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Biomedical subjects

S Zakarian

Publications and source records attributed to S Zakarian.

At least 19 recordsLinked to original sources
PubMed1989

Regulation of pro-opiomelanocortin biosynthesis and processing by transplantation immunity.

It is more than thirty years since Billingham and Medawar showed that adrenocorticotrophic hormone (ACTH) and cortisol can prolong the survival of skin allografts. It has since become clear that glucocorticoid hormones are critically involved in the regulation of immunity. The level of glucocorticoids secreted in response to antigenic challenge corresponds to the magnitude of the immune response and in general reaches immunosuppressive levels. Interestingly, not all immune responses enhance ACTH and glucocorticoid hormone production. In transplantation immunity, the reverse seems to be true: circulating glucocorticoid levels at the time of skin graft rejection are lower than control levels. Because beta-endorphin and ACTH originate from the same prohormone, pro-opiomelanocortin (POMC), and are closely related in their tissue-specific processing and coordinate release, we have investigated the role of pituitary beta-endorphin in transplantation immunity. We report here that POMC biosynthesis and processing in the pars intermedia, but not in the anterior pituitary, can be regulated by T cell-specific factors secreted in animals undergoing transplantation immunity.

Animals↗
PubMed1987

Distribution of the C-terminal glycopeptide of the vasopressin prohormone in rat brain: an immunocytochemical study.

The distribution of the C-terminal glycopeptide of the vasopressin prohormone was mapped in rat brain by an immunocytochemical method using antibodies to the sheep glycopeptide. The antibodies did not react with vasopressin, oxytocin or their related neurophysins. Stained neural perikarya were observed in the hypothalamus (suprachiasmatic, paraventricular, and supraoptic nuclei) and in the bed nucleus of the stria terminalis. Fibres were detected in the hypothalamus and in extrahypothalamic regions (the frontal cortex, the lateral septum, the bed nucleus of the stria terminalis, the medial nuclei of the thalamus, the lateral habenula, the amygdala, the mesencephalic central gray, the raphe nucleus of the solitary tract and the cervical spinal cord). The distribution of glycopeptide immunoreactive cells was generally similar in young rats (8 weeks old) to the distribution in older rats (13 weeks old) except in the bed nucleus of the stria terminalis where stained neurons were relatively sparse or absent in the younger animals. Similarly, in the young rats the density of fibres containing the glycopeptide was reduced in territories innervated by the bed nucleus. In both young and old rats the neuronal distribution of the glycopeptide was identical to the distribution of vasopressin, which suggests that the glycopeptide and vasopressin are co-transported from the sites of biosynthesis to the sites of release.

Aging↗
PubMed1982

Distribution of beta-endorphin-related peptides in rat pituitary and brain.

beta-Endorphin, the most potent known naturally occurring analgesic agent, is found in pituitary and brain in company with a series of structurally and biosynthetically related peptides that are essentially devoid of opiate activity. In studies of beta-endorphin it is important to discriminate between the active and inactive forms of the peptide. This review describes the use of chemical and immunological methods for localizing the peptides in the tissues, extracting and resolving the peptides by chromatography, and determining the concentrations of the peptides by radioimmunoassay. These approaches have allowed the distribution of beta-endorphin and its related peptides to be assigned unequivocally in regions of rat pituitary and brain. It has been found that the multifunctional corticotropin-endorphin prohormone can undergo processing by different mechanisms in different tissues, permitting the intrinsic activities of its fragments to be expressed selectively. The different processing patterns can be attributed to the existence of highly specific enzymes, characteristic of individual cells, which regulate the formation of this potent opiate.

Amino Acid Sequence↗
PubMed1982

Immunocytochemical localization of beta-endorphin (lipotropin C-fragment) in the developing rat spinal cord and hypothalamus.

Immunocytochemical studies have been performed on rat spinal cord and hypothalamus during development, using an antibody to beta-endorphin. Specific immunoreactivity was demonstrated in histological sections of spinal cord, in ventral and dorsal horn cells and nerve fibres, in the meningeal layer, the ependymal lining of the central canal, and in the endothelium of the ventral spinal artery and other blood vessels. beta-Endorphin immunoreactivity was also distributed widely in neurones, central and peripheral nerve fibres, and in non-neuronal cells in cultures of spinal cord tissue explanted from rat embryos 7--10 days before birth. Immunofluorescence disappeared abruptly after the 28th postnatal day in vivo, and in the fourth week of incubation of embryonic spinal cultures. In contrast, cultures of the ventral diencephalic (hypothalamic) region of embryonic brain at the same gestational age showed a characteristically different pattern of beta-endorphin immunoreactivity which persisted for more than 7 weeks. The results provide evidence for the biosynthesis of a beta-endorphin-like peptide in rat spinal cord during development. The biosynthesis terminates at an early stage both in vivo and in vitro, suggesting that control of the biosynthesis is intrinsic to spinal cord tissue and possibly to the peptide-producing cells themselves.

Acetylcholinesterase↗
PubMed1981

Beta-endorphin-related peptides in the pituitary gland: isolation, identification and distribution.

