Plasma Testosterone Titers Research Articles

The effects of terrestrial and breeding densities on corticosterone and testosterone levels in spotted salamanders, Ambystoma maculatum

We examined plasma concentrations of corticosterone (CORT) and testosterone in male free-living and captive spotted salamanders, Ambystoma maculatum (Shaw, 1802), to determine if (i) they mounted significant CORT responses to conspecifics in captive enclosures during potential competition for limited burrows; (ii) artificially induced, increased breeding densities altered CORT and testosterone levels in a free-living population; and (iii) testosterone in free-living males varied seasonally. We found increased baseline CORT in captive male spotted salamanders exposed to conspecifics under high densities (4 animals with only 1 burrow). Original residents of the cage, however, had significantly higher baseline CORT titers than did newly introduced animals, and titers were significantly higher in animals cohabiting a burrow than those remaining outside the burrow. This suggests that spotted salamanders perceive con specifics as threats for burrows and become stressed when forced to share these resources. In contrast, free-living spotted salamanders during breeding showed no significant increases in baseline CORT or testosterone in high-density treatments. This suggests that increased adult density during breeding is not stressful to these salamanders. Finally, spotted salamanders had greater plasma testosterone titers in fall than in spring, suggesting that they are dissociated breeders.

IDENTIFICATION OF REPRODUCTIVE STATUS IN FEMALE FROGS—A QUANTITATIVE COMPARISON OF NINE METHODS

Many techniques commonly used by herpetologists for monitoring amphibian populations and communities yield censuses of the total adult population size (N). However, for many studies, e.g., of reproductive output, development of populations and potential for evolutionary changes, the effective population size (Ne) must be known. While modern molecular techniques make it possible to measure Ne, they are expensive, work-intensive and may not be possible or necessary for many questions on amphibian reproduction. For females of two species of water frog (Rana lessonae and R. esculenta), we investigate the effectiveness of several techniques to determine the presence or absence of eggs. The direct methods are (1) dissection of dead frogs and (2) a small skin incision into the abdominal side of live females. The indirect methods, all applied to live frogs, include (3) visual inspection of body shape, (4) tactile inspection of the epidermis, (5) transillumination with a strong cold light source, (6) ultrasound, (7) electromagnetic measurement of total body electrical conductivity (TOBEC), (8) calculation of body condition index and (9) analysis of blood plasma testosterone titers. Only two indirect methods were somewhat successful at predicting whether females were gravid. Testosterone titers (9) yielded the best results (ca. 80–90% effective). Body condition (8) was also significantly related to egg presence or absence, but predicted gravidity only weakly. We suggest that a combination of skin incision and hormone analysis provides a fairly good estimate of gravidity. When complemented by mark-recapture techniques and performed on the same individuals at different times of the season, this combination yields estimates not only of the reproductive output of the study population but also of the relative contribution of different females.

The ontogeny of male Guinea pigs living under different housing conditions

This study investigated the behavioural development of 21 male Guinea pigs from their 30th to their 50th day of age, This time period began about 1 week after weaning and ended about 3 weeks before sexual maturity. Seven individuals (designated as CM) lived in colonies together with 12 adult males and 12 adult females (enclosure size: 7 m2); seven individuals (PM) were housed in pairs of one male and one female (enclosure size: 0.5 m2); seven individuals (SM) were housed singly (enclosure size: 0.5 m2). The different housing conditions significantly influenced the frequencies of specific behaviours. PM, for example, displayed courtship behaviour 20-30 times more often than CM. Play behaviour was most frequent in PM, while it only rarely occurred in SM. At 50 days of age CM had higher body-weights than PM or SM. While, at this age, CM plasma testosterone titers remained stable during an acute challenge (open-field test), PM and SM showed a significant decrease in their androgen concentrations. From these data it was concluded, that young male Guinea pigs develop more favourably in colonies than in pairs or singly. Stereotyped movements in zoo animals R. Templin FU Berlin, Institut fiir Neuropsychopharmakologie, Ulmenallee 30, D14050 Berlin, Germany Abstract Stereotyped movements performed over a long time and outside the original eliciting situation are described as established stereotypies. To investigate the spatial and temporal structure of established stereotypies, zoo animals performing these for more than a year were examined. The frequency of stereotyped walking in a lowland tapir ( Tapirus terrestris) was low in the first 15 min after being let out of its indoor cage and than increased toStereotyped movements performed over a long time and outside the original eliciting situation are described as established stereotypies. To investigate the spatial and temporal structure of established stereotypies, zoo animals performing these for more than a year were examined. The frequency of stereotyped walking in a lowland tapir ( Tapirus terrestris) was low in the first 15 min after being let out of its indoor cage and than increased to

