Elevated prolactin levels immediately precede decisions to babysit by male meerkat helpers

Recent studies suggest that decisions to care for the offspring of others in societies of cooperative vertebrates may have a hormonal basis. The crucial question of whether changes in hormone levels immediately precede or merely follow bouts of offspring care, however, remains largely unanswered. Here, we show that in wild groups of cooperatively breeding meerkats, male helpers that decided to babysit for the day had significantly higher levels of prolactin, coupled with lower levels of cortisol, before initiating a babysitting session compared with similarly aged individuals that decided to forage. In addition, these hormonal differences disappeared over the course of the day, suggesting that hormone levels changed in a fundamentally different way in meerkats that babysat versus those that foraged. In contrast, long-term contributions to babysitting were not significantly associated with plasma levels of prolactin, cortisol, or testosterone in individual male helpers. Our results show, for the first time, that elevated levels of prolactin may immediately precede bouts of helping behavior but differ from recent findings on the same study population in which plasma levels of cortisol, but not prolactin, were significantly and positively associated with rates of pup feeding by male helpers. Together, these results lend significant weight to the idea that decisions to help in cooperative vertebrates have a hormonal basis, although different hormones appear to be associated with different types of care.     

Do testosterone declines during the transition to marriage and fatherhood relate to men's sexual behavior? Evidence from the Philippines

Testosterone (T) is thought to help facilitate trade-offs between mating and parenting in humans. Across diverse cultural settings married men and fathers have lower T than other men and couples' sexual activity often declines during the first years of marriage and after having children. It is unknown whether these behavioral and hormonal changes are related. Here we use longitudinal data from a large study in the Philippines (n = 433) to test this model. We show that among unmarried non-fathers at baseline (n = 153; age: 21.5 ± 0.3 years) who became newly married new fathers by follow-up (4.5 years later), those who experienced less pronounced longitudinal declines in T reported more frequent intercourse with their partners at follow-up (p < 0.01) compared to men with larger declines in T. Controlling for duration of marriage, findings were similar for men transitioning from unmarried to married (without children) (p < 0.05). Men who remained unmarried and childless throughout the study period did not show similar T-sexual activity outcomes. Among newly married new fathers, subjects who had frequent intercourse both before and after the transition to married fatherhood had more modest declines in T compared to peers who had less frequent sex (p < 0.001). Our findings are generally consistent with theoretical expectations and cross-species empirical observations regarding the role of T in male life history trade-offs, particularly in species with bi-parental care, and add to evidence that T and sexual activity have bidirectional relationships in human males.     

粪便激素水平反映不同出生时期雄性布氏田鼠的繁殖策略

布氏田鼠是我国内蒙古草原的主要害鼠之一,具有明显的季节繁殖特征,不同季节出生个体可能具有不同的繁殖策略,但尚缺乏内分泌证据支持。本研究采用标志重捕法,连续监测大型自然围栏中不同年龄雄性布氏田鼠的繁殖状态和应激水平的季节变化,分析各年龄组雄鼠的繁殖发育策略。结果表明,越冬雄鼠可保持较高的睾丸下降率和睾酮水平至8月初;而部分5月生雄鼠的繁殖期睾酮水平较接近越冬鼠,但8月初已降至年内最低水平,而6月及以后出生雄鼠睾酮始终处于较低水平;这说明越冬鼠的繁殖状态可贯穿繁殖期始终,只有部分5月生雄鼠可能参与当年繁殖,而6月及以后出生雄鼠则不能在当年繁殖。越冬鼠皮质醇水平高于当年鼠,繁殖期高于非繁殖期,这可能是越冬鼠由于繁殖需要而保持较高应激状态,从而造成繁殖盛期后死亡率升高。这些结果说明,不同时期出生的雄性布氏田鼠具有不同的出生后性腺发育模式和繁殖策略,反映出生存与繁殖之间的权衡。     

The effects of social context on the hormonal and behavioral responsiveness of human fathers

We tested first-time fathers with their 22-month old toddlers to determine whether social context variables such as pre-test absence from the child and presence of the mother affected physiological measures associated with paternal responsiveness. Heart rate and blood pressure readings as well as blood samples to determine prolactin, testosterone and cortisol levels were taken before and after the 30-min father–toddler interactions. Fathers were tested on a day when they were away from their child for several hours before testing (‘without-child’ day) and on another day where they remained with their child throughout the day (‘with-child’ day). Most measures decreased over the 30-min test period but relative decreases were context-dependent. Men maintained higher prolactin levels when they were away from their children longer before testing on the ‘without-child’ day. Cortisol levels decreased during both tests and they decreased more on the ‘with-child’ day for men who had spent more time alone with their toddler before the test. Heart-rate and diastolic (but not systolic) blood pressure decreased more on the ‘with-child’ day than on the ‘without-child’ day. Fathers' testosterone levels decreased when their partners were less involved in the interactions. Compared to men with high responsiveness ratings on both days, men whose responsiveness increased after being away from their child on the ‘without-child’ day maintained higher systolic blood pressure and had a greater decrease in testosterone levels. We conclude that context may be more important in determining fathers' physiological responses to child contact than has previously been appreciated, particularly for some individuals.     

