Comparison of male reproductive parameters in three rat strains: Dark Agouti, Sprague-Dawley and Wistar

The choice of experimental animal can have a large impact on experimental results, an example is the anecdotal evidence suggesting that Dark Agouti (DA) rats have a lower reproductive capacity than other rat strains. In this paper we report on an investigation into male reproductive characteristics in three rat strains--Wistar, Sprague-Dawley (outbred strains) and DA (an inbred strain). Reproductive organ weights, blood testosterone levels and sperm counts were measured in mature age-matched male rats. DA animals had significantly smaller testis weights than the Sprague-Dawley and Wistar animals, and this did not appear to be related to the overall smaller body mass of the DAs. There were no differences between the three strains in testicular histology or sperm counts (per gram testis). Although there was also no significant difference in epididymal sperm count, the DA animals had a much greater variability in sperm count than the other strains. There were no differences in relative (to body weight) epididymal, seminal vesicle or ventral prostate weights or in the blood testosterone levels. These results suggest that differences in reproductive capacity in DAs are neither the result of morphological differences in the reproductive organs nor in circulating testosterone levels. Sperm production appears to be normal but the lowered testicular weight and variability in epididymal sperm counts suggests that there are other factors in the testicular or epididymal environment which alter male reproductive function.     

BODY SIZE,SPERM COMPETITION,AND DETERMINANTS OF REPRODUCTIVE SUCCESS IN MALE SAVANNA BABOONS

One component of sexual selection is sperm competition. It has been reasoned that the intensity of sperm competition may be reflected in the relative testicular sizes of animals. Among males residing in multimale breeding systems, testicular size is relatively larger than among males residing in unimale mating systems. Information on whether differences in testicular size within a species can account for differences in male reproductive success is unavailable for natural populations of primates. A population of six troops of savanna baboons in Kenya was surveyed for morphometric analysis, and one of these troops was the subject of extensive behavioral observations afterwards. Testicular weights could not be obtained, but measurements of linear dimensions were transformed into volumetric estimates. Male weight accounted for 30% of the variance in testicular volume. Neither body size nor testicular volume was associated with differences in male reproductive activity. The outcome of fights over access to females could not be related to male body size, and ejaculatory patterns of males were independent of testicle size. Both sperm competition and aggressive competition intensified during the four-day optimum conception period, but fights over access to consort females were infrequent. Among savanna baboons, the probability of an ejaculation resulting in a conception is fairly low, which may account for the infrequency of injurious fights. Although testicle size influences sperm production, it does not influence either the timing of mating or the fertilizing capacity of spermatozoa, and both of these factors probably account for a substantial fraction of the variance in male baboon paternity. Sperm competition is an adjunct to agonistic competition as a mechanism affecting male baboon reproductive success. It is concluded that male reproductive success in baboons is affected more by social factors than by morphological traits associated with size.     

Coevolution of male and female reproductive traits in a simultaneously hermaphroditic land snail

Inter- and intraspecific studies in gonochoristic animals reveal a covariation between sperm characteristics and the size of the female reproductive tract, indicating a rapid evolutionary divergence, which is consistent with the theory of post-copulatory sexual selection. Simultaneous hermaphrodites differ from species with separate sexes (gonochorists) in that they possess both functional male and female reproductive organs at the same time. We investigated whether in hermaphroditic animals intraspecific variation in reproductive traits results from divergent coevolution, by quantifying the variation in male and female traits among six natural populations of the snail Arianta arbustorum and examining the covariation in interacting traits. There was a significant among-population variation in spermatophore volume, number of sperm transferred and sperm length, as well as in volume of the sperm storage organ (spermatheca) and number of tubules, but not in spermatheca length. We found a positive association between sperm number transferred and spermatheca volume. This result suggests that the same post-copulatory mechanisms as in gonochorists drive the correlated evolution of reproductive characters in hermaphrodites.     