Simulated Drought Affects Male Reproductive Function in Deer Mice (Peromyscus maniculatus bairdii)

Reproduction stops during the breeding season of many rodent populations, including Peromyscus maniculatus. The proposition that water availability mediates the midseason breeding hiatus in male deer mice was evaluated in the present study. Paired testicular and epididymal weights (absolute and relative to body mass) were reduced after 10 wk of restricted water consumption. Spermatogenesis was also impaired by limited water intake. Blood plasma testosterone concentrations were reduced, but plasma luteinizing hormone (LH) titers were unaffected by water restriction. Finally, the number of offspring sired was reduced in mice with restricted access to water. Carcass water content did not significantly differ between animals with restricted (25% of ad lib.) or unrestricted access to water; however, body mass was reduced about 15% after chronic water intake restriction. Although reproductive function (i.e., reproductive organ mass, plasma testosterone titers, and sperm counts) was significantly depressed in water-restricted mice, the reproductive systems of about 25% of the animals were relatively unaffected by water restriction. In order to study the physiological factors associated with individual reproductive responses to water restriction, animals were rank ordered according to their epididymal sperm numbers; individuals in the top (Q₁) and bottom (Q₄) quartiles of epididymal sperm counts were further compared. Water-restricted Q₁ deer mice did not significantly differ on any parameter from mice with ad lib. access to water. No water-restricted Q₄ deer mice possessed any epididymal sperm. Deer mice in Q₄ significantly reduced paired testicular and epididymal masses as compared with animals in the top quartile. It was important that Q₄ deer mice reduced their body mass by 34%. Plasma LH titers were significantly depressed in Q₄ animals as compared with Q₁ mice or mice with ad lib. water. Body fat content was also reduced only in the Q₄ deer mice. Taken together, these findings suggest that water availability may act as an extrinsic cue to suppress fertility in deer mice independently of temperature and day length and somewhat independently from food because despite an absolute reduction in food consumption with the onset of water restriction, food intake corrected for body mass did not differ. Animals that stopped reproductive function (Q₄ mice) lost substantial body fat and total mass. Water-restricted males that maintained body fat levels also maintained reproductive function. Differential hydrolysis of adipose tissue in response to decreased testosterone titers may account for the phenotypic variation in reproductive responsiveness to water restriction. These results are discussed in terms of their ecological and evolutionary implications.

Naltrexone Normalizes the Suppression but not the Surge of Δ5-3β-Hydroxysteroid Dehydrogenase Activity in Leydig Cells of Stressed Rat Fetuses*

Rat fetuses from mothers stressed chronically by immobilization and high intensity illumination beginning on day 14 of gestation have higher than normal levels of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta HSD) activity in Leydig cells on day 17 of gestation and lower than normal levels on days 18 and 19. Plasma testosterone titers in normal and stressed male fetuses closely parallel the activity of 3 beta HSD in fetal Leydig cells. In the present study quantitative cytochemistry was used to determine whether the stress-induced alterations in 3 beta HSD activity could be prevented by treating the mother with naltrexone, an opioid receptor blocker, before each stress session. Naltrexone normalized 3 beta HSD activity on days 18 and 19 of gestation, suggesting that the stress-induced suppression involves the endogenous opioid system. In contrast, naltrexone did not prevent the elevation in enzyme activity seen on day 17 in stressed fetuses. The persistence of a stress-induced surge on day 17, in spite of naltrexone therapy, suggests that some nonopioid mechanism is operational at that time.

