Hormonal responses to different sexually related conditions in male rats

Plasma levels of corticosterone (C) and testosterone (T) increase after sexual activity in males of several species. However, the physiological significance of these increases has not been elucidated. In the present study, hormonal response to different conditions linked to sexual activity was assessed. In the first experiment, plasma levels of C and T were assessed both in sexually experienced and naive male rats after the following conditions: (A) control group, without sexual stimulation; (B) males exposed to ovariectomized females; (C) males exposed to intact, non-receptive females; (D) males exposed to receptive females with the vagina obstructed, to avoid intromission; (E) males exposed to receptive females: but separated by a grid that prevents physical contact; (F) males exposed to receptive females during 30 min. In a second experiment, experienced male rats were allowed to repeatedly copulate until reaching the criteria for sexual exhaustion, and 24 h later, they were allowed to copulate. Once sexually related conditions ended, males were killed and their blood was obtained. C and T plasma levels were assessed by HPLC with ultraviolet (UV) detection. Results indicate that T did not increase significantly in naive male in any sexual condition, while in the experienced males, significant increases were observed with the mere presence of a receptive female and also after ejaculation. These increases were significantly larger in experienced males. On the other hand, C also increased in all sexual conditions, both in experienced and naive rats; however, the increase observed was larger in experienced males. Regarding sexual satiety, both C and T increased after copulating ad libitum to satiety. T increased almost three-fold compared to control, while C increased two-fold. No significant changes were observed in either one of the steroids 24 h after sexual exhaustion, even though males remained with a receptive female during an hour. These results show that sexual experience has an important influence on the hormonal response to sexual activity. C rises could be directly related to sexual arousal involved in the different sexual conditions, while T rises seem to have a direct relationship with both the motivation and execution aspects of masculine sexual behavior.     

In vitro fertilization and preimplantation embryo development of African green monkeys (Cercopithecus aethiops)

Ovaries of five adult female African green monkeys were stimulated by repeated administrations of equine chorionic gonadotrophin (eCG), followed by a single administration of human chorionic gonadotrophin (hCG). Oocytes were collected from enlarged follicles 28 h after hCG administration and incubated in vitro for 288 h. Oocytes that had extruded the first polar body were inseminated with spermatozoa that had been incubated for 4 to 6 h in medium with caffeine and dibutyryl cyclic AMP. Of these oocytes, 66% were fertilized and the incidence of polyspermy was 37%. Eighty-two percent of the fertilized eggs cleaved, with some developing into expanded blastocysts. Am. J. Primatol. 43:43–50, 1997. © 1997 Wiley-Liss, Inc.     

Effects of gonadotropin-releasing hormone administration on the pituitary-gonadal axis in male and female dogs before and after gonadectomy

GnRH-stimulation tests were performed in 14 female and 14 male client-owned dogs of several breeds, before and 4 to 5 mo after gonadectomy. The aim of the study was to obtain more insight into the pituitary-gonadal axis in intact and neutered dogs and to establish reference values. Basal plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations were increased significantly after gonadectomy in both bitches and male dogs. In both males and females ranges of the basal plasma FSH concentrations, before and after gonadectomy, did not overlap as opposed to the overlap in ranges of the basal plasma LH concentrations. Before gonadectomy basal plasma LH concentrations were lower and basal plasma FSH concentrations were higher in bitches than in male dogs. After gonadectomy these basal values did not differ significantly. GnRH administration before gonadectomy resulted in an increase in plasma LH and FSH concentrations in both genders. GnRH administration after gonadectomy produced an increase only in plasma LH concentrations in both genders, and a just significant increase in plasma FSH in castrated male dogs. GnRH administration before gonadectomy resulted in a significant increase in plasma testosterone concentration in both genders. In males ranges of basal and GnRH-stimulated plasma testosterone concentrations before and after gonadectomy did not overlap. Basal plasma estradiol concentrations were significantly higher in intact males than in castrated males and their ranges did not overlap. The basal estradiol concentrations in bitches before and after ovariectomy were not significantly different. At 120 min after GnRH administration, ranges of plasma estradiol concentration of intact and ovariectomized bitches no longer overlapped. In conclusion, basal plasma FSH concentration appears to be more reliable than basal plasma LH concentration for verification of neuter status in both male and female dogs. The basal plasma testosterone concentration appears to be reliable for verification of neuter status in male dogs. The plasma estradiol concentration at 120 min after GnRH administration can be used to discriminate between bitches with and without functional ovarian tissue.     

