ACTH,cortisol and glucose responses after administration of vasopressin in cattle and sheep

The present study compared the effects of vasopressin on plasma concentrations of corticotropin, cortisol and glucose in cattle and sheep. After intravenous injection of 1, 0.1 and 0.01 g vasopressin per kg body weight, the plasma vasopressin concentration increased proportionally to the injected dose, and this increase was similar in cattle and sheep. Doses of 1 and 0.1 g per kg body weight of vasopressin triggered significant responses of corticotropin, cortisol and glucose in cattle and sheep. The corticotropin response to both doses was significantly greater in sheep, whereas the glucose response was greater in cattle. The cortisol response did not differ between species. The lowest dose of vasopressin (0.01 g per kg body weight) still induced a significant cortisol response without a substantial effect on plasma corticotropin, suggesting that a direct action of vasopressin on the adrenals may contribute to the observed cortisol response. The results demonstrate that vasopressin increases plasma levels of corticotropin, cortisol and glucose in cattle, as it does in sheep, but the intensities of the corticotropin and glucose responses to vasopressin differ between cattle and sheep. The reasons for these differences remain to be clarified.Abbreviations ACTH corticotropin - AVP vasopressin - bw body weight     

Maternal care and development of stress responses in baboons

The ability to mount a successful response to threats is critical for an organism's survival. A key element of the stress response is its nonspecificity toward the stress source, with similar endocrine and behavioral changes expected under a variety of stressors. In this project we utilized an experimental design that accounts for multiple sources of variation to further understand the nature of stress responsivity and its relationship to the early rearing environment. A sample of baboons (n=73) was observed during the early phase of life in their social group, and then tested as juveniles in a challenging situation. Maternal cortisol levels were measured during the peripartum period. The challenging situation (individuals were isolated for a few minutes in a single cage) was designed to be a moderate source of psychological stress. Patterns in individual differences during the stress test were "mapped" by means of multidimensional scaling (MDS). After the observation was made, the subject was sedated and a blood sample was taken to measure cortisol levels. Our results indicate that when juvenile baboons are confronted with a source of psychological stress, they show a multidimensional behavioral response, probably mediated by the activation and synergic interaction among different neurohormonal systems that, ultimately, act on the hypothalamus-pituitary-adrenal (HPA) axis. Different components of the multidimensional, or nonspecific, behavioral response are associated with the quality and quantity of interactions with their mothers during early life. Juveniles whose mothers displayed higher levels of positive interaction were characterized by vigilant but less active reactions to the stress test, whereas juveniles of mothers that displayed high levels of stress-related behaviors had higher cortisol and locomotion levels.     

Differences in stress reactivity of laboratory macaques measured by heart period and respiratory sinus arrhythmia

Some laboratory primates are more likely than others to react to anxiety-provoking stressors. Individuals that overreact to stressors may experience diminished psychological well-being and would be inappropriate for some experiments. The differences between reactive and nonreactive individuals may be reflected in heart period and respiratory sinus arrhythmia (RSA). Using surface electrodes and radio telemetry, we measured these two cardiac variables in seven male and ten female singly caged longtailed macaques (Macaca fascicularis) when they were exposed to two stressors, a sudden noise (whistle test) and an unfamiliar technician wearing capture gloves (glove test). Behavior was videotaped during both tests. For the whistle test, cardiac data were recorded before, during, and after two 1 min whistle blasts separated by 90 min. For the glove test, data were recorded in 1 min blocks every 8 min over 96 min before, during, and after 1 min exposure to the gloved technician. Heart period was decreased and RSA was suppressed during both the whistle and glove exposures. After the whistle test, the cardiac activity of most subjects returned to baseline levels within 10 min. The glove test produced more extended suppression, with greater individual differences, than the whistle test. There were greater individual differences in RSA than in heart period. These enhanced individual differences were used to define stress reactors that differed from nonreactors in their cardiac data profiles. Of 16 subjects that completed the glove test, five were identified as reactors. Am. J. Primatol. 45:245–261, 1998. © 1998 Wiley-Liss, Inc.     

A comparison of two tuberculins in nonsensitized macaques

Two tuberculins (mammalian and Old Tuberculin) were compared in three species of macaques after one of the tuberculins elicited nonspecific reactions up to 72 hours after intradermal inoculation in nontuberculous monkeys. A significant difference in initial intradermal eyelid reactivity between the tuberculins was found in some subjects. The heterogeneity of tuberculins and the necessity of accurate interpretation of intradermal testing are important components in addressing tuberculosis screening in nonhuman primate colonies.     

