraction of the extracted heparan sulfate proteoglycan (HSPG) appeared micelle-associated. In the absence of detergent these HSPG eluted in the void volume of Sepharose CL2B columns. In the presence of detergent these HSPG were included in Sepharose CL2B (Kav = 0.55) and 4B (Kav = 0.3) columns. This type of HSPG was specifically associated with isolated HLF cell membranes, suggesting that it may represent a fraction of integral membrane proteoglycans. Most of the HSPG in the HLF monolayers, however, eluted in the included volume of Sepharose CL2B (Kav = 0.4) and CL4B (Kav = 0.1) columns in the absence of detergent. This type of HSPG was not affected by detergent and was specifically retained in 'extracellular matrix' preparations. The medium of HLF monolayers contained HSPG of similar Mr as the membrane-associated HSPG. Of these three distinct HSPG fractions only the membrane-associated form could be incorporated in liposomes, confirming that the HSPG in this fraction may be integral membrane components.

Cell Membrane↗
PubMed1986

Activity-dependent depression of nerve action potential by phenytoin.

The action of the anticonvulsant drug phenytoin was investigated on the responsiveness of isolated amphibian and human nerves to repetitive stimulation. At low frequencies of stimulation (0.5-25 Hz) the drug (at a concentration of 0.1 mM) had no notable effect on the compound nerve action potential. By contrast, at higher rates of stimulation (50-300 Hz), it produced a progressive decrease in amplitude and integral of the compound action potential. This effect was positively correlated with the frequency of nerve activation and was markedly enhanced by elevating the extracellular K+ concentration. Thus, phenytoin induces a use- and frequency-dependent depression of axon conduction, which may contribute to its preferential suppression of the spread of high-frequency seizure discharge in the brain.

Action Potentials↗
PubMed1986

Frequency-dependent action of phenytoin on lamprey spinal axons.

The effect of the antiepileptic drug phenytoin (diphenylhydantoin, DPH) was tested on the conduction of intracellularly recorded action potentials in lamprey giant reticulospinal axons. When the isolated spinal cord was exposed to 80 microM DPH for up to 4 h, no significant effect was seen on the amplitude or conduction velocity of the action potential, although the maximum rate of rise was reduced from 247.8 to 149.6 V/s after 1 h. However, at higher stimulus frequencies both the amplitude and conduction velocity of the action potential were reduced progressively during a 500 stimulus train. The reduction was greater the higher the stimulus frequency, and was reversed upon return to 1 Hz stimulation. At frequencies greater than 40 Hz an all-or-none block developed. This also developed sooner the higher the stimulus frequency. Axons bathed in drug-free solutions did not show this effect at stimulus frequencies up to 100 Hz. Similar effects were seen in 16 microM DPH when the spinal cord was exposed to the drug overnight. This is close to the human therapeutic CSF level. The frequency-dependent depression of the action potential was greatly potentiated by increasing the extracellular potassium concentration from 2.1 to 5 mM. Under these conditions the axons rapidly developed block at stimulus frequencies as low as 2 Hz, and this was not reversible during a 5 h wash. In the absence of DPH, 5 mM potassium produced a 4-5 mV depolarization, but did not induce a frequency-dependent block. This effect of potassium may be important to the therapeutic effect of DPH because during epileptiform activity the extracellular K+ increases several fold.

Action Potentials↗
PubMed1986

Lower sperm characteristics in 36 brothers of infertile men, compared with 545 controls.

Among the men who volunteered to become semen donors for artificial insemination at the sperm bank of Centre d'Etude et de Conservation du Sperme Humain, Paris-Bicêtre, some were brothers of the infertile men of couples entering the Artificial Insemination with Donor program. Their sperm characteristics, compared with those of other donor candidates, are clearly lower. The difference is significant for count (78.0 versus 102.8, P less than 0.05) and very significant for the percentage of motile spermatozoa (61.5 versus 66.9, P less than 0.01) and for the percentage of normal forms (51.8 versus 62.7, P less than 0.00001). The differences are even more pronounced when the brothers of azoospermic men are considered. The possibility that some cases of infertility could have a genetic origin is discussed.

