Circulating thyroid hormone levels and iodothyronine deiodinase activities in Nile tilapia (Oreochromis niloticus) following dietary exposure to Endosulfan and Aroclor 1254

We evaluated the effects of two organochlorinated environmental contaminants, Endosulfan and Aroclor 1254 on peripheral thyroid hormone metabolism and thyroid hormone plasma levels in Nile tilapia (Oreochromis niloticus). Tilapia were exposed through diet to 0.1 and 0.5 microg g(-1) of Endosulfan and 0.5 microg g(-1) of Aroclor 1254 for 21 and 35 days. Decreased plasma T4 and rT3 levels were observed in tilapia exposed to the lower dose of Endosulfan, while treatment with a higher dose and Aroclor 1254 produced no changes. Plasma T3 levels were not affected by these compounds. Hepatic type I deiodinase (D1) activity was depressed by a lower dose of Endosulfan and hepatic type III (D3) activity was increased following 35 days of exposure to the lower dose of Endosulfan and following 21 and 35 days of exposure to Aroclor 1254; while type II (D2) remained unchanged in liver as well as in all other organs analysed. Apart from hepatic D3 activity, Endosulfan and Aroclor 1254 also increased D3 activity in gill, but not in other tested organs. It is concluded that dietary exposure of tilapia to Endosulfan or Aroclor 1254 can lead to changes in circulating thyroid hormone levels and/or in peripheral thyroid hormone metabolism. The changes in hormone metabolism differ between tissues, eventually reflecting tissue-specific differences in adaptation.     

Subspecies differences in hormonal and behavioral responses after group formation in squirrel monkeys

The behavioral and hormonal responses of squirrel monkeys of the Bolivian and Guyanese subspecies were compared after a group formation procedure. Two groups of each subspecies, consisting of five females and three males (later reduced to two) were observed daily during the week of group formation and for nine weeks following removal of a single male from each group. Measures of plasma cortisol were examined in the females after the initial group formation and after the groups were reduced by one male. The levels of plasma testosterone were assessed in all the males during the initial week of group formation. Linear dominance hierarchies were determined both within and across the sexes in both subspecies. The frequency and directionality of low-level aggressive interactions indicated that females of the Bolivian subspecies were dominant to the males, while the males of the Guyanese subspecies ranked over all the females. Additionally, the Bolivian squirrel monkey females showed an elevation of plasma cortisol on the day of group formation, which declined 48 hr later, then reelevated after the groups were reduced by one male and declined gradually over a nine-week period. Guyanese females showed little change in cortisol levels during both periods. This suggests fundamental hormonal, as well as behavioral, differences between the two subspecies. The change in plasma testosterone levels in the males during the initial week of group formation was positively correlated with social status. Furthermore, differences in the dynamics within individual groups for each subspecies were reflected by the levels of plasma cortisol of the female members.     

Effect of male and female multiple mating on the fecundity, fertility, and longevity of diamondback moth, Plutella xylostella (L.)

Abstract:  The effect of diamondback moth (DBM), Plutella xylostella (Lep., Plutellidae) male and female multiple mating on fecundity, fertility, and longevity was studied. Males could mate for five times with virgin females during scotophase. The successful copulation rates, fecundity of female, and longevity of both females and males decreased when male mating times increased, whereas copulation duration increased. Correlation coefficient between copulation duration and male mating times was significant ( r  = 0.7358, P = 0.0001, spearman rank-order correlation). There were linear relationships between mating history of males and longevities of males and females, and regression relationships between them were significant. Mated females had similar daily reproductive pattern, which laid the most eggs on the first day after mating in spite of their mates' mating history. Virgin females laid some infertile eggs before they died. Most of the females mated once during their lifespan but 19.9% of females mated twice when one female kept with one male during scotophase. There were no significant differences in the fecundity, fertility and longevity between the single- and twice-mated females. Correlation coefficient between copulation duration and female mating times was not significant ( r  = 0.0860, P = 0.8575). Results suggested that DBM females may be monandrous. Multiple mating did not increase male or female mating fitness.     

