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J Bernal

Publications and source records attributed to J Bernal.

14 recordsLinked to original sources
PubMed1979

Complement activation by parasites. A review.

Activation of complement by parasites (living parasites or purified parasite antigens) is involved in several mechanisms of the host parasite relationship. In most of the experiments performed in vitro, complement activation was found to be lethal for the parasites, but sometimes it could be essential for the development of parasitemia. Both classical and alternative complement pathways may be activated by parasites; the classical pathway nearly always requires the involvement of antibodies whereas the alternative pathway is activated directly by products released by the parasites or present in their teguments. Activation of complement, especially via the alternative pathway may also be a prerequisite for cellular adherence to parasites which can then cause their death.

Animals↗
PubMed1978

Thyroid hormone receptors from liver nuclei: characteristics of receptor from normal, thyroidectomized, and triiodothyronine-treated rats; measurement of occupied and unoccupied receptors, and chromatin binding of receptors.

The capacity and characteristics of liver nuclear receptors for T3 have been compared in normal rats, thyroidectomized rats, and thyroidectomized rats treated with different doses of T3. Receptor capacity was unchanged, with the exception of a decrease of total nuclear receptors in rats treated with 15 microgram T3/day, which is believed due to lack of complete dissociation of the endogenously bound hormone during incubation in vitro. During incubation of the isolated nuclei in 0.32 M sucrose plus 1 mM MgCl2 plus 20 mM Tris-Cl buffer, pH 7.85, about 50% of the nuclear receptors were released to the medium and no effect of T3 treatment on the amount released was found. The affinity of the receptors free in solution was 50% higher than that of receptors retained in the nuclei. Receptors from normal and thyroidectomized rats were studied by ultracentrifugation through sucrose gradients. No difference in sedimentation coefficient was found between the groups of rats, whether the receptors were filled with the labeled hormone before or after centrifugation and separation of the gradient fractions. Occupied and unoccupied receptor capacity was estimated by incubation of receptor preparations at 20 and 0 C for 2 h. Observed capacity at 20 C represents unoccupied plus approximately 80% of occupied sites, while observed capacity at 0 C represents unoccupied plus 10% of occupied site. Binding of receptors to the chromatin was studied by incubating nuclear extract from normal rats with chromatin and measuring the amount of receptor that was not bound and remained free in the supernatant. Receptor not bound to chromatin was incubated at 0 and 20 C, with a saturating concentration of [125I]T3, to measure occupied and unoccupied sites. Both occupied and unoccupied receptor decrease in the supernatant after incubation with the chromatin when the concentration of chromatin in the incubation medium is increased. No saturation of the chromatin-binding sites was achieved by increasing the concentration of receptor several-fold, and no difference in the binding of occupied and unoccupied receptors to chromatin was observed. These data rule out the possibility that the concentration of receptors in the nucleus is under control of the hormone. Major molecular changes of the receptor that could be induced by T3, such as dissociation into subunits, are also ruled out. Binding studies to the chromatin are not necessarily conclusive, as nonspecific binding may be masking the physiological binding of the receptors to a limited number of acceptor sites.

Animals↗
PubMed1978

Abnormalities of triiodothyronine binding to lymphocyte and fibroblast nuclei from a patient with peripheral tissue resistance to thyroid hormone action.

T3 binding to lymphocyte nuclei has been studied in normal individuals and in a patient (MaG) with peripheral resistance to thyroid hormone action. This syndrome is defined by the presence of hypothyroidism or euthyroidism with high plasma levels of thyroid hormone. T3 bound to a single set of binding sites in normal adult lymphocyte nuclei with a mean Ka of 8.9 +/- 7.1 x 109 M-1, and a capacity of 4.4 +/- 2.9 fmol/100 micrograms DNA. A single binding site was also disclosed in MaG's lymphocytes with a Ka of 0.43 x 109 M-1 and a capacity of 10.5 fmol/100 micrograms DNA. This low affinity was not due to the presence of high plasma T3 level in the patient, since administration of 100 micrograms T3 to normal adult volunteers induced the presence of two different binding sites. The mechanism responsible for this phenomenon is unknown. To binding was also studied using cultured fibroblasts which were incubated in serum-less medium before the binding experiments. One single binding site (Ka, 1.9 x 10(10) M-1, capacity, 12.9 fmol/100 micrograms DNA) was detected in normal fibroblast nuclei. In contrast, a curvilinear Scatchard plot was obtained when MaG's fibroblasts were used. This result could be compatible with the presence of either two different binding sites or negative cooperativity. In support of the latter possibility, Hill plots gave a number lower than unity. The results suggest that the syndrome of peripheral tissue resistance to thyroid hormone action due to a defect at the level of the nuclear receptor. The possible existence of similar syndromes due to an alteration at the level of a post-T3-binding mechanism is not eliminated.

Adolescent↗
PubMed1978

[The experience in dental education of Cayetano Heredia University of Peru].

This article describes the educational experience gained in the dentistry program of Cayetano Heredia University in Peru. The programs for professional and auxiliary personnel training were drawn up after analyzing the health needs of the population and the services required to meet them, which resulted in the elaboration of an original methodology and taxonomy. Learning is an integral experience, one that takes place in the dental clinic, the hospital, and the community. The curriculum includes the following components: units for the intensive learning of clinical functions, fewer preclinical activities, clinical training with the ongoing assistance of auxiliary staff, extended interaction with marginal urban communities, rural internships, and hospital externships. A summary account is given of the gains made, the difficulties encountered, and plans for devising in-service teaching approaches that more effectively meet the needs of the community.

Community Dentistry↗
PubMed1977

The action of thyroid hormone.

Thyroid hormone affects both developmental and metabolic processes. It has a relatively specific effect on the synthesis of a number of enzymes and other proteins. The fundamental cellular mechanism of action seems to be at the level of genetic regulation. It involves interaction with nuclear receptors, leading to an activation of the protein synthesizing machinery. How binding to receptors is coupled to genetic activation is completely unknown. At least part of the metabolic effects of thyroid hormone could be mediated through an interaction with mitochondria and cell membrane, and with some enzymatic systems such as adenylcyclase.

Animals↗
PubMed1977

Thyroid hormone receptors: release of receptor to the medium during in vitro incubation of isolated rat liver nuclei.

Isolated rat liver nuclei show a substantial amount of T3 receptor release to the medium during in vitro incubation. This has been shown to be a general feature of nuclei compared after several methods of isolation and incubation. About 50% of nuclear receptors are released to the medium when incubated in sucrose-MgCl2-Tris, pH 7.85, for 2 h at 20 C.DNA, histones, and non-histone proteins (NHP) are also released. CaCl2 inhibits about 90% of the release of DNA and histones, but has less effect on inhibiting leakage of NHP and nuclear T3-binding protein (NTBP). The highest leakage for each fraction was found when incubating nuclei in the presence of EDTA. The receptor released to the medium has an affinity virtually identical to the receptor remaining in the nuclei. At least 1 mM dithiothreitol is needed to avoid degradation of the receptor. The NTBP has a sedimentation constant of 4.5 S when studied in low ionic strength gradients. Increasing KCl concentration decreases progressively its sedimentation constant, and in gradients containing 0.4 M KCl the receptor sediments as a single peak of 3.4 S. Since release of receptor to incubation medium decreases free T3 concentration, it must be taken into account in calculating receptor affinity. Total nuclear capacity in vitro is obviously underestimated, unless receptor released to medium is measured. Receptor exchange between cytosol and nucleus may be of physiologic significance.

Animals↗