A comparative study on testicular microstructure and relative sperm production in gorillas, chimpanzees, and orangutans

We performed histological analyses for comparing testicular microstructure between the gorilla, chimpanzee, and orangutan. Testicular samples were obtained by autopsy or biopsy from 10 gorillas, 11 chimpanzees, and 7 orangutans from several zoos and institutes. The seminiferous epithelia were thick in the chimpanzee and orangutan but thin in the gorilla. Leydig cells in the interstitial tissue were abundant in the gorilla. The acrosomic system was extremely well developed in the orangutans. Our study reveals that the cycle of seminiferous epithelium in orangutan testis can be divided into ten stages, whereas that in human, chimpanzee, and gorilla testes can be divided into only six stages. Phylogenetic analyses of the number of divisions may indicate that the seminiferous epithelium of our common ancestor has changed since the orangutan diverged from it. Furthermore, we performed comparative analyses of testicular microstructure to estimate relative sperm production among these three animals, and proposed a new indicator (namely the spermatogenic index, SI) closely related to sperm production. The SI indicated that a chimpanzee usually produces about 223 times more sperm than a gorilla and about 14 times more than an orangutan. Our data demonstrate the significance of the SI for estimating sperm production, thus aiding our understanding of the reproductive strategy as well as testis weight and relative testis size in investigated primates.     

Testicular Volume and Reproductive Status of Wild <Emphasis Type="Italic">Callithrix jacchus</Emphasis>

The social relationship dynamic among callitrichid females is well known. Breeding exclusivity by dominant females involves female-female competition, usually resulting in the inhibition of subordinate reproduction. However, the strategies to maintain the male breeding position are still unclear. Researchers have observed no overt aggression between males, and differences in testosterone levels between dominant and subordinate individuals do not correlate with differences in reproductive success. In Callithrix monogamy is the predominant mating system, and testicular size is compatible with the absence of sperm competition. We analyzed testicular volume during development in 95 individuals at different ages (infant n = 12, juvenile n = 9, subadult n = 15, and adult n = 59). We also investigated if the ratio between testicular volume and body mass correlates with breeding position in the social group. The ratio was significantly higher in breeding males and a positive correlation between body mass and testicular volume is significant only for nonbreeding males. The findings suggest that testicular size varies with male reproductive status in the social group and that the enlargement of testicular volume in breeding common marmoset males seems to be a result of proximate causes and to depend on social and reproductive contexts acting together or separately.     

Functional parameters of chimpanzee (Pan troglodytes) sperm from ejaculates collected by rectal probe electrostimulation and by artificial vagina

This study compares functional parameters of sperm from ejaculates collected from 15 adult male chimpanzees using rectal probe electrostimulation (RPE) and from 10 adult male chimpanzees trained to use an artificial vagina (AV). Computer assisted motion analysis (CAMA) showed no significant differences in mean values for straight line velocity (VSL), linearity (LIN), curvilinear velocity (VCL), and lateral head movement (ALH) of sperm from ejaculates collected by RPE and by AV. There was, however, a significant difference (P < 0.01) in the population distribution for VSL and LIN, which indicates that sperm swim in a more convoluted manner in ejaculates collected by RPE than in ejaculates collected by AV. In the hamster zona-free ovum penetration assay (SPA), there were no significant differences in the percentages of hamster oocytes penetrated by sperm or in the number of sperm which penetrated each oocyte after 4 or 24 h incubation using sperm from ejaculates collected by RPE and by AV. Therefore, the lack of success using sperm from ejaculates collected by RPE to initiate pregnancy in the chimpanzee does not appear to result from abnormalities in sperm fertilizing capacity as measured in SPA. © 1996 Wiley-Liss, Inc.     

