Endocrine aspects of social instability in the olive baboon (Papio anubis)

The relationships among social status and the cortisol and testosterone stress-response were studied in the non-natal male members of a troop of olive baboons (Papio anubis) before and during a period of social instability. The unstable period was characterized by dominance interactions that were more frequent, more inconsistent, and produced less linear hierarchies than during the stable period. These changes occurred predominantly among the high-ranking males. Such males engaged in coalitions and consortship harassments at a higher rate during the unstable period than during the stable period. Finally, high-ranking males had the highest rates of involvement in and initiation of escalated fighting during the unstable period, in contrast with the stable period. A number of endocrine correlates of instability emerged. During the stable period, high-ranking males (by reproductive criteria) showed an endocrine profile different from that of subordinates. They had the lowest basal cortisol titers, the largest and fastest increases in cortisol titer during stress, and had elevated testosterone titers during stress. None of these attributes was found in high-ranking males during the unstable period. Males during the unstable period had elevated basal cortisol titers, suppressed cortisol responsiveness to stress, and no longer showed elevated testosterone titers during stress. When psychological advantages associated with social status in a stable social environment were lost, endocrine efficiency previously associated with social status was apparently also lost. Further, high-ranking males, who were most aggressive exclusively during the unstable period, had the highest absolute titers of testosterone exclusively during the unstable period. Thus, elevated testosterone and high levels of aggression were unrelated to social status during the period of social stability, but were traits associated with dominant individuals during the unstable period.     

A pilot study of the social correlates of levels of urinary cortisol,prolactin, and testosterone in wild long-tailed macaques (Macaca fascicularis)

Urine samples were collected from individuals in a wild population of Sumatran long-tailed macaques (Macaca fascicularis), and the levels of cortisol, immunoreactive prolactin, and (for males) testosterone were determined. The amount of foraging during the 2 hr preceding urine collection were found to affect the levels of urinary cortisol, but not those of the other hormones. Immigration into a new group and having one's infant kidnapped led to increased levels of cortisol. Levels of cortisol and testosterone were correlated both within and between individuals, whereas prolactin varied independently. The effects of age, reproductive status, and social rank on the mean values of individuals were also examined. Lactating females had higher prolactin levels than non-lactating ones; reproductive state interacted with the age effect on prolactin and possibly cortisol. No effects of social status were found in spite of a small, but consistent effect of rank on birth rate in this population. Among males, age and rank are strongly linked. The low ranking old males had increased levels of cortisol, even though the younger high-ranking males were involved in the fiercest conflicts.     

Plasma testosterone and male dominance in a Japanese macaque (Macaca fuscata) troop compared with repeated measures of testosterone in laboratory males

Plasma testosterone levels measured by radioimmunoassay did not correlate with dominance rank or aggressive behavior in 21 adult males of a natural troop of Japanese macaques (Macaca fuscata). The data were replicated during two consecutive breeding seasons. Levels of male dominance and aggressive behavior were highly correlated from year to year, but testosterone levels of individual males were not. Nor were individual levels of testosterone correlated in five laboratory males sampled every 15 min over a 2-hr period. These laboratory males showed multiple, apparently random peaks but the mean testosterone level of 11.73 ng/ml did not vary significantly throughout the 120 min that were studied. By demonstrating that the stress of blood collection did not depress plasma testosterone titers in laboratory males, these data validated the method used in the study of the natural troop.     

Testosterone and cortisol jointly regulate dominance: Evidence for a dual-hormone hypothesis

Traditional theories propose that testosterone should increase dominance and other status-seeking behaviors, but empirical support has been inconsistent. The present research tested the hypothesis that testosterone's effect on dominance depends on cortisol, a glucocorticoid hormone implicated in psychological stress and social avoidance. In the domains of leadership (Study 1, mixed-sex sample) and competition (Study 2, male-only sample), testosterone was positively related to dominance, but only in individuals with low cortisol. In individuals with high cortisol, the relation between testosterone and dominance was blocked (Study 1) or reversed (Study 2). Study 2 further showed that these hormonal effects on dominance were especially likely to occur after social threat (social defeat). The present studies provide the first empirical support for the claim that the neuroendocrine reproductive (HPG) and stress (HPA) axes interact to regulate dominance. Because dominance is related to gaining and maintaining high status positions in social hierarchies, the findings suggest that only when cortisol is low should higher testosterone encourage higher status. When cortisol is high, higher testosterone may actually decrease dominance and in turn motivate lower status.     