Effect of neuraminidase on luteinizing hormone/chorionic gonadotrophin binding to the ovarian and testicular membranes from different mammalian species

After treatment of the ovarian and testicular membranes from several mammalian species an elevation in the specific binding of human [¹²⁵I]-labelled CG could be observed. With the assumption that this effect is due to sialic acid-masked receptors, the presence of such receptors seem to be a common property of most mammalian gonads. An interesting observation was the abnormally high hormone binding capacity of the Syrian hamster ovary, as compared to other hamster species, and the lack of a neuraminidase effect in the ovary of the Syrian hamster.     

Regulation of testicular function in men: implications for male hormonal contraceptive development

In the adult male, the testes produce both sperm and testosterone. The function of the testicles is directed by the central nervous system and pituitary gland. Precise regulation of testicular function is conferred by an elegant feedback loop in which the secretion of pituitary gonadotropins is stimulated by gonadotropin hormone-releasing hormone (GnRH) from the hypothalamus and modulated by testicular hormones. Testosterone and its metabolites estradiol and dihydrotestosterone (DHT) as well as inhibin B inhibit the secretion of the gonadotropins both directly at the pituitary and centrally at the level of the hypothalamus. In the testes, LH stimulates testosterone synthesis and FSH promotes spermatogenesis, but the exact details of gonadotropin action are incompletely understood. A primary goal of research into understanding the hormonal regulation of testicular function is the development of reversible, safe and effective male hormonal contraceptives. The administration of exogenous testosterone suppresses pituitary gonadotropins and hence spermatogenesis in most, but not all, men. The addition of a second agent such as a progestin or a GnRH antagonist yields more complete gonadotropin suppression; such combination regimens effectively suppress spermatogenesis in almost all men and may soon bring the promise of hormonal male contraception to fruition.     

Sexual steroids during puberty in male African catfish (Clarias gariepinus): serum levels and gonadotropin-stimulated testicular secretion in vitro

Blood serum and testicular tissue samples were collected from 3 to 13-month-old African catfish (groups A-G) in order to study their pubertal development. The sampling covered the period from before the beginning of spermatogenesis until full maturity. Testes of fish in group A contained spermatogonia alone. In testes of group B, spermatogonia, spermatocytes and spermatids were present. Spermatozoa were first observed in group C and became predominant as the fish attained full maturity (group G). Several sex steroids were determined in the blood samples. Testosterone was the quantitatively dominating androgen in the blood serum (3–5 ng·ml^-1) in groups B and C (fish in group A were too small to collect blood samples). In group D, the concentrations of 11-ketotestosterone and 11-hydroxyandrostenedione increased to levels similar to those of testosterone. Androstenedione that was undetectable before (below 0.4 ng·ml serum^-1), also increased to 3–5 ng·ml^-1 in group D. The levels of androgens kept increasing until the fish attained full maturity (group G). In order to monitor the responsiveness to gonadotropic hormone and the steroid secretion capacity, the in vitro secretion of two steroids (11-hydroxyandrostenedione and 17,20-dihydroxy-4-pregnen-3-one) by testicular tissue was quantified at the different stages of development. Testicular maturation was accompanied by changes of both the steroid secretion capacities and of the sensitivity to gonadotropic hormone. The most important changes occurred just after the initiation of spermatogenesis, as spermatocyte/spermatid formation was associated with a drop of the secretory capacity (amount of steroid secreted per milligram of tissue incubated) and with a reduced sensitivity to gonadotropic hormone. At later stages, when the testicular weight substantially increased concurrently with the formation of numerous spermatozoa, both the secretory capacity and the responsiveness to gonadotropic hormone increased again to reach the levels typical of adult fish. The blood levels of androgens appeared to be positively related to the increasing testicular weight in the later phases of development.Abbreviations 17,20P 17,20-dihydroxy-4-pregnen-3-one - A2 androstenedione - A3 androstenetrione - BPG-axis brain-pituitary-gonadal axis - FSH follicle stimulating hormone - GnRH gonadotropin-releasing hormone - GTH gonadotropic hormone - GSI gonado-somatic index - hCG human chorionic gonadotropin - HEPES N-(2-hydroxyethyl)piperazine-N-(2-ethanesulphonic acid) - KT 11-ketotestosterone - LH luteinizing hormone - OHA 11-hydroxyandrostenedione - OHT 11-hydroxytestosterone - PE pituitary extract from adult fish - PE_juv pituitary extract from juvenile fish - RIA radio immunoassay - T testosterone     