Social group size, potential sperm competition and reproductive investment in a hermaphroditic leech, Helobdella papillornata (Euhirudinea: Glossiphoniidae)

Social group size may affect the potential for sperm competition, and this in turn may favour ontogenetic adjustments in testicular mass according to the likely requirements for sperm and spermatophore production. In a number of comparative analyses of testis mass among vertebrate species that differ in mating system or social organization, increasing potential for sperm competition is associated with larger testis size. Intraspecific phenotypic plasticity should be able to produce the same pattern if social group size is heterogenous and reflects differing degrees of average sperm competition, but this intraspecific effect is less well studied. We tested the effect of social groups on both male and female investment in the simultaneously hermaphroditic leech, Helobdella papillornata. Leeches were placed in groups of one, two, four or eight. Sexual investment at the onset of reproductive maturity was quantified as the total testisac volume for male function and total egg volume for female function. We found that testisac volume (statistically adjusted for body size) showed a significant increase with increasing group size. Total egg volume (also adjusted for body size) was unaffected by group size. Our findings indicate adaptive developmental plasticity in male gonad investment in response to the potential for sperm competition.     

Seasonal changes in plasma concentrations of immunoreactive inhibin and testicular activity in male Japanese monkeys

Seasonal changes in plasma immunoreactive (ir-) inhibin, testosterone, LH, and FSH concentrations were examined in five sexually mature male Japanese monkeys (Macaca fuscata fuscata) housed indoors individually, to explore the reproductive cyclicity in the male. Blood samples were collected monthly throughout one year, and testicular size, semen volume, and number of sperm in the semen were ascertained at the same time in the same animals. Semen samples were obtained by penile electrostimulation. The results showed a clear seasonal increase in all parameters: plasma ir-inhibin, testosterone, testicular size, semen volume, and total number of sperm in the liquid portion of the semen during the autumn and winter months in synchrony with the natural breeding season. In contrast, plasma LH and FSH remained unchanged throughout the year, although plasma FSH tended to increase during the breeding season concomitant with an increase in plasma ir-inhibin. A significant positive correlation between FSH and ir-inhibin was observed in two of five monkeys. The positive correlations between plasma ir-inhibin and testicular activities during both the developing and regressing phases of the testicular cycle indicate that plasma ir-inhibin is a useful indicator of testicular activity as well as an indicator of Sertoli cell function in the Japanese monkey.     

Effects of larval exposure to sublethal concentrations of the ecdysteroid agonists RH-5849 and tebufenozide (RH-5992) on male reproductive physiology in Spodoptera litura

Sublethal concentrations of the bisacylhydrazine moulting hormone agonists, RH-5849, and tebufenozide (RH-5992) were fed to sixth (final) instar larvae of Spodoptera litura. Both RH-5849 and tebufenozide adversely affected the mating success of S. litura when the surviving treated males were crossed with normal females. The ecdysone agonists decreased the longevity of treated males and of untreated females when crossed with treated males. The number of eggs laid by untreated females mated to treated males was decreased, and the fertility (percentage of hatching success) of the resulting eggs was reduced. These effects on male reproductive success were at least in part explained by a reduction in the number of sperm transferred during mating. The adverse effects of tebufenozide on male reproductive function were qualitatively the same as those of RH-5849, but tebufenozide was active at lower concentrations. To understand the reason for these adverse effects on male reproduction, we investigated the effects of the insecticides on male reproductive physiology. Male reproductive tract development and testicular volume of resulting adult moths were adversely affected by sublethal larval exposure to the ecdysone agonists. Dose-dependent reductions occurred in the production of eupyrene and apyrene spermatozoa in the adult testes, and in the number of spermatozoa released from the testes into the male reproductive tract. The descent into the male tract of both eupyrene and apyrene sperm was found to start at the normal stage of development in both normal and treated insects, but the daily rhythm of sperm descent was subsequently disturbed in the insecticide-treated moths. This affected the numbers of sperm in the upper vas deferens (UVD), seminal vesicle (SV), and duplex (duplex). Injections of RH-5849 given to pharate adult or newly emerged adult S. litura also caused drastic reduction in the number of sperm in the upper regions of the male tract, when measured 24 h after injection. The possible importance of pest population reduction through the sublethal anti-reproductive effects of insecticides is discussed.     