Testosterone and cortisol jointly regulate dominance: Evidence for a dual-hormone hypothesis

Traditional theories propose that testosterone should increase dominance and other status-seeking behaviors, but empirical support has been inconsistent. The present research tested the hypothesis that testosterone's effect on dominance depends on cortisol, a glucocorticoid hormone implicated in psychological stress and social avoidance. In the domains of leadership (Study 1, mixed-sex sample) and competition (Study 2, male-only sample), testosterone was positively related to dominance, but only in individuals with low cortisol. In individuals with high cortisol, the relation between testosterone and dominance was blocked (Study 1) or reversed (Study 2). Study 2 further showed that these hormonal effects on dominance were especially likely to occur after social threat (social defeat). The present studies provide the first empirical support for the claim that the neuroendocrine reproductive (HPG) and stress (HPA) axes interact to regulate dominance. Because dominance is related to gaining and maintaining high status positions in social hierarchies, the findings suggest that only when cortisol is low should higher testosterone encourage higher status. When cortisol is high, higher testosterone may actually decrease dominance and in turn motivate lower status.     

Endocrine correlates of rank,reproduction, and female-directed aggression in male Japanese macaques (Macaca fuscata)

Fecal testosterone and cortisol levels in six wild male Japanese macaques (Macaca fuscata), three of high rank and three of low, were analyzed to investigate the hormonal correlates of rank, reproduction, and female-directed aggression. The study encompassed the 6-month mating season, from October 1999 to March 2000, during which time 251 fecal samples and approximately 550 h of behavioral data were collected. Dominant males were not found to differ from subordinate males in overall rates of aggressive or copulatory behavior. Likewise, testosterone excretion, which peaked in the early part of the mating season and declined gradually thereafter, did not differ significantly by rank. High-ranking males, however, were observed to excrete significantly higher levels of cortisol than low-ranking males, suggesting that dominance may carry costs. The two hormones were found to be inversely correlated in the two most dominant males, but independent in all others. Rate of noncontact aggression was significantly correlated with testosterone, while no significant relationships were observed between testosterone and contact aggression nor any aspect of copulatory behavior. These data further support the contention that social subordinance and stress are not inexorably linked, as well as suggest that elevated glucocorticoid concentrations in high-ranking males may reflect increased metabolic costs associated with dominant male reproductive strategy.     

The implications of stress on male mating behavior and success in a sexually dimorphic polygynous mammal, the grey seal

Studies on primates and other taxa have shown that the physiological response of an individual to stress reflects their social status. We combined behavioral observations with measures of stress to test the hypothesis that stress is an important physiological determinant of mating behavior and success in the male grey seal. Known-age males (N=19) were studied during the breeding seasons of 2004 and 2005 at Sable Island, Canada. The stressor was a capture and restraint period of 35 min and serial samples of cortisol and testosterone were taken as measures of stress. The mean baseline concentrations of cortisol and testosterone were 9.7+/-0.5 ug/dl and 6.2+/-0.6 ng/mL, respectively. The baseline cortisol concentration was negatively correlated with the duration of time a male spent at a site (r=-0.507, P=0.027), which was a strong correlate of mating success (r=0.659, P=0.002). All males experienced an increase in the concentration of cortisol during the restraint period (79.1+/-8.4%; CV=46.1%). The percentage rise in cortisol during restraint was correlated with the mean duration of time spent at a site (r=0.544, P=0.016) and thus success. The concentration of testosterone also increased during the restraint period (32.8+/-9.7%). This might be an adaptive response to maintaining the ability to reproduce while under stress. Our study indicates that stress is an important determinant of success in male grey seals. More successful males might exhibit an adaptive response to stress by maintaining low concentrations of cortisol during breeding.     