Adrenal cortex and stomach lesions associated with stress in wild male African green monkeys (Cercopithecus aethiops) in the post-capture period

The objective of this study was to look for early pathological changes in stress target organs, adrenal glands, and stomachs in captured wild African green monkeys (AGMs). Three wild-caught male AGMs and seven singly housed wild AGMs were euthanized on day 1 and day 45 post-capture, respectively, and compared with four wild males euthanized with a rifle as controls. Morphometric analyses of the adrenal cortices and the cortical zones were done using an image analyzer. By day 45, the confined animals were clinically healthy, but had lost 47% mean body weight despite ad libitum feeding. The width of zona fasciculata in the controls was significantly smaller compared with that of 45-day monkeys (P < 0.05). Numerous acidophilic, hyperplastic and hypertrophic cells were present in the zona fasciculata of the 1-day confined AGMs. In the 45-day monkeys, there was glandular hyperplasia in the zona glomerulosa and the acini were distended and vacuous; yellow, granular pigmentation was distributed in the zona fasciculata. Acute stomach lesions represented by petechiation were seen in one monkey on day 1. Deep, circular, mucosal erosions, one to five in number and measuring from 0.5 to 1 mm in diameter, were present in three monkeys on day 45 post-capture. There were no adrenal cortex or stomach lesions in the rifle-shot monkeys. In conclusion, pathological lesions in the adrenal glands, and stomachs of the wild AGMs and weight loss occurred within the initial 45-day period following capture and confinement.     

Effects of cranial cervical ganglionectomy and castration of male lambs. III. Hormonal responses following administration to gonadotrophin releasing hormone (GnRH)

Entire and castrate male lambs, which were cranial cervical ganglionectomized (GX) or untreated, were utilized in a study of responses to intravenous GnRH; 24 animals were treated at both 101 and 277 days of age. GX caused a reduction in basal LH concentrations of both wethers and rams at the first sampling, but increased pre-injection levels of this hormone in 277 day old wethers. Basal LH levels of castrates were substantially higher than those of entires, but GX had no significant influence on pretreatment testosterone secretion in rams. GnRH treatment elevated plasma LH levels in all animals, while in entires increases in testosterone concentrations also occurred. Castration significantly increased peak LH levels together with total LH output. At neither age were the LH or testosterone reponses influenced significantly by GX, nor was the interaction of castration and GX significant for LH response data. The major effect of age at GnRH treatment was that markedly higher testosterone responses were recorded from the older rams.     

A comparison of the annual changes in testicular activity and serum androgen levels between the early and delayed maturing groups of male Cottus hangiongensis

Synopsis Annual changes in testicular activity and concentration of two serum androgens were monitored in two groups of the river-sculpin Cottus hangiongensis collected from the upper and lower reaches of a river at southern Hokkaido, Japan. One of them (early maturing group) underwent testicular maturation with aberrant spermatids and spermatid masses produced during the reproductive cycle. Moreover, regular seasonal changes in serum testosterone and 11-ketotestosterone concentrations were observed. On the other hand, in the other group (delayed maturing group), although body size of the fish was large enough to undergo reproduction, annual changes in gonadosomatic index and testicular activity did not vary much. During the months of active testicular development in the early maturing group, spermatogenesis was observed to begin in some regions of the testes of delayed maturing fish, but always resulted in the formation of aberrant spermatids and spermatid masses. Moreover, concentration of serum androgens did not significantly vary throughout the year. Results suggest that low androgen production is a proximal factor for delayed sexual maturity in the delayed maturing group, and that the occurrence of aberrant spermatids and spermatid masses during spermatogenesis is not linked to the delayed maturity.     