Social suppression of female reproductive maturation and infanticidal behavior in cooperatively breeding Mongolian gerbils

In several cooperatively breeding species, reproductively suppressed, nonbreeding females are attracted to infants and routinely provide alloparental care, while breeding females may attack or kill other females' infants. The mechanisms underlying the transition from alloparental to infanticidal behavior are unknown. In this study, we tested the hypothesis that this transition is associated with cessation of reproductive suppression and onset of ovarian activity in the Mongolian gerbil (Meriones unguiculatus), a cooperatively breeding rodent. Young female gerbils were housed with their natal family (FH), with a female pairmate (PH) or singly (SH). When females were either 11-13 or 16-18 weeks of age, we characterized their behavioral responses to an unfamiliar pup, reproductive development, and plasma progesterone, cortisol, and prolactin concentrations. In both age groups, FH females were significantly less likely to attack pups than PH or SH females and in fact never did so. FH females also had smaller ovaries and uteri, less developed scent glands, and lower progesterone levels, and were more likely to be anovulatory than PH or SH females, especially in the 11- to 13-week-old age group. Prolactin concentrations did not differ with reproductive status but were significantly higher in females that did not attack pups than in those that did. We found no other significant associations, however, between reproductive or endocrine measures and behavioral responses to pups. These results suggest that cohabitation with the natal family inhibits both infanticidal behavior and reproductive maturation in young female gerbils but that these two effects may not be causally related.     

Changes in pain perception and hormones pre- and post-kumdo competition

The psychological stress of competition is a powerful stimulus affecting numerous hormones, which in turn change how pain is perceived. This study investigated whether a kumdo (kendo) team competition may be related to changes in hormones and pain. Seventeen healthy male kumdo practitioners participated in this experiment. Pain experiments were conducted by applying noxious stimuli with a thermal stimulator 10 min before a kumdo competition and 30 min post-competition. Serum testosterone, cortisol, beta-endorphin levels, pain thresholds, pain ratings at 48 °C and during blood sampling (sampling pain), anxiety, blood pressure, and heart rate were measured pre- and post-competition. Anxiety, pain threshold, testosterone/cortisol ratio, and blood pressure were significantly higher pre-competition compared to post-competition, while cortisol and pain ratings were significantly lower pre-competition than post-competition. There were significant correlations between the number of previous competitions and testosterone levels both pre-competition and post-competition. In pre-competition measurements, sampling pain increased with an increase in systolic blood pressure, heart rate, and beta-endorphins, and a decrease in age. In post-competition measurements, sampling pain increased with an increase in diastolic blood pressure and a decrease in testosterone levels. These results indicate that severe psychological pre-competition stress was associated with reduced pain ratings, perhaps in order to improve athletic performance. This also suggests that competitors may be at risk of potential injury due to changes in pain perception, and careful consideration should be taken to avoid potential injury before and during competition.     

圈养雄性麋鹿血清睾酮和皮质醇含量在发情期的变化

2000年7-8月在北京麋鹿苑采集不同繁殖状态雄鹿（发情前3头、发情3头和发情后4头）血液样品,用放射免疫分析法测定血清睾酮和皮质醇含量。结果显示发情雄鹿的睾酮浓度显著高于发情前、后,而3种状态雄鹿的皮质醇浓度无差异,并且与睾酮浓度无关。本苑麋鹿睾酮水平的变化与同类野生动物一致。     

四川成都市郊正常成年男性血清生殖激素水平及其频数分布

本文用放射免疫测定法(RIA),测定了200～290例中国四川成都市郊30～73岁的正常成年男性血清睾酮(T)促黄体激素(LH).卵泡刺激素(FSH)及泌乳激素(PRL)的水平及其分布,进行了不同年龄水平差异显著性的观察,见到睾酮与泌乳激素水平无显著差异,促黄体激素及卵泡刺激素水平,随年龄之增加而升高,差异有显著性,并测得它们在血清中水平的分布:LH、FSH及PRL均为对数正态公布,T既非正态又非对数正态,但其频率分布较对称,接近正态分布。     