Social cues and hormone levels in male Octodon degus (Rodentia): a field test of the Challenge Hypothesis

Social interactions are important factors determining and regulating individual behaviors. Testosterone has been related to agonistic interactions, while glucocorticoids have been related to social stress, especially during interactions of dominance. We compared testosterone and cortisol concentrations in male degus (Octodon degus, Rodentia) under laboratory conditions without male social interactions, with data from wild males in nature. Under natural conditions, males should present higher levels of testosterone during the breeding season due to social interactions (Challenge Hypothesis). Alternatively, intense social instability could act as a stressing environment, raising glucocorticoids, which inhibit testosterone concentrations. Our results show a significant increase in agonistic interactions between males during the breeding season, and disappearance of non-agonistic male interactions during this period. Hormone levels in breeding season show nonsignificant differences between laboratory groups, but testosterone concentrations in field males were significantly higher than in laboratory males. Testosterone levels were similar among pre-breeding and breeding periods, but in field animals the concentration was approximately 30% higher than in laboratory degus. In field animals, we found two different mating strategies: resident males, with territorial behavior, and transient males, displayed an opportunistic approach to females. Finally, cortisol presents a similar pattern in both laboratory and field animals; pre-breeding values of cortisol are higher than during the breeding season. This suggests that social interactions in O. degus activate a rise in testosterone, supporting the Challenge Hypothesis, and could be considered as partial support of the Social Stress Hypothesis.     

A multidisciplinary study on social status and the relationship between inter-individual variation in hormone levels and agonistic behavior in a Neotropical cichlid fish

Social animals with hierarchal dominance systems are particularly susceptible to their social environment. There, interactions with conspecifics and hierarchal position can greatly affect an individual's behavior, physiology and reproductive success. Our experimental model, Cichlasoma dimerus, is a serially-monogamous Neotropical cichlid fish with a hierarchical social system, established and sustained through agonistic interactions. In this work, we aimed to describe C. dimerus social structure and its association with hormonal profiles and testicular cellular composition. We recorded and quantified agonistic interactions from the territorial pair, i.e. the top ranked male and female, and the lowest ranked male of stable social groups. Plasma levels of 11-ketotestosterone (11-KT), testosterone, 17β-estradiol (E₂) and cortisol were measured by ELISA. Results show that territorial pairs cooperatively guarded the territory, but rarely attacked in synchrony. Territorial males had higher testosterone and 11-KT plasma levels than non-territorial males, while E₂ and an index of its metabolization from testosterone were higher in non-territorial males. No difference was observed in cortisol levels. Plasma 11-KT and an index of the conversion of testosterone to 11-KT, positively correlated with the frequency of aggressiveness, while E₂ showed the opposite pattern. Territorial males had a higher gonadosomatic index than non-territorial males. The quantification of testicular cellular types revealed that the percentage of spermatocytes and spermatids was higher in non-territorial males, while territorial males showed a greater percentage of spermatozoa. Thus, C. dimerus male social position within a stable hierarchy is associated with distinct behaviors, steroid levels and testicular degree of development.     

Hormonal and behavioural correlates of male dominance and reproductive status in captive colonies of the naked mole-rat,Heterocephalus glaber.

Naked mole-rat colonies are societies with a high reproductive skew, breeding being restricted to one dominant female (the ''queen'') and 1-3 males. Other colony members of both sexes are reproductively suppressed. Experimental removal of breeding males allowed us to investigate the relationship between urinary testosterone and cortisol, dominance rank, and male reproductive status. Dominance rank was strongly correlated with body weight, age, and urinary testosterone titres in males. No relationship between urinary cortisol levels and male reproductive status or dominance was found. Breeding males were among the highest-ranking, heaviest and oldest males in their respective colonies, and were succeeded by other high-ranking, large, old colony males. In contrast to females, no evidence of competition over breeding status was observed among males. Male-male agonism was low both before and after removal of breeders and mate guarding was not observed. The lower reproductive skew for males compared with female skew or queen control over male reproduction may explain why males compete less strongly than females over breeding status after removal of same-sexed breeders.     

A preliminary investigation of urinary testosterone and cortisol levels in wild male mountain gorillas

Urinary steroid hormone levels were measured in wild male mountain gorillas (Gorilla gorilla beringei) to determine how levels of testosterone and cortisol corresponded with age and social rank. Urine samples were collected noninvasively from 18 males, ranging in age from 3–26 years, in three groups of wild mountain gorillas at the Karisoke Research Center, Rwanda, Africa, and samples were analyzed using radioimmunoassay procedures. Males were classified as being immature (<7 years), maturing (10–13 years), or adult (+13 years of age). Immature males had significantly lower levels of testosterone and higher levels of cortisol than both maturing and adult males. No differences in testosterone or cortisol levels were found between maturing and adult males. Dominant males exhibited a trend toward significantly higher levels of testosterone than subordinate males, but no difference was found between cortisol levels of dominant and subordinate males. These results suggest that the increase in testosterone associated with puberty occurs prior to any outward sign of development of secondary sexual characteristics. Within-group male–male competition may affect testosterone levels, but the lack of difference in cortisol levels between dominant and subordinate males suggests that subordinate males are not socially stressed, at least as measured by cortisol. Am. J. Primatol. 43:51–64, 1997. © 1997 Wiley-Liss, Inc.     