Aerobic fitness and sympatho-adrenal response to short-term psycho-emotional stress under field conditions

A possible relationship between aerobic fitness (AF), measured by maximal cycle ergometry (CE) and sympatho-adrenal response to acute, short lasting psycho-emotional stress was investigated by monitoring heart rate (f _c) and excretion of catecholamines. The activation of the sympatho-adrenal system was characterised by the noradrenaline : adrenaline ratio. A group of 11 healthy men [22.8 (SD 2.52) years] lived under identical environmental conditions; their mean maximal oxygen uptake ( ) was 47.1 (SD 3.9) ml · min^–1 · kg^–1. After the physiological and psychological laboratory tests had been completed thef _c of the subjects was monitored continuously during the guerilla slide and parachute jump by night, two emotionally stressful military tasks. Maximalf _c (f _{c, max}) attained during these events was 84.5% and 83% off _{c, max} during CE (f _{c, max, CE}), respectively. A significant relationship (r=–0.92,P<0.0002) betweenf _{c, max} reached during the stressful tasks and was found only for the guerilla slide, which was preceded by physical strain, sleep deprivation and energy deficit. One subject with some prior experience in parachuting showed the lowestf _c response and the lowest sympatho-adrenal activation in both events, independent of the degree of AF. In conclusion, AF was found to influence the sympatho-adrenal and fc response to acute, short-lasting emotional stress when the stressful event was aggravated by preceding physical strain, the magnitude of the stress response depending largely on individual experience and effective mechanisms for coping with specific stimuli.     

Antibody responses to two encephalomyocarditis virus vaccines in rhesus macaques (Macaca mulatta)

Abstract: Two groups of rhesus macaques (Macaca mulatta) housed in rodent-controlled outdoor corrals were inoculated with two different encephalomyocarditis virus (EMCV) vaccines. One group (n = 45) received a vaccine made from an inactivated field isolate of virus cultured during an outbreak at a zoo in Florida. This vaccine produced fourfold increases in the titers of 28 animals (62%); the increases persisted for at least 18 months (last test) after a single injection of the vaccine. The other group (n = 51) received a vaccine made from an inactivated porcine field strain of the virus. This vaccine did not produce titers in any of the vaccinees.     

Prenatal stress alters reproductive responses of rats in behavioral estrus and paced mating of hormone-primed rats

Adult female offspring of dams exposed to gestational stress (prenatal stress, PNS) may show altered reproductive behavior, exploration in novel environments, and/or social interactions than do their non-PNS counterparts. These behavioral differences may be more readily observed in a seminatural, paced mating paradigm, in which females have greater control of their sexual contacts, than in a standard mating situation. Adult offspring of dams exposed to restraint and lights for 45 min on Gestational Days 14-20 (PNS) were compared with those not subjected to stress (non-PNS, control condition). The motor, reproductive, and sociosexual behaviors of hormone-primed (Experiment 1) or cycling adult offspring in behavioral estrus (Experiment 2) were examined following 20 min of restraint stress under bright lights (postnatal stress). Hormone-primed PNS rats displayed less motor behavior in a novel arena than did non-PNS rats. In a standard mating test, hormone-primed PNS females tended to be more aggressive toward the male than were non-PNS rats. In a seminatural mating situation, hormone-primed PNS females showed increased avoidance behavior, such as longer latencies to the initial intromission, greater return latencies following mounts and intromissions, and more exiting subsequent to mounts and intromissions, than did non-PNS rats. PNS rats in behavioral estrus had decreased incidence and intensity of lordosis, and fewer solicitation behaviors, in both standard or paced mating situations, in which latency to and number of mounts were also increased. Thus, hormone-primed PNS rats exposed to restraint showed more avoidance behaviors in paced mating situations, while cycling PNS rats in behavioral estrus had greater disruption of reproductive responses in standard or paced mating paradigms than did non-PNS control rats.     

