SEARCH · PubMed Health

Results for “Reproductive parameters”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16Linked to original sources

PubMed2002

The impact of Leptospira seropositivity on reproductive performance in sows in southern Viet Nam.

A serologic survey was conducted among sows in the Mekong delta in southern Viet Nam to investigate associations between leptospiral seropositivity and reproductive performance. Data were collected from a total of 339 sows in lactation or gestation, from four large-scale state farms on three occasions. The seroprevalence for Leptospira interrogans serovar (sv) autumnalis was 32%, for L. interrogans sv bratislava 29%, for L. kirschneri sv grippotyphosa 13%, for L. interrogans sv icterohaemorrhagiae 27%, for L. interrogans sv pomona 5%, and for L. borgpetersenii sv tarassovi 13%. The reproductive parameters number of days from weaning to service (WSI), number of piglets born, number of piglets born dead, and number of piglets born weak, were evaluated. Seropositivity for sv tarassovi was associated with 0.8 more dead piglets per litter (P = 0.06), and sv grippotyphosa with a 1 day longer WSI (P = 0.06). There were no significant associations between reproductive performance and sv autumnalis, sv bratislava, sv pomona, and sv icterohaemorrhagiae. It is concluded that seropositivity for Leptospira can be associated with impaired reproductive performance even in areas where a high degree of immunity among sows is expected.

Animal Husbandry↗

PubMed1984

The effect of Aroclor 1254 (PCB) on the physiology of reproduction in the female rat--I.

Daily oral exposure of rats to 30 mg/kg of Aroclor 1254 for 1 month caused deleterious effects on the reproductive process, which were reflected in a decrease in the reproductive potential. The following disturbances were observed: prolongation of the estrous cycle; decrease in sexual receptivity; delay in timing of copulation; vaginal bleeding during gestation; decrease in litter size and delay in the time of parturition. The offspring, whether exposed to PCBs either prenatally and/or postnatally, showed a slower rate of body weight gain than controls. This was accompanied by high mortality until weaning of treated pups. Vaginal opening in the PCB-treated (as young) females occurred precociously, while other reproductive parameters were not affected at adulthood. Discontinuance of PCB treatment reversed the above symptoms.

Animals↗

PubMed1989

The effects of uranium on reproduction, gestation, and postnatal survival in mice.

Uranyl acetate dihydrate was tested for its effects on reproduction, gestation, and postnatal survival in Swiss mice. Four groups of animals, each of which consisted of 25 males and 25 females, were administered 0, 5, 10, and 25 mg/kg/day of uranyl acetate dihydrate. Mature male mice were treated orally for 60 days prior to mating with mature virgin female mice treated orally for 14 days prior to mating. Treatment of the females continued throughout mating, gestation, parturition, and nursing of the litters. One-half of the dams in each group were sacrificed on Day 13 of gestation and the remaining dams were allowed to deliver and wean their offspring. Postnatal development was monitored after 0, 4, and 21 days of lactation. No adverse effects on fertility were evident at the doses employed in this study. Nevertheless, embryolethality could be observed in the 25 mg/kg/day group. Significant increases in the number of dead young per litter were seen at birth and at Day 4 of lactation in the 25 mg/kg/day group. The growth of the offspring was always significantly lower for the uranium-treated animals. However, the present results suggest that uranium does not cause any adverse effects on fertility, general reproductive parameters, or offspring survival at the concentrations usually ingested by man.

Animals↗

PubMed1986

Studies on reproduction in rats with pirmenol, an antiarrhythmic agent.

Fertility and perinatal-postnatal studies were performed in CD rats given pirmenol, an antiarrhythmic agent, at dosages of 0, 25, 50, and 100 mg/kg. The drug was administered orally as diet admixtures in all studies. In the male fertility study, mature male rats were treated for 61 days prior to mating with virgin, untreated female rats. In the female fertility study, mature virgin female rats were treated for 15 days prior to mating with untreated partners with treatment continuing throughout mating, pregnancy, parturition, and weaning of the litters. In both studies, one-half of the dams in each group were killed on Day 21 of pregnancy and the remaining dams were allowed to deliver and wean their offspring and postnatal development was monitored. At weaning, two males and two females were arbitrarily selected from each litter, allowed to mature on unmedicated diet, and then mated within treatment groups to produce the F2 generation. In the perinatal-postnatal study, pregnant females were treated continuously from Day 15 of pregnancy until weaning of the litters on Day 21 postbirth. No adverse effects on fertility, general reproductive parameters, or offspring survival and development were evident at doses employed in these studies.