Reduced sperm counts in guppies (Poecilia reticulata) following exposure to low levels of tributyltin and bisphenol A.

There is increasing evidence that normal male reproductive function can be disrupted by exposure to pollutants in the environment that can exogenously mimic, antagonize or block sex-hormone function. One possible consequence of exposure to these xenobiotics is disruption to spermatogenesis, but results thus far provide only indirect and inconsistent evidence. In this study we exposed adult male guppies (Poeciliidae: Teleostei) to environmentally relevant levels of the common xenobiotics tributyltin (11.2-22.3 ngl-1) and bisphenol A (274-549 micrograms l-1) in experimental aquaria. After 21 days of exposure, we found significant declines (by 40-75%) in total sperm counts for male fishes exposed to tributyltin and bisphenol A compared with controls. This short-term decline in sperm count is unlikely to be the result of endocrine-mediated alteration of the germ line, and we found no change in testis size or sperm lengths between treatments. However, Sertoli cells, which facilitate the transport of maturing sperm into the testicular deferent duct (where they are stored prior to ejaculation), are directly sensitive to xenobiotic action and it is therefore possible that spermatogenesis was inhibited through in vivo interference with normal Sertoli-cell function.     

Effects of vanadate on male rat reproductive tract histology, oxidative stress markers and androgenic enzyme activities

Vanadium has been recognized as industrial hazards that adversely affect male reproductive systems of humans and animals. However, less information is available concerning the underlying mechanism in the pathogenesis of male reproductive dysfunction. The present study investigated the possible involvement of oxidative stress to induce oxidative deterioration of testicular functions in adult rats. The results of in vitro and in vivo studies demonstrate that vanadium treatment resulted in a significant dose- and time-dependent increase in the testicular lipid peroxidation, marked inhibition in the level of superoxide dismutase and catalase activities, decreased sperm counts, and substantially inhibited the activities of Delta(5)3beta- and 17beta-hydroxysteroid dehydrogenase as well as serum testosterone level. Histopathological examination revealed inhibition of spermatogenesis and the preferential loss of maturing and elongated spermatids along with increased percent of abnormal sperm. Taken together, the results suggest that an increase in free radical formation relative to loss of antioxidant defense system during vanadium exposure may render testis more susceptible to oxidative damage leading to their functional inactivation. Thus the toxic effects of vanadium are cumulative and that vanadium produced damages in testes are dose- and time-dependent.     

Licorice extract does not impair the male reproductive function of rats.

The effect of water extract of licorice (Glycyrrhiza uralensis), one of the most widely used medicinal plants in Oriental nations and in Europe, on male reproductive function was investigated in rats. Licorice extract was prepared as in Oriental clinics and orally administered at doses of 500, 1,000 or 2,000 mg/kg, the upper-limit dose (2,000 mg/kg) recommended in the Toxicity Test guideline of the Korea Food and Drug Administration, to 6-week-old male rats for 9 weeks. Licorice extract neither induced clinical signs, nor affected the daily feed consumption and body weight gain. There were no significant changes in testicular weights, gross and microscopic findings, and daily sperm production between vehicle- and licorice-treated animals, in spite of slight decreases in prostate weight and daily sperm production at the high dose (2,000 mg/kg). In addition, licorice did not affect the motility and morphology of sperm, although the serum testosterone level tended to decrease without significant difference, showing a 28.6% reduction in the high-dose (2,000 mg/kg) group. The results suggest that the no observed adverse-effect level of licorice extract is higher than 2,000 mg/kg, the upper-limit dose, and that long-term exposure to licorice might not cause profound adverse effects.     