Adult↗
PubMed1986

Genetic screening for artificial insemination by donor (AID). Results of a study on 676 semen donors.

We report the results of our ten-year experience in the Centre for Study and Conservation of Human Semen (CECOS) in Paris-Bicêtre. A total of 676 potential semen donors were interviewed by a geneticist and karyotyped; 6.0% were excluded, i.e. 2.6% for a cytogenetic reason and 3.4% for a genic reason. Our experience stresses the subjectivity and difficulty of the exclusion decision. It also shows how useful it is to take into account the recipient's familial pathology when choosing the donor. Finally, it reveals the importance of the geneticist's participation in the functioning of a centre.

Chromosome Aberrations↗
PubMed1986

Differential distribution of tubulin epitopes in human spermatozoa.

Two monoclonal antibodies (16 D3 and 24 E3) were used to map tubulin domains in human spermatozoa by indirect immunofluorescence. Their specificity to tubulin in these cells was established by Western blotting. Whereas 16 D3 uniformly stained the principal piece of the flagellum, the staining provided by 24 E3 decreased along the tail to become very weak 30 micron further away from the midpiece. This latter antibody also reacted with the proximal centriole as well as the midpiece, but not all spermatozoa stained identically at this level indicating heterogeneity within the population of sperm cells from a given donor. 16 D3 reacted weakly with the head, and the staining was interrupted after a bright spot in the neck. The study of a pathological case (the short tail spermatozoon) with an abnormal arrangement of dense fibers was consistent with a correlation between the distribution of the epitope defined by 24 E3 and that of peri-axenomal structures. The existence of tubulin domains interacting with these structures is postulated.

Antibodies, Monoclonal↗
PubMed1986

Dynamic interaction of 111indium-labeled monoclonal antibodies with surface antigens of solid tumors visualized in vivo by external scintigraphy.

Two 111indium-labeled murine monoclonal antibodies (MoAb), D3 and 9.2.27, directed to tumor antigens of L-10 hepatocarcinoma and human melanoma, respectively, selectively localized antigen-positive target cells in guinea pigs and nude mice. The fate of MoAb differed in the two antigen-antibody systems after reacting with their corresponding tumor antigens in vivo as reflected by patterns of distribution and turnover in vivo. The 9.2.27 localized in melanoma xenograft in nude mice after intravenous administration with slow loss from tumor but more rapid loss from normal tissues and thus demonstrated optimal imaging of small tumors (approximately equal to 5 mm) between 3 and 6 days after injection of the radiolabeled antibody. In contrast, D3 demonstrated a biphasic localization in guinea pig L-10 hepatocarcinoma with a maximal activity on the 2d day after administration and showed rapid loss from both tumor and normal tissues. Nonspecific localization of antibodies in liver and in kidney was found both in syngeneic (nude mice) and xenogeneic (guinea pig) hosts but was more pronounced in the xenogeneic species. These results indicate that the nature of the antigen-antibody interaction may be of importance in selecting MoAb for both diagnosis and therapy of malignant diseases.

Animals↗
PubMed1985

Frequency-dependent effects of phenytoin on frog junctional transmission: presynaptic mechanisms.

The action of the antiepileptic drug, phenytoin, on junctional transmission at various frequencies of synaptic activation was studied in frog nerve-muscle preparation. Intracellular recordings were made from muscle end-plates, and extracellular focal and subsendothelial recordings were obtained from motor nerve terminals and their parent axons, respectively. When the motor nerve was stimulated at 100-200 Hz, exposure to the drug (0.1-0.3 mM) induced intermittent failures of junctional transmission which appeared faster as the rate of stimulation was increased. At these and at lower stimulation frequencies (30-50 Hz), in which failures of transmission occurred only rarely, phenytoin markedly limited the buildup of end-plate potential amplitude during the period of repetitive nerve stimulation (tetanic potentiation). Several lines of evidence suggest that both drug effects are consequent to a frequency-dependent depression of the action potential at motor axons and terminals, which could lead to an intermittent conduction block at the higher rates of stimulation. The selective action of phenytoin on high frequency synaptic transmission may contribute to the specificity shown by this drug in suppressing epileptic seizures while sparing neuronal activity.

