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Biomedical subjects

K B Mathur

Publications and source records attributed to K B Mathur.

48 records · Page 3Linked to original sources
PubMedDate not supplied

Effect of some novel synthetic analogues of CCK-4 on insulin and glucagon secretion.

The biologic activities of three synthetic analogues of CCK-4 (Trp-Met-Asp-Phe-NH2) in which (i) the C-terminal residue Phe was N-methylated (peptide I); (ii) the C-terminal Phe residue was N-methylated and Ser is substituted for Met in position 2 (peptide II); (iii) Pro was substituted for Trp in position 1 and the C-terminal amino nitrogen was methylated (peptide III), have been described. Peptides I and II have been found to inhibit the release of both insulin and glucagon, while peptide III was found to be a potent releasing agent for insulin and an inhibitor for glucagon.

Amino Acid Sequence↗
PubMedDate not supplied

Stimulation of insulin secretion by peptides analogous to the C-terminal tetrapeptide amide of cholecystokinin.

Two tetrapeptides, Glp-Met-Asp-Phe-NH2 (I) and Pro-Met-Asp-Phe-NH2 (II), analogous to the C-terminal tetrapeptide amide of cholecystokinin (CCK-4) have been synthesized and their effect on the release of insulin from the isolated Langerhans islets of rat pancreas compared with that of synthetic CCK-4. Both the new congeners exhibited significant insulin-releasing activity at 10(-8) M and 10(-6) M concentrations, suggesting that the biological activity is retained when the N-terminal Trp residue of CCK-4 is replaced by Glp or Pro.

Animals↗
PubMedDate not supplied

Synthetic analogs of cholecystokinin terminal tetrapeptide that stimulate insulin but not glucagon release from pancreatic islets.

Two synthetic analogs of CCK-4, Glp-Met-Asp-Phe-NH2 (I) and Pro-Met-Asp-Phe-NH2 (II) reported earlier to stimulate insulin release from the isolated rat pancreatic islets in vitro at concentrations as low as 10(-10) M, have now been found to be totally ineffective as glucagon releasers at concentrations as high as 10(-6) M or higher. It is evident that the replacement of Trp in CCK-4 by Glp and Pro residues leads to peptides which exhibit insulin releasing activity without stimulating the release of glucagon.

Animals↗
PubMedDate not supplied

Selective stimulation of insulin secretion by CCK-4 analogues having N-terminal modifications.

Synthetic analogues of CCK-4 in which Trp was replaced by D-Pro (peptide I), Thz (peptide II) and delta Pro (peptide III) have been studied for their insulin and glucagon releasing activities from the islets of Langerhans in vitro. Peptide I has been found to be the most potent insulin releaser among the three analogues and its activity is comparable to that of CCK-4. Unlike CCK-4, its three analogues (peptides I-III) do not stimulate the release of glucagon with basal concentration of glucose in the medium. However, with increasing glucose concentration, all the three analogues potentiate the glucose stimulus for insulin release.

Animals↗
PubMedDate not supplied

Lymphokines production by concanavalin A-stimulated mouse splenocytes: modulation by Met-enkephalin and a related peptide.

Methionine-enkephalin (ME) and its synthetic congener Tyr-D-Ala-Gly-Me-Phe-Gly-NH.C3H7-iso (82/205), in a concentration-dependent biphasic manner modulated the concanavalin A (Con A)-stimulated phagocytosis-promoting (PP)-activity elaboration in the culture supernatants of mouse splenocytes in vitro. Both these peptides at 1 x 10(-5) and 1 x 10(-6) M inhibited the production of PP activity; conversely, at 1 x 10(-7)-1 x 10(-9) M they augmented it. Peptide 82/205 was nearly 1.2-fold more inhibitory and approximately 1.8-fold more potent in augmenting the PP activity elaboration. The PP activity appeared to be due to lymphokines (LK) gamma interferon and interleukin-4 as the neutralizing concentrations of monoclonal antibodies against these LK significantly (p < 0.05) inhibited it. Cycloheximide (50.0 micrograms/ml) completely inhibited the production of LK indicating their de novo synthesis. The peptides appeared to exert their inhibitory and augmenting effects via delta- and mu-opioid receptors, respectively, as pretreatment of splenocytes with 100-fold higher (1 x 10(-3) M) concentration of naloxone was required to block their inhibitory effect; the augmenting effect was blocked by 1 x 10(-5) M only. None of the peptides or naloxone could directly stimulate the splenocytes for PP-LK elaboration.