Effect of paired encounters on plasma androgens and behaviour in males and females of the spiny damselfish Acanthochromis polyacanthus

Sexually mature male and female spiny damselfish, Acanthochromis polyacanthus (Pomacentridae) were introduced to resident fish of both sexes in paired encounter trials and the effect on activity, agonistic behaviour and plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) in males, and T and 17β-estradiol (E₂) in females, and cortisol in both sexes was determined. Introduced males showed suppressed levels of T in the presence of both resident males and females, whereas resident males showed elevated T in response to introduced males but not females. Plasma 11-KT levels were unchanged in either resident or introduced males. Resident males showed increased activity in the presence of males but not females. Resident females showed an increase in activity when paired with introduced females and greater aggressive behaviour towards females than males. There were no differences in plasma hormone levels in either resident or introduced female fish. Plasma cortisol levels were low in all fish and stress effects did not appear to account for differences in T levels in males. The results of the present study show that elevations in plasma T levels in resident male spiny damselfish are associated only with male presence but that suppression of T in introduced fish occurs irrespective of the sex of the resident. In contrast resident females, which show stronger evidence of aggressive behaviour do not show changes in plasma androgen levels. This suggests that aggressive behaviour in male and female fishes may be mediated by different endocrine pathways.     

The influence of social cues on the reproductive endocrinology of male brown-headed cowbirds: field and laboratory studies

Captive male brown-headed cowbirds exposed to long days exhibit gonadal growth and have elevated plasma testosterone (T) levels. This photoperiodic response is enhanced if males are housed with female cowbirds: Photostimulated males with females increase plasma testosterone levels sooner than do individually housed photostimulated males. Peak plasma T levels are similar in both groups, although peak levels are maintained longer in males housed with females. The gonadal cycle is similarly affected; males in the presence of females have earlier gonadal recrudescence and maintain mature gonads longer than do photostimulated males without females. Plasma corticosterone levels increase in the unpaired males, suggesting that removal of social cues is stressful for these birds. Free-living paired males have significantly higher plasma testosterone levels than do unpaired/unknown males early in the season, when social relationships are being established; the levels are similar thereafter. There is no difference between the two groups in testicular maturation rates; nor do they differ in plasma corticosterone levels at any time of the season. These results suggest that social stimuli are important in modulating the secretion of testosterone in males early in the season when pairing occurs, and possibly late in the season as well, probably to prevent termination of breeding prior to that of females.     

尼罗罗非鱼生长激素及其受体的cDNA克隆与mRNA表达的雌雄差异

尼罗罗非鱼(Oreochromis niloticus)雌雄鱼生长差异明显,为了探讨其原因,本文采用RT-PCR方法克隆了尼罗罗非鱼生长激素(Growthhormone,GH)及其受体(Growth hormone receptor,GHR)的cDNA序列,并应用半定量RT-PCR方法比较了雌、雄尼罗罗非鱼垂体GHmRNA、肝脏GHRmRNA、肌肉GHRmRNA的表达差异。序列分析表明:GH开放阅读框为615bp,共编码204个氨基酸;GHR开放阅读框为1908bp,共编码635个氨基酸。以RT-PCR方法研究了GH、GHR在各组织的分布情况,结果表明:GH仅在垂体中检测到有表达,而GHR在所检测的18种组织中均有表达,其中以肝脏、肌肉、性腺、下丘脑、胸腺表达量较高。以半定量RT-PCR方法进一步比较了雌、雄尼罗罗非鱼垂体GHmRNA、肝脏GHRmRNA、肌肉GHRmRNA的表达量,结果表明:雄鱼垂体GHmRNA和肝脏GHRmRNA的表达量均显著高于雌鱼,肌肉GHRmRNA的表达量则无显著差异,推测垂体GHmRNA和肝脏GHRmRNA表达的雌雄差异是尼罗罗非鱼雌雄生长差异的主要原因之一。     

Hormonal responses to female conspecifics in hyperprolactinemic male rats and mice

Exposure to a female results in an acute release of LH and testosterone (T) in normal male rats and mice. This study was conducted to determine whether these hormonal responses are altered in hyperprolactinemic (hyperPRL) male rats in which copulatory behavior is known to be suppressed and in hyperPRL male mice in which it is not. Adult male CDF (F-344) rats were made hyperPRL either by grafting of three anterior pituitaries under the kidney capsule or by treatment with diethylstilbestrol (DES). Exposure of control males to receptive females for 10-15 min produced the expected two- to fourfold statistically significant elevations in plasma LH levels. In contrast, plasma LH levels in pituitary grafted or DES-treated males were not altered by female exposure. Male mice were pituitary grafted (two pituitaries per recipient) or sham-operated and housed individually with a female for 1 week. The resident females were then replaced with novel females in half of the cages and blood samples were taken from the males after 5 min exposure for determination of LH levels or after 45-60 min exposure for T levels. Female-induced LH and T elevations occurred in both hyperPRL and control groups. Failure of hyperPRL male rats to experience an increase in plasma LH levels in response to a female suggests abnormality of mechanisms controlling LHRH release. Suppression of LHRH release may be involved also in the induction of deficits of sexual behavior in these animals.     

