Age diminishes the testicular steroidogenic response to repeated intravenous pulses of recombinant human LH during acute GnRH-receptor blockade in healthy men

Testosterone (Te) concentrations fall gradually in healthy aging men. Postulated mechanisms include relative failure of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and/or gonadal Te secretion. Available methods to test Leydig cell Te production include pharmacological stimulation with human chorionic gonadotropin (hCG). We reasoned that physiological lutropic signaling could be mimicked by pulsatile infusion of recombinant human (rh) LH during acute suppression of LH secretion. To this end, we studied eight young (ages 19-30 yr) and seven older (ages 61-73 yr) men in an experimental paradigm comprising 1) inhibition of overnight LH secretion with a potent selective GnRH-receptor antagonist (ganirelix, 2 mg sc), 2) intravenous infusion of consecutive pulses of rh LH (50 IU every 2 h), and 3) chemiluminometric assay of LH and Te concentrations sampled every 10 min for 26 h. Statistical analyses revealed that 1) ganirelix suppressed LH and Te equally (> 75% median inhibition) in young and older men, 2) infused LH pulse profiles did not differ by age, and 3) successive intravenous pulses of rh LH increased concentrations of free Te (ng/dl) to 4.6 +/- 0.38 (young) and 2.1 +/- 0.14 (older; P < 0.001) and bioavailable Te (ng/dl) to 337 +/- 20 (young) and 209 +/- 16 (older; P = 0.002). Thus controlled pulsatile rh LH drive that emulates physiological LH pulses unmasks significant impairment of short-term Leydig cell steroidogenesis in aging men. Whether more prolonged pulsatile LH stimulation would normalize this inferred defect is unknown.     

Joint synchrony of reciprocal hormonal signaling in human paradigms of both ACTH excess and cortisol depletion

The hypothalamo-pituitary-adrenal axis is a stress-adaptive neuroendocrine ensemble, in which adrenocorticotropin (ACTH) drives cortisol secretion (feedforward) and cortisol restrains ACTH outflow (feedback). Quantifying direction- and pathway-specific adjustments within this and other interlinked systems by noninvasive means remains difficult. The present study tests the hypothesis that forward and reverse cross-approximate entropy (X-ApEn), a lag-, scale-, and model-independent measure of two-signal synchrony, would allow quantifiable discrimination of feedforward (ACTH --> cortisol) and feedback (cortisol --> ACTH) control. To this end, forward X-ApEn was defined by employing serial ACTH concentrations as a template to appraise pair-wise synchrony with cortisol secretion rates and vice versa for reverse X-ApEn. Coupled hormone profiles included normal ACTH-normal cortisol, high ACTH-high cortisol, and high ACTH-low cortisol concentrations in 35 healthy subjects, 21 patients with tumoral ACTH secretion, and 9 volunteers given placebo and a steroidogenic inhibitor, respectively. We used forward and reverse X-ApEn analyses to identify marked and equivalent losses of feedforward and feedback linkages (both P < 0.001) in patients with tumoral ACTH secretion. An identical analytical strategy revealed that ACTH --> cortisol feedforward synchrony decreases (P < 0.001), whereas cortisol --> ACTH feedback synchrony increases (P < 0.001), in response to hypocortisolemia. The collective outcomes establish precedence for pathway-specific adaptations in a major neurohormonal system. Thus quantification of directionally defined joint synchrony of biologically coupled signals offers a noninvasive strategy to dissect feedforward- and feedback-selective adaptations in an interactive axis.     

Evaluation of the flow-dialysis technique for analysis of protein-ligand interactions: an experimental and a monte carlo study

Flow dialysis has found widespread use in determining the dissociation constant (KD) of a protein-ligand interaction or the amount of available binding sites (E0). This method has the potency to measure both these parameters in a single experiment and in this article a method to measure simultaneously the KD and E0 is presented, together with an extensive error analysis of the method. The flow-dialysis technique is experimentally simple to perform. However, a number of practical aspects of this method can have a large impact on the outcome of KD and E0. We have investigated all sources of significant systematic and random errors, using the interaction between mannitol and its transporter from Escherichia coli as a model. Monte Carlo simulations were found to be an excellent tool to assess the impact of these errors on the binding parameters and to define the experimental conditions that allow their most accurate estimation.     

