Male Adulthood Research Articles

Critical androgen‐sensitive periods of rat penis and clitoris development

Androgen control of penis development/growth is unclear. In rats, androgen action in a foetal ‘masculinisation programming window’ (MPW; e15.5–e18.5)’ predetermines penile length and hypospadias occurrence. This has implications for humans (e.g. micropenis). Our studies aimed to establish in rats when androgen action/administration affects development/growth of the penis and if deficits in MPW androgen action were rescuable postnatally. Thus, pregnant rats were treated with flutamide during the MPW ± postnatal testosterone propionate (TP) treatment. To assess penile growth responsiveness, rats were treated with TP in various time windows (late foetal, neonatal through early puberty, puberty onset, or combinations thereof). Phallus length, weight, and morphology, hypospadias and anogenital distance (AGD) were measured in mid-puberty (d25) or adulthood (d90) in males and females, plus serum testosterone in adult males. MPW flutamide exposure reduced adult penile length and induced hypospadias dose-dependently; this was not rescued by postnatal TP treatment. In normal rats, foetal (e14.5–e21.5) TP exposure did not affect male penis size but increased female clitoral size. In males, TP exposure from postnatal d1–24 or at puberty (d15–24), increased penile length at d25, but not ultimately in adulthood. Foetal + postnatal TP (e14–postnatal d24) increased penile size at d25 but reduced it at d90 (due to reduced endogenous testosterone). In females, this treatment caused the biggest increase in adult clitoral size but, unlike in males, phallus size was unaffected by TP during puberty (d15–24). Postnatal TP treatment advanced penile histology at d25 to more resemble adult histology. AGD strongly correlated with final penis length. It is concluded that adult penile size depends critically on androgen action during the MPW but subsequent growth depends on later androgen exposure. Foetal and/or postnatal TP exposure does not increase adult penile size above its ‘predetermined’ length though its growth towards this maximum is advanced by peripubertal TP treatment.

Sexual dimorphism in the lasting effects of moderate caloric restriction during gestation on energy homeostasis in rats is related with fetal programming of insulin and leptin resistance

AimWe aimed to characterize the lasting effect of moderate caloric restriction during early pregnancy on offspring energy homeostasis, by focusing on the effects on food intake and body weight as well as on the insulin and leptin systems.MethodsMale and female offspring of 20% caloric restricted dams (from 1 to 12 days of pregnancy) (CR) and from control dams were studied. These animals were fed after weaning with a normal-fat (NF) diet until the age of 4 months, and then moved to a high-fat (HF) diet. Blood parameters were measured under fed and 14-h fasting conditions at different ages (2, 4 and 5 months). Food preferences were also assessed in adult animals.ResultsAccumulated caloric intake from weaning to the age of 5 months was higher in CR animals compared with their controls, and this resulted in higher body weight in adulthood in males, but not in females. Both male and female CR animals already showed higher insulin levels at the age of 2 months, under fed conditions, and higher HOMA-IR from the age of 4 months, compared with their controls. CR male animals, but not females, displayed higher preference for fat-rich food than their controls in adulthood and higher circulating leptin levels when they were under HF diet.ConclusionIt is suggested that hyperinsulinemia may play a role in the etiology of hyperphagia in the offspring of caloric restricted animals during gestation, with different outcomes on body weight depending on the gender, which could be associated with different programming effects on later leptin resistance.

Fatigue resistance during high-intensity intermittent exercise from childhood to adulthood in males and females