Direct estimate of the spontaneous germ line mutation rate in African green monkeys

Here, I provide the first direct estimate of the spontaneous mutation rate in an Old World monkey, using a seven individual, three‐generation pedigree of African green monkeys. Eight de novo mutations were identified within ～1.5 Gbp of accessible genome, corresponding to an estimated point mutation rate of 0.94 × 10^?8 per site per generation, suggesting an effective population size of ～12000 for the species. This estimation represents a significant improvement in our knowledge of the population genetics of the African green monkey, one of the most important nonhuman primate models in biomedical research. Furthermore, by comparing mutation rates in Old World monkeys with the only other direct estimates in primates to date–humans and chimpanzees–it is possible to uniquely address how mutation rates have evolved over longer time scales. While the estimated spontaneous mutation rate for African green monkeys is slightly lower than the rate of 1.2 × 10^?8 per base pair per generation reported in chimpanzees, it is similar to the lower range of rates of 0.96 × 10^?8–1.28 × 10^?8 per base pair per generation recently estimated from whole genome pedigrees in humans. This result suggests a long‐term constraint on mutation rate that is quite different from similar evidence pertaining to recombination rate evolution in primates.     

Noninvasive measurement of blood pressure in African green monkeys (Cercopithecus aethiops)

Indirect measurements of arterial blood pressure were made in African green monkeys (Cercopithecus aethiops) employing a Doppler ultrasound stethoscope and standard cuff and an Infrasonde automatic blood pressure recorder. Measurements were obtained from anesthetized (10 mg/kg ketamine (HCI) and unanesthetized (1.5 mg/kg ketamine HCI) animals. Ketamine had no significant effect on blood pressure. Indirect measurements from the brachial artery were compared with direct femoral artery measurements and with each other. Systolic blood pressures measured by the Doppler (r = .948) and Infrasonde (r = .920) methods correlated closely with direct measurements but were significantly lower than systolic blood pressures measured by the direct method. Diastolic blood pressures measured by the Infrasonde method agreed closely with direct measurements (r = .947). Systolic blood pressures measured by the indirect methods correlated closely in both anesthetized (r = .973) and unanesthetized (r = .834) animals and were not significantly different. Mean blood pressures calculated from direct and Infrasonde measurements also correlated closely (r = .963), with direct measurements being 4 mmHg higher on the average. Mean blood pressures are less influenced by methodology and are more reproducible than other pressures. These noninvasive methods can be used to obtain simple and accurate measurements of blood pressure from anesthetized and unanesthetized monkeys and are of value in long-term studies in monkeys.     

Age-related changes of immunoglobulin levels in African green monkeys (Cercopithecus aethiops)

Serum IgG, IgA, and IgM levels were measured in domestically bred African green monkeys (Cercopithecus aethiops) ranging in age from 0 day to 49 months as well as in adult (5 years or older) animals of wild origin. Transplacental transfer of IgG was observed. IgG, IgA, and IgM levels increased with increasing age except for a temporal decrease of IgG level in the first month of life.     

The ultrastructure of the cells of Leydig in the white-crowned sparrow (Zonotrichia leucophrys gambelii) in relation to plasma levels of luteinizing hormone and testosterone

In male White-crowned Sparrows subjected to 20 h daily photoperiods there is an approximately 3-fold increase in the plasma concentration of luteinizing hormone (LH) on the first long day after which a quasi-stable level is maintained for at least 42 days. This increase is followed by an increase in numbers of cells of Leydig and an enhancement of their steroidogenic features, a decrease in transitional interstitial cells, and an increase in plasma level of testosterone. With the decline in plasma LH, as photorefractoriness develops, the steroidogenic features of the cells of Leydig undergo disorganization. For as yet unexplainable reasons the plasma levels of testosterone decline before the decrease in plasma LH and before the degeneration of the steroidogenic features of the cells of Leydig.     