Hormonal correlates of dominance in meerkats (Suricata suricatta)

In cooperatively breeding meerkats (Suricata suricatta), individuals typically live in extended family groups in which the dominant male and female are the primary reproductives, while their offspring delay dispersal, seldom breed, and contribute to the care of subsequent litters. Here we investigate hormonal differences between dominants and subordinates by comparing plasma levels of luteinizing hormone (LH), estradiol and cortisol in females, and testosterone and cortisol in males, while controlling for potential confounding factors. In both sexes, hormone levels are correlated with age. In females, levels of sex hormone also vary with body weight and access to unrelated breeding partners in the same group: subordinates in groups containing unrelated males have higher levels of LH and estradiol than those in groups containing related males only. When these effects are controlled, there are no rank-related differences in circulating levels of LH among females or testosterone among males. However, dominant females show higher levels of circulating estradiol than subordinates. Dominant males and females also have significantly higher cortisol levels than subordinates. Hence, we found no evidence that the lower levels of plasma estradiol in subordinate females were associated with high levels of glucocorticoids. These results indicate that future studies need to control for the potentially confounding effects of age, body weight, and access to unrelated breeding partners before concluding that there are fundamental physiological differences between dominant and subordinate group members.     

Are Trichogramma bourarachae and the perkinsi species group really distinct from Trichogramma buesi and the pintoi group,respectively?

Abstract:  The two Trichogramma species T. bourarachae and T. buesi belonging to two closely related groups, perkinsi and pintoi , were compared. The inter-species crossings did not result in hybrids and, therefore, the two species show complete genetic isolation. Eleven morphometric characteristics (eight from male genitalia and three from male antennae) and seven ratios between the latter characters confirmed the validity of these species. Significant differences (P < 0.01) actually exist for 56% of the measured characters and the calculated ratios. Among the morphometric characters analysed, five contribute to the definition of the perkinsi and pintoi groups and allow for comparisons to be made. However, only two of them (40%) show a difference between the groups (P< 0.01). Such a result, in accordance with those from other studies, has led to the combination of the two groups synonymously, under the name of perkinsi .     

Lack of species-specific primer effects of odours from female Atlantic salmon, Salmo salar, and brown trout, Salmo trutta

We exposed, in two successive spawning seasons, individually placed precocious male Atlantic salmon ( Salmo salar ) and brown trout ( Salmo trutta ) parr to odour stimuli (ovarian fluid and urine mix) from ovulated conspecific or heterospecific anadromous females. Atlantic salmon parr had significantly higher plasma concentrations of the hormones 17α,20β-dihydroxy-4-pregnen-3-one (17,20β-P), 11-ketotestosterone (11-KT) and testosterone (T) after exposure to odours from conspecific females or from brown trout females compared to parr exposed to a control solution (0.9% NaCl). We did not observe any significant differences between the hormone levels in salmon parr exposed to the two female odours. The salmon parr exposed to conspecific odours had significantly higher volumes of strippable milt compared to the controls, but we did not find any significant differences when comparing the effect of the two female odours. Brown trout parr had significantly higher plasma 17,20β-P levels following exposure to heterospecific female odours compared to control males, but there was no significant difference between males exposed to the different female odours. We did not observe any significant differences in plasma levels of T and 11-KT and in milt volumes between exposed and control trout. Taken together, the results from both tested species indicate that the potency of heterospecific stimuli in stimulating increased plasma sex steroid hormone levels in male parr was as strong as stimuli from conspecific females. The results are discussed in connection to observed hybridisation between the two sympatric species.     