Animals↗
PubMed1985

Heparan sulfate-chondroitin sulfate hybrid proteoglycan of the cell surface and basement membrane of mouse mammary epithelial cells.

Chondroitin sulfate represents approximately 15% of the 35SO4-labeled glycosaminoglycans carried by the proteoglycans of the cell surface and of the basolateral secretions of normal mouse mammary epithelial cells in culture. Evidence is provided that these chondroitin sulfate-carrying proteoglycans are hybrid proteoglycans, carrying both chondroitin sulfate and heparan sulfate chains. Complete N-desulfation but limited O-desulfation, by treatment with dimethyl sulfoxide, of the proteoglycans decreased the anionic charge of the chondroitin sulfate-carrying proteoglycans to a greater extent than it decreased the charge of their constituent chondroitin sulfate chains. Partial depolymerization of the heparan sulfate residues of the proteoglycans with nitrous acid or with heparin lyase also reduced the effective molecular radius of the chondroitin sulfate-carrying proteoglycans. The effect of heparin lyase on the chondroitin sulfate-carrying proteoglycans was prevented by treating the proteoglycan fractions with dimethyl sulfoxide, while the effect of nitrous acid on the dimethyl sulfoxide-treated proteoglycans was prevented by acetylation. This occurrence of heparan sulfate-chondroitin sulfate hybrid proteoglycans suggests that the substitution of core proteins by heparan sulfate or chondroitin sulfate chains may not solely be determined by the specific routing of these proteins through distinct chondroitin sulfate and heparan sulfate synthesizing mechanisms. Moreover, regional and temporal changes in pericellular glycosaminoglycan compositions might be due to variable postsynthetic modification of a single gene product.

Animals↗
PubMed1985

Suppression by phenytoin of convulsant-induced afterdischarges at presynaptic nerve terminals.

The mechanisms underlying the induction of afterdischarges at presynaptic nerve terminals by convulsant aminopyridines and their suppression by the anticonvulsant drug phenytoin were studied at the frog neuromuscular preparation. Addition of aminopyridine to the perfusing solution induced the appearance of afterdischarges in motor nerve fibres following their primary response to a single nerve stimulus. The afterdischarges seemed to originate at or near the nerve terminals and to propagate both antidromically and orthodromically. The latter resulted in repetitive activation of the neuromuscular synapse. Focal recordings of nerve terminal potentials suggested that aminopyridines may induce afterdischarges by slowing spike repolarization and thereby producing a prolonged depolarization of nerve terminals. Phenytoin suppressed the aminopyridine-induced afterdischarges and the resultant repetitive excitation of the postsynaptic muscle fibres. This effect of phenytoin was associated with a depression of the action potential at the motor nerve terminals but not at their parent axons. These results single the presynaptic nerve terminals as preferential sites for convulsant and anticonvulsant actions.

4-Aminopyridine↗
PubMed1985

Polymorphous endocytotic organelles in the receptor-mediated endocytosis of gold-labelled alpha 2-macroglobulin complexes by human fibroblasts.

The receptor-mediated endocytosis of gold-labelled alpha 2-macroglobulin complexes with trypsin or methylamine (alpha 2M-T-Au or alpha 2M-MA-Au) was studied by electron microscopy in human skin fibroblasts. The gold label was found in coated structures and very small tubules as well as in tubulovesicular structures and in multivesicular bodies/lysosomes. Thick sections (200 nm), but especially serial thin sections, clearly showed the polymorphic character of the cellular structures involved in endocytosis. Numerous intercommunications were particularly obvious between the tubulovesicular structures, the larger vesicles and the multivesicular bodies (MVB). Continuities between MVBs and endoplasmic reticulum and interconnections between MVBs were also observed. The specificity of the staining reaction was confirmed by indirect labelling of intracellular alpha 2M by polyclonal and by monoclonal antibodies on ultracryosections. These findings are discussed in relation to observations made on epithelial cells with other ligands.

Endocytosis↗