Dispersal Status Influences Hormones and Behavior in the Male Spotted Hyena

Male spotted hyenas (Crocuta crocuta) reach puberty at 24 months of age and then invariably emigrate from their natal clans 1 to 38 months later. Thus there are two classes of reproductively mature males in everyCrocutaclan: adult natal males born in the clan and adult immigrant males born elsewhere. In one free-living hyena population in Kenya, these two groups of males were compared with respect to measures of aggression, social dominance, sexual behavior, and circulating hormone levels. Adult natal males engaged in higher hourly rates of aggression than did immigrants, won all fights with immigrants, and were socially dominant to immigrants. In addition, adult natal males engaged in far lower hourly rates of sexual behavior with resident females than did immigrants, and natal males were never observed to copulate with natal females. Mean basal plasma cortisol values did not differ between the two groups of adult males, but cortisol concentrations in immigrants were positively correlated with tenure in the clan and with immigrant male social rank. Adult natal males had plasma testosterone levels significantly lower than those of immigrants. Social rank and plasma testosterone values were positively correlated among immigrant males. Thus two different relationships appear to exist between circulating testosterone and social rank in maleCrocuta:one apparent in immigrants and the other in natal adult males. Our results suggest that dispersal might disinhibit testosterone secretion in postpubertal male hyenas.     

Defense of females, but not social status, predicts plasma androgen levels in male spotted hyenas

A positive correlation between male social status and testosterone levels is expected and often found in social species with high rates of agonistic interactions or when social relationships among males are unstable. In contrast, in species with low rates of agonistic interactions or when social relationships are stable, testosterone levels should not correlate with social status. The "challenge hypothesis" predicts that androgen levels should rise during periods of courtship or mate guarding. We addressed these questions in free-ranging spotted hyenas, a species with low rates and low intensities of aggression among males but where males spend extensive effort to court females. In males, we measured testosterone, its precursor androstenedione, and its metabolite 5alpha-dihydrotestosterone. As predicted, testosterone levels were significantly higher and androstenedione levels tended to be higher in males that, at the time of sampling, defended a female, compared with males that did not defend a female. Also, as predicted, there was no correlation between social status and androgen levels in male spotted hyenas.     

Circulating androgens are influenced by parental nest defense in a wild teleost fish

While social interactions influence vertebrate endocrine regulation, the dynamics of regulation in relation to specific behaviors have not been clearly elucidated. In the current study, we investigated whether androgens (testosterone) or glucocorticoids (cortisol) play a functional role in aggressive offspring defense behavior in wild smallmouth bass (Micropterus dolomieu), a teleost fish with sole paternal care. We measured circulating testosterone and cortisol concentrations in plasma samples taken from parental males following a simulated nest intrusion by a common nest predator, the bluegill sunfish (Lepomis macrochirus). To understand whether endocrine regulation changes across the parental care period, we looked both at males guarding fresh eggs and at males guarding hatched embryos. Plasma testosterone levels increased in males subjected to a simulated nest intrusion when compared to sham controls. Testosterone concentrations in males guarding embryos were lower than in males guarding fresh eggs, but circulating testosterone was positively correlated with the level of aggression towards the nest predator at both offspring development stages. However, there was no increase in cortisol levels following a simulated nest intrusion, and no relationship between cortisol and any measured parameter. These results suggest that androgens play an important role in promoting aggressive nest defense behavior in teleost fish.     

