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At least 703 records · Page 39Linked to original sources
PubMed1991

Opposite variations of two epididymal components and blood plasma testosterone in two breeds of rams.

1. Testicular volume (T Vol), blood plasma testosterone (T) concentration, seminal plasma alpha-glucosidase (alpha-G) specific activity, L-carnitine (L-C) concentration as well as semen characteristics were compared in eight Finnish Landrace (F) and eight Suffolk (S) rams throughout 21 months. 2. Only T Vol and T exhibited a typical seasonal variation in both breeds, whereas L-C, alpha-G and live sperm output presented a seasonal profile only in S rams. 3. L-C and alpha-G variations were opposite to those of T in S rams, while they fluctuated in F rams throughout the entire experiment, as did live sperm output. 4. Only the number of ejaculates and T were significantly higher in F rams (3.50 +/- 0.08 in 5 min and 7.62 +/- 0.40 ng/ml) than in S rams (2.30 +/- 0.05 in 5 min and 5.5 +/- 0.30 ng/ml); these two characteristics might therefore be considered as two indexes of sexual activity in rams. 5. By contrast, among all characteristics measured, only alpha-G was significantly higher in S rams than in F rams (1.33 +/- 0.04 vs 0.77 +/- 0.03 mU/mg proteins); this result, as well as seasonal alpha-G profile present in only S rams, allowed us to conclude that alpha-G might be considered as an additional index of seasonal reproduction in rams.

Animals↗
PubMed1986

The photoperiodic entrainment and induction of reproductive rhythms in male blackheaded buntings (Emberiza melanocephala).

Groups of photosensitive, unstimulated or stimulated, male blackheaded buntings were subjected to photoregimes of 15 hr of green light of three intensities and 9 hr of dark per day. In some groups green light was interrupted with 90 min of bright fluorescent light at different times in the subjective day. While gonads did not develop or regressed in some groups, birds in others behaved as if exposed to long daylengths. The results besides suggesting the involvement of endogenous circadian rhythm during initiation and maintenance of gonadal growth indicate that the reproductive rhythms are entrained and induced by environmental photoperiod.

Animals↗
PubMed1985

An estrogen test to determine the times of potential fertility in women.

Defined changes in the concentration of estrone glucuronide in daily samples of early morning urine have been used to locate the limits of the fertile period and the time of maximum conception probability during 118 cycles (106 menstrual, 12 conceptional) in 73 women. The peak day of urinary luteinizing hormone was used as an index of ovulation. Follicular growth was monitored daily by ultrasonography throughout 38 cycles, and the time of maximum follicular diameter was used as an alternative reference point to define the times of potential fertility according to the life spans of the gametes. With optimized algorithms and the best index of ovulation, the estrogen test delineated the limits of the fertile period in 89% of the tests (mean length, 10.8 days; range, 5 to 17 days) and the time of maximum conception probability in 82% of the cycles, with a mean time to the maximum follicular diameter of 0.42 days (range, -4 to +4 days).

Adult↗
PubMed1977

Reproductive strategy of winged and wingless morphs of the aphids Sitobion avenae and Metopolophium dirhodum.

The reproduction of apterous and alate morphs of the aphids Sitobion avenae and Metopolophium dirhodum is compared on the basis of fecundity in 5- and 10-day periods of adult life. Apterae of both species are consistently more fecund than alatae of comparable weight, producing about three more nymphs on average in any 5-day period. The reproductive differences are related to the number and quality of embryos at eclosion and to ovulation rates, both of which in turn appear to be linked to wing-muscle maintenance. These relationships between weight, embryos and reproduction may be used to predict a newly moulted adult aphid's fecundity, a method which may facilitate the assessment of resistance to aphids in new cereal varieties, by obviating lengthy recording of reproduction. The strategies by which alatae of these and other aphid species minimize the difference between their fecundity and that of apterae are discussed.

Age Factors↗
PubMed1985

Plasma androgens and their association with the reproductive cycle of the male fence lizard, Sceloporus undulatus.

