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Biomedical subjects

J Petit

Publications and source records attributed to J Petit.

At least 235 records · Page 13Linked to original sources
PubMed1985

Lipid solvation of the aqueous form of the myelin proteolipid apoprotein: evidence and characterization of two lipid populations by fluorescence polarization, differential calorimetry, and sucrose gradient centrifugation.

The interaction between dipalmitoylphosphatidylcholine (DPPC) and the aqueous form of the myelin proteolipid apoprotein (PLA) has been investigated. Lyophilization was found to be an efficient and nonperturbing method for membrane reconstitution. Mixtures of different lipid/protein ratios were analyzed by means of differential calorimetry, fluorescence polarization, and sucrose gradient centrifugation. The presence of two coexisting lipid populations, termed "bulk" and "interacting" lipids, was demonstrated by these three techniques. By differential calorimetry, 23 DPPC molecules per molecule of protein (30 kDa) were shown to be excluded from the lipid phase transition. By fluorescence polarization, we detected above the phase-transition temperature a large perturbation of the lipid acyl chain dynamics induced by the aqueous form of PLA. Increasing the protein content above 35% by weight within the recombinants caused drastic changes in both delta H values and the fluorescence anisotropy parameter, which could stem from protein aggregation.

Animals↗
PubMed1985

Lack of summation of dynamic and static components in the responses of cat tendon organs.

Discharges of single tendon organs of cat peroneus tertius muscle were recorded during tetanic contractions of motor units. On combined stimulation of several motor units activating the same tendon organ, the static components of responses sum, although not linearly, whereas the dynamic component of a response superimposed on a pre-existing discharge does not sum at all with this discharge.

Animals↗
PubMed1985

Activation of cat muscle spindles by static skeletofusimotor axons.

The discharges from primary and secondary spindle endings of the cat peroneus tertius muscle were recorded during stimulation of static skeletofusimotor (static beta) axons at frequencies comparable with the presumed range of motoneuronal firing rates. When stimulated at 20-40/s, static beta-axons exerted typical static actions on the spindles they innervated, including activation of primary endings with reduction of their dynamic sensitivity and activation of secondary endings. For these frequencies, the extrafusal portions of static beta-motor units developed unfused contractions producing oscillations of tension within the muscle. After suppression of extrafusal contractions, the effects of the stimulation of static beta-axons on spindle discharge could persist unaltered, showing that extrafusal events need not interfere with the specific intrafusal actions of static beta-axons. Stimulation of a static beta-axon at 20-40/s often elicited a response of primary endings in which the discharge exactly followed the stimulation frequency, i.e. it was driven 1:1. Purely mechanical excitation of a spindle by unfused extrafusal contractions could also drive its discharge at the stimulation frequency. The persistence of static beta-driving after suppression of extrafusal contraction provided evidence for its intrafusal origin. Driving elicited by static beta-axons could persist during changes in muscle length, but small fluctuations in the delay between each impulse and the preceding stimulus were observed. These fluctuations were clearly related to the changes in muscle length, indicating that although the primary ending discharge remained driven 1:1 at the stimulation frequency, the receptor was not totally insensitive to length changes.

Action Potentials↗
PubMed1985

Responses of tendon organs to unfused contractions of single motor units.

The discharges of individual tendon organs of peroneus longus and tertius muscles were examined in anesthetized cats during stimulation of single motor units at frequencies that elicit unfused contraction (5-50/s). At these frequencies nearly all the fast-contracting motor units activating a tendon organ elicited responses whose discharge rates reproduced the stimulation frequency ("1:1 driving"), whereas slow-contracting motor units elicited responses in which the discharge rate was higher than the stimulation frequency. When a motor unit stimulated at 40/s developed a gradually potentiating tension, the tendon organ discharge could remain locked on stimulation frequency over an appreciable range of the increasing tension as if the receptor responded to the tension oscillations rather than to the mean level of tension. The only visible effect of the gradual increase in mean tension on the tendon organ response was a gradual decrease of the delay between each stimulus and the corresponding impulse. Driving of tendon organ discharge at the stimulation frequency occurred not only when relatively large oscillations were superimposed on a low level of static tension but also when the static component of the tension was quantitatively preponderant. These observations suggest that during unfused contractions the dynamic component of the stimulus (i.e., oscillation of tension) exerts a prevailing influence on the discharge pattern of tendon organs. Computed simulations of tendon organ responses confirmed that a relatively strong dynamic sensitivity could account for the observed behavior of the receptor.