Adaptive responses to fescue toxicosis under thermoneutral and heat stress conditions

This study determined the potential for short-term adaptation to fescue toxicosis and heat stress in rats. Male CD outbred rats (n=24) were implanted with temperature transmitters (Respironics, Bend, OR) to measure core temperature (Tc) and general activity. All rats were initially fed diets with ground, uninfected tall fescue seed (E−) and exposed to 21 °C (thermoneutral, TN) to establish baseline values. In Period 1, all groups were maintained at TN for 7 days, with one group fed a diet containing ground, endophyte-infected tall fescue seed (E+, approximately 165 μg ergovaline/kg BW/d) and two groups fed E− diet. Ergovaline is thought to be the primary toxin responsible for many symptoms associated with fescue toxicosis. Period 1 was followed by 7 days at 31 °C (heat stress, HS, Period 2) on the same diets. All animals were fed E− diet during the second 7 day of HS (Period 3). In the final 7 day (Period 4), E+ diet was returned to the original group and fed to one of the previously E− groups, with the third group remaining on E− diet. A 40% decrease in FI occurred with E+ treatment at TN (P<0.05), with a comparable BW reduction (P<0.05) after 4 day. Both responses worsened during HS. Treatment with E+ in Period 4 indicated that FI and BW had not adapted to fescue toxicosis. A reduction in daily Tc occurred with E+ treatment at TN (P<0.05) followed by hyperthermia during the initial stage of HS (P<0.05). Although feed intake and growth rate showed no change over time, there was a reduction in fescue toxicosis-induced hyperthermia in the heat with repeat treatment. Conditioning animals to fescue toxicosis and heat stress prior to exposure may be beneficial in reducing impacts on thermal status of the animal.     

A novel larval diet interacts with nutritional stress to modify juvenile behaviors and glucocorticoid responses

Developmental plasticity can allow the exploitation of alternative diets. While such flexibility during early life is often adaptive, it can leave a legacy in later life that alters the overall health and fitness of an individual. Species of the spadefoot toad genus Spea are uniquely poised to address such carryover effects because their larvae can consume drastically different diets: their ancestral diet of detritus or a derived shrimp diet. Here, we use Spea bombifrons to assess the effects of developmental plasticity in response to larval diet type and nutritional stress on juvenile behaviors and stress axis reactivity. We find that, in an open‐field assay, juveniles fed shrimp as larvae have longer latencies to move, avoid prey items more often, and have poorer prey‐capture abilities. While juveniles fed shrimp as larvae are more exploratory, this effect disappears if they also experienced a temporary nutritional stressor during early life. The larval shrimp diet additionally impairs juvenile jumping performance. Finally, larvae that were fed shrimp under normal nutritional conditions produce juveniles with higher overall glucocorticoid levels, and larvae that were fed shrimp and experienced a temporary nutritional stressor produce juveniles with higher stress‐induced glucocorticoid levels. Thus, while it has been demonstrated that consuming the novel, alternative diet can be adaptive for larvae in nature, doing so has marked effects on juvenile phenotypes that may recalibrate an individual''s overall fitness. Given that organisms often utilize diverse diets in nature, our study underscores the importance of considering how diet type interacts with early‐life nutritional adversity to influence subsequent life stages.     

Expression analysis of the two ferrochelatase genes in Arabidopsis in different tissues and under stress conditions reveals their different roles in haem biosynthesis

The Arabidopsis thaliana genome has two genes (AtFC-I and AtFC-II), encoding ferrochelatase, the terminal enzyme of haem biosynthesis. The roles of the two enzymes in the synthesis of haem for different haemoproteins was investigated using reporter gene analysis. A 1.41 kb fragment from the 5' upstream region of the AtFC-II gene was fused to the luciferase gene, and then introduced into tobacco plants, followed by luciferase activity measurements. AtFC-II-LUCwas expressed in all aerial parts of the plant, and was highest in flowers, but it was not expressed in roots. It was unaffected by viral infection, and considerably reduced by wounding or oxidative stress. Similarly, a 1.76 kb region of the AtFC-I promoter was fused to the uidAgene encoding -glucuronidase. AtFC-I-GUS was expressed in all tissues of the plant, but was higher in roots and flowers than in leaves or stems. It was induced by sucrose, wounding and oxidative stress and, most markedly, by plants undergoing the hypersensitive response to TMV infection. Levels of endogenous ferrochelatase activity were increased in pea chloroplasts isolated from wounded leaves, indicating that the induction in promoter activity is likely to result in increased haem biosynthetic potential. Salicylic acid, but not methyl-jasmonate was able to replace the stress treatment in induction of AtFC-I expression, suggesting that the requirement for haem synthesis is part of the defence response. The implications of the results for the different roles of the two ferrochelatases in haem biosynthesis are discussed.     

