Associations between stress reactivity and sexual and nonsexual risk taking in young adult human males

Release of the hormone cortisol represents a distress response to novel or stressful situations. Individual differences in such reactivity have been conceptualized as representing a relatively enduring, generalizable trait. In this study, cortisol responses to two experimentally manipulated "sexual" and "nonsexual" stressors were used to examine whether stress reactivity is related to sexual and nonsexual risk behavior in young adult males. Analyses were based on 150 males 18 to 25 years old; risk behavior was assessed in confidential, self-administered questionnaires. Analyses indicated that both stressors effectively elicited cortisol increases. Generalized reactivity, defined as a cortisol response to both stressors, was inversely associated with deviance (e.g., theft, substance use) and with two indicators of sexual risk taking (lifetime number of intercourse partners and frequency of condom use). Findings are discussed in terms of cross-situational consistency of stress responses, the utility of stress reactivity for understanding individual differences in risk taking, and the interpretive limitations imposed by study design.     

Does non-exercise activity thermogenesis contribute to non-shivering thermogenesis?

We wanted to examine if spontaneous physical activity contributes to non-shivering thermogenesis. Ten lean, healthy male subjects wore a physical activity, micro-measurement system while the room temperature was randomly altered at two hourly intervals between thermoneutral (72 °F), cool (62 °F) and warm (82 °F) temperatures. Physical activity measured during the thermoneutral, cooling and warming periods was not significantly different. Cooling increased energy expenditure above basal and thermoneutral values 2061±344 kcal/day (p<0.01). Thus, the increase in energy expenditure associated with short-term environmental cooling in lean, healthy males does not appear to be due to increased spontaneous physical activity or fidgeting.     

Urinary cortisol analysis for monitoring adrenal activity in elephants

Cortisol was measured in dichloromethane-extracted elephant urine using an ¹²⁵I solid-phase radioimmunoassay (RIA). The cortisol RIA was validated by demonstrating 1) parallelism between dilutions of pooled urinary extracts and the standard curve, 2) significant recovery of exogenous cortisol added to elephant urine, and 3) a relationship between changes in peripheral and urinary cortisol after an adrenocorticotropin hormone (ACTH) challenge. One African (Loxodonta africana) and one Asian (Elephas maximus) elephant were given three injections of ACTH (1.25 mg) at 2 h intervals. Serum cortisol increased four- to eightfold within 30 min after the first injection and peaked (nine- to twelvefold increase) after the second injection. Serum concentrations began to decline 2–3 h after the last injection but were still approximately fourfold higher than baseline at the end of the collection period (hour 8). In the urine, cortisol concentrations were increased in the first sample postinjection (1.5–4 h) and peaked twenty- to fortyfold by ～6 h. Urinary cortisol remained elevated at 8 h, but returned to baseline the following morning. Analysis of high performance liquid chromatography fractions of extracted urine revealed that immunoactivity was associated with free cortisol (～90% of total immunoactivity) and a more polar, unidentified metabolite. A method for preserving urine was developed to allow storing unfrozen samples. One pool of urine from each of one African and two Asian elephants was divided into aliquots, placed in tubes containing absolute ethanol (10%), sodium azide (0.1%) or distilled water (control), and frozen after 0, 1, 2, 3, 4, 6, 8, 10, 12, and 24 weeks of storage at ～25°C. In unpreserved samples, cortisol concentrations were reduced 46% by 2 weeks and 95% by 24 weeks. In contrast, ethanol- and sodium azide-preserved samples retained 100 and 95% of cortisol immunoactivity through 8 weeks and 93 and 85% of activity through 12 weeks, respectively. We infer from these data that changes in urinary cortisol excretion in the elephant reflect fluctuations in adrenal activity and may be a useful indicator of stress. Additionally, urine samples can be collected and stored unfrozen for at least 2 months before any appreciable loss in cortisol immunoactivity occurs, a finding potentially useful to field application of this technique. © 1995 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America

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The competitive interactions of man and deer in prehistoric California

A hypothetical model concerning the structure of aboriginal California trophic systems is presented. The dynamics of each possible state of the system is generated theoretically and then tested using previously published data. It is determined that a state of competitive coexistence of a fish-regulated predatorprey competition relationship between the deer and human populations limited the growth of both populations and should be considered a determinant of aboriginal California population levels.     

Modification of chemical reactivity via a novel interaction of light and matter — A review

A new interaction of light, in the VIS region, and matter is presented. Theoretical preliminaries are introduced to support the experiments, in which different physical systems are irradiated with 546 nm; the experimental results show the time of irradiation to be an essential parameter. A tentative theory is presented and the prospect of using the effect in the field of molecular computers is briefly outlined.     