Animals↗
PubMed1985

[Pulmonary valve stenosis. The medical solution].

Pulmonary valvular stenosis had been diagnosed since infancy in a 3 year-old girl. Cyanotic episodes occurring when the child cried led to the decision to remove the stenosis, whose gradient was 58 mmHg. Transluminal dilatation through the femoral vein, after premedication and local anesthesia induced a decrease of the gradient to 18 mmHg with a good angiographic result. This technique, which may be used in numerous types of pulmonary stenosis, allowed avoidance of the disadvantages of surgery under general anesthesia with median sternotomy and cardiopulmonary by-pass.

Angioplasty, Balloon↗
PubMed1985

[Aortic subvalvular stenosis caused by accessory mitral tissue].

Three cases of subaortic stenosis due to accessory mitral tissue are presented. The diagnosis of the cause of obstruction was correctly established in each child before surgery, by 2D echocardiography and cineangiography. Resection of the accessory mitral tissue through a simple aortotomy gave excellent results. The eight previously published cases are discussed, emphasising the importance of accurate preoperative diagnosis. The cause of obstruction is difficult to determine at surgery, which may have disastrous consequences, whilst simple resection of the abnormal tissues leads to a complete and definitive cure.

Aortic Stenosis, Subvalvular↗
PubMed1985

[Surgical closure of interventricular communications before 2 years of age. Long-term clinical and electrocardiographic course].

The long-term follow-up of the first 100 children under 2 years of age, presenting with ventricular septal defect (VSD) who underwent surgical closure between 1972 and 1976 at the Centre Chirurgical Marie-Lannelongue, was studied. Only cases with isolated VSD were taken into account except for 18 cases with ductus arteriosus related to operation and 41 cases with atrial septal defect (ASD) or persistent foramen ovale. This study included clinical and electrocardiographic investigations focused on the long-term follow-up of conduction disorders. Clinical tolerance was excellent with only one Eisenmenger's syndrome induced by a residual VSD. Three secondary cases of aortic regurgitation without present functional repercussions were observed. Conduction disorders were considered as unchanged or even improved. There were no sudden death, no secondary atrioventricular block (AVB), no trifascicular block even after one case with transitory immediate postoperative AVB.

Age Factors↗
PubMed1985

[Retroperitoneal fibrosis. Surgical or medical treatment. Apropos of 15 cases].

15 patients suffering from retroperitoneal fibrosis with ureteral obstruction have been treated. 6 patients were operated at the first onset, 3 after an attempt of corticotherapy and 6 patients had exclusive corticotherapy. Results of surgery referred to kidney units are 9 good results out of 12 and these of corticotherapy 11 good results out of 16. Besides, in the literature, the complications of surgery are frequent and serious. Medical treatment, with renal drainage, when needed is so to consider first, surgical treatment being kept for corticotherapy failure.

Adrenal Cortex Hormones↗
PubMed1984

Pharmacokinetic study of 3H-labelled PAF-acether II. Comparison with 3H-labelled lyso-PAF-acether after intravenous administration in the rabbit and protein binding.

The blood and plasma kinetics of intravenously administered 3H-labelled PAF-acether were determined in seven rabbits. PAF-acether was rapidly distributed and slowly eliminated. Individual variations were very small. The main route of metabolism involves deacetylation of the PAF-acether into lyso-PAF-acether, leading to an equilibrium between the two molecules (10%/90%). This equilibrium, observed within 30 minutes, was still the same after 6 hours suggesting in vivo reacetylation of lyso-PAF-acether into PAF-acether. However, this could not be verified. After intravenous administration of lyso-PAF-acether in two rabbits, PAF-acether could not be found in any blood sample. The pharmacokinetic behaviour of both PAF-acether and lyso-PAF-acether can be described by a three-compartment model.