This study examined the maturation pattern of fatigue resistance (FR) from childhood to adulthood in females and males during high-intensity intermittent exercise and compared FR between females and males in childhood and adolescence. Thirty males (boys 11.3 +/- 0.5 years, teen-males 14.7 +/- 0.3 years, men 24.0 +/- 2.1 years) and 30 females (girls 10.9 +/- 0.6 years, teen-females 14.4 +/- 0.7 years, women 25.2 +/- 1.4) participated in this study. They performed high-intensity intermittent exercise (4 x 18 maximal knee flexions and extensions with 1-min rest) on an isokinetic dynamometer at 120 degrees s(-1). Peak torque of flexors (PTFL) and extensors (PTEX), and total work (TW) were measured. FR was calculated as % of PTEX, PTFL, and TW in 4th versus 1st set. FR was greater (P < 0.05) in boys versus teen-males and men, and in teen-males versus men. In females, FR was greater (P < 0.05) in girls versus teen-females and women, but not different between teen-females and women. FR was not different in boys versus girls and in teen-males versus teen-females. FR for PTFL, PTEX, and TW correlated negatively (P < 0.001) with the respective peak values (r = -0.68 to -0.84), and FR for TW with peak lactate (r = -0.58 to -0.69). In addition, age correlated (P < 0.01) with FR for males (r = -0.75) and females (r = -0.55). In conclusion, FR during high-intensity intermittent exercise undergoes a gradual decline from childhood to adulthood in males, while in females the adult profile establishes at mid-puberty (14-15 years). The maturation profile of FR in males and females during development appears to reflect the maturation profiles of peak torque, short-term muscle power, and lactate concentration after exercise.

Masculinity, Matrimony and Generation: Reconfiguring Patriarchy in Drum 1951–1983*

In this article, I discuss some of the ways in which Drum tended to ascribe ‘modernity’ to particular practices and processes in opposition to other practices and processes portrayed as ‘traditional’. In mid-twentieth-century South Africa, dominant discourses tended to signal (white) male adulthood through independent decision making alongside financial autonomy. In contrast African discourses tended to signal male adulthood through proximity to family members, through respect for age and seniority and through deference to the praxis of ‘tradition’. In the representations of black men in its pages, Drum magazine negotiated a somewhat disorderly path through these competing racialised discourses. I suggest that Drum's claim that black males were indeed men, was made through highlighting and condoning practices that demonstrated similarities and continuities between subordinate black and dominant white versions of manhood. In challenging the racial discourse the magazine paradoxically found itself simultaneously reinforcing western rather than African versions of manhood.

Creatinine corrections for estimating children's and adult's pesticide intake doses in equilibrium with urinary pesticide and creatinine concentrations

A urine contaminant concentration per se has uncertain meaning for human health because of dilution by hydration. However, the estimation of the health-related daily intake dose of pollutant (mg/kg/day) that equilibrates with a spot urinary concentration of a pesticide residue or metabolite, or other analyte, can be made using creatinine-corrected toxicant levels (mg analyte/mg creatinine) multiplied by an estimate of the subjects' expected creatinine excretion rates (mg creatinine/kg/day). The objective was to develop a set of equations predicting a person's expected daily creatinine excretion (mg/kg) as a function of age, gender, race and morphometry, from birth to old age. We review the creatinine excretion literature where infants, children and adults provided 24 h total urine samples for creatinine analysis. Equations are developed for infants (<or=3 years), children (3-18 years) and adults (>or=18 years) that match at 3 and 18 years. A series of equations that estimate daily creatinine excretion (mg/day) are developed that are piecewise continuous from birth through infancy through adolescence and through adulthood for males and females, and Black and White races. Complicating factors such as diet, health status and obesity are discussed. We propose that these equations, with caveat, can now be used with measured urine concentrations to consistently estimate the corresponding equilibrium intake doses of toxicants at ages from birth to 92 years for the healthy non-obese. We recommend that this system of equations be considered for future development and reporting of applied doses in mg/kg/day of pollutants and toxicants that are measured in urine samples, as in the National Health and Nutrition Examination Survey.