Use of gonadotropin releasing hormone to improve reproductive responses of ewes introduced to rams during seasonal anestrus

Three experiments were conducted on anestrous ewes of Suffolk, Dorset, and Katahdin breeding to examine the potential value of GnRH to improve ovulation and pregnancy in response to introduction of rams. In Experiment 1, treatment with GnRH 2 d after treatment with progesterone (P₄; 25 mg i.m.) at introduction of rams was compared to treatment with P₄ alone at the time of introduction of rams. Treatment with GnRH did not increase percentages of ewes with a corpus luteum (CL) 14 d after introduction of rams, pregnant 32 d after treatment with PGF₂α 14 d after introduction of rams, or percent of treated ewes lambing to all services. In Experiment 2, treatments with GnRH on day 2, 7, or both after introduction of rams were compared. Treatments did not differ in mean estrous response, percentages of ewes with a detectable CL or number of CL present on day 11, or mean pregnancy and lambing rates. Therefore, neither one nor two injections of GnRH at these times appeared to be effective to induce anestrous ewes to breed. In Experiment 3, treatments compared included GnRH 4 d before introduction of rams, GnRH 4 d before and 1 d after introduction of rams, ram introduction alone, and treatment with P₄ (25 mg i.m.) at the time of introduction of rams. Percentages of ewes with concentrations of P₄ greater than 1 ng/mL (indicating formation of CL had occurred) 7 d after ram introduction tended to be greater (P < 0.07) in ewes treated with GnRH or P₄ than in control ewes treated with ram introduction alone. However, there was no difference in P₄ concentrations between groups by day 11 or 12 after introduction of rams. Estrous response rates and percentages of ewes pregnant 95 d after PGF₂α was administered (on day 12 after introduction of rams) tended to be greater (P = 0.08 and 0.06, respectively) in ewes treated with GnRH or P₄ than in ewes exposed to rams only. There was no difference in response variables between ewes treated with GnRH 4 d before introduction of rams and ewes treated with GnRH 4 d before and 1 d after introduction of rams. In conclusion, treatment with GnRH 4 d before ram introduction showed promise as an alternative to treatment with P₄ to improve the ovulatory response and reproductive performance of ewes introduced to rams during seasonal anestrus.     

Immunization against GnRH in the male camel (Camelus dromedarius): Effects on sexual behavior, testicular volume, semen characteristics and serum testosterone concentrations

The effect of immunization against gonadotrophin releasing hormone (GnRH) on sexual behavior, total scrotal size, semen characteristics and serum concentrations of testosterone, was evaluated for 24 wks in sexually mature camels (Camelus dromedarius). Eight bull camels were randomly divided into a treatment and control group. Four male camels were immunized using 2 mg GnRH - tandem-dimer conjugated to ovalbumin, (Pepscan Systems, the Netherlands) administered subcutaneously, 4 wks apart. Control male camels received the same amount of saline solution. Significant decline in serum testosterone level was observed in three immunized camels out of four, whereas one camel showed no effect. The testosterone levels reached to <1.0 ng/mL serum by week 4 after booster injection and remained suppressed through the course of the study. The total testicular volume was not affected until the end of the experiment. In treated animals, the sexual behavior negatively affected after the booster injection. Anti-GnRH vaccine had a seriously detrimental effect on the acrosin amidase activity and normal acrosome percentages in treated male camels. It is concluded that the vaccine was effective in reducing serum testosterone levels and libido, and it had a serious harmful effect on the acrosin amidase activity and percentages of spermatozoa with normal acrosome. The immunogen did not affect the total testicular volume.     

Endocrine changes in male stumptailed macaques (Macaca arctoides) as a response to odor stimulation with vaginal secretions

In mammalian species, social chemosignals are important in modulating endocrine reproductive functions. In nonhuman primates, previous studies have described a high frequency of mounting behavior by females in the follicular and periovulatory phases of the menstrual cycle. Stumptailed macaque females do not signal receptivity by means of sexual swellings, as do others macaques, therefore providing a good model in which to study chemical signaling of reproductive status. We exposed anesthetized stumptailed males to vaginal secretions of either late follicular or menses phase or to saline solution to determine the endocrine changes promoting male sexual behavior. In males exposed to follicular secretions, plasma testosterone concentrations were sustained up to 120 min after exposure. Such an effect was not observed in animals exposed to menses or saline odor sources. A luteinizing hormone surge, occurring 30 minutes after exposure to late follicular phase secretion swabs, preceded this sustained testosterone effect. The fact that late follicular scents induce sustained testosterone concentrations provides support to the idea that stumptailed males draw information concerning female reproductive status from the female's vaginal odor.     

