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Biomedical subjects

S Levine

Publications and source records attributed to S Levine.

At least 451 records · Page 25Linked to original sources
PubMed1980

Regulation of platelet arachidonic acid oxygenation by cyclic AMP.

Intracellular cyclic adenosine monophosate (AMP) levels regulate the generation of thromboxane by platelets by inhibiting the hydrolysis of arachidonic acid from membrane phospholipids. However, there is conflicting evidence regarding the role of cyclic AMP in the control of the subsequent oxygenation of arachidonic acid by cyclooxygenase. We studoed the regulation of cyclooxygenase activity by agents that elevate platelet cyclic AMP (dibutyryl cyclic AMP and prostaglandins), measuring arachidonate-induced aggregation, O2 consumption, and malonaldehyde formation. In platelet-rich cyclic AMP. This inhibitory effect of cyclic AMP was absent in gel-filtered platelets suspended in buffer containing 0.5% albumin, and was progressively restored as plasma was added in increasing concentrations. Increasing the albumin concentration in platelet buffer suspensions likewise increased the ability of cyclic AMP to block the arachidonate-induced O2 burst and MDA production. We conclude that (1) the presence of plasma proteins is important in investigating platelet plasma milieu or at least in the presence of physiologic albumin concentrations.

Arachidonic Acids↗
PubMed1980

Experimental allergic encephalomyelitis. Inhibition of clinical signs and paradoxical enhancement of lesions in second attacks.

Experimental allergic encephalomyelitis (EAE) was induced in rats by immunization with neural antigens, with or without adjuvants. A second attack was induced after an interval of 3-24 weeks. When the second attack was produced by moderately intense active immunization or by passive transfer, the rats were protected from clinical signs. Paradoxically, the second attack regularly produced more lesions in the cerebellum than in naive contols. Inhibition of clinical signs and the accompanying paradoxical enhancement of cerebellar lesions were independent of the type of antigen or adjuvant used for either attack, the severity of the attacks, and the time interval between them. Nor did non-specific adrenal-mediated stress play any role in these phenomena. Even in the absence of clinical signs, the second attack produced many lesions in the spinal cord, but these were sometimes less severe than those produced in naive controls. The observation that an initial attack of EAE had different influences on susceptibility to a second attack in different parts of the nervous system is more readily explained by local tissue factors than by systemic regulatory influences.

Adjuvants, Immunologic↗
PubMed1979

Mother-infant separation in group-living rhesus macaques: a hormonal analysis.

Adrenocortical responsiveness to separation in group-living rhesus macaque mother-infant pairs was determined. Cortisol evaluations were complemented by behavioral observations of mother-infant interactions and group social behavior. Infants, but not their mothers, showed cortisol elevations that could be attributed specifically to separation. Steroid-behavior relationships suggested that the infants of high dominant mothers evinced the greatest adrenocortical response to separation. These data exemplify the complexities involved in determining endocrine/behavior relationships in a group-living situation.

Animals↗
PubMed1979

Long-term consequences of early iron deficiency in the rat.

A period of severe early iron deficiency (birth to 28 days of age) produced a persistent deficit (22%) in brain non-heme iron in adult rehabilitated animals. Long-term effects on behavior and physiological responsiveness were also observed. Although rehabilitated and control animals did not differ either in basal levels of plasma corticosterone or in the time course of the stress response following ether and cardiac puncture, possible differences in pituitary-adrenal responsiveness appeared to emerge following testing in an exploratory task. In addition, significant differences between rehabilitated and control animals were observed in both active and passive avoidance learning. Rehabilitated males made more intertrial responses than control males during active avoidance learning, and rehabilitated animals of both sexes performed better (i.e. showed longer reentry latencies) in a passive avoidance situation. It was suggested that shock may differentially affect motivation or arousal in rehabilitated and control animals.

Animals↗
PubMed1979

Schedule-induced polydipsia suppresses pituitary-adrenal activity in rats.

The effects of schedule-induced polydipsia (SIP) on pituitary-adrenal activity, as indicated by plasma levels of corticosterone, were examined in a series of experiments. Male (Experiments 1 and 3) and female (Experiment 2) rats were reduced to 80% of their free-feeding weight and given daily sessions on an intermittent-feeding schedule (fixed time of 60 sec). Half of the subjects in each experiment had water available during experimental sessions and the other half did not. Animals with water available in the experimental chamber exhibited SIP in all three experiments. In Experiment 1, blood samples were collected following (a) food consumption in the home cage, (b) a session on FT 60 sec, and (c) a session with pellets available in a cup in the experimental chamber. In Experiment 2, blood samples were taken prior to and following an FT 60-sec session, and following a session with pellets available in a cup in the chamber. In Experiment 3, pre- and postsession samples were obtained as in Experiment 2 (Part A). Subsequently, the opportunity to drink during sessions was removed, and the effect on corticoids was examined (Part B). The results indicate that (a) schedule-induced drinking suppresses pituitary-adrenal activity, (b) corticoid suppression may become a conditioned response to drinking in the chamber, and (c) corticoids return to presession levels following removal of water from the chamber. In view of these findings, it is hypothesized that SIP may serve an arousal-reducing role in intermittent-feeding situations.

Animals↗
PubMed1979

Fine structure of contrasting choroid plexus lesions caused by tertiary amines or cyclophosphamide.

Hydropic alterations of the fine structure of the choroid plexus epithelium following administration of three different tertiary amines to rats were compared with alterations produced by cyclophosphamide and with normal choroid plexus. Single doses of 2,7-bis(2-diethylamino)-ethoxy)-4-methyl-1,8-naphthyridine HCl or 2,6-di-(omega-dimethyl aminoethoxy)-pyridine produced dramatic accumulations of membrane-limited vacuoles. Multiple doses of 2,7-bis-(diethylaminoethoxy)fluoren-9-one HCl (tilorone) produced accumulations of dense cytoplasmic bodies in choroid epithelial cells in addition to the hydropic vacuoles. Differential responses to these agents suggested functional specialization or temporal variation in function among adjacent choroidal cells. Despite the occurrence of pronounced plasma exudation in the plexitis following cyclophosphamide treatment, there was no hydropic vacuolization.

Animals↗