Animals↗

PubMed2001

Safety assessment of DHA-rich microalgae from Schizochytrium sp.

Schizochytrium sp. dried microalgae (DRM) contains oil rich in highly unsaturated fatty acids (PUFAs). Docosahexaenoic acid (DHA n-3) is the most abundant PUFA component of the oil. DHA-rich oil extracted from Schizochytrium sp. is intended for use as a nutritional ingredient in foods. As part of a comprehensive safety assessment program, the reproductive toxicity of DRM was examined in Sprague-Dawley-derived rats Crl:CD(SD)BR (30/sex/group) provided DRM in the diet at concentrations of 0, 0.6, 6.0, and 30%. These dietary levels corresponded to overall average dosages of approximately 400, 3900, and 17,800 mg/kg/day for F0 males (premating) and 480, 4600, and 20,700 mg/kg/day for F0 females, respectively. Prior to mating, males and females of the F0 generation were treated for 10 and 2 weeks, respectively. Treatment of males continued throughout mating and until termination (approximately 3 weeks after mating). Treatment of the females was continued throughout gestation and through lactation day 21. The females were killed after raising their young to weaning at 21 days of age. Food consumption was measured weekly throughout the study (except during mating) and body weights were recorded at least weekly during premating, gestation, and lactation. Reproductive parameters including estrus cycle duration, mating performance, fertility, gestation length, parturition, and gestation index were evaluated. Litter size and offspring body weights were recorded, offspring viability indices were calculated, and physical development (vaginal opening and preputial separation) was assessed for the F1 generation. All adult F0 and F1 animals were subjected to a detailed necropsy. DRM treatment had no effect on estrus cycles or reproductive performance including mating performance, fertility, gestation length, parturition, or gestation index. Litter size, sex ratio, and offspring viability indices were similarly unaffected and there were no effects of DRM treatment on the physical development of F1 animals.

Administration, Oral↗

PubMed2004

Stampidine is a potential nonspermicidal broad-spectrum anti-human immunodeficiency virus microbicide.

OBJECTIVE: Stampidine (2,'3'-didehydro-3'-deoxythymidine-5'-(p-bromophenyl methoxy alaninyl phosphate) is a novel aryl phosphate derivative of stavudine/d4T with broad-spectrum anti-HIV activity in vitro and in vivo. This study investigated the potential utility of stampidine as a nonspermicidal microbicide. DESIGN: Prospective, controlled study. SETTING: Center for Advanced Preclinical Sciences and Reproductive Biology Department. PATIENT(S): Seven sperm donors. ANIMAL(S): Fifty-two sexually mature, female and twenty-four male New Zealand white rabbits. INTERVENTION(S): Human semen and genital tract epithelial cells were exposed to stampidine (up to 1 mM). Ovulated does in subgroups of 12 were artificially inseminated with rabbit semen pretreated with stampidine (1 mM) or vehicle. Does in subgroups of four and three, respectively, were exposed intravaginally to a gel or a thermoreversible ovule formulation with and without 0.5%, 1.0%, or 2.0% stampidine (9 to 36 mM) for 14 days. MAIN OUTCOME MEASURE(S): Effect of stampidine on human sperm motility, kinematics, penetration through cervical mucus, and epithelial cell viability. Reproductive parameters on gestation day 8. Vaginal tissues were histologically scored 24 hours after dosing. RESULT(S): Exposure of human sperm to stampidine even at a concentration 10(6)-times higher than its in vitro anti-HIV-1 activity (50% inhibitory concentration = 1 nM) had no adverse effect on sperm motility, kinematics, cervical mucus penetrability, or the viability of vaginal and endocervical epithelial cells. Reproductive indices of pregnancy rate, embryo implantation, and preimplantation losses were not affected by pretreatment of rabbit semen with stampidine. Gel formulations of 0.5% to 2.0% stampidine (9 to 36 mM) lacked mucosal toxicity. CONCLUSION(S): The broad-spectrum anti-HIV agent stampidine had no adverse effect on sperm functions, was not cytotoxic, and did not induce mucosal toxicity. Stampidine has clinical potential as a prophylactic microbicide without contraceptive activity.

Animals↗

PubMed1998

Reproductive efficiency of Egyptian buffaloes in relation to oestrous detection systems.

