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Biomedical subjects

N Segal

Publications and source records attributed to N Segal.

At least 19 recordsLinked to original sources
PubMed1990

Heritability of substance abuse and antisocial behavior: a study of monozygotic twins reared apart.

Thirty-two sets of monozygotic twins reared apart since shortly after birth (31 pairs and one set of triplets; median age at separation was 0.2 years) were interviewed separately and blindly using the Diagnostic Interview Schedule for presence of DSM-III Axis I psychiatric disorders and antisocial personality. Because the sample was recruited from a nonclinical population, predictably few subjects met criteria for such disorders. However, items counting toward diagnoses were cumulated into four scores: alcohol-related problems, drug-related problems, childhood antisocial behavior, and adult antisocial behavior. The scores showed within-scale cohesion as measured by Cronbach's coefficient alpha. The drug scale and both antisocial scales showed significant heritability (p less than 0.1), but the alcohol scale had an estimated heritability of zero (albeit with a broad confidence interval). There appeared to be substantial commonalities in the genetic factors responsible for these traits.

Adolescent↗
PubMed1989

Genetic factors in the electrocardiogram and heart rate of twins reared apart and together.

Important physiologic mechanisms have been thought not to exhibit large amounts of variability, due in part to the assumption that critical biologic functions will have evolved to an evolutionary optimum. The attainment of this optimum would necessarily eliminate individual differences in these variables. Using a sample of monozygotic and dizygotic twins reared apart since birth or early infancy, 12-lead electrocardiographic recordings and vectorcardiograms were obtained. Values of these variables for monozygotic and dizygotic twins reared together were obtained from other studies. Maximum likelihood tests of genetic and environmental components of variation for PR interval, QRS duration, QT interval and ventricular rate indicated a significant contribution of genetic effects (most heritabilities ranged from 30 to 60%), with a negligible contribution from common familial environmental effects.

Electrocardiography↗
PubMed1989

Beta-cell memory to insulin secretagogues: characterization of the time-dependent inhibitory control system in the isolated rat pancreas.

Most secretagogues, in addition to their acute stimulatory effect on insulin release, modify the responsiveness of the islet to subsequent stimulations. According to the nature and duration of the stimulus, the generated islet memory may either amplify [time-dependent potentiation, (TDP)] or diminish [time-dependent inhibition (TDI)] the responsiveness of the beta-cell. This work characterizes the kinetic parameters of TDI in the isolated rat pancreas. When subjected to a low dose (8.3 mmol/liter) glucose stimulus, maximal TDI was observed after 5 min of priming, while at a higher dose (16.7 mmol/liter) shorter exposures were sufficient. Longer periods of stimulation (10-40 min) resulted in the predominance of TDP, thus amplifying the release rate. TDI was not affected by previous generation of TDP; 40-min priming with 16.7 mmol/liter glucose markedly augmented the subsequent insulin responses to a pair of 6.9 mmol/liter stimuli, but the response to the second stimulus was inhibited, as in unprimed pancreas. Stimulation with arginine (5.0 mmol/liter) in the presence of basal (3.3 mmol/liter) glucose activated TDI only, and hence revealed monophasic insulin release. Tolbutamide (100 micrograms/ml), glucagon (5 micrograms/ml), and isobutylmethylxanthine (0.1 mmol/liter) also demonstrated TDI when given as a pair of 10-min stimuli; they all elicited monophasic insulin responses during prolonged stimulation. Arginine was chosen for detailed characterization of TDI because of its potency. Using identical concentrations of arginine for the generation and expression of TDI, a similar degree of inhibition (60-80%) was observed at all doses tested (0.5-5.0 mmol/liter). However, there existed competition between TDI and the acute secretory signal. Thus, TDI generated by 1.0 mmol/liter arginine had a minimal effect on insulin release induced by 2.0-5.0 mmol/liter amino acid, while it was fully inhibitory of the response to 1.0 mmol/liter arginine. Similarly, inhibition of the insulin response to 5.0 mmol/liter arginine was dependent on the dose (0.5-5.0 mmol/liter) of the priming pulse of arginine. The generation of TDI was unaffected by the insulin release rate during priming, since synergistic augmentation (combined arginine-glucose or arginine-isobutylmethylxanthine stimulation) or partial inhibition (arginine plus epinephrine) of the response had no effect on the subsequent expression of TDI. It is concluded that TDI and TDP are two distinct regulatory systems that independently control the rate of insulin release, most probably operating through different mechanisms.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1985