Animals↗
PubMed1984

[Immune disorders during postoperative peritonitis].

Despite major diagnostic and therapeutic advances, postoperative peritonitis appeared to be still associated with a severe prognosis. The failure to react to delayed hypersensitivity skin tests was recently shown to identify patients at increased risk for sepsis. In an attempt to clarify the mechanisms of this anergy, cellular and humoral immunity was studied with in vitro tests in 12 patients treated for postoperative peritonitis. Complement was decreased in 33.3% of cases and normal in the others. No significant change was found in IgG and IgM titres, but IgA concentrations were increased in 80% of cases. A decrease in the total number of lymphocytes was observed in 41.7% of patients, related to the reduction in the total T lymphocyte count. Mitogen-induced lymphocyte transformation was studied with phytohaemagglutinin, concanavalin A, pokeweed-mitogen, and tuberculin purified protein derivative. Six patients had decreased or negative response to at least three mitogens; 91,7% had no response to tuberculin. The leukocyte migration inhibition test was negative in all cases. These abnormalities in cell mediated immunity may have been related to underlying diseases (severe nutrition depletion in 7 cases), to sepsis (septic shock in 10 cases), to repeated anaesthesias and surgical procedures, and even to drugs (e.g. antibiotics). The presence of serum inhibitors may have been the cause of the anergy and further studies are required.

Adult↗
PubMed1984

[Withdrawal syndrome during epidural administration of morphine after stopping treatment with clonidine].

A 70 year old hypertensive patient who had undergone a gastrectomy experienced withdrawal symptoms 10 h after a second epidural injection of morphine (150 micrograms X kg-1) for postoperative analgesia. A clonidine treatment had been stopped 129 h earlier. These symptoms disappeared shortly after a third epidural injection of morphine. Clonidine was then reintroduced. The later progressive interruption of epidural morphine analgesia did not introduce any further symptoms of withdrawal. Since physical dependence on a drug is related to repeated and prolonged administration of that drug, opiate withdrawal symptoms were highly unlikely after epidural morphine used to relieve immediate postoperative pain. Abrupt discontinuation of a long-term treatment by clonidine may produce a withdrawal syndrome, but clinical and biological signs usually occur earlier than noted in this case. Recent experimental and clinical data has provided support for the existence of a complex presynaptic regulation of noradrenergic transmission in the central nervous system, both alpha 2 and opiate receptors being implicated. The activation of such presynaptic receptors inhibits further transmitter release. Suddenly stopping the chronic administration of alpha 2 or opiate agonists was responsible for a rebound excitation of these noradrenergic neurons, inducing a withdrawal syndrome. The related withdrawal symptoms may have resulted from an interaction between the discontinuation of clonidine and the decrease in morphine activity. Practitioners should be warned of this possible side-effects.

Aged↗
PubMed1984

[Hepatocellular carcinoma with cirrhosis: treatment with doxorubicin. Phase II evaluation].

Twelve patients with unresectable hepatocellular carcinoma associated with cirrhosis were treated with Doxorubicin which was given intravenously (30 to 50 mg/m2) every three weeks. Six patients were given only one dose of Doxorubicin. No clinical response was observed. Five patients has serum alphafoetoprotein (AFP) determination during the treatment. AFP concentration rose in 4 patients and fell in 1 patient. Survival rate after 3 and 8 months of treatment was 58 and 33 per cent. These results suggest that Doxorubicin is not an effective treatment for hepatocellular carcinoma.

Carcinoma, Hepatocellular↗
PubMed1984

[Resection-suture of the ureter. A study of 26 cases].

The authors analyze twenty six cases of urethral resection and suture performed for short strictures secondary to trauma of iatrogenic or infectious origin. The results were good or very good in 78 per cent of cases. The main indications are post-traumatic or iatrogenic strictures without infection or prior dilatation. The procedure was performed, in every case, late after the trauma, though other authors have advocated shortening the delay. Postoperative sexual impotence was more often the result of the initial trauma than of the surgical procedure, but the patient must always be warned of this risk.

Adolescent↗