No abstract

Several glucagon analogs were synthesized in an effort to find derivatives that would bind with high afflinity to the glucagon receptor of rat liver membranes but would not activate membrane-bound adenylate cyclase and, therefore, would serve as antagonists of the hormone. Measurements on a series of glucagon/secretin hybrids indicated that replacement of Asp9 in glucagon by Glu9, found in secretin, was the important sequence difference in the N terminus of the two hormones. Further deletion of His' and introduction of a C-terminal amide resulted in des-His'-[Glu']glucagon amide, which had a 40% binding affinity relative to that of native glucagon but caused no detectable adenylate cyclase activation in the rat liver membrane. This antagonist completely inhibited the effect of a concentration of glucagon that alone gave a full agonist response. It had an inhibition index of 12. The pA2 was 7.2. An attempt was made to relate conformation with receptor binding. The peptides were synthesized by solid-phase methods and purified to homogeneity by reverse-phase high-performance liquid chromatography on C18-silica columns.Due to the renewed interest in the role ofglucagon in diabetes and the maintenance of normal blood glucose levels (1), the development of antagonists of glucagon has become increasingly important. The recent discoveries of dual cell membrane binding sites for glucagon and secretin, which lead not only to the activation of adenylate cyclase but also to stimulation ofthe hydrolysis ofphosphatidylinositol bisphosphate and the events that follow, have already demonstrated the value of selective analogs of these hormones (2, 3). Our initial efforts to design potential antagonists of glucagon, based on the synthesis of replacement analogs with altered peptide chain conformation, led to some derivatives that were completely inert toward activation of adenylate cyclase in the liver plasma membrane but retained weak binding affinity and could be demonstrated to reversibly inhibit the action of glucagon (4). Our next approach to the search for antagonists was based on the idea that secretin, which has significant homology with glucagon but does not bind to the glucagon receptors of the hepatocyte (5), may have evolved from glucagon or a common precursor by a series of steps such that the intermediates retained significant affinity for the glucagon receptor but lost the ability to transduce the signal to activate adenylate cyclase (6). If that were true, hybrids of secretin and glucagon might have the desired properties. A comparison of the structure of secretin relative to that of glucagon shows only three sequence changes in the first 12 N-terminal residues: Asp3 for Gln3, Glu9 for Asp9, and Arg12 for Lys12. Initial studies showed that the synthetic hybrids [Asp3,Glu9,Arg12]glucagon and [Asp3,Glu9]glucagon were totally inactive (<0.001%) in terms of cAMP production but retained approximately 2% of glucagon binding affinity and could completely inhibit a concentration of glucagon that alone gave a maxim...

No abstract

This cohort study investigates the presence of COVID-19 vaccine mRNA in the expressed breast milk of lactating individuals who received the vaccination within 6 months after delivery.

Polybrominated diphenyl ether(s) (PBDE) are ubiquitous environmental contaminants that bind and cross the placenta but their effects on pregnancy outcome are unclear. It is possible that environmental contaminants increase the risk of inflammation-mediated pregnancy complications such as preterm birth by promoting a proinflammatory environment at the maternal-fetal interface. We hypothesized that PBDE would reduce IL-10 production and enhance the production of proinflammatory cytokines associated with preterm labor/birth by placental explants. Second trimester placental explants were cultured in either vehicle (control) or 2 μM PBDE mixture of congers 47, 99 and 100 for 72 h. Cultures were then stimulated with 106 CFU/ml heat-killed Escherichia coli for a final 24 h incubation and conditioned medium was harvested for quantification of cytokines and PGE2. COX-2 content and viability of the treated tissues were then quantified by tissue ELISA and MTT reduction activity, respectively. PBDE pre-treatment reduced E. coli-stimulated IL-10 production and significantly increased E. coli-stimulated IL-1β secretion. PBDE exposure also increased basal and bacteria-stimulated COX-2 expression. Basal, but not bacteria-stimulated PGE2, was also enhanced by PBDE exposure. No effect of PBDE on viability of the explants cultures was detected. In summary, pre-exposure of placental explants to congers 47, 99, and 100 enhanced the placental proinflammatory response to infection. This may increase the risk of infection-mediated preterm birth by lowering the threshold for bacteria to stimulate a proinflammatory response(s).