Seasonal variation in plasma androgen levels was determined for males of the lizard Sceloporus undulatus. Plasma androgens peaked in both spring and in fall prior to brumation, coinciding with periods of maximum testicular enlargement and advanced spermatogenic development. Plasma androgen concentrations were minimal during summer, following testicular regression and breeding in spring. Epididymal masses were positively correlated to plasma androgen levels, while abdominal fat body masses demonstrated a negative correlation.

Androgens↗
PubMed1992

Endocrine and testicular changes associated with season, artificial photoperiod, and the peri-pubertal period in stallions.

The seasonal reproductive cycle of stallions is characterized by an annual regression and recrudescence in testicular function and concentrations of LH, FSH, and testosterone in serum. Maximum reproductive capacity occurs during the increasing day lengths of spring and summer. The annual cycle in LH secretion may reflect a seasonally associated and photosensitive reduction and replenishment in pituitary content of LH. Similar to other seasonal breeders, it appears that stallions may possess an endogenous circannual rhythm in reproductive function that is subject to manipulation by altering the light:dark ratio, i.e., photoperiod. The application of a long-day photoperiod (16 hours light:8 hours dark) in December, following 20 weeks of short days (8 hours light:16 hours dark), was effective in hastening the seasonal sexual recrudescence of stallions but was not effective in prolonging the interval of heightened reproductive capacity. The infantile period in colts lasts approximately 32 weeks and is characterized by low gonadotropin concentrations and little gonadal activity. The start of the pre-pubertal period is marked by changes in the hypothalamic-pituitary axis which result in increased amounts of LH and FSH secretion between 32 and 40 weeks of age. Testosterone concentrations in serum exhibit a dramatic increase at 75 to 80 weeks of age, with puberty (defined as the age when the first ejaculate was obtained containing a minimum of 50 x 10(6) sperm with greater than or equal to 10% progressive motility) occurring at 83 weeks of age.

Animals↗
PubMed2002

Temperature-dependent prolactin secretion and reproductive biology of the newt Triturus carnifex Laur.

The effects of temperature on pituitary prolactin (PRL) gene expression and peripheral levels were studied in both male and female newts obtained from wild conditions during reproductive (Experiment I) and nonreproductive (Experiment II) periods; moreover, changes in parameters related to reproductive function are also described. Male and female newts were taken from a pond in February (Experiment I, reproductive period) and maintained for 1 month in tanks at 4 and 18 degrees C. In male newts kept at 4 degrees C, increase of PRL mRNA in the pituitary and plasma PRL was found compared with that measured in those kept at 18 degrees C. The increase in PRL secretion was parallel to that of plasma androgens and related secondary sexual characteristics (SSC) in males and of plasma estradiol-17beta and vitellogenin in females. On the contrary, in nonreproductive newts (Experiment II), taken from the field in May, no significant changes in plasma PRL, androgens, and SSC were found in those maintained at low temperature (4 degrees C), whereas low temperature significantly increased PRL mRNA expression in the male pituitary and PRL mRNA plus plasma PRL levels in females. These findings suggest that low temperature regulates PRL secretion in this urodele species, showing a sex- and season-related control mechanism; moreover, low temperature failed to influence the reproductive biology of newts taken from the field in May, after naturally occurring reproduction during winter months.

Animals↗
PubMed1983

Photoperiodic time measurement in seasonal reproduction of the weaver bird (Ploceus philippinus).

Use of a circadian clock in photoperiodic time measurement is demonstrated in the tropical photoperiodic weaver bird with the help of resonance, ahemeral, and asymmetrical skeleton photoperiods. Different asymmetrical skeleton photoperiods and seasonal scotophase scans indicate (1) that light entrains endogenous circadian rhythms (ECR) of photosensitivity and the position of the photoinducible phase shifts according to the length of the basic photoperiod, (2) a seasonal variation in response to asymmetrical skeleton photoperiods, and (3) dissociation in the two gonadotrophins LH and FSH and a possibility of two distinct ECRs of photosensitivity for LH and FSH. Annual phasing of the ECRs of photosensitivity of the two gonadotrophins and/or interaction of hormones might be involved in the seasonal reproduction and photosensitivity of this bird.

Animals↗
PubMed1992

Biological rhythms in reproductive processes.