A total of 57 buffalo cows were divided into two groups and subjected to different intensities of oestrous detection. In the first group (G1), oestrus was checked at 6-h intervals, four times daily starting at 0600 h as compared to twice daily in the second group (G2) at 0800 h and 1500 h. The year was also divided into two seasons: cool from November to April; and hot from May to October. Ovulatory activity was monitored by measuring progesterone concentrations in blood serum. Samples were obtained every 3 or 4 days post-partum until conception was confirmed. More frequent detection practices produced shorter intervals for all of the reproductive parameters. Calving interval was less for cows in G1 in the cool season (363.5 +/- 16.0 vs. 400.3 +/- 14.3 days) than in the host season (387.0 +/- 15.3 vs. 441.5 +/- 14.3 days). Oestrous detection efficiency was higher (P < 0.01) in G1 in both seasons. Season of calving produced a significant effect (P < 0.05) on the number of services per conception. The cool season calvers had better reproductive performance than cows calved during the hot season.

Animal Husbandry↗

PubMed2004

[Genetic demographic description of the Ust-Aldan rural population of Sakha Republic (Yakutia): ethnic, sex, and age compositions, vital statistics, and surname structure].

Information on the sex, age, and ethnic compositions; reproductive parameters; intensity of natural selection (Crow's indices); and surname diversity of three rural populations (the Byadi, Dyupsya, and Cheriktey villages) of the Ust-Aldan ulus (district) of Sakha Republic (Yakutia) has been analyzed. The rural Yakut population of the Ust-Aldan ulus is demographically young (the mean age 25-31 years) and characterized by low outbreeding, unfavorable sex ratio in both prereproductive and reproductive ages, and high fertility (3.58-5.45 children surviving until the reproductive age per woman that has completed the reproductive period), although the actual reproductively active period is shorter than half its physiological duration. In the structure of total selection, the differential-fertility component is considerably greater than the differential-mortality component (Itot = 0.625, Im = 0.093, and If = 0.487). In the villages studied, some surnames are accumulated (45-65% of the population have five most frequent surnames), which determines the low surname diversity (alpha = 11.62-25.19) and high random isonymy (Ir = 0.0391-0.0823).

Age Distribution↗

PubMed1994

[Use of a body condition index (BCI) for the study of the reproduction in snakes].

A body condition index (BCI = actual body mass/optimal theoritical body mass of the studied animal) was estimated in females of 3 species of snake. From dissections of 88 Vipera aspis and 18 Coluber viridiflavus, strong relationships between body reserves (such as mass of fat bodies and liver) and BCI were found. Furthermore, BCI explained most of the variance in the mass of the fat bodies and in the mass of the liver; however BCI and body length together increased the percentage of variation explained. Thus, a satisfactory estimation of body reserves in relation to body length is possible in living snakes. We have studied reproductive parameters (clutch size and litter size) in Vipera aspis (Viperidae) and Elaphe longissima (Colubridae) during a 3 year period. In the two species positive relationships between maternal body length and number of offspring were found. At the beginning of vitellogenesis, litter size is related to the BCI level in V. aspis but not in E. longissima. In both species, BCI must exceed a threshold value for reproduction to take place. However this threshold value is much lower in E. longissima (0.55) than in V. aspis (0.70). This indicates that in the latter species, large body reserves are necessary for the induction of vitellogenesis. In E. longissima, maternal body length is an important determinant of reproductive success, body reserves playing a minor role. In contrast, in female V. aspis the reproductive success is related to BCI and to a lesser extent to body length.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2004

Life-stage-dependent sensitivity of zebrafish (Danio rerio) to estrogen exposure.