Gender and gonadal status differences in zona reticularis expression in marmoset monkey adrenals: Cytochrome b5 localization with respect to cytochrome P450 17,20-lyase activity

Neonatal marmosets express an adrenal fetal zone comparable to humans. While adult males fail to express a functional ZR, with barely detectable blood DHEA levels, females produce higher levels of DHEA than males in adulthood. We investigated the presence of a putative functional ZR in adult female marmosets. In contrast to males, immunohistochemical analysis showed the ZR marker cytochrome b5 was elevated in the innermost zone in cycling females (compared to testis-intact males), further elevated in the adrenals from anovulatory females, and substantially elevated and continuous in ovariectomized females. As a functional test in vivo, following overnight dexamethasone treatment, cycling and anovulatory females showed higher levels of DHEA relative to males, but DHEA failed to increase in response to ACTH. In direct contrast, while ovariectomized females exhibited lower initial DHEA levels, clear increases were detectable after ACTH administration (p<0.05), suggesting an adrenal origin. The apparent differences in cytochrome b5 expression between groups were also further verified by Western blotting of adrenal microsomes, and compared to 17,20-lyase activity; the two parameters were positively correlated (p<0.01) across multiple treatment groups. We conclude that the cycling female marmoset expresses a rudimentary ZR with at least a capacity for DHEA production that becomes significantly ACTH-responsive after anovulation. Expression of cytochrome b5 in this region may be directly or indirectly controlled by gonadal function, and is, at least in part, a critical determinant in the development of an adrenal ZR that is more defined and significantly ACTH-responsive.

Male chicks are more costly to rear than females in a monogamous seabird, the Common Murre

Feeding rates and mass loss during chick rearing were compared for individually marked parents of male and female Common Murre (Uria aalge) chicks at Great Island, Newfoundland, Canada, from 1997–2001. Both parents in this socially monogamous seabird species share parental care duties until colony departure, after which the single chick is fed only by its father. Because murres provision their single chicks with one clearly visible fish per trip, it is possible to accurately determine whether parents differentially feed male and female chicks. Based on slightly greater mass of males in adulthood, possibly favored by sex differences in breeding roles, we predicted that male nestlings would be fed more than females. Fathers’ feeding rate to sons, but not daughters, increased with chick age, whereas maternal feeding rate increased with chick age for both sexes. When year-corrected feeding rates of pairs rearing both sexes were compared, both mothers and fathers fed their sons significantly more than their daughters in the later part of the chick-rearing period. Moreover, parents rearing male chicks lost mass at a significantly higher rate than those rearing females. There was no difference in fledging age for sons and daughters. These results indicate that differential parental allocation occurs and has measurable costs even in a species with only slight adult sexual dimorphism.

The Influence of Pubertal Timing on Alcohol Use and Heavy Drinking Trajectories

Early pubertal timing has been associated with increased alcohol use, drunkenness, and alcohol use disorders in both boys and girls during adolescence. It is not clear, however, whether the effect of early pubertal timing persists into late adolescence and young adulthood, whether its effect differs by gender, and if contextual factors (e.g., peer alcohol use) amplify such effect. This study attempts to address these questions by examining the trajectories of alcohol use and heavy drinking from early adolescence to young adulthood in males and females using data from the National Longitudinal Study of Adolescent Health (Add Health). Results show that for both males and females, early pubertal timing was associated with higher alcohol use and heavy drinking trajectories. These effects persisted into young adulthood and were found to be stronger for males than for females. Moreover, there was a significant interaction effect between friends’ drinking and pubertal timing on alcohol use and heavy drinking trajectories; but the interaction effect also differed for males and females. These findings suggest that early pubertal timing is a risk factor for alcohol use and has long-term implication for individuals’ health.

Characteristics of the association between the marine copepod, Gastrodelphys clausii, and its fanworm host Bispira volutacornis

Characteristics of the association of the marine copepod Gastrodelphys clausii with its fanworm host Bispira volutacornis were investigated from October 1997 to August 1999. Of the 982 hosts examined, 22.6% were infected, with male copepods outnumbering females. Prevalence varied between 3 and 90% during the study period and showed a seasonal pattern with a summer and late autumn/winter peak. Hosts were observed to harbour both single and multiple infections. The aggregation of parasites within the host population was overdispersed, displaying a characteristically clumped pattern. G. clausii reaches adulthood in males at ca. 800 μm in length, with recorded total lengths extending to 1,875 μm. Females at maturity were recorded to be ca. 1,000 μm, with a maximum total length of 3,250 μm recorded for an ovigerous female. Copepods were mobile within the branchial crown and showed no statistical preference for branchial crowns of different sizes. A positional pattern, however, was observed with juvenile copepods observed to occupy radioles further from the prostomium, as the branchial crown increases the number of radioles in each spiral. Contrary to this, the majority of female copepods were located attached to the radioles closest to the prostomium irrespective of crown size.

