Biological evidence for limits to the duration of life

Projections of duration of life for humansbased on mathematical models have led someresearchers to claim that there is no lowerlimit to death rates or upper limit to lifeexpectancy, and that a life expectancy of 100will be achieved in the 21st century. Toassess the biological plausibility of theseclaims, we examined temporal aspects ofbiological phenomena in three mammalianspecies. Our examination revealed that: (1)physiological declines associated withreproduction consistently occur at ages thatare less than one-third of the median age atdeath, (2) physiological parameters associatedwith aging in humans lose eighty percent oftheir functional capacity by age 80, and (3)young versus old individuals can bedistinguished by the pathologies detected atdeath. The biological evidence suggests thatorganisms operate under warranty periods thatlimit the duration of life of individuals andthe life expectancy of populations. We usethese findings to discuss the issue of limitsto the duration of life and the validity ofmathematical models used to forecast humanlongevity.     

老年性骨质疏松所致骨折患者血清钙磷和TGF-β 1分析

1临床资料2003-06／2004—12收治髋部骨质疏松性骨折患20(男14，女6)例，年龄58—80(平均68．5)岁，股骨颈骨折13例，粗隆间骨折7例．对照组为老年性骨关节病或颈腰椎病患20例．均抽空腹静脉血4mL，3000r／min离心5min分离血清，4h内测定血清钙、磷，留血清-20℃保存备用，测定TGF-β1．用Au-2700全自动生化分析仪测定血清钙、磷，试剂由日本欧林巴斯公司提供．血清TGF-β1检测采用ELISA法，     

胰岛素样生长因子-I和人绒毛膜促性腺激素对成年大鼠Leydig细胞葡萄糖转运蛋白基因表达调控

目的:研究胰岛素样生长因子I(IGF I)和人绒毛膜促性腺激素(hCG)对成年大鼠睾丸Leydig细胞中葡萄糖转运蛋白(GLUT)基因表达的影响,为进一步探讨Leydig细胞中睾酮的合成、分泌与葡萄糖代谢的关系提供依据。方法:采用改良的Klinefelter方法从成年大鼠睾丸中分离获得Leydig细胞;用反转录聚合酶链技术检测IGF I和hCG对原代培养的Leydig细胞中GLUT基因表达的调控作用。结果:分离得到纯度为98%的大鼠Leydig细胞,并与对照组比较,hCG可显著增加Leydig细胞中GLUT8基因mRNA的表达水平(P<0.001),且此作用具有剂量依赖性与时效性。当在试验组细胞中单独加入IGF I或IGF I和hCG作用于细胞后,发现IGF I(100ng mL)可显著增加Leydig细胞中GLUT8基因mRNA的表达(P<0.01),也可与hCG协同作用显著提高GLUT8基因的mRNA表达,该结果与IGF I(100ng mL)和hCG(10ng mL)能协同作用极显著增加睾酮合成水平(P<0.001)的结果是相吻合的。在大鼠Leydig细胞中,无论10ng mL或100ng mL还是两者同时作用于细胞,都不能影响GLUT1和GLUT3基因的mRNA水平。结论:在成年大鼠Leydig细胞中,IGF I和hCG对细胞中的GLUT8基因表达的调节作用具有特异性,其协同作用能显著提高细胞中GLUT8基因mRNA水平,增强细胞摄取葡萄糖的能力,给细胞提供更多的代谢能源,最终增加Leydig细胞睾酮的合成与分泌。     

High resolution spectral analysis of plasma adrenocorticotropin reveals a multifactorial frequency structure.

Time series of plasma ACTH concentrations were analyzed with a high resolution spectral analysis program based on digital Fourier transforms. Both coherent signal and stochastic aspects of the time series were analyzed. Samples were collected at 2- and 15-min intervals in control rats and rats immunoneutralized against CRH. The individual and composite spectral distributions revealed significant structure at both the higher and lower ranges of frequencies studied, with multiple periodicities between 4-220 min in both groups. CRH immunoneutralization consistently reduced the amplitude by 82% and compressed the frequency distribution for waveforms with periods longer than 15 min by 23%. A systematic break in the slopes of the background continua occurred between 10 and 15 min in the 2-min time series. This break was unaffected by CRH immunoneutralization. Digital Fourier transform analysis of our ACTH time series suggests a system with a more complex high frequency structure than has previously been appreciated. Our analyses suggest a biological system with the following characteristics: 1) both a fast and a slow response to a fairly constant unspecified fast forcing; 2) the slow response is initiated by the fast response and represents an imperfect integration due to feedback processes; 3) CRH alters the ability of the fast forcing to elicit a slow response without altering the fast response or ACTH clearance; and 4) this alteration consists of both amplitude and frequency modulation in the signal output. This view of ACTH secretion suggests an adaptive and energy-efficient system.     

Unprotected Anal Intercourse in HIV-Positive and HIV-Negative Gay Men: The Relevance of Sexual Arousability,Mood, Sensation Seeking,and Erectile Problems

Reduction of unprotected anal intercourse (UAI) in gay men infected with HIV is important in preventing further spread of this infection. In previous studies, personality trait measures relevant to sexual arousability and the effects of anxiety have been shown to relate to UAI in both gay and heterosexual men. Are HIV+ gay men similar in these respects or are there other personality-related factors that influence their sexual risk taking? This question was addressed using a convenience sample of 156 HIV+ gay men and 155 HIV? gay men, matched for age and UAI risk. There were no significant differences between these two groups on measures of sexual arousability, inhibition of sexual arousal in risky situations, sensation seeking, depression and anxiety proneness, or tendency to increased sexual interest in negative mood states. HIV+ men were, however, more likely to report erectile problems and higher scores on an associated trait measure, inhibition of arousal due to threat of performance failure. As this association was not anticipated, questions about whether erectile problems preceded the seroconversion were not asked. Such problems could be associated with reluctance to use condoms, thus increasing the likelihood of seroconversion and/or disease transmission. Alternatively, erectile problems could be a consequence of HIV infection. In each case, this has implications for prevention. The associations among HIV status, erectile problems, and UAI need to be specifically addressed in future research.