Behavioral responses of Barbary macaques (Macaca sylvanus) to variations in environmental conditions in Algeria

In this study, the behavioral responses of Barbary macaques to seasonal and interhabitat variations in resource availability were analyzed over an entire annual cycle. Two groups, one in an evergreen cedar–oak forest (Djurdjura) and the other in a deciduous oak forest (Akfadou), were observed. In this paper, references to data on resource availability published elsewhere are made. Time budget has been studied. Variations in foraging and moving time, in day–range lengths, and in time moving in trees have been considered to estimate the variations in foraging effort and thus energy expenditure. Great monthly variations in foraging effort and other activities were observed in both habitats. In early spring, when resource availabilities were maximal, foraging effort was low while monkeys maximized their feeding time (about 5 h/day). In June, during the peak of the birth season and the rearing period, monkeys minimized their feeding time to the benefit of social interactions (to 1.6–2.7 h/day), whatever the food availability, which was low in Akfadou and high in Djurdjura. In addition, foraging effort remained low in Djurdjura, while it increased in Akfadou. Thus, at the beginning of the dry summer period, monkeys in Akfadou were in a less favorable position than those in Djurdjura. At both sites, in periods of food shortage in summer or in winter, monkeys displayed two different strategies. In the former case, their foraging effort increased, while in the second one it remained relatively low. Whatever the foraging effort, monkeys did not reach the same amount of feeding time as in early spring. In the poorest site of Akfadou, foraging effort was globally greater than in the richest site of Djurdjura, especially for adults. At both sites, adult males spent more time feeding than juveniles and less time in social interactions. Results are discussed according to rearing period, temperatures, and day length constraints. The limits of adaptability to different habitats are considered in light of the demographic parameters. Am. J. Primatol. 43:285–304, 1997. © 1997 Wiley-Liss, Inc.     

Heart rate patterns under stress in three species of macaques

Cardiac responses during one hour exposures to three stressful experimental conditions were compared among juvenile females of three species of the genus Macaca (M. mulatta, M. radiata, and M. fascicularis). M. fascicularis showed the highest overall heart rate, and M. mulatta the lowest, in all three conditions. The principal difference between species was in the pattern of change in heart rate over the test sessions. Heart rate declined during the hour for all three species in the first two conditions (home cage novel environment), and the change was most rapid in M. mulatta and slowest in M. fascicularis. In the third and most stressful condition (physical restraint), each species showed a distinct temporal pattern. Heart rate increased over the hour in M. fascicularis, declined in M. radiata, and increased rapidly then declined gradually in M. mulatta. Individual differences in heart rate tended to be consistent within and across conditions. Correlations between behavioral measures of somatic activity and heart rate were generally modest. The results are in accord with other behavioral and physiological differences obtained for the same subjects, and suggest that responses to environmental stimuli reflect fundamental aspects of temperament that may vary substantially even among closely related species. © 1994 Wiley-Liss, Inc.     

Plasma cortisol responses to stress in lactating and nonlactating female rhesus macaques

Lactating female rats without their pups exhibit lower HPA responsiveness to stress than nonlactating females. However, responsiveness to stress is similar when lactating females are tested with their pups and the stressor involves a potential threat to the offspring. This study constitutes the first comparison of stress responsiveness in lactating and nonlactating female nonhuman primates. Subjects were 53 multiparous female free-ranging rhesus macaques. Approximately half of the females were lactating and half were nonpregnant/nonlactating. Blood samples were obtained after capture and after overnight housing in an individual cage. Lactating females were tested with their infants. Lactating females had significantly higher plasma cortisol levels than nonlactating females on both days. Having or not having an infant was also a better predictor of plasma cortisol levels among all females than their age, dominance rank, group of origin, time of day at which the sample was obtained, and time elapsed since beginning of the sampling procedure or since anesthesia. Plasma cortisol levels of lactating females were not significantly correlated with post-partum stage or with the cortisol levels of their infants. Capture, handling, and individual housing in a cage are powerful psychological stressors for free-ranging primates. We suggest that the higher plasma cortisol levels exhibited by lactating females reflect greater responsiveness to stress associated with perception of risks to infants. Hyporesponsiveness to stress may not be a general characteristic of lactation in all mammalian species, but a short-term effect of infant suckling that is most apparent with stressors unrelated to the offspring.     