Androgens exert opposite effects on body mass of heavy and light meadow voles

The influence of gonadal hormones on body mass of adult male meadow voles varied systematically as a function of the animals' baseline body weight; heavier voles decreased and lighter voles increased their body mass after castration. Testosterone replacement reversed the effects of castration; changes in body mass during hormone treatment were negatively correlated with changes observed after castration. Body mass of intact males was not correlated with plasma testosterone titers. Individual differences in body mass of male voles appear to reflect variations among animals in substrate responsiveness to hormones rather than differences in circulating hormone levels.

Short-term responses of plasma norepinephrine, epinephrine, glucocorticoid and testosterone titers to social and non-social stressors in male guinea pigs of different social status

The short-term effects on norepinephrine (NE), epinephrine (E), glucocorticoid (CS) and testosterone (T) levels of (a) taking blood samples, and (b) an agonistic encounter in an experienced fighter's home cage were examined in 15 male guinea pigs living in large heterosexual colonies for 8 to 19 months. Four tests were performed 1 month apart. In the 1st, 2nd and 3rd test 3 blood samples were taken from each male in a strange room within 30 min (sampling times were designated as 0, 20 and 30 min, respectively). In the 4th test blood samples were taken on the same time schedule, however, the males were given 10 min agonistic encounters 10 min after the initial blood sampling. The main findings were as follows: (1) in response to taking blood samples and fighting CS and NE titers increased significantly, whereas E values did not change in a significant way. T titers decreased 10 min after the agonistic encounter. (2) The % changes of NE, E, CS and T at 20 and 30 min did not differ whether an agonistic encounter took place or only blood samples were taken. (3) According to their behaviors displayed in the colonies the males were divided into high (N=6) and low (N=9) ranking individuals. When only blood samples were taken the males' social status was only reflected by a tendency towards higher T levels in high ranking males, however not by NE, E and CS titers. (4) High ranking males showed lower NE titers than low ranking males directly after the agonistic encounter. No further relationships between long-term social status and short-term endocrine responses were found. (5) According to their behaviors displayed during the agonistic encounters the males were divided into fighters (F) (5 out of 6 high and 3 out of 9 low ranking individuals), and non-fighters (NF) (1 high, 6 low ranking individuals). F and NF did not differ in T and CS values, NE titers, however, were significantly higher in NF compared with F before, directly after the encounter as well as 10 min later. E was significantly higher in NF than in F directly after the encounter. One month before the contest prospective NF showed higher NE levels at 0, 20 and 30 min sampling times than prospective F when only blood samples were taken. These findings point to a more important role of catecholamines than CS and T in guinea pig intermale agonistic encounters. NE responsiveness may have predictive value for the behavior in contest situations.

Diurnal sensitivity of the neuroendocrine-reproductive axis to the antigonadotrophic influence of melatonin in male Syrian hamsters with experimentally altered cortisol rhythms.

Two different experimental models were used to test if a temporal relationship exists between the rhythm of adrenal steroid secretion and the vulnerability of the hamster reproductive system to short photoperiod exposure or to the daily afternoon injection of melatonin. In the first experiment adrenalectomized hamsters were implanted with a cortisol pellet to provide a sustained, rather than rhythmic, level of the hormone. The animals were either placed in short photoperiod or given a daily afternoon melatonin injection. In both cases the gonads underwent atrophy. In the second experiment adrenalectomized hamsters were given a cortisol injection either in the morning (approx. 8 hr before the subsequent afternoon injection of melatonin) or in the afternoon (approx. 1 hr before the subsequent melatonin injection). Measurements of testicular and accessory organ weights 7 weeks later indicated regression of the reproductive system in both the groups when compared with their appropriate controls. Depressed levels of plasma LH, PRL, testosterone and thyroxine (T4) in these animals confirmed the melatonin induced gonadal collapse. The results suggest that apparently there is no temporal correlation between the rhythm of secretion of the adrenal steroids and the responsiveness of the reproductive system to late afternoon injection of melatonin. Interestingly, all the adrenalectomized cortisol injected control animals (not receiving melatonin) had depressed plasma LH and PRL while the testicular weights and plasma testosterone titers remain unaffected.

