Effects of GTP on binding of (3H) glucagon to receptors in rat hepatic plasma membranes.

In this study, we report the preparation of [3H]glucagon and its characteristics of binding to receptors in the rat liver plasma membrane. Binding of the labeled hormone is optimal at pH 7.0. In the absence of GTP, [3H]glucagon binding to receptors is slow and the time of equilibration is inversely proportional to the hormone concentration. In the presence of GTP, equilibrium is reached within 30 s regardless of hormone levels, and the kinetics of binding are in accord with the kinetics of activation of adenylate cyclase by native glucagon in the presence of the nucleotide. Equilibrium binding measurements indicate that, in the absence of GTP, the binding isotherm is sigmoidal with an apparent Kd of 2 nM. The addition of GTP results in a complex binding isotherm with about 90% of the binding sites having a considerably lower apparent dissociation constant (greater than 10 nM) and a small population of sites having high affinity for the hormone. The binding properties of [3H]glucagon are compared with those of 125I-glucagon, and the implications of the actions of GTP on glucagon binding are discussed in relation to the overall regulation of adenylate cyclase by hormone and the nucleotide.     

Activation by bacterial lipopolysaccharide causes changes in the cytosolic free calcium concentration in single peritoneal macrophages

Variations in the cytosolic free Ca2+ concentration [( Ca2+]i) upon LPS exposure were studied in single rat peritoneal macrophages loaded with fura-2 under carefully controlled conditions. Of a total of 60 cells examined, 47% responded to LPS (1 microgram/ml) with an increase in [Ca2+]i. Macrophages were heterogeneous with regard to the LPS response, with individual cells exhibiting single rapid and transient increases in [Ca2+]i, multiple transients, or slower and more sustained variations. In 62% of the responding cells, a second exposure to LPS elicited a [Ca2+]i rise, although usually to a slightly lower peak value. Thus, rapid desensitization to LPS does not occur in the majority of these macrophages. EGTA did not abolish the response of those cells that exhibited a single rapid transient in [Ca2+]i, indicating that the source of the initial [Ca2+]i rise was the intracellular stores. There was no obvious correlation between the type of response to LPS and the initial morphologic features (rounded vs polarized) of the cells. Our present work shows unequivocally that LPS induces increases in macrophage [Ca2+]i and, thereby, lends substantial support to the hypothesis that [Ca2+]i is a second messenger in LPS-mediated activation of the macrophage.     

A mass fragmentographic method for the quantitative evaluation of brain prostaglandin biosynthesis.

A method for the evaluation of PGF-2alpha and PGE-2 biosynthesis in rat cerebral cortex is described. Tissue slices were incubated without any added precursor for different lengths of time. The analytical procedure involves prostaglandin extraction, purification and quantitative determination by mass fragmentography. Significant amounts of both prostaglandins were synthesized. The biosynthesis reached a plateau after 30 minutes and the ratio of PGF-2alpha to PGE-2 was approximately 3.     

A mass fragmentographic method for the quantitative evaluation of brain prostaglandin biosynthesis

A method for the evaluation of PGF_2α and PGE₂ biosynthesis in rat cerebral cortex is described. Tissue slices were incubated without any added precursor for different lengths of time. The analytical procedure involves prostaglandin extraction, purification and quantitative determination by mass fragmentography. Significant amounts of both prostaglandins were synthesized. The biosynthesis reached a plateau after 30 minutes and the ratio of PGF_2α to PGE₂ was approximately 3.     

Circulating adiposity-related microRNAs as predictors of the response to a low-fat diet in subjects with obesity

Recent studies have revealed the critical role of several microRNAs (miRNAs) in energy homeostasis and metabolic processes and suggest that circulating miRNAs can be used as early predictors of weight loss in the design of precision nutrition. Thus, the aim of this study was to investigate circulating adiposity-related miRNAs as biomarkers of the response to two specific weight loss dietary treatments. The expression of 86 miRNAs was investigated in plasma of 78 subjects with obesity randomized to two different diets [moderately high-protein diet (n = 38) and low-fat diet (n = 40)] and in 25 eutrophic controls (BMI ≤ 25 kg/m²). Bioinformatic analyses were performed to explore the target genes and biological pathways regulated by the dysregulated miRNAs. As results, 26 miRNAs were found differently expressed in eutrophic and volunteers with obesity. Moreover, 7 miRNAs (miR-130a-3p, miR-142-5p, miR-144-5p, miR-15a-5p, miR-22-3p, miR-221-3p and miR-29c-3p) were differentially expressed between responders and non-responders to a low-fat diet. Furthermore, after adjustment for basal glucose levels, 1-SD increase in miR-22-3p expression was associated with reduction in the risk of non-response to low-fat diet [OR = 0.181, 95% CI (0.084-0.947), P = .043]. Bioinformatic analyses evidenced that these 7 miRNAs regulate the expression of genes participating in important metabolic pathways. Conclusively, 7 circulating miRNAs related to adiposity could be used for predicting the response to a low-fat diet intervention prescribed to lose weight.     

Developmental plasticity and evolutionary explanations

Developmental plasticity looks like a promising bridge between ecological and developmental perspectives on evolution. Yet, there is no consensus on whether plasticity is part of the explanation for adaptive evolution or an optional “add‐on” to genes and natural selection. Here, we suggest that these differences in opinion are caused by differences in the simplifying assumptions, and particular idealizations, that enable evolutionary explanation. We outline why idealizations designed to explain evolution through natural selection prevent an understanding of the role of development, and vice versa. We show that representing plasticity as a reaction norm conforms with the idealizations of selective explanations, which can give the false impression that plasticity has no explanatory power for adaptive evolution. Finally, we use examples to illustrate why evolutionary explanations that include developmental plasticity may in fact be more satisfactory than explanations that solely refer to genes and natural selection.