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C Coutant

Publications and source records attributed to C Coutant.

6 recordsLinked to original sources
PubMed2000

Programmable control of column selectivity for temperature-programmed GC

A computer-driven pressure controller connected to the junction point of a series-coupled ensemble of two capillary GC columns having different stationary-phase selectivity is used to obtain on-the-fly (programmable) changes in ensemble selectivity. Changes in the junction-point pressure result in differential changes in the local carrier gas velocity in the two columns, and this results in changes in the pattern of peaks eluting from the ensemble. When used with relatively fast temperature programming (30 degrees C/min), the pattern of eluting peaks can be very sensitive to the time at which a selectivity (junction-point pressure) change is implemented. These elution pattern changes are described for a set of six PCB congeners that elute with a small range of retention times. The components are considered as a group, and changes in their elution pattern are described for a single junction-point pressure change, which is implemented at various times after sample injection. If the pressure change is implemented after the components have migrated across the junction point, the final pressure has relatively little impact on the ensemble retention pattern. Pressure changes implemented prior to the components reaching the junction can have a large effect and usually result in a pattern of peaks similar to the pattern obtained when the final pressure is used for the entire separation. For pressure changes made when the group of components is near the junction point, the observed peak pattern may be very sensitive to the time of the pressure change. The time at which the junction-point pressure change occurs is varied in 1.0-s intervals. Artifacts such as peak doubling and peak focusing or broadening are observed if a migrating band is crossing the column junction point at the time of the programmed pressure change.

Journal Article↗
PubMed1996

Disk diffusion interpretive criteria for fusidic acid susceptibility testing of staphylococci by the National Committee for Clinical Laboratory Standards method.

Fusidic acid is used in many countries for the treatment of multiresistant staphylococcal infection, especially multiresistant Staphylococcus aureus infection (MRSA). We collected consecutive fusidic acid-resistant isolates of staphylococci from the routine laboratory over several years, and compared these strains with fusidic acid-susceptible staphylococci to establish interpretive criteria for disk diffusion testing by National Committee for Clinical Laboratory Standards (NCCLS) methods. The minimum inhibitory concentrations (MICs) and zone diameters for strains of S. aureus (n = 102), including MRSA, S. saprophyticus (n = 20) and other coagulase-negative staphylococci (n = 115) were determined by NCCLS agar dilution and disk diffusion tests using a 2.5-micrograms disk of fusidic acid. MICs were bimodally distributed. No isolates had MICs of 0.5 or 1 microgram/ml; thus, we chose these values to define strains of intermediate susceptibility. The error-rate-bounded method was used to determine interpretive zone diameters for disk testing. Interpretive zone diameter criteria were found to be: susceptible > or = 22 mm, intermediate 18-21 mm, and resistant < or = 17 mm. All S. saprophyticus were intrinsically resistant to fusidic acid (MIC > or = 2 micrograms/ml).

Anti-Bacterial Agents↗
PubMed1989

Effects of photoperiod, melatonin implants and castration on molting and on plasma thyroxine, testosterone and prolactin levels in the European badger (Meles meles).

1. The seasonal molt, which lasts six months in the badger, begins in mid-July and ends at the beginning of winter. It occurs under natural long-day conditions, following the seasonal drop in plasma testosterone levels, concomitant with high levels of thyroxine and prolactin. 2. To examine the role of the different factors involved (day length, prolactin, thyroxine, testosterone), different groups of badgers, divided into subgroups of castrated or intact animals, were subjected to the influence of long days (20L: 4D), short days (4L:20D) or the effect of subcutaneous melatonin implants. 3. In all cases, castration resulted in a significantly earlier onset of molting 1-3 months, depending on the group, regardless of the experimental conditions (20L:4D, 4L:20D, melatonin). 4. However, molting started earliest in animals subjected to long days, irrespective of whether they were castrated or intact. 5. In the melatonin-implanted badgers, molting started either early (castrated animals), or late or not at all (intact animals). 6. Lastly, in castrated badgers subjected to experimental photoperiods (short days or long days) or melatonin implants, the period of molting was shortened from 6 months (intact outdoor animals) to 4 months. 7. The advance in shedding was always related to an early drop in testosterone (or an absence of testosterone in the castrated animals) and to a higher or earlier increase in thyroxine levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Thyroid and gonadal regulation of hair growth during the seasonal molt in the male European badger, Meles meles L.

In the male badger we showed that hair growth and molt are related to plasma testosterone and thyroxine cycles. We established the action of testosterone by castration and subcutaneous testosterone implants, and the action of thyroxine by thyroidectomy and dietary supplementation with thyroxine. The following groups of animals were studied: controls, thyroidectomized, thyroidectomized and thyroxine-treated, castrated, castrated and thyroxine-treated, thyroidectomized and castrated and thyroxine-treated, castrated and testosterone-implanted, and intact testosterone-implanted. In control animals, molt and hair growth occurred during the summer, with a maximum growth in autumn. Molt ended at the beginning of winter when the plasma testosterone level had started to rise, and began again after this level had started to decline. Both the start of molt and the period of maximum hair growth coincided with high thyroxine levels of about 20 ng/ml. Castration advanced molt and hair follicle activity, whereas testosterone implants delayed both molt and hair growth. In thyroidectomized badgers, neither hair growth nor seasonal molt was observed. However, when thyroxine levels were restored to 20 ng/ml or more by dietary T4 supplementation, molting was resumed in animals that had undergone either thyroidectomy or thyroidectomy plus castration. In those that underwent castration only, the molt was advanced leading to early hair growth further stimulated by the suppression of testosterone. Testosterone had an inhibitory effect on the molt--since testosterone implants in intact control animals delayed it by 4 weeks--but did not inhibit it completely. On the other hand, a T4-enriched diet advanced the date of the molt. However, the molt could not be induced, nor could hair follicle growth be reactivated, at all times during the annual cycle. Thus, in castrated animals. T4 enrichment of the diet in early January, at the end of the molt, caused follicle reactivation only toward the end of May, despite the lack of testosterone. This 18-week latency period from January to May might therefore constitute a "refractory period" in this species. The above findings show that the regulation of the seasonal molt and hair growth in the European badger involves both the thyroid and genital axes. This regulation is discussed in terms of joint control by the hypothalamus and pituitary governed, in turn, by an external factor--the photoperiod--considered to be the main synchronizer.

Animals↗
PubMed1986

[Effect of thyroidectomy on variations during the spring and summer of the testicular activity and blood prolactin in the mink].

The possible role of thyroid hormones in the setting of sexual quiescence was investigated in the mink, since levels of thyroid hormones were earlier shown to rise while testicular activity decreased. When performed at the beginning of the sexual period, thyroidectomy transiently stimulated testosterone production, and significantly prolonged the duration of maximal testicular development. These results indicate that mink conforms to a pattern of inhibitory thyroid-testis interactions similar to that previously described in several species of birds and mammals. Thyroidectomy was unable, however, to prevent ultimately the installation of sexual quiescence which also appears independent of the photoperiod. On the other hand, thyroidectomy did not modify, from February to October, the general pattern of prolactin secretion, even though the vernal stimulation of prolactin secretion, induced by increasing daylength, was significantly enhanced in the absence of thyroid hormones.

Animals↗