A new procedure is described for isolation of four forms of beta-endorphin from bovine pituitary. The four peptides are: the C-fragment of lipotropin (bovine lipotropin residues 63-93, or beta-endorphin, the alpha, N-acetyl derivative of the C-fragment, the C'-fragment (bovine lipotropin residues 63-89) and the alpha, N-acetyl derivative of the C'-fragment. Of these peptides, beta-endorphin alone possesses potent analgesic activity. The procedure has been applied in studying the distribution of beta-endorphin-related peptides in two regions of the pituitary. The results show that in the anterior pituitary of the pig and the rat, beta-endorphin is produced with a high degree of specificity in its opiate active form. In contrast, in the pars intermedia of both species at least six peptides related to beta-endorphin are elaborated and beta-endorphin represents only a minor component. The principal peptides in the pars intermedia have been identified as acetylated derivatives of lipotropin C'-fragment: in the pig the predominant peptide is alpha,N-acetyl C'-fragment and in the rat the major peptide appears to be an epsilon-acetylated derivative of alpha,N-acetyl C'-fragment. Thus, beta-endorphin is activated in the anterior pituitary and inactivated in the pars intermediate. The results demonstrate selective and specific processing of the 31K ACTH-endorphin prohormone in the different regions of the pituitary. In the anterior pituitary two biologically active peptides, ACTH and beta-endorphin, are generated together; in the pars intermedia alpha-melanotropin (alpha-MSH) is accompanied by forms of beta-endorphin that have been inactivated by acetylation and proteolysis.

Analgesia↗
PubMed1980

Selective processing of beta-endorphin in regions of porcine pituitary.

The prohormone of beta-endorphin is unusual in that it is the precursor of more than one biologically active peptide (Fig. 1). The activation of this prohormone, to produce corticotropin (ACTH), alpha-melanotropin (alpha-MSH) and beta-endorphin, would seem to be relatively complex as its processing pattern is known to differ between tissues. Thus ACTH is produced in the anterior pituitary whereas alpha-MSH is formed in the pars intermedia; similarly, lipotropin and beta-endorphin seem to predominate in the anterior pituitary whereas beta-endorphin alone has been thought to be the principal component in the pars intermedia. We report here a study of the distribution of beta-endorphin-related peptides in various regions of porcine pituitary. The main products in the anterior pituitary were lipotropin and the potent analgesic form of beta-endorphin, whereas the main products in the pars intermedia were the inactive lipotropin C'-fragment and its N-acetyl derivative. Thus the processing of the C-terminal region of the beta-endorphin prohormone differs markedly between the two regions of porcine pituitary.

Animals↗
PubMed1979

Distribution of active and inactive forms of endorphins in rat pituitary and brain.

The recent isolation and identification of alpha-N-acetyl forms of the C-Fragment of lipotropin (beta-endorphin, residues 61-91) and the C'-Fragment (residues 61-87) [Smyth, D.G., Massey, D.E., Zakarian, S. & Finnie, M. (1979) Nature (London) 279, 252-254] has led to a study of their distribution in the pituitary and brain of the rat. Regions were mapped by the method of immunofluorescent staining and the reactive peptides were determined by immunoassay after extraction, gel filtration, and ion exchange chromatography. The major immunoreactive peptides in both lobes of the pituitary were found to be C'-Fragment and N-acetyl C'-Fragment, which are weakly active or inactive as opiates; the C-Fragment and its N-acetyl derivative represented minor components. This indicates that in the rat the circulating "endorphins" released from pituitary would have little morphinomimetic activity. The same four immunoreactive peptides were observed in rat brain. In the hippocampus the C'-Fragment was the principal component in the midbrain there was more C-Fragment but C'-Fragment predominated; in the hypothalamus the C-Fragment was the major peptide, almost to the exclusion of the other peptides. The results demonstrate that the processing of lipotropin is under differential control in anatomically distinct regions of the central nervous system. The processing of lipotropin in the hypothalamus is directed specifically to the production of lipotropin C-Fragment.

Amino Acid Sequence↗
PubMed1972

Studies on normal and immune lymphocyte transfer reactions in guinea pigs, with special reference to the cellular contribution of the host.

Using guinea pigs of strains 2 and 13 and their F(1) hybrids as experimental subjects, various lines of evidence have been obtained that in this species, as in all others tested, the only significant cellular antigens with which donor lymphocytes engage when normal and immune lymphocyte reactions are incited are radiosensitive leukocytes. Constitutive cells of the skin are unimportant. (a) The intensities of these reactions in irradiated subjects are dependent upon the peripheral leukocyte concentration. When this falls below a certain threshold no reactions are incitable. (b) Highly leukopenic animals are capable of developing immune lymphocyte transfer (ILT) reactions if normal lymphoid cells of their own genetic constitution are mixed with the putative attacking donor cells, as "supplementing antigen," before inoculation. (c) Radiation-chimeric strain 13 animals having F(1) hybrid leukocytes in their bloodstream give typical ILT reactions when challenged intradermally with strain 13 anti-2 node cells. Exposure of strain 2 animals to 600 R does not prevent their becoming actively immunized if, 24 hr later, they are injected intradermally with strain 13 lymphocytes. However, this sensitization, revealed by the host's capacity to give delayed hypersensitivity reactions, wanes as leukopenia progresses. On the basis of this and other findings it is argued that the flare-up stage of the NLT reaction in preirradiated hosts is mainly an expression of host sensitivity against the transferred alien cells. Two unexpected observations have been made in the course of this study: (a) F(1) hybrid animals developed what appeared to be a strong delayed hypersensitivity after intradermal inoculation with parental strain lymphoid cells or antigenic extracts prepared from them. (b) If strain 13 guinea pigs which had been sensitized against strain 2 tissue antigens by intradermal injection of lymphocytes 7 days beforehand were inoculated intravenously with strain 2 antigenic extract a significant proportion of the animals developed severe delayed necrotizing reactions, recall flares, at some or all of the healed skin inoculation sites.

Animals↗