The aim of this study was to identify periods in zebrafish (Danio rerio) development when estrogen exposure has long-term consequences on reproductive capabilities at the adult stage. To this end, zebrafish were exposed to 10 ng/L ethynylestradiol (EE(2)) during three stages of gonadal differentiation: (i) the juvenile hermaphroditic stage when gonads display the morphology of an immature ovary (in our zebrafish colony this lasted from 15 to 42 days post-fertilization [dpf]), (ii) the gonad transition stage when the hermaphroditic gonad differentiates into either testes or ovary (from 43 to day 71 dpf), and (iii) the premature stage of testicular and ovarian development (from 72 to 99 dpf). The consequences of stage-specific exposure to EE(2) were assessed by determining time to first spawning, fecundity (number of eggs per female per day), fertilization success (percentage of fertilized eggs) and sex ratio of the adults. Exposure during the gonad transition period induced a delay in the onset of spawning and a significant reduction of fecundity and fertilization success, whereas exposure during the hermaphroditic stage or during the premature stage had no significant impact on the reproductive parameters of adult fish. The results from this experiment pointed to the gonad transition stage as being most susceptible to persistent effects of developmental estrogen exposure. In a second experiment, the concentration dependency of the EE(2)effects was evaluated by exposing zebrafish during the gonad transition stage (43-71 dpf) to 1.67, 3 or 10 ng EE(2)/L. Significant effects of EE(2) on adult reproduction were found with 3 and 10 ng EE(2)/L, but not with 1.67 ng/L. Histological examination of the gonads revealed that at termination of EE(2) exposure (71 dpf), all individuals in the 3 and 10 ng EE(2)/L treatment possessed ovaries. However, this feminising effect appeared to be reversible since at the adult stage (190 dpf), both fish with ovaries and with testes were found. Thus, EE(2) exposure during the gonad transition stage seems to have no persistent effect on gonad histology but on reproductive capabilities.

Animals↗

PubMed2004

The reproductive toxicology of ammonium perfluorooctanoate (APFO) in the rat.

Ammonium perfluorooctanoate (APFO) is a surfactant used primarily as an aid in processing various fluoropolymers. Many toxicology and epidemiological studies have been conducted with APFO; however, no specific information regarding functional reproduction was previously available. Therefore, the potential reproductive toxicity of APFO across two generations of offspring was studied using current EPA OPPTS 870.3800 guidelines. Male and female Sprague-Dawley rats were dosed orally with 0, 1, 3, 10, or 30 mg/kg APFO. Parental (P) generation rats ( approximately 6 weeks old) were dosed at least 70 days prior to mating and until sacrificed (after mating for male rats; after weaning for female rats). F(1)-generation rats were dosed similarly, beginning at weaning. The F(2)-generation pups were maintained through 22 days of lactation. Reproductive parameters evaluated in P- and F(1)-generation rats included estrous cycling, sperm number and quality, mating, fertility, natural delivery, and litter viability and growth. Age at sexual maturation in F(1), anogenital distance in F(2), and presence of nipples (males) in F(2)-generation pups were also determined. Feed consumption, body-weight gain, selected organ-weights, gross pathology and appropriate histopathology were evaluated. Reproductive endpoints including mating, fertility, and natural delivery were not affected in either generation. P- and F(1)-generation male rats showed decreased body weight, and liver and kidney weight increases at all doses. The 30 mg/kg F(1)-generation pups had decreased birth weight. Viability was reduced in the 30 mg/kg F(1)-generation pups in apparent relationship to reduced body weight at birth and weaning; however, F(2)-generation pups at 30 mg/kg, although somewhat lighter, did not show a loss in viability. Preputial separation and vaginal opening were somewhat delayed at 30 mg/kg, but these rats went on to show normal reproductive performance. No-observed-adverse-effect-levels were >30 mg/kg for reproductive function of P- and F(1)-generation rats, 10 mg/kg for F(1)-generation pup mortality, birth weight, and sexual maturation, and less than 1mg/kg for male body-weight and organ-weight changes.

Animals↗

PubMed2004

A novel approach to intrauterine viral inoculation of swine using PCV type 2 as a model.

Experimentally intrauterine (IU) viral inoculation has been commonly used to circumvent maternal interference with transplacental infection of fetuses and to assess the effect of viral infection on fetal development or reproductive parameters. However, IU inoculation requires surgical procedures such as laparatomy and surgical incision of the uterus. Post-surgical complications, that frequently result in abortion or fetal death, have been a major disadvantage. An animal trial was conducted to evaluate the non-surgical procedure of ultrasound needle-guided transabdominal injection for IU inoculation of porcine circovirus type 2 (PCV2) since this virus has been reported to cause reproductive failure in pigs. Two groups of seven pregnant sows at mid- and late-gestation, respectively, were inoculated with PCV2 using an ultrasound needle-guided technique that delivered PCV2 directly into one of the fluid-filled fetal compartments. The effect of transabdominal in utero virus challenge on fetuses and sows was assessed until term. While five of six sham-inoculated control sows had no or minimal adverse affects from in utero injection, 10 of 14 virus-inoculated sows had dead and/or stillborn piglets and PCV2 infection was evident by polymerase chain reaction and/or immunohistochemistry. These results supported previous field and experimental observations that PCV2 may cause reproductive failure. In conclusion, ultrasound needle-guided transabdominal injection was a safe and efficient method for IU inoculation of virus in pigs.