Paradoxes in exogenous androgen treatments of bluegill

Three experiments were conducted to investigate the effect of oral administration of trenbolone acetate and 17a-methyltestosterone on sex determination in 28-day-old bluegill, Lepomis macrochirus Rafinesque, fry. Multiple androgen doses and various treatment durations were tested. All treatments produced fewer males and females than did the control group (P < 0.01). All concentrations of both androgens produced a high proportion of intersex fish (38–81%). The number of males and females declined with the increase in androgen dose or treatment duration. Sterile fish were found in treatments with a higher dose rate or a longer treatment period. The predominance of intersex fish and reductions of both males and females in the androgen treatments suggest that gonadal development of both genotypic male and female fish were being altered by the hormone treatment.     

Polymorphisms in the lipoprotein lipase and hepatic lipase genes and plasma lipid values in the Czech population

We have determined the genotypes of two common polymorphisms in the lipoprotein lipase (S447X) and hepatic lipase (-480C/T) genes in a cohort of 285 representative selected Czech probands (131 male and 154 female), examined in 1988 and reinvestigated in 1996. The genotype distributions of both polymorphisms were in Hardy-Weinberg equilibrium and did not differ between male and female subjects. The rare allele frequency of the lipoprotein lipase polymorphism did not differ significantly from the other European populations. Compared to the German populations, the frequency of the hepatic lipase -480T allele was significantly higher in the Czech group (20% vs. 36%, p<0.0001). There were no significant associations between the lipoprotein lipase gene variants and lipid parameters measured either in 1988, or in 1996 or with changes of lipid parameters over the 8-year period. The carriers of the T-480 allele of the hepatic lipase polymorphism were found to have higher HDL cholesterol levels (p=0.02). However, this difference was confined to female subjects only. The male carriers of the -480T allele had higher concentrations of total cholesterol (p=0.03) as compared to CC-480 subjects. Both associations were observed in 1996 only. In the Slavic Czech population, a common polymorphism in the hepatic lipase gene (-480C/T), but not in the lipoprotein lipase gene (S447X), is a significant determinant of plasma HDL cholesterol in females and plasma total cholesterol in males and indicates the importance of gender-associated effects in the genetic determinations of plasma lipids.     

Effect of small doses of naloxone on sexual exhaustion in White New Zealand male rabbits

The objective of the present study was to determine the effect of small doses of naloxone on sexual exhaustion in White New Zealand male rabbits. Twelve young and 12 adult male rabbits 6–12 months old and 14–20 months of age, respectively, were selected from a commercial farm. Each male rabbit was housed individually in galvanized cages (90 cm × 60 cm × 40 cm). The rabbits were housed in an open shed exposed to natural photoperiod (12 L 12 D, 19°N). Daily temperature fluctuated through the year from 28 to 16 °C. Humidity was 45 ± 5%. Water and food (rabbit chow PMI) was supplied ad libitum. After sexual behaviour for each studied group was established, the males were given a 6-day rest, and 3 days before next trial, six males of each group (treated) received a subcutaneous implant of 8 mg of naloxone in a crystalline nitrocellulose pellet formulated to be completely absorbed in 15 days. The remaining six males were sham-treated (control). At the end of the resting period as previously described, the sexual behavior of each group was studied and compared using a Mann–Whitney statistical U-test. The effect of naloxone on sexual behavior was analyzed with a Wilcoxon test for correlated samples. With regard to sexual activity between young and adult rabbits, it was observed that there was a significant difference between groups (P = 0.00275, Z = 2.8823, adjusted Z = 2.99.43) showing that younger rabbits mounted/ejaculated from 9 to 10 females compared with 6 to 8 mounted/ejaculated by older rabbits. When naloxone was administered to both groups, there was a significant difference when comparing sexual behavior before and after administration of naloxone (table first and second trial). Young rabbits treated with naloxone mounted/ejaculated 11–12 females while older rabbits mounted nine females before reaching sexual exhaustion. A significant difference was observed when comparing the number of estrous females that were mounted/ejaculated between groups. Environmental photoperiod and temperature changes were not considered. It was concluded that endogenous opioids are important modulators of behavioral and hormonal interactions related to sexual behavior.     