Diurnal patterns of testosterone, dihydrotestosterone, estradiol, and cortisol in serum of rhesus males: Relationship to sexual behavior in aging males

This study was carried out to determine differences between old and young rhesus males in levels and diurnal patterns of testosterone, dihydrotestosterone, cortisol, and estradiol, and to determine correlations between these hormones and sexual behavior of the old males. Blood was drawn from old (n = 9) and young (n = 9) rhesus males over 5 consecutive days at 0900, 1300, and 2100 hr. The two groups of males did not differ in mean serum levels of testosterone, dihydrotestosterone, or estradiol at any time. Although the old and young did not differ in cortisol levels at 0900 and 1300 hr, the cortisol levels at 2100 hr were lower in the old males. Diurnal variations in testosterone, dihydrotestosterone, and cortisol were comparable in old and young males. Mean serum levels of estradiol were significantly higher at 0900 hr than at 1300 hr in the old males, whereas in the young males estradiol levels did not differ with time of day. There was a significant positive correlation between testosterone and yawning rate, and cortisol levels were correlated positively with rate of contacting, rate of mounting, and percentage of tests with erections. The decline in sexual performance of old rhesus males cannot be attributed to changes in the levels or diurnal patterns of testosterone, dihydrotestosterone, or estradiol, but lower cortisol levels in old males may contribute to the decline in sexual behavior.     

Baseline and stress-induced glucocorticoids during reproduction in the variable flying fox, Pteropus hypomelanus (Chiroptera: Pteropodidae)

Baseline and stress-responsive glucocorticoid (GC) levels were assessed during early pregnancy, late pregnancy, and lactation in female variable flying foxes (Pteropus hypomelanus) and in males over the same time period. Animals were maintained in a breeding colony in captivity. High levels of both cortisol and corticosterone were detected, with total plasma GC levels being among the highest documented in vertebrates (up to 3000 ng/ml in individual animals, with cortisol being the primary GC, accounting for approximately 78% of total GCs), and significantly greater in males than in females. Plasma levels of cortisol and corticosterone showed nearly identical profiles within each sex, with the exception of females in late pregnancy, in which corticosterone, but not cortisol, increased significantly. Baseline levels of plasma cortisol were highest in September (when pups were between 1 and 2 months of age) in both sexes, which may be related to the approaching onset of the mating period. There was a continuum in the magnitude of the response to stress (handling and sampling) over time in females, with the greatest stress response in early pregnancy, a dampened response during late pregnancy, and no significant stress response during lactation. Surprisingly, males failed to exhibit elevated GCs after this stress, but did have significant stress-induced hyperglycemia and suppression of plasma testosterone levels. This may be due to their high (perhaps maximal) baseline levels, which suggests that being in a breeding group was chronically stressful for males.     

Neuroendocrine response to female ovulatory odors depends upon social condition in male common marmosets, Callithrix jacchus

Male mammals show rapid behavioral and hormonal responses to signals from sexually receptive females. However, rapid endocrine responses to female signals have not been observed in a nonhuman primate. Here, we tested the behavioral and hormonal response of male common marmosets (Callithrix jacchus) to isolated scent secretions from ovulatory females or to vehicle control scent. Fifteen males were tested in their home cage for behavioral and hormonal responses. These males showed increased investigative and arousal behaviors to the ovulatory scent compared to the vehicle scent. Time sniffing the scent substrate and the duration of erections were significantly elevated in relation to the vehicle scent. Thirty minutes after presentation of ovulatory scent, males showed a significant increase in testosterone compared to the vehicle, but there was no difference in cortisol values. To better control for scent presentation, 15 additional males were tested under a controlled scent exposure. Current social housing condition influenced the male's testosterone response to the ovulatory scent. Single and paired males showed significant increases in testosterone levels with the ovulatory scent but did not increase cortisol levels. Single males also showed the highest change in testosterone with the ovulatory scent, but fathers showed no changes. These results indicate that a rapid hormonal response to sexually arousing cues occurs in marmosets, and the data suggest that a male's social condition influences how he responds to sexually relevant cues.     

Behavioral coping strategies in a cichlid fish: the role of social status and acute stress response in direct and displaced aggression