ORIGINAL ARTICLE: Evaluation of miosis,behavior and cholinesterase inhibition from low‐level,whole‐body vapor exposure to soman in African green monkeys (Chlorocebus sabeus)*

Background Relatively little is known about the effects of very low‐level exposures to nerve agents where few signs or symptoms are present. Methods African green monkeys (Chlorocebus sabeus) (n = 8) were exposed for 10 min, whole‐body, to a single concentration of soman (0.028–0.891 mg/m³). Results EC₅₀ values for miosis were determined to be 0.055 mg/m³ and 0.132 mg/m³ when defined as a 50 percent reduction in pupil area and diameter, respectively. In general, performance on a serial probe recognition task remained unchanged at lower concentrations, but responding was suppressed at the largest concentration tested. Soman produced concentration‐dependent inhibition of acetylcholinesterase activity and, to a lesser extent, butyrylcholinesterase activity. Conclusions These results characterize threshold soman exposure concentrations that produce miosis in the absence of other overt signs of toxicity and extend previous studies indicating that miosis is a valuable early indicator for the detection of soman vapor exposure.     

Sex steroids modulate changes in social and sexual preference during juvenile development in zebra finches

Zebra finches, like many other animals, have close social relationships mainly with the family at young ages but begin to express interest in opposite-sex extra-family animals as they enter the late juvenile period and sexual maturity. This experiment tested a set of hypotheses that sex steroids are involved in this developmental transition. At 25-30 days, subjects were implanted subcutaneously with Silastic tubes that were empty (controls), filled with testosterone propionate, filled with estradiol benzoate, or filled with a combination of ATD (an aromatization inhibitor) and flutamide (an anti-androgen). Once a week between ages 30 and 90 days, they were given three-choice tests where the three stimulus types were the family members, unpaired males, or unpaired females. The preferred category was defined as the one adjacent to the proximity zone in which the subject spent the most time. Control males were more likely to prefer females and less likely to prefer the family as they got older, and control females were increasingly likely to prefer males. Males treated with testosterone or estradiol showed a premature increase in preferences for females. Females treated with ATD plus flutamide failed to show the normal increase in preferences for males shown by controls. These results indicate an involvement of sex steroids in the maturation of sexual preferences in a socially monogamous species that relies on visual and auditory, rather than olfactory, cues for sexual or other social behavior.     

Hormonal, behavioral, and thermoregulatory responses to bacterial lipopolysaccharide in captive and free-living white-crowned sparrows (Zonotrichia leucophrys gambelii)

Exposing vertebrates to pathogenic organisms or inflammatory stimuli, such as bacterial lipopolysaccharide (LPS), activates the immune system and triggers the acute phase response. This response involves fever, alterations in neuroendocrine circuits, such as hypothalamo-pituitary-adrenal (HPA) and -gonadal (HPG) axes, and stereotypical sickness behaviors that include lethargy, anorexia, adipsia, and a disinterest in social activities. We investigated the hormonal, behavioral, and thermoregulatory effects of acute LPS treatment in a seasonally breeding songbird, the white-crowned sparrow (Zonotrichia leucophrys gambelii) using laboratory and field experiments. Captive male and female sparrows were housed on short (8L:16D) or long (20L:4D) day lengths and injected subcutaneously with LPS or saline (control). LPS treatment activated the HPA axis, causing a rapid increase in plasma corticosterone titers over 24 h compared to controls. Suppression of the HPG axis occurred in long-day LPS birds as measured by a decline in luteinizing hormone levels. Instead of a rise in body temperature, LPS-injected birds experienced short-term hypothermia compared to controls. Birds treated with LPS decreased activity and reduced food and water intake, resulting in weight loss. LPS males on long days experienced more weight loss than LPS males on short days, but this seasonal effect was not observed in females. These results paralleled seasonal differences in body condition, suggesting that modulation of the acute phase response is linked to energy reserves. In free-living males, LPS treatment decreased song and several measures of territorial aggression. These studies highlight immune-endocrine-behavior interrelationships that may proximately mediate life-history tradeoffs between reproduction and defense against pathogens.