Sex difference in testosterone response to a video game contest

Testosterone (T) and cortisol (C) were assayed from saliva samples given by young men (n = 28) and women (n = 32) before, during, and after competing with a same-sex partner in a video game. The T response to the competition is different in each sex; the C response is the same. Male results confirm prior reports of a precontest rise in testosterone. Male results did not confirm previous findings that, after a contest, the testosterone of winners is higher than that of losers, perhaps because the video game contest produced little mood difference between male winners and losers. Unlike male testosterone, female testosterone generally decreased throughout the experiment. Trends in T and C are parallel in women but not in men. Apparently T works differently in competition between men than between women.     

Diurnal and seasonal cortisol, testosterone, and DHEA rhythms in boys and girls during puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07:45, 08:00, 08:30, 12:00, 16:50, and 21:00 h. The participants' ages ranged from 8-14 yrs, and each participant was tested three times at six-month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1-3) but not later puberty (stages 4-5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

Responses of the steroid circadian system to alcohol in humans: Importance of the time and duration of intake

Reports provide conflicting data about the effects of alcohol consumption on the hormonal system. Any study of these effects must control for a number of variables, including sex, alcohol status (alcoholic addiction vs. non-addiction), medical status (malnutrition, liver disease), and conditions of alcohol exposure, including an acute or continuous pattern of intake. The latter appears to be an especially critical factor in interpreting these effects. The authors therefore conducted a trial with a circadian design in which alcohol was administered repeatedly and regularly over a 26 h period for a total dose of 256 g. Because this protocol involves continuous alcohol administration, it is similar to administration among alcoholics and thus sheds new light on alcohol's effect on hormone secretion. Using healthy volunteers rather than alcoholics, however, prevents any confounding due to liver disorders and nutritional deficiencies, and thus makes it possible to focus on the direct role of alcohol in hormonal modifications. In these conditions, the continuous administration of alcohol did not affect cortisol secretion, but serum testosterone levels were significantly higher at all time points during the alcohol session than at the corresponding time points during the control session. These data are not consistent with previously reported findings for the relation between alcohol and both cortisol and testosterone, because in the current experiment the action of ethanol on steroid secretion should involve the circadian clock more than the hormonal system itself.     

Women's intercollegiate athletic competition: Cortisol,testosterone, and the dual-hormone hypothesis as it relates to status among teammates

Recent research suggests that testosterone and cortisol jointly regulate dominance motivation and, perhaps, the status relationships that are affected by it. For this article, the results of six different studies of women's intercollegiate athletic competition were combined to give a sample size of almost ninety women for whom we had before- and after-competition values for salivary cortisol and testosterone for at least one and sometimes two competitions. For many of these women, we had surveys that allowed us to assess their status with teammates. In no matter what sport (soccer, softball, volleyball, and tennis) levels of salivary cortisol and testosterone increased when women participated in athletic competition. Salivary levels of C and T appear to rise in parallel during competition and increases in levels of one hormone are significantly related to increases in the other. Salivary levels of these hormones typically decreased for teammates who did not play but watched the competition from the sidelines. For women who played in two competitions, individual differences in the positive effect of competition on cortisol and testosterone were conserved from one competition to the next, affirming the personal consistency of endocrine responses to competition. Status with teammates was positively related to before-competition levels of testosterone, but only for women with relatively low before-competition levels of cortisol. This result provides novel support for the “dual-hormone hypothesis” as it relates to predicting social status in women's athletic teams — natural social groups of individuals who know each other and whose social hierarchy has evolved over the course of practice and play for at least one and, in some cases, several years of intercollegiate athletic competition.     

Influence of Circadian Time Structure on Acute Hormonal Responses to a Single Bout of Heavy-Resistance Exercise in Weight-Trained Men