Animals↗

PubMed2003

Effect of early feed restriction on reproductive performance in Japanese quail (Coturnix coturnix japonica).

Reproductive performance of quail (Coturnix coturnix japonica) was evaluated following feed restriction (100, 85, and 70% of ad libitum) between 2 to 5 wk of age with three replicates of 12, 2-wk-old chicks per replicate. Body weight, feed conversion, and leucocyte distribution were measured during feed restriction. After experimental feed treatment, BW, age at first egg, egg production, fertility, hatchability, and embryonic mortality were evaluated from five replicates of two females and one male per treatment. Feed-restricted female chicks had lower BW from 3 to 5 wk of age, but male weights were depressed only during the most severe restriction at 4 and 5 wk. No treatment differences were observed among BW within a sex from 6 to 13 wk. Body weights at first egg were significantly heavier for females fed 70% ad libitum than for birds on other treatments. Fertility, age at first egg, feed conversion, egg production, and egg weight were unaffected by feed restriction. Although hatchability was unaffected by feed restriction, percentage of late dead and total dead embryos were significantly reduced in eggs from restricted quail. Thirty quail fed 70% of ad libitum control intake had significantly increased egg specific gravity. Feed restriction increased the percentage of heterophils and basophils and the heterophil/lymphocyte ratio, whereas the percentage of lymphocytes and eosinophils decreased. Feed can be restricted to 85 or 70% of ad libitum feed intake from 2 to 5 wk of age without detrimentally affecting reproductive parameters between 6 to 13 wk of age.

Aging↗

PubMed2001

Photoperiodic modulation of GnRH mRNA in the male Syrian hamster.

Male Syrian hamsters (Mesocricetus auratus) are seasonal breeders. They show marked testicular regression when exposed to short autumnal photoperiods, and then remain sexually quiescent for several months. By mid-winter, however, they show a loss in responsiveness to the inhibitory influence of short photoperiods and their testes begin to recrudesce. To shed light on the neuroendocrine mechanism responsible for mediating these reproductive changes, we examined the influence of photoperiod on the expression of GnRH mRNA in the hamster forebrain. Adult males were either exposed to short photoperiods (6L:18D) for 16 weeks or were maintained under long photoperiods (14L:10D); additional animals were exposed to short or long photoperiods for 22 weeks. As expected, exposure to short photoperiods for 12 weeks resulted in a marked decrease (P<0.01) in testicular mass and serum testosterone levels, but after 22 weeks these reproductive parameters were once again significantly elevated (P<0.01). In contrast, quantitative in situ hybridization histochemistry revealed no difference (P>0.05) between the GnRH mRNA levels of the short-photoperiod hamsters and their aged-matched long-photoperiod controls, although an age-related decrease (P<0.05) was evident in both photoperiod-treatment groups. These data emphasize that GnRH mRNA is highly expressed in hamsters even when their reproductive axis has been rendered sexually quiescent by exposure to short photoperiods, and that photoperiod-induced changes in GnRH secretion, rather than synthesis, are more likely to regulate the timing of the breeding season. On the other hand, the data indicate that GnRH mRNA levels show an aging-related decrease, regardless of photoperiod, suggesting that in the long term a decrease in GnRH gene expression may contribute to the reduced fertility of old hamsters.

Aging↗

PubMed1999

Seasonal effects on reproduction in the domestic sow in Finland--a herd record study.

Seasonal effects on fertility of the domestic sow were assessed by retrospective analysis of the Finnish national computerised data management system covering 1081 herds in 1993. Multivariate analyses were used, where the reproductive parameter of interest (repeat breeding, weaning to oestrus interval, age of gilts at first farrowing, litter size, culling due to anoestrus or no conception) was designed as the response variable. The months of the year (each month compared with January) and all herds and breed were included in the models as explanatory variables. The study demonstrated clear seasonal effects on various aspects of fertility in the domestic sow. The poorest reproductive performance was consistently observed in late summer and autumn and was demonstrated in a number of ways. Firstly, the gilts born between December and April were older (> 5 days) at farrowing than those born during the rest of the year (p < 0.01). Secondly, the risk that a culled sow would be culled due to anoestrus was significantly increased during the autumn months (Odds Ratio (OR) ranged from 1.10 to 1.36). Thirdly, the risk of a repeat breeding was higher from July to November (OR = 1.16). Risk of a prolonged weaning-to-oestrus beyond day 10 was the highest from August to October (OR ranged from 1.70 to 1.77). Risk of a sow to be culled due to no conception was the highest in January and February (weaned in October-November). In addition, descriptive data gathered in a slaughterhouse in 1993 (a subpopulation of the sows included in the herd records) suggest that incidence of inactive ovaries is increased in summer-autumn (p < 0.05). In conclusion, a marked reduction in fertility of the domestic sow in Finland is reported between July and November.

