23 research outputs found
A Validated Age-Related Normative Model for Male Total Testosterone Shows Increasing Variance but No Decline after Age 40 Years
The diagnosis of hypogonadism in human males includes identification of low serum testosterone levels, and hence there is an underlying assumption that normal ranges of testosterone for the healthy population are known for all ages. However, to our knowledge, no such reference model exists in the literature, and hence the availability of an applicable biochemical reference range would be helpful for the clinical assessment of hypogonadal men. In this study, using model selection and validation analysis of data identified and extracted from thirteen studies, we derive and validate a normative model of total testosterone across the lifespan in healthy men. We show that total testosterone peaks [mean (2.5-97.5 percentile)] at 15.4 (7.2-31.1) nmol/L at an average age of 19 years, and falls in the average case [mean (2.5-97.5 percentile)] to 13.0 (6.6-25.3) nmol/L by age 40 years, but we find no evidence for a further fall in mean total testosterone with increasing age through to old age. However we do show that there is an increased variation in total testosterone levels with advancing age after age 40 years. This model provides the age related reference ranges needed to support research and clinical decision making in males who have symptoms that may be due to hypogonadism.Publisher PDFPeer reviewe
Reactive oxygen species and male reproductive hormones
Reports of the increasing incidence of male infertility paired with decreasing semen quality have triggered studies
on the effects of lifestyle and environmental factors on the male reproductive potential. There are numerous exogenous
and endogenous factors that are able to induce excessive production of reactive oxygen species (ROS) beyond that of
cellular antioxidant capacity, thus causing oxidative stress. In turn, oxidative stress negatively affects male reproductive
functions and may induce infertility either directly or indirectly by affecting the hypothalamus-pituitary-gonadal (HPG)
axis and/or disrupting its crosstalk with other hormonal axes. This review discusses the important exogenous and
endogenous factors leading to the generation of ROS in different parts of the male reproductive tract. It also highlights
the negative impact of oxidative stress on the regulation and cross-talk between the reproductive hormones. It further
describes the mechanism of ROS-induced derangement of male reproductive hormonal profiles that could ultimately
lead to male infertility. An understanding of the disruptive effects of ROS on male reproductive hormones would
encourage further investigations directed towards the prevention of ROS-mediated hormonal imbalances, which in turn
could help in the management of male infertility
La correspondencia de Valencia : diario de noticias : eco imparcial de la opinión y de la prensa: Año XXXVII Número 16155 - 1914 Noviembre 09
Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 200
SPILLOVERS AND ABSORPTIVE CAPACITY IN A PATENT RACE
This paper explores the impacts of absorptive capacity on the behavior of innovating firms competing in a dynamic patent race. We introduce spillovers and absorptive capacities in the Fudenberg, Gilbert, Stiglitz and Tirole patent race with memory. First, we show that incorporating absorptive capacity has different effects according as the firm leads or follows in the race. While the leader is getting soft, the follower revives, allowing him to possibly catch up with the leader. Second, we find that spillovers with absorptive capacities tend to increase the pace of innovation, a somewhat paradoxical outcome. Copyright Blackwell Publishing Ltd and The University of Manchester, 2006.