Both testosterone (T) and cortisol (C) exhibit circadian rhythmicity being highest in the morning and lowest in the evening. T is a potent stimulator of protein synthesis and may possess anti-catabolic properties within skeletal muscle, and C affects protein turnover, thereby altering the balance between hormone-mediated anabolic and catabolic activity. Physiological reactions of these hormones and training adaptations may influence the post-exercise recovery phase by modulating anabolic and catabolic processes, therefore affecting metabolic equilibrium, and may lead to intensification of catabolic processes. We investigated the effect of the circadian system on the T and C response of weight-trained men to heavy resistance exercise. Thirteen young (21.8±2.2 yr) weight-trained men (12 months training experience) performed an eight-station heavy-resistance exercise protocol on two separate occasions (AM: 06:00 h and PM: 18:00 h), completing 3 sets of 8–10 repetitions at 75% of each subject's one-repetition maximum (1-RM). Blood samples were obtained prior to, during, and following the exercise bout, and serum total T and C concentrations were determined by competitive immunoassay technique. Performing the single bout of heavy-resistance exercise in the PM as compared to the AM positively altered the C and T/C ratio hormonal response. Pre-exercise C concentrations were significantly lower (p < 0.05) in the PM session, which resulted in a lower peak value, and the accompanying increased T/C ratio suggested a reduced catabolic environment. These data demonstrate that the exercise-induced hormonal profile can be influenced by the circadian time structure toward a profile more favorable for anabolism, therefore optimizing skeletal muscle hypertrophic adaptations associated with resistance exercise.     

The effects of short-term resistance training on endocrine function in men and women

This investigation examined hormonal adaptations to acute resistance exercise and determined whether training adaptations are observed within an 8-week period in untrained men and women. The protocol consisted of a 1-week pre-conditioning orientation phase followed by 8 weeks of heavy resistance training. Three lower-limb exercises for the quadriceps femoris muscle group (squat, leg press, knee extension) were performed twice a week (Monday and Friday) with every other Wednesday used for maximal dynamic 1 RM strength testing. Blood samples were obtained pre-exercise (Pre-Ex), immediately post-exercise (IP), and 5 min post-exercise (5-P) during the first week of training (T-1), after 6 weeks (T-2) and 8 weeks (T-3) of training to determine blood concentrations of whole-blood lactate (LAC), serum total testosterone (TT), sex-hormone binding globulin (SHBG), cortisol (CORT) and growth hormone (GH). Serum TT concentrations were significantly (P ≤ 0.05) higher for men at all time points measured. Men did not demonstrate an increase due to exercise until T-2. An increase in pre-exercise concentrations of TT were observed both for men and women at T-2 and T-3. No differences were observed for CORT between men and women; increases in CORT above pre-exercise values were observed for men at all training phases and at T-2 and T-3 for women. A reduction in CORT concentrations at rest was observed both in men and women at T-3. Women demonstrated higher pre-exercise GH values than men at all training phases; no changes with training were observed for GH concentrations. Exercise-induced increases in GH above pre-exercise values were observed at all phases of training. Women demonstrated higher serum concentrations of SHBG at all time points. No exercise-induced increases were observed in men over the training period but women increased SHBG with exercise at T-3. SHBG concentrations in women were also significantly higher at T-2 and T-3 when compared to T-1 values. Increases in LAC concentrations due to exercise were observed both for men and women for all training phases but no significant differences were observed with training. These data illustrate that untrained individuals may exhibit early-phase endocrine adaptations during a resistance training program. These hormonal adaptations may influence and help to mediate other adaptations in the nervous system and muscle fibers, which have been shown to be very responsive in the early phase of strength adaptations with resistance training. Accepted: 11 December 1997     

Quantifying blood leakage into the oral mucosa and its effects on the measurement of cortisol, dehydroepiandrosterone, and testosterone in saliva

The impact of blood leakage due to microinjury to the oral cavity on the measurement of salivary hormones was examined. Saliva samples were collected before, immediately after, and then every 15 min for 1 h following vigorous tooth brushing. Blood in saliva was quantified by visual inspection of discoloration, Hemastix reagent strips to detect hemoglobin, and an immunoassay for transferrin. The presence of blood in saliva immediately after microinjury was confirmed by all methods. Hemoglobin and transferrin levels remained elevated over baseline for at least 30 min. Levels of salivary testosterone increased over baseline and remained elevated for 30 min in response to microinjury. Microinjury induced change in salivary testosterone was more closely associated with the change in transferrin than hemoglobin levels or discoloration ratings. On average, levels of salivary dehydroepiandrosterone (DHEA) did not increase in response to microinjury. However, individual differences in microinjury induced change in DHEA were associated with discoloration ratings. Salivary cortisol levels, on average, were neither responsive to microinjury, nor were individual differences in cortisol change associated with blood contamination measures. Neither diurnal nor gender-related differences in baseline hormone levels predicted the impact of blood leakage on quantitative salivary measurements. The findings suggest ecologically valid minor-to-moderate level microinjuries to the oral cavity have negligible effects on the measurement of salivary cortisol, but may be important to quantify and control when assessing other hormones especially testosterone.