Changes in binding of a 27-kilodalton chimpanzee cauda epididymal protein glycoprotein component to chimpanzee sperm

Motility patterns of caput epididymal chimpanzee sperm, caput epididymal chimpanzee sperm incubated in vitro with chimpanzee cauda epididymal fluid, and cauda epididymal chimpanzee sperm were assessed quantitatively. Sperm recovered from the caput epididymis showed no motility, whereas sperm recovered from cauda epididymis showed progressive forward motility. After incubation in cauda fluid, approximately 25% of caput epididymal sperm showed some motile activity. Electrophoretic analysis of ¹²⁵I-labeled sperm plasma membrane preparations revealed that the surface of caput epididymal sperm, incubated in cauda fluid, was modified by the appearance of a major protein-glycoprotein surface component with an apparent molecular weight of 27 kilodaltons (kD). THis 27-kD component was not detected on caput epididymal sperm incubated in buffer or in caput fluid. However, it was present in cauda fluid and on cauda epididymal sperm. Binding to caput epididymal sperm was cell specific in that chimpanzee erythrocytes incubated in cauda fluid did not bind this 27-kD cauda fluid component. Motility patterns of ejaculated chimpanzee sperm and of ejaculated chimpanzee sperm incubated in the uterus of adult female chimpanzees also were assessed quantitatively. Ejaculated sperm showed progressive forward motility, whereas in utero incubated ejaculated sperm showed hyperactivated motility typical of capacitated sperm. Electrophoretic analysis of ¹²⁵I-labeled sperm plasma membrane preparations revealed the loss of a 27-kD component from the surface of ejaculated sperm after in utero incubation. No significant change in the ¹²⁵I-distribution pattern was detectable when ejaculated sperm were incubated in buffer. These results suggest that the lumenal fluid component, which becomes adsorbed to the surface of chimpanzee sperm during maturation in the epididymis and which is removed from the surface of mature chimpanzee sperm in the female reproductive tract, affects sperm motility.     

Inhibition of prolactin secretion and androgenic function in the adult male rat

The effects of bromocriptine induced hypoprolactinemia on the testicular function were studied in adult rats. Bromocriptine treatment (1500 micrograms/day for 24 days) reduced serum and pituitary Prolactin levels, indicating a decrease in prolactin secretion and synthesis. No change in reproductive organ weights was seen in treated animals. Hypoprolactinemia had no effect on plasma testosterone or androstenedione levels and testicular androstenedione content, but decreased significantly testicular testosterone content. These findings indicated that experimental hypoprolactinemia induced a decrease in testicular testosterone content without affecting androgens levels.     

Involvement of testicular DAAM1 expression in zinc protection against cadmium‐induced male rat reproductive toxicity

In order to verify the effects of exposure to Cd and Zn on testicular DAAM1 gene and protein expression and also to ascertain their involvement in the protective role of Zn in prevent the testicular toxicity Cd‐induced in male offspring rats at adult age after gestational and lactational exposure, male offspring rats, from mothers receiving either tap water, Cd, Zn, or Cd + Zn during gestation and lactation periods, were scarified on postnatal days (PND) 70. The reproductive organ (testis, epididymis, and vesicle seminal) were collected, weighed, and analyzed. The results showed that exposure to Cd in utero and through lactation decreased the relative reproductive organ weight, altered the testicular histology at the interstitial and tubular levels, and causing a significant reduction in the daily sperm production (DSP) per testis and per gram of testis, and other then altering the epididymal sperm quality. Furthermore, both mRNA and protein expression of rat testicular DAAM1 were also inhibited in Cd‐treated group. Zn supply has completely corrected the most of these toxic effects. Our results imply that Zn could prevent Cd‐induced testicular toxicity and sperm quality alteration in adult male rat after gestational and lactational exposure, probably via the restoration of the testicular DAAM1 expression inhibited by Cd.     