Wounding patterns in three species of captive macaques

The incidence of wounding in captive groups of rhesus (Macaca mulatta), pigtail (M. nemestrina), and stumptail (M. arctoides) macaques was studied for 21 months. Groups were monitored daily for evidence of wounding. Wounded animals were captured, treated by veterinary staff, and returned following recovery. Records were kept on the age, sex, and species of the recipient, along with the type and location of wound. In each species of macaque, adult males incurred the highest frequency of wounds and multiple wounds of any age-sex class. This contrasted with previously reported behavioral data indicating low frequencies of aggression received by adult males, especially contact aggression and bites. These discrepancies indicate wounding frequencies do not necessarily correspond with behavioral measures of aggression. Inhibition of aggression directed toward infants and the selective avoidance of bites directed to vital body regions were presented as possible mechanisms that modify intragroup aggression. Increased wounding in the birth season under captive conditions suggests that the pattern of increased wounding reported during the breeding season under freeranging conditions may reflect xenophobic responses to immigrating males, rather than direct male-male competition for estrous females.     

Peroxidative stress selectively down-regulates the neuronal stress response activated under conditions of endoplasmic reticulum dysfunction

Oxidative stress has been implicated in mechanisms leading to neuronal cell injury in various pathological states of the brain. Here, we investigated the effect of peroxide exposure on the expression of genes coding for cytoplasmic and endoplasmic reticulum (ER) stress proteins. Primary neuronal cell cultures were exposed to H(2)O(2) for 6 h and mRNA levels of hsp70, grp78, grp94, gadd153 were evaluated by quantitative PCR. In addition, peroxide-induced changes in protein synthesis and cell viability were investigated. Peroxide treatment of cells triggered an almost 12-fold increase in hsp70 mRNA levels, but a significant decrease in grp78, grp94 and gadd153 mRNA levels. To establish whether peroxide exposure blocks the ER-resident stress response, cells were also exposed to thapsigargin (Tg, a specific inhibitor of ER Ca(2+)-ATPase) which has been shown to elicit the ER stress response. Tg exposure induced 7.2-fold, 3.6-fold and 8.8-fold increase in grp78, grp94 and gadd153 mRNA levels, respectively. However, after peroxide pre-exposure, the Tg-induced effect on grp78, grp94 and gadd153 mRNA levels was completely blocked. The results indicate that oxidative damage causes a selective down-regulation of the neuronal stress response activated under conditions of ER dysfunction. This down-regulation was only observed in cultures exposed to peroxide levels which induced severe suppression of protein synthesis and cell injury, implying a causative link between peroxide-induced down-regulation of ER stress response system and development of neuronal cell injury. These observations could have implications for our understanding of the mechanisms underlying neuronal cell injury in pathological states of the brain associated with oxidative damage, including Alzheimer's disease where the neuronal stress response activated under conditions of ER dysfunction has been shown to be down-regulated. Down-regulation of ER stress response may increase the sensitivity of neurones to an otherwise nonlethal form of stress.     

Photochemical responses and oxidative stress in two clones of Coffea canephora under water deficit conditions

The effects of water deficit on photochemical parameters and activities of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as, cellular damages were investigated in two clones of Coffea canephora differing in drought tolerance. After 6 days without irrigation, predawn leaf water potential fell to −3.0 MPa that was accompanied by the suppression of net photosynthesis in both clones. The variable to maximum chlorophyll fluorescence ratio remained unchanged regardless of the imposed treatments. Both clones showed a similar decline (about 25%) in the photochemical quenching coefficient, but only the drought-sensitive clone exhibited an enhancement (31%) of thermal deactivation under water deficit conditions. The quantum yield of electron transport decreased similarly in both genotypes. Under drought conditions, activities of SOD, CAT and APX increased to a greater extent in the drought-tolerant clone than in the drought-sensitive one. This seemed to be matched with higher protection against oxidative stress, as judged from the lower levels of lipid peroxidation and electrolyte leakage in the drought-tolerant clone. Thus, the ability to increase the antioxidant system activity in order to limit cellular damages might be an important attribute linked to the drought tolerance in C. canephora.     