Finding communalities, making differences, performing masculinities: reflections of young men on military service

In Finland more than 80% of the male population participates in military service. Going to the army is an important step in the transition to male adulthood and a period for further education. This paper explores reflections on the army of 20‐year‐old men, some of whom have it already behind them and some others with their military service forthcoming. The focus is on exploring the kinds of masculinities that are constructed when talking about experiences or expectations. The paper suggests that, when talking about the army, male bonds are established which unite men from different cultural, educational and social backgrounds, as well as different generations. This communality is discussed in relation to differences. I concentrate on the making of differences due to the formal hierarchies within the army, between men and the women who participate in military service and between Finns and immigrants in the army. The final discussion is on attitude, endurance and the construction of ‘proper’ masculinity. The paper draws from interviews of 21 young men conducted in a longitudinal, ethnographically grounded study on youth transitions.

The male genital system of the cellar spider Pholcus phalangioides (Fuesslin, 1775) (Pholcidae, Araneae): development of spermatozoa and seminal secretion

BackgroundMost arthropods pass through several molting stages (instars) before reaching sexual maturity. In spiders, very little is known about the male genital system, its development and seminal secretions. For example, it is unknown whether spermatozoa exist prior to-, or only after the final molt. Likewise, it is unclear whether sperm are produced throughout male adulthood or only once in a lifetime, as is whether seminal secretions contain factors capable of manipulating female behavior. In order to shed light on these aspects of the reproductive biology of spiders, we investigated the male genital system of the common cellar spider Pholcus phalangioides, with special emphasis on its development and seminal secretions.ResultsTestes already display all stages of spermatogenesis in subadult males (about four weeks before the final molt). Their vasa deferentia possess proximally a very voluminous lumen containing dense seminal fluid and few spermatozoa, whereas the distal part is seemingly devoid of contents. Spermatoza of P. phalangioides are typical cleistospermia with individual secretion sheaths. In male stages approximately two weeks prior to the final molt, the lumina of the testes are wider and filled with a dense secretion. The wide, proximal portion of the vasa deferentia is filled with secretion and a large number of spermatozoa, and the narrow distal part also contains secretion. In adult males, the wide lumina of the testes are packed with spermatozoa and secretions. The latter are produced by the somatic cells that bear microvilli and contain many vesicles. The lumina of the vasa deferentia are narrow and filled with spermatozoa and secretions. We could identify a dense matrix of secretion consisting of mucosubstances and at least three types of secretion droplets, likely consisting of proteinaceous substances.ConclusionThis study reveals that spermatogenesis begins weeks before maturity and takes place continuously in the long-lived males of P. phalangioides. Possible functions of the various types of secretion in the seminal fluid and previously investigated female secretions are discussed in the light of sexual selection.

Adolescent Friendship as a Dynamic System: Entropy and Deviance in the Etiology and Course of Male Antisocial Behavior

A dynamic systems framework was applied to understand the influence of friendship on antisocial behavior from childhood (age 9-10) through adulthood (age 24-25) for Oregon Youth Study males (N = 206). Boys were videotaped interacting with a friend at ages 14, 16, and 18, and deviant content and interpersonal processes were independently coded. Conditional dyadic interpersonal processes were studied as a communication system and summarized by an index of information entropy (F. Attneave, 1959). High entropy scores represent disorganized, unpredictable patterns of interaction, whereas low entropy scores reflect an organized dialogue. Conversations of early-onset antisocial boys and their best friends were less organized and included more deviant content than those of well-adjusted controls. Prediction analyses, however, revealed an interaction between entropy and deviant talk. Consistent with expectation, males with well-organized interactions (i.e., low entropy) but elevated levels of deviant content were most likely to continue antisocial behavior into adulthood. Findings suggest that individual risk for maladaptation may be amplified by early adolescent friendship dynamics organized around deviance.