Effects of the opioid analgesic oxymorphone hydrochloride on reproductive function in male and female rats

BACKGROUND: Endogenous opioids seem to regulate hypothalamic gonadotropin release in both males and females, as evidenced by the effects of opioid agonists and antagonists on LHRH release and reproductive hormone levels. The effects of long‐term oral administration of opioid analgesics on reproductive function have not been well characterized. METHODS: The reproductive effects of oxymorphone, a potent opioid agonist, were investigated in male and female Crl:CD(SD) IGS BR rats at oral doses of 0, 5, 10, and 25 mg/kg/day (25 animals/sex/group). Males were treated for approximately 9 weeks (mated after 4 weeks of dosing). Females were treated for 14 days before mating, and through Gestation Day (GD) 7. Estrous cycling was evaluated during the premating period. On GD15, pregnancy status and the numbers of corpora lutea, implantation sites, live and dead embryos were determined. Epididymal and testicular sperm counts and epididymal sperm motility and morphology were evaluated in males. RESULTS: Two males given 25 mg/kg/day died. Behavioral changes and deficits in body weight gain occurred at all doses. There were no effects of oxymorphone on reproductive function or sperm parameters in males. The estrous cycle was prolonged in females given 25 mg/kg/day (mean of 5.3 vs. 4.3 days in controls). A small, but consistent decrease in the numbers of corpora lutea (with associated decreases in implantation sites and embryos) occurred in females given ≥10 mg/kg/day. There were no effects on mating or fertility in females. CONCLUSIONS: Oxymorphone seems to partially inhibit ovulation in female rats, with no significant effects on male reproductive outcome. Birth Defects Res (Part B) © 2007 Wiley‐Liss, Inc.     

Are non-reproductive male highveld mole-rats, Cryptomys hottentotus pretoriae physiologically suppressed while in the confines of the natal colony?

The highveld mole-rat, Cryptomys hottentous pretoriae is a social, subterranean, co-operative breeder with a high reproductive skew. The relationship between reproductive status and reproductive physiology in male highveld mole-rats was investigated. Testicular morphometrics, histological parameters, plasma testosterone concentrations and sperm motility parameters were studied in 31 males (14 reproductive and 17 non-reproductive males). Reproductive males were significantly larger than non-reproductive males, with testicular mass and volume corrected for body mass considerably larger for the reproductive males. Circulating plasma testosterone concentrations of reproductive males were not significantly higher than non-reproductive males (reproductive males 10.3±1.8 nmol l⁻¹ vs non-reproductive males 7.3±1.74 nmol l⁻¹). Sperm motility parameters were measured, but no significant differences were found between reproductive and non-reproductive males. All 14 reproductive males had motile sperm, whereas 13 of the 17 (76%) of non-reproductive males possessed motile sperm. A typical ejaculate of a reproductive male contains 48.3% motile sperm characterized by a high percentage of flagellar defects, whereas the non-reproductive male has an ejaculate containing 45.6% motile sperm with a high percentage of head defects. It is apparent that non-reproductive males are not physiologically suppressed from reproducing. Moreover, the non-reproductive males are excluded from incestuous matings as a result of being the offspring of the reproductive female.     

Effects of dispersal status on pituitary and gonadal function in the male spotted hyena

Male spotted hyenas (Crocuta crocuta) reach puberty at 24 months of age and then usually emigrate from their natal clans one to 52 months later. Recent work has shown that reproductive success is very low among adult males still residing in their natal groups, and it is similarly low among recent or "short-term" immigrants. Long-term immigrants father the vast majority of cubs born. Here we inquired whether these differences in reproductive success might be associated with variation among males in pituitary or gonadal function. In one free-living hyena population in Kenya, we compared baseline levels of plasma luteinizing hormone (LH) and testosterone (T) among adult natal males, short-term immigrants, and long-term immigrants, and we also compared their pituitary and gonadal responses to GnRH challenge. Mean basal plasma LH values did not differ among groups, but mean basal T concentrations in long-term immigrants were higher than those in either natal males or short-term immigrants. Similarly, pituitary response to GnRH challenge did not vary significantly among groups, but testicular response to challenge was greater in long-term immigrants than in natal males or short-term immigrants. Thus adult natal and immigrant males exhibited similar pituitary function but testicular function was attenuated among adult males that had not yet left their natal groups and also among males attempting to become established in new social groups. This suggests that, like the act of emigration itself, the process of social integration during immigration may have important physiological consequences for male mammals transferring between groups.