Mouthbrooding in the black-chinned tilapia, Sarotherodon melanotheron (Pisces: Cichlidae): the presence of eggs reduces androgen and estradiol levels during paternal and maternal parental behavior

The black-chinned tilapia (Sarotherodon melanotheron) is considered a paternal mouthbrooder in which the male churns the eggs in his mouth for 14-18 days after they are fertilized. We previously showed that plasma androgen and estradiol concentrations increased significantly between the beginning and end of mouthbrooding. Here we provide evidence that androgen and estradiol are relatively high in prespawning male tilapia, decrease significantly with the initiation of mouthbrooding, and return to and slightly surpass prespawning levels by the end of mouthbrooding. We then test the hypothesis that the initiation of mouthbrooding causes a decrease in androgen and estradiol. We raised single pairs of tilapia in seawater aquaria and conducted two experiments. In the first, we removed eggs from males on the morning of Day 1 of mouthbrooding, followed changes in plasma androgen and estradiol in the afternoon of Day 1 and on Days 6, 11, and 16, and compared them to levels in control males who kept their eggs. Removing eggs from mouthbrooding males on the morning of Day 1 eliminated the decrease in plasma androgen and estradiol observed in the afternoon of Day 1 of mouthbrooding. This demonstrates that the eggs are necessary for the decrease. We observed that, infrequently, the female of the pair would pick up the eggs to brood them in her mouth. In a second experiment, in the afternoon of Day 1, we sampled both the male and female of pairs in which the female brooded eggs. In female-brooding pairs, the females had significantly lower androgen and estradiol levels than prespawning females. The black-chinned tilapia in captivity exhibits both paternal and maternal parental behavior. In both sexes the initiation of mouthbrooding triggers a decrease in androgen and estradiol concentrations. We conclude that the presence of eggs inhibits the pituitary-gonadal axis in both males and females and hypothesize that a chemical signal from the eggs is delaying the initiation of the next brood.     

Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae)

Adult males and females of the seasonally breeding lizardCalotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17β-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in theC. versicolor.     

Effect of dietary dextrin levels on the growth performance,blood chemistry,body composition,hepatic triglicerides and glycogen of Lebranche mullet juveniles (Mugil liza Valenciennes 1836, Mugilidae)

The effects of increasing levels of dietary dextrin on growth performance, body composition, blood chemistry and hepatic triglycerides and glycogen levels were evaluated for juvenile Lebranche mullet, Mugil liza Valenciennes 1836, Mugilidae). Five diets were formulated to be isonitrogenous (350 g kg^?1) and isolipidic (6 g kg^?1) with increasing dextrin levels (D150: 150 g kg^?1; D200: 200 g kg^?1; D250: 250 g kg^?1; D300: 300 g kg^?1; D350: 350 g kg^?1). The experimental diets were offered to the fish for 34 days, four times per day, until apparent satiation. Each treatment was tested in triplicate, with nine fish per tank (mean weight 4.69 ± 0.31 g). Fish were reared in a recirculating aquatic system of 15 fibreglass tanks each containing 50 L of saltwater. Growth parameters and body composition of the mullets were not significantly affected (P > 0.05) by the dietary treatments. Plasma glucose concentration declined (P < 0.05) when dietary dextrin increased from D250 to D300, but recovered to the previous values (in reference to D150 and D200) when fish were fed with D350. Glycated haemoglobin, plasma proteins, triglycerides and cholesterol showed no significant differences among these treatments. Hepatic glycogen reached a maximum in treatment D250, followed by D350, D200 and D300, with the lowest concentration of liver glycogen found in D150 (P < 0.05). The concentration of liver triglycerides showed an increase (P < 0.05) in treatments D300 and D350 compared with D200. In conclusion, Mugil liza juveniles can be fed diets with high levels of dietary dextrin with no deleterious effects to their growth or plasma biochemistry, hepatic glycogen or triglycerides.     

Male-male competition and female choice in brown trout

In some salmonid species, the females have been assumed to choose their mates on the size of the male's adipose fin. This hypothesis was tested in a stream water aquarium, in which 19 brown trout, Salmo trutta, females were allowed to choose between two males of the same body size but with different adipose fin sizes. The two males were separated from each other in cages. After the female had started to prepare her nest close to one of them, the males were released and allowed to fight each other for the opportunity to spawn. Out of 19 females, 14 prepared a nest closest to the male with the larger adipose fin. However, only six of the 14 females spawned with this male. Males that spawned were more dominant (i.e. were more likely to win fights). When the female spawned with the male she chose, he was less aggressive towards her than when she spawned with the other male. There were no significant differences in the plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) between the chosen males and those not chosen. However, the dominant males had significantly higher plasma levels of T and 11-KT both before and after the experiment. The results support the view that female brown trout exhibit mate choice, but their choice is overruled by male-male competition. Copyright 1999 The Association for the Study of Animal Behaviour.     