Amino Acid Sequence↗
PubMedDate not supplied

Delta-opioid receptor antagonist inhibits immunomodulation by Met-enkephalin analogs.

The methionine-enkephalin (Met-enkephalin, Tyr-Gly- Gly-Phe-Met) analogs Tyr-D-Ala-Gly-MePhe-Met NHC(3)H(7)-iso (1) and Tyr-D-Ala-Gly-MePhe-Gly-NHC(3)H(7)-iso (2) have been shown to enhance human T cell proliferation in in vitro treatment. Their immunomodulatory activities were completely blocked by naloxone, an opioid antagonist. Now we demonstrate that a selective delta-opioid receptor antagonist, ICI-174,864, completely blocks enhancement of T cell proliferation by analogs (1) and (2). The T cell-stimulatory effect was only partially inhibited by the mu-receptor-selective antagonist, beta-funaltrexamine hydrochloride. The kappa-opioid receptor antagonist, nor-binaltorphimine dihydrochloride, showed no effect on T cell-proliferation stimulated by analogs (1) and (2). These observations suggest that analogs (1) and (2) of Met-enkephalin stimulate T cell proliferation predominantly via delta-opioid receptor present on T cells.

Adjuvants, Immunologic↗
PubMedDate not supplied

Molecular biology of opioid receptors: recent advances.

Endogenous opioid peptides and opiates like morphine produce their pharmacological effects through the membrane bound opioid receptors. These receptors belong to a superfamily of G-protein-coupled receptors, all of which possess seven membrane-spanning regions. Structure-activity relationship studies of opioids opened up new avenues for the pharmacological characterization of the opioid receptors. As a further advancement in this direction, molecular cloning has led to the identification of three different types of opioid receptors -- OP1 (delta), OP2 (kappa) and OP3 (mu) -- thereby supporting the results of earlier pharmacological studies which postulated their existence. The three opioid receptors are highly homologous. Consequent to the development of highly specific and selective agonists and antagonists, it was proposed that the three types of opioid receptors could be further categorized into different subtypes. However, the molecular biology data generated so far do not support the presence of the various subtypes of the three well-characterized opioid receptors. Recent strides towards the advancement of our knowledge relating to the molecular biology of these receptors have been reviewed in this article.

Animals↗
PubMedDate not supplied

Enkephalins-modulation of Plasmodium cynomolgi antigens-induced colony-stimulating factors elaboration by macrophages.

Methionine-enkephalin (M-Enk) and its analogue compound 82/205 (10(-5) and 10(-6) M) inhibited elaboration of Plasmodium cynomolgi total antigens soluble in culture medium (P.c.SA)-induced colony-stimulating factors (CSFs) by monkey blood monocyte-derived macrophages, in vitro. Paradoxically, lower concentrations (10(-7)-10(-9) M) of both the peptides greatly augmented CSFs elaboration; 82/205 appeared to be nearly 2.3-fold more potent. Naloxone (10(-5) M) pretreatment of macrophages inhibited only the M-Enk- and 82/205-induced enhanced CSFs elaboration, suggesting an opiate receptors-mediated mechanism of action. None of the peptides or naloxone (10(-5)-10(-9) M) had any direct effect on the CSF elaboration by unstimulated macrophages.

Animals↗