Continuities in depression from adolescence to young adulthood: Contrasting ecological influences

The prevalence, recurrence, and incidence of depression in adolescence and young adulthood are substantial for both males and females. In this study, we examined social setting variables that influence depression in males and females from adolescence to young adulthood. Rather than focusing on single ecological factors, we examined multiple settings including families, peers, and neighborhoods using longitudinal data from 372 families living in a large eastern urban area. We found that variables related to depression differed for males and females depending on the developmental period being examined. Family and peer variables in adolescence were significantly related to change in depression during the transition to adulthood for males, whereas family and neighborhood variables were marginally significant for females. Family and neighborhood variables in adulthood were significantly related to change in depression for females, and peer variables were significant for both males and females. Overall, contextual variables in adolescence had a more significant impact on change in depression for males, whereas contemporary variables in young adulthood had a more significant impact on change in depression for females.

Effects of testosterone on the development of neuromuscular systems and their target tissues involved in courtship and copulation in green anoles ( Anolis carolinensis)

Male green anole lizards court females using a red throat fan (dewlap) and copulate by intromitting one of two penises (hemipenes). These structures begin sexually monomorphic, but by adulthood males have larger dewlaps, only males have hemipenes, and many of the neuromuscular components of both systems show male-biased dimorphisms. We hypothesized that testosterone (T), which increases in juvenile males but not females about a month after hatching, facilitates masculinization. To test this idea, on post-hatching day 30, gonadally intact females received either a blank or T implant, and males were either castrated or sham-castrated. At day 90, juveniles were euthanized and the length of the cartilage and cross-sectional areas of the muscle fibers and motoneurons required for dewlap extension were examined. We also measured the cross-sectional areas of the hemipenes and associated muscle fibers and motoneurons, and counted the motoneurons. T-treated females had longer cartilages and larger dewlap muscle fibers compared to those with blank implants. No effects on motoneurons were detected, and no females possessed hemipenes or associated musculature. In males, castration produced shorter dewlap cartilages and smaller hemipenes; other measures were not affected by treatment. These data indicate that components of the dewlap system differentiate relatively late in development, that T likely mediates the process, and that although components of the copulatory system are plastic in juvenile males, sexual differentiation of peripheral features is complete before day 30. The data also suggest that target structures (dewlap cartilage and hemipenes), compared to their neuromuscular effectors, are particularly sensitive to developmental T exposure.

Endothelium-dependent responses in coronary arteries are changed with puberty in male pigs.

In humans, cardiovascular disease begins in young adulthood and is more prevalent in males than females. However, little is known about vascular function during transition to adulthood in males. The aim of this study was to define changes in production of endothelium-derived nitric oxide (NO) and coronary arterial responses during puberty. Plasma was collected from juvenile (2-3 mo of age) and adult (5-6 mo of age) male pigs (n = 8/group) for measurement of NO, and aortic endothelial cells were collected for measurement of mRNA and protein for endothelial NO synthase (eNOS). Although plasma NO was higher in juvenile (67.0 +/- 25.6 microM) than in adult (15.0 +/- 7.1 microM) male pigs, eNOS protein was similar in both groups. However, levels of mRNA for eNOS were lower in aortic endothelial cells from juvenile pigs. In rings of coronary arteries suspended in organ chambers for measurement of isometric force and contracted with PGF2alpha, relaxations to an alpha2-adrenergic agonist were significantly inhibited by indomethacin only in juvenile pigs [EC50 (-log M), 6.7 +/- 0.3 with indomethacin and 7.7 +/- 0.3 under control conditions]. NG-monomethyl-l-arginine (l-NMMA) inhibited relaxations in both groups. On the contrary, in the presence of indomethacin, relaxations to bradykinin were inhibited by l-NMMA only in arteries from adult pigs [EC50 (-log M), 8.9 +/- 0.3 with indomethacin and 8.6 +/- 0.3 with addition of l-NMMA]. These results suggest that hormonal changes associated with sexual maturity may affect posttranscriptional and/or translational regulation of eNOS protein and result in lower plasma NO in adult male pigs. In addition, endothelium-derived inhibitory cyclooxygenase products seem to predominate in juveniles.