Dose‐response effects of the antioxidant α‐lipoic acid in the liver and brain of pompano Trachinotus marginatus (Pisces,Carangidae)

This study evaluated the effect of different doses of the antioxidant α‐lipoic acid (LA) administered by intraperitoneal injection on the detoxifying capacity (activity of glutathione‐S‐transferase, GST) and oxidative damage (lipids and proteins) in the pompano, Trachinotus marginatus. The plasma glucose levels showed that there were no differences between the treatments (P > 0.05). In the brain, GST activity was significantly higher (P < 0.05) in fish injected with 40 mg LA kg^?1 when compared with the control group. In the muscle, GST activity was not influenced by LA treatment (P > 0.05). In the liver, fish injected with 20 mg LA kg^?1 showed higher GST activity than the control group (P < 0.05); however, higher doses (40 and 60 mg LA kg^?1) led to a reduction of GST activity in the liver, which was comparable to that observed in the control group (P > 0.05). The two highest LA doses (40 and 60 mg kg^?1) had opposite effects, depending on the tissue examined: LA was an antioxidant in the brain, reducing lipid peroxidation (P < 0.05), and a pro‐oxidant in the liver, augmenting oxidative lipid damage (P < 0.05). The latter effect was accompanied by an increase in the free iron concentration in the liver at higher LA doses. These results indicate the need to thoroughly evaluate the antioxidant effects on aquatic organisms, since at some doses and/or in some organs their beneficial effects can be lost.     

Effects of reproductive and social variables on fecal glucocorticoid levels in a sample of adult male ring-tailed lemurs (Lemur catta) at the Beza Mahafaly Reserve, Madagascar

Glucocorticoids, a group of adrenal hormones, are secreted in response to stress. In male primates, variables such as breeding seasonality, dominance hierarchy stability, and aggressive and affiliative interactions can affect glucocorticoid levels. In this study, we examined interindividual differences in mean fecal glucocorticoid (fGC) levels among males in three groups of wild ring-tailed lemurs to better understand the physiological costs of group living for males in a female-dominant species that exhibits strict reproductive seasonality. Fecal and behavioral data samples were collected during one mating and two postmating seasons (2001 and 2003). The mean fGC levels were examined in relation to reproductive season, male rank, number of resident males, intermale and female-male agonism, and affiliative behavior with females. The mean fGC levels were not significantly elevated during mating season compared to the postmating period. During the mating season, male dominance hierarchies broke down and rank effects could not be tested; however, there was no relationship between male rank and fGC levels in the postmating periods. In 2001, males that resided in the group with the fewest males exhibited lower fGC levels during the postmating period. They also affiliated more with females than did males in the other groups. During the mating season of 2003, males engaged in more affiliative behaviors with females compared to the postmating season, but female-male agonism did not differ by season. However, rates of intermale agonism were significantly higher during mating compared to postmating periods, but such heightened agonism did not translate to a higher stress response. Thus, neither male-male competition for mates nor heightened agonism between males during the breeding season affected male fGC levels. Fewer males residing in a group, however, did have some effect on male-female affiliation and male fGC levels outside of the mating period. Males that live in a group with only a few (two or three) males may experience less physiological stress than those that live in groups with more males.     

Selective actions of growth hormone on rat liver estrogen binding proteins

Levels of hepatic estrogen receptor were 9.0 ± 2.4 fmoles/mg cytosol protein in intact females compared to 3.4 ± 2.2 in hypophysectomized females. Likewise, levels of receptor were 9.8 ± 1.5 fmoles/mg cytosol protein in intact males and 2.7 ± 1.8 in hypophysectomized males. Hypophysectomy abolished the sex differences in a second class of binding sites termed higher capacity lower affinity binding sites by increasing female levels and decreasing male levels. Treatment of hypophysectomized male or female rats with growth hormone (2 units/kg body wt, two times daily) restored normal levels of hepatic estrogen receptor. Administration of growth hormone to hypophysectomized rats did not reverse the effects of hypophysectomy on higher capacity lower affinity binding sites. These studies demonstrate that growth hormone exerts selective actions on different forms of hepatic estrogen binding proteins.