Animals↗

PubMed2004

Effect of melatonin and stobadine on maternal and embryofoetal toxicity in rats due to intrauterine hypoxia induced by phenytoin administration.

The aim of the present study was to test the hypothesis that the natural antioxidant melatonin (MEL) and the synthetic antioxidant stobadine (STO) could reduce the incidence of maternal and embryofoetal toxicity in rats due to intrauterine hypoxia. Chronic hypoxia was induced pharmacologically by the administration of the anticonvulsant phenytoin (PHT) during the entire period of pregnancy. PHT disturbed the normal course of pregnancy, affected reproductive parameters and increased the incidence of skeletal anomalies. MEL did not protect the PHT-induced development toxicity in rat. On the other hand, STO partially prevented PHT-induced reduction of foetal and placental weights. Administration of STO also decreased the frequency of pre- and post-implantation loss and resorptions in the PHT group. We concluded that pretreatment of pregnant rats with STO prevented to a certain extent reproductive and foetal development alterations caused by chronic intrauterine hypoxia.

Abnormalities, Drug-Induced↗

PubMed2004

In utero exposure to low-dose 2,3',4,4',5-pentachlorobiphenyl (PCB 118) impairs male fertility and alters neurobehavior in rat offspring.

Neurobehavior (motor activity and developmental reflexes) and male reproductive parameters were evaluated in rat offspring after in utero exposure to a low dose of PCB 118 comparable to human exposure levels. Sprague-Dawley dams were treated on gestation day 6 by gavage with a single dose of 375 microg PCB 118/kg body weight or peanut oil (control). The dose was calculated to be approximately 100-fold higher than that found in human breast milk. Postnatal reflexes, motor activity and male reproductive performance were evaluated in rat offspring after exposure to PCB 118. Evaluation of locomotor activity for five consecutive days during puberty (PND 70-74) revealed hyperactivity in offspring from PCB 118-exposed dams. In adult males (PND 170), clear effects on reproductive organs were observed in PCB-exposed animals which had smaller testes, epididymides and seminal vesicles (absolute and relative weights). Decreases in sperm and spermatid numbers and impairment of daily sperm production were also observed. Our results clearly demonstrate that low-dose exposure to PCB 118 alters neurobehavior and impairs adult male fertility in offspring. This is in contrast to the reported increases in sperm production and testis weight in rat after high dose PCB exposures. PCBs appear to possess variable dose-related effects and therefore low-dose studies are important to obtain a complete picture for human risk assessment.

Administration, Oral↗

PubMed1981

Photoperiodicity in the male albino laboratory rat.

Animals inhabiting areas where there are drastic changes in the environment often reproduce only during limited time periods to ensure that young are raised in optimal environmental conditions. The lack of a well defined breeding season in many domesticated animals, presumably because the selective pressures for seasonal breeding have been minimized, suggests that the neuroendocrine events controlling seasonal cyclicity have been bred out of these animals. Little is known about the underlying neuroendocrine changes which may occur during the evolution of a species from a seasonal to a nonseasonal breeder. Whereas the changing photoperiod is the primary environmental cue which initiates and/or terminates the reproductive season in many animals, this is not so in the albino rat Rattus norvegicus, a model nonseasonal breeder. Nevertheless, daylength can influence various reproductive parameters in laboratory rats, suggesting that some of the neuroendocrine components that controlled seasonal breeding previously are still extant in this species. To test this hypothesis, we investigated the effect of daylength on the responsiveness of the neuroendocrine--gonadal axis to the negative-feedback effects of testosterone. This paradigm was chosen because of the important role played by photic-induced changes in steroid feedback sensitivity in the control of seasonal reproduction. We report here that although daylength has very little effect on neuroendocrine--gonadal function in the intact male laboratory rat, it seems that some component(s) of a photoperiodic system involving the pineal gland has been preserved.

Animals↗