Redox regulatory mechanisms in cellular stress responses

BACKGROUND: Reactive oxygen species are produced in a highly localized and specific pattern in biological stress responses. The present review examines the redox regulatory aspects of a number of molecular stress response mechanisms in both prokaryotes and eukaryotes. SCOPE: The present review provides examples representing both the cytoplasmic stress response, often studied as the heat shock response, as well as the stress response of the endoplasmic reticulum, known as the unfolded protein response. The examples have been selected to illustrate the variety of ways that redox signals mediate and affect stress responses. CONCLUSIONS: Redox regulatory mechanisms are intricately embedded in both the cytoplasmic and endoplasmic reticulum stress responses at multiple levels. Many different stimuli, both internal and external, activate endogenous production of reactive oxygen species as a necessary part of the intracellular communication system that activates stress responses.     

Physiology and proteome responses of two contrasting rice mutants and their wild type parent under salt stress conditions at the vegetative stage

Salinity is one of the major environmental limiting factors that affects growth and productivity of rice (Oryza sativa L.) worldwide. Rice is among the most sensitive crops to salinity, especially at early vegetative stages. In order to get a better understanding of molecular pathways affected in rice mutants showing contrasting responses to salinity, we exploited the power of 2-DE based proteomics to explore the proteome changes associated with salt stress response. Our physiological observations showed that standard evaluation system (SES) scores, Na⁺ and K⁺ concentrations in shoots and Na⁺/K⁺ ratio were significantly different in contrasting mutants under salt stress condition. Proteomics analysis showed that, out of 854 protein spots which were reproducibly detected, 67 protein spots showed significant responses to salt stress. The tandem mass spectrometry analysis of these significantly differentially accumulated proteins resulted in identification of 34 unique proteins. These proteins are involved in various molecular processes including defense to oxidative stresses, metabolisms, photosynthesis, protein synthesis and processing, signal transduction. Several of the identified proteins were emerged as key participants in salt stress tolerance. The possible implication of salt responsive proteins in plant adaptation to salt stress is discussed.     

Urinary cortisol responses of longtailed macaques to five cage sizes,tethering, sedation,and room change

Urinary free cortisol responses to five cage sizes, cage level, room change, tethering adaptation, chronic catheterization, and ketamine sedation were measured in 14 female and 14 male wild-born adult Macaca fascicularis. Urinary free cortisol, a physiological measure of psychological well-being that can be collected unobtrusively, provided a measure of the animals' general adrenocortical response to various conditions over a time course of hours. Urinary free cortisol values in response to stimulation with adrenocorticotropic hormone (ACTH) validated the measure as a reflection of blood values. Cortisol values were expressed as a ratio to creatinine, which normalized for differences in urinary output and body weight (muscle mass). Cage size (20–140% of regulation floor area) and housing level (upper vs. lower cage) had no effect on stress, as measured by cortisol excretion. Room change elicited a slight increase in cortisol excretion for the first day, but not to a level suggesting stress. Sedation, surgery, some aspects of tethering adaptation, and chronic catheterization produced urinary cortisol evidence of stress. Even so, animals varied in their responses and all showed adaptation. Males and females did not differ in normal mean values but females tended to have higher cortisol levels in response to potential stressors investigated in this study. Cortisol levels continued to decline gradually throughout the study. © 1993 Wiley-Liss, Inc.     

Male endocrine responses to females: Effects of social cues in cynomolgus macaques

This study tested the hypothesis that the hormonal responses of male macaques to sexually receptive females are mediated by specific socioenvironmental cues. Twelve, socially living male Macaca fascicularis were exposed to two-ovariectomized, estrogen-primed females under pair test, peer group, and peer group without dominant male conditions. Preexposure to postexposure changes in serum cortisol levels and testosterone levels were examined in relation to male dominance rank, age, and conditions of access to stimulus females. The males displayed significantly lower cortisol increases and greater testosterone increases with females under peer group than pair test conditions. Dominant males displayed greater testosterone increases than subordinate males under peer group conditions. The testosterone levels of subordinate males were greatly enhanced by removing the dominant male from each group. Adult males displayed greater cortisol responsivity to changes in conditions of access to females than did subadult males. Subadult males displayed greater testosterone responsivity to removal of the dominant male from the group than did adult males. It is concluded that specific social cues can greatly influence the endocrine responses of males to receptive females, and further, that there may be optimal socioenvironmental parameters for eliciting testosterone increases in male primates.