Photoperiodic regulation of testis function in rats: mediation by a circadian mechanism.

Laboratory rats traditionally are classified as nonphotoperiodic because variations in daylength have little or no effect on their gonadal function. After olfactory bulbectomy, however, rats show clear evidence of photoperiodic regulation of the gonads. The present study demonstrates, by means of resonance experiments, that the testicular response to daylength in rats is mediated by a circadian photoperiodic time measurement system similar to that of photoperiodic rodents. Olfactory-bulbectomized rats were maintained in fixed photoperiods in which a 6 h light period was coupled with dark periods of 18, 30, 42, or 54 h (6L:18D, 6L:30D, etc.); a fifth group was maintained in a 45L:10D photoperiod. Rats from the 6L:30D, 6L:54D and 14L:10D photoperiods had testes and seminal vesicle weights, plasma testosterone titers and spermatogenesis indices indicative of functional reproductive status. Rats exposed to the 6L:18D and 6L:42D photoperiods had reduced testicular and seminal vesicle weights, lower testosterone levels and reduced spermatogenesis. We hypothesize that photo- and nonphotoperiodic rodent species use similar mechanisms for distinguishing long from short photoperiods, but differ in the extent to which discrimination of short daylengths is transduced into altered gonadal activity.

Social influences on plasma testosterone levels in male talapoin monkeys

Three social groups of laboratory-housed talapoin monkeys ( Miopithecus talapoin) consisting of four adult males and four or five adult females, were observed over a 4-year period. All females were ovariectomized and given estradiol implants at intervals to render them sexually attractive; except for two castrated males with testosterone implants, all males were intact. Sexual and aggressive interactions were recorded, and testosterone levels were measured in plasma taken from males twice weekly. In each group males formed a linear dominance order, defined in terms of the direction of aggression between animals. The hormonal responses of intact males were monitored with respect to the presence of attractive females, access to these females, and transfer from the social group to isolation. In all groups the behavioral and endocrine responses of males to these treatments were rank related. In some instances, rising in rank was associated with elevated testosterone and falling in rank with decreased testosterone; these hormonal changes were associated with changes in sexual and aggressive interactions. The effects of sexual and aggressive behavior on plasma testosterone titers are discussed.

Testosterone determinations in lines of chickens selected for differential mating frequency

This study was designed to evaluate the relationship between plasma testosterone titers and mating behavior in lines of chickens that had undergone bidirectional selection for high and low mating frequency and in the unselected population from which the selected lines originated. Plasma testosterone (T) concentrations were determined by radioimmunoassay procedures. Also measured were packed blood cell volumes (PCV) and two behaviors, courtship and completed matings. Significant differences were found among lines for all measures with the high mating line ranking above the low mating line and the unselected control line being intermediate to the selected lines for all measures. Also found was a positive correlated response of plasma T titers to selection for the cumulative number of completed matings.

Dominant-subordinate relationships in castrated male mice bearing testosterone implants.

This study tested the hypothesis that subordination in male mice is directly related to reduced levels of circulating testosterone. Several measures of aggressiveness and submissiveness were quantified during or after daily encounters between pairs of intact males, castrated males, or castrated males bearing testosterone implants that were designed to maintain plasma testosterone titers at levels slightly above those of intact males. Behavioral measures included the total amount of fighting that resulted from daily pairing, the tendency for subordinates to fight back, and the relative frequency of urine marking. In all these regards, pairs of testosterone-implanted, castrated males formed dominant-subordinate relationships that involved apparently normal submissive behavior (compared to intact control pairs). Thus we found no evidence that submissive behavior was directly related to a reduction in circulating testosterone titers.