WEIGHT BEARING PHYSICAL ACTIVITIES DURING YOUTH ARE POSITIVELY RELATED TO HEEL BONE MASS AT ADULT AGE.

PURPOSE To investigate the relation of physical activity (PA) of males and females during adolescence (13–17 years) and young adulthood (21–32 years) with the bone mass in the heel at age 36. METHODS The bone mass was measured in 376 males and females at age 36 years with ultrasound in the heel of both feet with a CUBA Clinical (McCue, UK) using broadband ultrasonic attenuation (BUA) and velocity of sound (VOS). PA was measured longitudinally with maximal nine and minimal three repeated measurements between age 13 and age 36 years. The amount of PA was measured with an interviewer administered questionnaire, that estimated total time per week spent on all physical activities (school, work, freetime, sports, transportation and stair climbing). From the activities two indicator scores are derived: (1) metabolic component (METPA) and (2) mechanic component (MECHPA). The physical activity scores over the adolescent and young adult period are regressed to the heel bone mass at age 36. Gender, body weight and calcium intake were included as covariates in the linear regression analyses. RESULTS In both sexes, no significant relation was found for METPA or MECHPA during adolescence with BUA and VOS at age 36. BUA is only significantly related with METPA during young adulthood (β = 0.002; p = 0.03) in both sexes. BUA at age 36 shows significant relationships with MECHPA during young adulthood in males (β = 3.3; p = 0.001) but not in females. VOS at age 36 also significantly related with MECHPA during young adulthood in males (β = 6.2; p = 0.002). CONCLUSION It can be concluded for males that weight bearing activities during young adulthood can increase the heel bone mass at adult age.

Posttreatment victimization and violence among adolescents following residential drug treatment.

This article examines the relationships among experiences of childhood abuse, psychiatric disorders, self-reported victimization, and violent behavior, with a focus on gender differences. Data were obtained from treatment entry and 5-year post-treatment interviews of 446 adolescent clients in therapeutic community (TC) drug treatment programs throughout the United States and Canada. Fifty-eight percent of the sample indicated that they engaged in serious violent behaviors (e.g., beatings, threatening or using weapons against other people, or violent crimes such as assaults, rapes, murders) in the 5 years following their separation from TC treatment. Multivariate logistic regression analyses revealed that victimization in the posttreatment period was the most significant factor associated with violent behavior, and pretreatment childhood abuse experiences and psychiatric disorders were not significantly related to the odds of violent behavior. There were significant gender differences in self-reported victimization and violent behavior. The findings suggest that violence in young adulthood for males is related to increasing involvement in violent lifestyles that include drug trafficking, while violence among females is associated with the social and psychological consequences of drug involvement and victimization. High rates of violent involvement and victimization among former adolescent clients suggests the utility of incorporating interventions such as safety-oriented strategies for females or interventions that address involvement in the drug use lifestyles (i.e., use and dealing) for both males and females into residential treatment to reduce the likelihood of future violence.

Trajectories of Gender Role Orientations in Adolescence and Early Adulthood: A Prospective Study of the Mental Health Effects of Masculinity and Femininity

Adolescence is the segment of the life course when gender differences in mental health emerge and gender becomes a more salient factor shaping orientations toward oneself and views of one's place in the social world. This study uses mixture modeling, to identify trajectories of masculinity and femininity between ages 12 and 25, and OLS regression, to examine the effects of those trajectories on mental health in young adulthood (measured as depressive symptoms and alcohol problems at age 25). Four waves of prospective data from the Rutgers Health and Human Development Project are used; respondents (n = 447) are age 12 at Wave 1 (1979-81), 15 at Wave 2 (1982-84), 18 at Wave 3 (1985-87), and 25 at Wave 4 (1992-94). Results indicate that having relatively high and increasing levels of masculinity over adolescence decreases depressive symptoms in early adulthood for both males and females. Reflecting the privileging of males over females, the findings suggest that masculinity, but not femininity, is a central axis on which advantages and disadvantages across some dimensions of mental health accumulate over adolescence.