Relationship Between Circulating Leptin and Energy Expenditure in Adult Men and Women Aged 18 Years to 81 Years

SUSAN B. ROBERTS, MARGERY NICHOLSON, MYRLENE STATEN, GERALD E. DALLAL, ANA L. SAWAYA, MELVIN B. HEYMAN, PAUL FUSS, ANDREW S. GREENBERG. Relationship between circulating leptin and energy expenditure in adult men and women aged 18 years to 81 years. Recent studies suggest that leptin may be an important metabolic signal for energy regulation in rodents, but the role of leptin in human energy regulation remains uncertain. Because adaptive variations in energy expenditure play an important role in human energy regulation, we investigated the relationship between leptin and energy expenditure parameters in 61 weight-stable men and women aged 18 years to 81 years who were not obese. Measurements were made of circulating leptin in the fasting state, body fat and fat free mass, resting metabolic rate (n=61), free-living total energy expenditure (n=52), and the thermic effect of feeding (n=33). After statistically accounting for age, body fat, and fat free mass, there was no association between leptin and any measured energy expenditure parameter. In addition, there was no effect of age on the relationship between circulating leptin and body fat mass. These results indicate that physiological variations in circulating leptin are not linked with adaptive variations in energy expenditure in humans, in contrast to indications of this phenomenon in the ob/ob mouse.     

Reactivity of δ-substituted α,β-unsaturated cyclic lactones with antileishmanial activity

The present study examines a set of 43 compounds for their antileishmanial activities and cytotoxicities. Negative lowest unoccupied molecular orbitas and similar values for the electrophilic Fukui function condensed at the β-position for a subset of δ-substituted α,β-unsaturated cyclic lactones classify them as strong Michael acceptors. There was a well-defined trend of increasing antileishmanial activity with increasing cytotoxicity and large selectivity indices for the most active compounds. Softer compounds were more active than harder ones as observed from the experimental data and rationalised by calculated reactivity indices.     

Fecal corticoid metabolite measurement in the cheetah (Acinonyx jubatus)

This longitudinal study addresses the relationship of cortisol excretion to ovarian activity in captive female cheetahs. A radioimmunoassay was developed and validated to measure corticoid metabolite concentrations in feces. A restraint experiment was used to demonstrate that fecal cortisol is detectable following stressful episodes. In studies of 7 females, fecal cortisol output indicated that they could be placed into 3 different categories. Females of the high-in-cortisol category (∼200 ng/g feces, n = 2) were independently rated by caretakers as the most nervous individuals in the collection (n = 24). These females appeared to be compromised in their ovarian cycling, as indicated by fecal estrogen measurements. In contrast, reproducing females fell into the low and intermediate cortisol excretion categories. A non-cycling high-cortisol female had an episodic cycle following a period of relatively low (intermediate) cortisol levels, followed by resumption of acyclicity and high cortisol excretion. Stress and reproductive failure may, therefore, be associated in the female cheetah. The close proximity of conspecifics as a potential source of stress and, consequently, suppressed ovarian activity in some females is suggested by these results. Zoo Biol 16:133–147. 1997 © 1997 Wiley-Liss, Inc.     

Common Pool Resources, Buffer Zones, and Jointly Owned Territories: Hunter-Gatherer Land and Resource Tenure in Fort Irwin, Southeastern California

Anthropologists have described, but seldom explained, the existence and persistence of common pool resource systems among hunting and gathering populations. Land tenure practices in the Fort Irwin area of the Mojave desert, California are explored. Ecological, ethnographic, archeological, and ethnohistoric information suggests that this area was jointly owned and intermittently used by several distinct ethnic groups. Although the region was important as a buffer against resource shortfall during certain seasons, sporadic use and meager and variable resource yield may have made exclusive ownership difficult and costly. A jointly managed region with common pool resources better served surrounding groups, while simultaneously creating a spatial buffer to diffuse social tensions. Following presentation of the Fort Irwin case, the paper considers the formation of such land tenure practices among hunting and gathering populations.     

Late pleistocene population dynamics: An alternative view

An attempt is made to argue for a more dynamic view of huntergatherer population behavior in place of the largely static one that has been widely accepted. Following a review of how the concept of carrying capacity has been used in both huntergatherer and ecological studies, attention is drawn to the role of stochastic factors in producing fluctuations over time among populations that are small in size. Some of the implications of this alternative view are briefly discussed.Research supported in part by NIH Grant GM 20467-03.This is a revised version of a paper presented at the symposium, Systems and Their Environments, at the Annual Meeting of the American Anthropological Association, 1973, New Orleans.