Retinyl ester hydrolase of bovine retina and pigment epithelium: comparisons to the rat liver enzyme.

The hydrolysis of 3H-retinyl ester was examined in the retinal pigment epithelium (RPE) and neural retina of cattle eyes and compared to that in homogenates of rat liver. The optimum pH for hydrolysis was 4.0-4.5 for RPE and 7.5-8.0 for liver. The RPE activity, which shows no variability between individual animals, is localized mainly in the lysosomal fraction of the cell. It is strongly inhibited by bile salts at concentrations as low as 0.2-0.5% and conversely, is strongly activated by Triton X-100, with maximum stimulation found at a concentration of approximately 1%. The apparent Vmax for hydrolysis of labeled retinyl ester in the RPE is 2.7 nmoles/hr/mg protein, a value approximately 1/150 to 1/200 of the rate of retinol esterification in these cells. Little or no hydrolytic activity could be detected in neural retina or in rod outer segments. Studies on the specificity of the RPE retinyl ester hydrolase activity revealed unexpectedly high hydrolytic activity toward both cholesteryl oleate and triolein, approximately 20 and 5 times greater, respectively, than in rat liver. The hydrolytic activity for cholesteryl oleate in the RPE was mainly at pH 3.5, while that for triolein showed three pH maxima, one at pH 4.5-5.0, a second near neutral pH and the third at pH 8. These findings reflect an active and complex pattern of fatty acyl ester lipid-metabolizing enzymes in cattle RPE whose interrelationships to one another require further clarification.

Animals↗
PubMed1979

Subcellular distribution of free and esterified forms of vitamin A in the pigment epithelium of the retina and in liver.

1. The distribution of vitamin A was examined in various subcellular fractions of rat liver and bovine retinal pigment epithelium. In rat liver, the major portion of the vitamin is in the cytosol, whereas in pigment epithelium, it is concentrated mainly in the microsomes. The microsomal vitamin A of pigment epithelium is tightly bound to membranes, as shown by the inability to release it except by organic solvent extraction or incubation with Triton X-100. 2. In both tissues, two different forms of cytosol vitamin A could be distinguished by ultracentrifugation. The major portion in liver is in the floating lipid phase and consists mainly of retinyl ester. The remainder (less than 10% of the total) is in the underlying infranatant; about 90% of the vitamin A in this fraction is esterified. By contrast, two-thirds of the vitamin A of pigment epithelial cell cytosol is in the infranatant; it consists of both esterified and unesterified retinol. The floating layer in the pigment epithelial cytosol consists entirely of retinyl ester. 3. These two forms of cytosol vitamin A in the pigment epithelium could also be separated by gel filtration on Sephadex G-100 which yielded two distinct fluorescent peaks. The first, which appeared in the void volume and corresponded in all probability to the floating layer obtained by ultracentrifugation, consisted only of retinyl ester. The second peak, which was eluted in approximately the same position as myoglobin, contained only unesterified retinol. It was abolished completely by preincubation with pronase. These findings support the view that the second peak represents the endogenous retinol-retinol binding protein complex of pigment epithelial cytosol. The fluorescent enhancement of the retinol bound to protein in this peak was about 4--5-fold compared to retinol in organic solvents.

Animals↗
PubMedDate not supplied

[The geographic environment--a risk factor in eyelid tumors?].