Lamellipodium-driven tissue reshaping: a parametric study

We recently showed that lamellipodia are able to generate forces of the right type to drive convergent extension (CE), an important class of tissue reshaping, in early stage embryos. The purpose of the present work is to quantify the mechanics of this process using parametric analyses. We use finite elements to implement a gamma-mu model in which a net interfacial tension gamma acts along each cell boundary and the cytoplasm exhibits an effective viscosity mu. The stress-strain characteristics of a rectangular patch of model tissue are investigated in terms of the rate r at which lamellipodia form and the relative strength q of their contractions. In tissues that are not constrained in-plane by adjacent tissues, the rate of tissue reshaping is proportional to r the rate of lamellipodium formation and its dependence on q is nonlinear and, near its expected value of 2 highly sensitive to q. Cell elongation, a central characteristic of CE, and stress is found to vary linearly with e the degree of kinematic restraint. Relevant "mechanical pathways" are also identified.     

Characterization of microsatellite DNA markers in a critically endangered species,Mekong giant catfish,Pangasianodon gigas

Microsatellite DNA markers for a critically endangered Mekong giant catfish (Pangasianodon gigas Roberts and Vidthayanon, 1991) were developed from fin clips collected from captive fish using (GT)₁₅ probe. The number of alleles per locus ranged from two to four. The expected heterozygosities ranged from 0.13 to 0.68. Also, these primers were successfully amplified in four closely related species, Pangasius bocourti, Pangasius conchophilus, Pangasius larnaudii and Pangasius sanitwongsei with the number of alleles per locus ranged from 1 to 13, 1 to 16, 1 to 12 and 1 to 4, respectively. These markers should prove to be very useful for the evaluation of genetic diversity for this species and other related Pangasius species.     

Conservation of copper-transporting P(IB)-type ATPase function

Copper-transporting P(IB)-type ATPases are highly conserved, and while unicellular eukaryotes and invertebrates have only one, a gene duplication has occurred during vertebrate evolution. Copper-induced trafficking of mammalian ATP7A and ATP7B from the trans-Golgi Network towards the plasma membrane is critical for their role in copper homeostasis. In polarized epithelial cells ATP7A and ATP7B traffic towards the basolateral and apical membranes respectively. We examined the localization and function of DmATP7, the single Drosophila melanogaster orthologue, in cultured D. melanogaster and mammalian cells to explore the conservation of P(IB)-type ATPase function. Comparative genomic analysis demonstrated motifs involved in basolateral targeting and retention of ATP7A were conserved in DmATP7, whereas ATP7B targeting motifs were not. DmATP7 expression was able to correct the copper hyper-accumulation phenotype of cultured fibroblasts from a Menkes disease patient expressing a null ATP7A allele. DmATP7 was able to transport copper to the cupro-enzyme tyrosinase and under elevated copper conditions DmATP7 was able to traffic towards the plasma membrane and efflux copper, essentially phenocopying ATP7A. When expressed in polarized Madin-Darby Canine Kidney cells, DmATP7 translocated towards the basolateral membrane when exposed to elevated copper, similar to ATP7A. These results demonstrate DmATP7 is able to functionally compensate for the absence of ATP7A, with important trafficking motifs conserved in these distantly related orthologues.     

Dynamic testosterone responses to near-physiological LH pulses are determined by the time pattern of prior intravenous LH infusion

The long-lived glycoprotein hormone, human chorionic gonadotropin (hCG), downregulates testosterone (T) biosynthesis in vitro and in vivo in animals and humans. The degree to which short-lived pulses of pituitary luteinizing hormone (LH) do so, particularly at physiological concentrations, is not known. We test the hypothesis that continuous LH infusion compared with bolus injections of LH every 1 h or every 2 h overnight downregulates T secretory responses to a subsequent fixed template of three consecutive intravenous pulses of a physiological amount of recombinant human (rh) LH (triple stimulus). Nineteen healthy men ages 18-49 yr each underwent four separate randomly ordered overnight gonadotropin-releasing hormone-receptor antagonist treatments with superimposed intravenous infusions of saline or rhLH (1-h pulses, 2-h pulses, or continuously). Each 12-h infusion protocol was followed by the triple rhLH-pulse stimulus the next morning. During the triple stimulus, basal (nonpulsatile) as well as total (basal plus pulsatile) T secretion was higher after overnight 2- and 1-h rhLH pulses than after continuous rhLH or saline delivery. Approximate entropy, a probabilistic measure of feedforward-induced irregularity of T concentration time series, was higher after 1-h rhLH pulses than after continuous rhLH. Analytical estimation of pulsatile rhLH-T dose-response measures revealed higher T secretory sensitivity and greater rhLH potency (lower EC(50)) after exposure to 1-h than 2-h rhLH pulses. Collectively, these data indicate that in vivo dynamics of LH-stimulated T secretion under standardized conditions in men depend on the prior time mode of LH delivery in the bloodstream.     