Effects of testosterone on spermatogenesis and luteinizing hormone release in Japanese quail

Testosterone or testosterone propionate was administered to Japanese quail ( Coturnix coturnix japonica) via intraperitoneal Silastic capsules to assess the role of these androgens on spermatogenesis and luteinizing hormone (LH) release. Testosterone was released from Silastic capsules at relatively constant rates and in direct proportion to capsule length. Increasing lengths of testosterone-filled Silastic capsules induced and maintained differential increments in plasma testosterone titers and caused a concomitant decline in plasma immunoreactive LH levels in castrated quail. In intact birds, testosterone implants ranging between 40 and 320 mm caused a graded reduction in paired testis weight, spermatogenic activity, and circulating LH titers, but plasma testosterone levels remained within the range noted in intact control birds. Marked increases in plasma testosterone concentrations were noted in intact birds receiving 600- and 1200-mm testosterone or 500-mm testosterone propionate implants. Importantly, paired testis weight and the relative number of germ cells were maintained at near normal levels when plasma testosterone titers were raised about 18-fold above normal. The results indicate that the continuous administration of small amounts of testosterone (about 1 mg/day) suppressed spermatogenesis by inhibiting LH release and that spermatogenesis was maintained during the continuous administration of large amounts of testosterone (about 12 mg/day) even though LH secretion remained suppressed. The present findings support the hypothesis that testosterone exerts a differential effect on the quail testis that depends, in part, upon the amount of androgen administered.

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.

Plasma testosterone titers during the annual reproductive cycle of starlings ( Sturnus vulgaris)

To clarify the role of testosterone in the annual reproductive cycle of seasonally breeding birds, annual variations in plasma testosterone titers, the condition of the reproductive organs and behavior were monitored in adult male starlings ( Sturnus vulgaris). Wild starlings were bled to death immediately after capture, and the testosterone titers in their plasma were determined using a competitive protein-binding assay. Testicular weights, seminiferous tubule diameters, germinal epithelium condition, interstitial Leydig cell condition, and seminal sac weights were assessed using appropriate histological techniques. Plasma testosterone titers varied from 0.5 ng/10 ml during the postbreeding period to 4.2 ng/10 ml at the height of breeding. Strong correlations were found between testosterone titers and the condition of the interstitial cells of the testes and between testosterone titers and seminal sac weight. Postbreeding testicular regression and cessation of spermatogenesis corresponded temporally with ebbing testosterone titers. Expressions of masculine behavior, such as courtship and territorial aggression, corresponded with periods of elevated testosterone titers.

Response of the rabbit seminiferous epithelium to testosterone administered via polydimethylsiloxane capsules.

Testosterone-filled polydimethylsiloxane (PDS) capsules, ranging between 800 and 25,600 mm2 in surface area, were placed subcutaneously in mature male rabbits to examine the capacity of testosterone to 1) maintain the seminiferous epithelium, and 2) reinitiate spermatogenesis after suppressing germ cell development with testosterone. Placement of 800 mm2 PDS testosterone capsules for 60 or 65 days consistently induced gonadal atrophy whereas capsules providing 25,600 mm2 maintained normal testis weight and spermatogenic activity. Importantly, serum LH declined at least 7-fold below normal in rabbits receiving PDS implants inducing testis atrophy or supporting spermatogenesis. In contrast to LH, plasma testosterone levels increased in proportion to the surface area of PDS capsules between 3,200 and 25,600 mm2. Increases in seminal vesicle weight paralleled increases in plasma testosterone titers but neither body weight nor prostate, vesicular and bulbourethral gland weights were affected (p > 0.10). Comple...