The paper shows the role of the geographical environment in the incidence of various ophthalmological diseases and tries to make connections between different factors of pollution and the appearance of cancer, using epidemiological data. In Bihor district, the analysis of ocular tumors during a 25 years period shows 34 cases of malignant melanoma, 6 cases of glioma, 14 epibulbar malignant tumors opposing to 487 palpebral tumors, 3 tumors of the lacrimal sac and 8 cases of trichoepithelioma. Histopathologically, 173 of them were spinal cell epithelioma, 210 were basal cell epithelioma, 48 were sudoriferous, 40 were non-differentiated and 16 16 were mixed forms. The authors propose the district distributed study of the morbidity of various ocular diseases, which lead to the achievement of an ophthalmo-geography.

Age Factors↗
PubMedDate not supplied

[Obesity as a risk factor in diabetic retinopathy].

The relations between the glucidic and lipidic metabolism fatness and diabetes are known for a long time. The fatness as a factor of risk for the diabetic retinopathy and consecutively for the appearance of the cecity have less been studied. There are studied the variations of lipids, cholesterol, the fatness (for 3 degrees by Broca) for a group of diabetic patients, type I or II, the age of the patients (between 18-80 years old) there are presented the retinal modifying: arterial, venous, microaneurysm, haemorrhages, the macular modifying. In comparison to the normoponderal diabetic patients, for these who are fat patients especially I or II degree, all the modifying are exaggerated. There was chosen the fatness from the lots of the factors of diabetes'risk, because I think it may be influenced. The treatments of retinopathy are few and less encourage. The doxium and the photocoagulation could eventually make the cecity to be late but they belong to the group of treatment, but it is not a prophylactic element for cecity. The real prophylaxis has to begin since the childhood with a normocaloric food diet. The prophylaxis of the diabetes is the true prophylaxis of the cecity.

Diabetes Complications↗
PubMedDate not supplied

[Hyphema, a risk factor in the glaucomatous eye].

A hemorrhage in the anterior chamber is a frequent phenomenon, very often treated too easily. Our investigation followed for 3 years (1985-1987) the way in which hyphema were resorbed after the eye contusions in the patients operated by cataract or glaucoma. The causes of hyphemas, their onset, the aspect of the blood and the resorption period are analyzed. The majority of hyphemas were resorbed in the first 7 days (in the case of contusions 87%, after operation of cataract 84%) but in the glaucomatous patients the resorption in the first 7 days appeared only in 50% of the cases; the blood remained in the anterior chamber in 12.5% of cases even after 21 days. The blood in the anterior chamber is resorbed by the excretory ducts, mainly as intact erythrocytes; in the glaucomatous patients the ducts are altered and the erythrocytes are more difficulty eliminated. The liquid in the anterior chamber is eliminated by the fistulization opening, but the erythrocytes do not pass as they cannot be resorbed in the subconjunctival space. The blood in the anterior chamber of an eye with ocular hypertension (decompensated glaucoma or contusions with hypertension) favours the hematic impregnation of the cornea, and the macrophages loaded with hemosiderin are deposited at the level of the excretory ducts, thus increasing the danger of hemolytic secondary glaucoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Cataract↗
PubMedDate not supplied

[Is it possible to give genetic counseling in pigmentary retinopathy?].

The author tries to change the opinion still prevailing today according to which any pigmentary retinopathy may represent a handicap to the descendants. Pigmentary retinopathy may have several etiologies--hereditary, sex-linked, dominant autosomal or recessive autosomal, metabolic, within the framework of various mucopolysaccharidoses, secondary post inflammatory or post traumatic. Hereditary transmission is discussed recalling for isolated cases the empirical calculus of H. Maumenee on 1000 Swiss families. Genetic advice, the same as other medical prognosis must form integral part of clinical medical practice. Genetic advice must be based on perfect knowledge of the patient and his family, yet the final decision remains with the family.

Adult↗