The African cichlid fish, Astatotilapia burtoni, has a complex social system with a sophisticated social hierarchy that offers unique opportunities to understand how social rank and its physiological substrates relate to behavioral strategies. In A. burtoni, a small fraction of the males are dominant (T, territorial), as distinguished by being large, brightly colored, reproductively active, and aggressively defending territories. In contrast, the majority of males are non-dominant (NT, non-territorial), being smaller, drably colored, sexually immature, and typically schooling with females. The social system is regulated by aggressive interactions between males and behavioral responses to aggression can be direct or displaced with respect to the animal that acts. To determine whether direct and displaced behaviors are differentially exhibited by T and NT males, individuals were shown a video presentation of a dominant male displaying aggressively. Analysis of aggressive acts toward the video display and displaced activity toward a tank mate revealed that T males exhibited more direct behavior (toward the video display), while NT males engaged in more displaced behavior (toward tank mates). Because similar experiments with primates suggest that shifts in behavioral strategies are linked to changes in the stress response (as measured by circulating cortisol levels), we measured cortisol levels of T and NT males following exposure to the aggressive stimulus. Although in some animals subordinate males are reported to have higher cortisol levels, here we show that in A. burtoni the endocrine response to specific situations can vary considerably even among animals of the same status. Interestingly, NT males with intermediate cortisol levels showed more directed behavior while NT males with both high and low cortisol levels showed more displaced. This suggests an optimal physiological stress response in NT males that predisposes them to challenge aggressors perhaps making it more likely for them to ascend in status.     

Hormones and behavior of prepubertal and peripubertal chimpanzees

Twenty-one chimpanzees ranging in age from 2.9 to 9.2 years at the midpoint of a study consisting of five 4-week blocks were studied behaviorally in four groups of five or six animals per group, balanced for age and sex. Blood samples for radioimmunoassay of follicle-stimulating hormone (FSH), luteinizing hormone, 17 beta-estradiol, testosterone, dehydroepiandrosterone (DHA), DHA sulfate (DHAS), and cortisol were obtained once each 4-week block. Sex differences were found only in the categories of play duration and initiative and genital inspection, all of which were greater for the males. Several categories (6) of play and other affiliative behaviors were negatively correlated with age and/or body weight for the males, whereas fewer of those categories (2) were so correlated in the females. Hierarchical behavior, genital inspection, solitary behavior other than play, and autogrooming were all positively correlated with age and/or body weight for the males, and only autogrooming for the females. FSH and testosterone levels and testicular volume were positively correlated with age and body weight in the males, whereas for the females cortisol was negatively correlated with body weight and only FSH and the ratios of DHA and DHAS to cortisol were positively correlated with age and/or body weight. Most of the behaviors that were significantly correlated with age and body weight for the males were also correlated in the same direction with FSH and testosterone levels and testicular volume, but not with DHA or DHAS levels. The data are consistent with the view that testosterone, but not the adrenal androgens DHA and DHAS, contributed to the behavioral development of the males. There were few significant correlations between hormones and behavior for the females and interpretation is not clear. The absence of age-related increases in DHA and DHAS of both the males and females, in contrast to the pattern of FSH (and testosterone for the males), supports the growing consensus that adrenarche and puberty are independent developmental processes. The absence of any strong correlations between behavior and levels of the adrenal androgens in either the males or females suggests that adrenarche per se is not a significant event in the behavioral development of chimpanzees.     

Adrenal-testicular-pituitary relationships in the cheetah subjected to anesthesia/electroejaculation

The influence of electroejaculation on the acute response in serum cortisol, testosterone and luteinizing hormone (LH) was studied in the South African cheetah . Males were either anesthetized with CT-1341 and 1) serially bled only (controls, n = 7) or 2) serially bled during and following a regimented protocol of rectal probe electroejaculation (n = 14). In the control cheetahs , mean cortisol concentrations declined over time (P less than 0.05) and neither testosterone nor LH varied over the 145-min sampling interval. Serum cortisol rose immediately in electroejaculated cheetahs , peaked at the end of electroejaculation in 13 of 14 males and then declined during the next 90 min. Temporal profiles and serum levels of testosterone and LH were similar in the electroejaculated and control groups (P greater than 0.05). Within individual cheetahs , serum levels of LH and testosterone were highly correlated (r = 0.77, P less than 0.01). Awake (n = 2) and CT-1341 anesthetized (n = 2) cheetahs also were bled and then challenged with an i.m. injection of 25 IU adrenocorticotropic hormone (ACTH, Cortrosyn). Serial blood samples were collected during the next 2 h and assayed. Cortisol concentrations prior to ACTH administration were greater in awake than in anesthetized males. In all animals, cortisol rose immediately and peaked within 30-60 min of injection. Whereas all 4 ACTH-treated cheetahs produced cortisol titers in excess of 200 ng/ml, only 4 of 14 electroejaculated males produced cortisol levels comparable to this concentration range. Neither testosterone nor LH profiles were affected by ACTH-induced elevations in cortisol.(ABSTRACT TRUNCATED AT 250 WORDS)