Prolactin secretion in healthy adults is determined by gender, age and body mass index

Background

Prolactin (PRL) secretion is quantifiable as mean, peak and nadir PRL concentrations, degree of irregularity (ApEn, approximate entropy) and spikiness (brief staccato-like fluctuations).

Hypothesis

Distinct PRL dynamics reflect relatively distinct (combinations of) subject variables, such as gender, age, and BMI.

Location

Clinical Research Unit.

Subjects

Seventy-four healthy adults aged 22–77 yr (41 women and 33 men), with BMI 18.3–39.4 kg/m².

Measures

Immunofluorometric PRL assay of 10-min samples collected for 24 hours.

Results

Mean 24-h PRL concentration correlated jointly with gender (P<0.0001) and BMI (P = 0.01), but not with age (overall R² = 0.308, P<0.0001). Nadir PRL concentration correlated with gender only (P = 0.017) and peak PRL with gender (P<0.001) and negatively with age (P<0.003), overall R² = 0.325, P<0.0001. Forward-selection multivariate regression of PRL deconvolution results demonstrated that basal (nonpulsatile) PRL secretion tended to be associated with BMI (R² = 0.058, P = 0.03), pulsatile secretion with gender (R² = 0.152, P = 0.003), and total secretion with gender and BMI (R² = 0.204, P<0.0001). Pulse mass was associated with gender (P = 0.001) and with a negative tendency to age (P = 0.038). In male subjects older than 50 yr (but not in women) approximate entropy was increased (0.942±0.301 vs. 1.258±0.267, P = 0.007) compared with younger men, as well as spikiness (0.363±0.122 vs. 0463±2.12, P = 0.031). Cosinor analysis disclosed higher mesor and amplitude in females than in men, but the acrophase was gender-independent. The acrophase was determined by age and BMI (R² = 0.186, P = 0.001).

Conclusion

In healthy adults, selective combinations of gender, age, and BMI specify distinct PRL dynamics, thus requiring balanced representation of these variables in comparative PRL studies.     

大苞藤黄化学成分研究及其互变异构体超高效液相色谱质谱联用分析

从大苞藤黄枝叶的混合粉碎物中分离到11个化合物,运用光谱手段分别鉴定为neobractatin(1),brasixanthone B (2),5-O-methylxanthone V1 (3),10-O-methylmacluraxanthone (4),isobractatin (5),xanthone V1(6),xerophenone A (7),xerophenone B (8),bractatin (9),macluraxanthone (10)和3-O-methylneobractatin (11).本文首次应用超高效液相色谱-质谱联用技术分离了异构体7和8并测定了其精确分子量.其中化合物6～8为首次从该植物中发现.     

Assessing the mechanical energy costs of various tissue reshaping mechanisms

Early-stage embryos must reshape the tissues of which they are made into organs and other life-sustaining structures; and if non-mammalian embryos fail to complete these tasks before the energy provided by their yolk runs out, they die. The aim of this study is to use a cell-level computational model to investigate the energetic cost of a variety of mechanisms that can drive an in-plane reshaping pattern known as convergent extension—a motif in which a tissue narrows in one in-plane direction and expands in another. Mechanisms considered include oriented lamellipodia, directed mitosis, stress fibers, and anisotropic external tension. Both isolated patches of tissue and actively contracting tissues that deform adjacent passive areas are considered. The cell-level finite element model used here assumes that the cell membrane and its associated proteins generate a net tension γ along each cell–cell interface and that the cytoplasm and its embedded networks and structures have an effective viscosity?μ. Work costs are based exclusively on mechanical considerations such as edge lengths and tensions, and because a traditional mechanical efficiency cannot be calculated, mechanisms are compared on the basis of the work they must do to the tissue to cause a specified rate of in-plane reshaping. Although the model contains a number of simplifications compared to real embryonic tissues, it is able to show that the work requirements for tissue reshaping by mitoses and by lamellipodia are of the same order. Lamellipodia are energetically most effective when their tensions are approximately twice as large as the interfacial tensions in the surrounding cells. The model also shows that stress fibers or other direct stretch or compression mechanisms are at least five times more efficient for tissue reshaping than are mitoses or lamellipodia and that the work needed to deform a typical cellular tissue is more than thirty times greater than if it did not contain cell boundaries. Collectively, these findings indicate that common tissue reshaping mechanisms have mechanical efficiencies of less than one percent and that mechanical efficiency is not the primary determinant of which mechanism(s) an embryo uses to reshape its tissues.