The Gender Perspective of Civil-Military Relations in Israeli Society

The exceptional centrality of security to the national existence of Israel has led scholars to investigate the impact of the military on the political and civil system. Nevertheless, this research had been limited in scope. It has been claimed that the army is a `citizen army', that Israel is a `nation in arms', and that therefore the army does not reflect a specific group in society. The newer `generation' of scholars emphasizes the effect of armed conflict on the larger society, on its attitudes and values. One subject, however, which has been neglected so far is the gender perspective. This is astonishing because Israel is unique in the sense that Jewish Israeli women have been conscripted since the foundation of the state of Israel. In China women are also conscripted, but as not even 10 percent of each age group are called up this is negligible. Thus - from the perspective of sheer numbers - Israel serves as a very interesting case study of the impact of an advanced integration of female citizens in the defence forces on society and on the defence forces themselves. The article examines whether, although (Jewish) women are conscripted, the military in Israel is the main force in shaping male identity and whether military service can be understood as a rite of passage to male adulthood. It also analyses whether the dominance of security and of the military discourse leads to gender inequality in society at large.

Influence of the beta2-adrenergic receptor Arg16Gly polymorphism on longitudinal changes in obesity from childhood through young adulthood in a biracial cohort: the Bogalusa Heart Study.

The beta2-adrenergic receptor (ADRB2) plays a major role in regulating energy expenditure by stimulating lipid metabolism in human adipose tissue. Polymorphisms in the ADRB2 gene have been associated with obesity and various weight-related traits in cross-sectional studies of adults, but little is known about the effects of the ADRB2 gene on childhood obesity or the propensity to gain weight over time. To assess the effects of a polymorphism in codon 16 (Arg16-->Gly) of the ADRB2 gene, which has been associated with a decrease in beta2-receptor density and efficiency, on longitudinal changes in obesity from childhood to young adulthood in a biracial cohort. Seven cross-sectional screenings of children and five cross-sectional screenings of young adults who were previously examined as children produced longitudinal data from childhood to young adulthood. Height, weight and subscapular and triceps skinfolds were measured by trained examiners following identical protocols over the course of the study. Gender- and age-stratified analyses using random coefficients models were used to examine longitudinal genetic effects on obesity in 1151 African-American and Caucasian males and females who attended an average of six examinations over a 24 y period from childhood to young adulthood. Age-stratified analyses showed no clear genetic relationships with changes in obesity measures over time in females, but an age-dependent association was observed in males, where the relationship between the Arg16Gly polymorphism and obesity became stronger with age. In males who were 4-9 y of age at the beginning of the study in 1973, body mass index (BMI) was 4% higher in Gly/Gly and Arg/Gly males compared to those with Arg/Arg by 26 y of age. Subscapular skinfold measurements in Gly/Gly males became significantly different from Arg/Arg males (20% higher) by age 20. In the oldest male cohort (10-14 y of age in 1973), BMI increased at a significantly greater rate (0.4%/y) in males carrying the Gly16 form of the receptor relative to Arg/Arg males. BMI was significantly different between homozygous genotypes by approximately 26 y of age, and reached 8% higher in Gly/Gly males by age 32. Subscapular skinfolds also increased at a significantly greater rate (2%/y) in Gly/Gly males compared to Arg/Arg males, becoming significantly different (27%) by approximately 22 y of age and reaching a maximum difference of 50% by age 32. Our data suggest that the beta2-adrenergic receptor is associated with the propensity to gain weight from childhood to young adulthood in males. An increased understanding of genetic influences on the development of obesity may improve the effectiveness of interventions designed to reduce excess body weight and help define the role of genetic factors in diabetes and cardiovascular disease.