Biological rhythms play an important role in the regulation of many different physiological systems, including the reproductive system. The 24-hour clock system plays a role in regulating the production, release, synthesis and action of reproductive hormones and in the timing of critical events in the ovarian cycle. Research into the importance of biological rhythms on human reproduction is just beginning, future work is likely to reveal new and unexpected ways in which these rhythms affect human reproduction.

Activity Cycles↗
PubMed1990

Annual rhythm of human reproduction: I. Biology, sociology, or both?

The annual rhythm of human reproduction was analyzed on the basis of more than 3000 years of monthly birth rates covering 166 regions of the globe. The following variables were used to characterize the annual rhythm of human conception (birth minus 9 months): amplitude, phase of maximum and minimum, phase and length of the time span when rates are above the annual mean (alpha), and the steepest upward slope (delta max) of the curve fitted to the rates. The waveform of the annual rhythm is characteristic for geographical regions (e.g., unimodal or bimodal) and persists as such for many years. In most countries, the onset of alpha coincides with delta max and lies close to the spring equinox. This phase of the rhythm is the most stable over time. In many populations, the rhythm has changed in recent years, specifically in amplitude and phase. The phase of the rhythm depends on latitude, with a 6-month difference between the Northern and Southern Hemispheres. The latitudinal distribution of amplitudes is less systematic. In spite of the many social influences on timing of conceptions, we conclude that the seasonal component in human reproduction is based on biological factors.

Birth Rate↗
PubMed2002

Lack of significant alteration in the prostate or testis of F344 rat offspring after transplacental and lactational exposure to bisphenol A.

Bisphenol A (BPA), a compound of great concern as an estrogenic xenobiotic, was assessed for its ability to cause alteration in the accessory sex organs and spermatogenesis in male offspring exposed preneonatally and neonatally. In a series of experiments focusing on rat sensitivity to gestational and lactational exposure to BPA, we investigated its effects on gestation period and reproductive organs in male offspring. In the first instance, BPA was administered to F344 female rats by gavage at 0, 7.5, 120 mg/kg/day during pregnancy and lactation period. There were no observable adverse effects in pregnant rats and the treatment did not induce any morphological abnormalities in the accessory sex organs of male offspring. However, lowered numbers of sperm in the testis were found with a dose of 120 mg/kg/day. In the second study, the same protocol with a higher number of male offspring was applied, but no reduction in the sperm count was apparent. We conclude that transplacental and lactational exposure to BPA dose not exert any adverse effects on morphogenesis of rat accessory sex organs or spermatogenesis.

Animals↗
PubMed1989

An evaluation of the BIOSELF 110 fertility indicator.

The BIOSELF 110 is a hand-held, non-invasive electronic instrument that measures basal body temperature and cycle length, and automatically identifies the fertile and infertile phases of the menstrual cycle with flashing red light and green light signals, respectively. The device was evaluated in 77 cycles from 33 ovulatory women in Kuala Lumpur, Malaysia. Ultrasound monitoring of maximum follicular diameter (MFD) and urinary LH measurements with Ovustick were used as reference methods to estimate the time of ovulation and the fertile period. Based on the MFD day, the BIOSELF correctly identified the entire fertile period, and at least four fertile days, in 89% and 94% of the cycles studied, respectively. The mean duration of the fertile period as determined by the number of flashing red light days was 11.0 days (SD 2.9). The device correctly identified the onset of the postovulatory infertile phase in 94% of cycles, with a mean duration of about 10 (green light) days. The results were similar using the LH peak day as the reference method. The mean interval from the onset of the fertile period (first flashing red light day) to the MFD day was 6.9 days (SD 2.6), and from the MFD day to the end of the fertile period, 3.1 days (SD 2.2). The BIOSELF 110 showed itself to be a reliable device for identifying the fertile and infertile phases of the menstrual cycle and, thus, should be a useful aid for couples seeking pregnancy. Prospective clinical trials are underway to assess the contraceptive effectiveness of the device.

Adult↗
PubMed1989

Photoperiod and temperature affect reproductive and nonreproductive functions in male prairie voles (Microtus ochrogaster).

Adult male prairie voles (Microtus ochrogaster) were housed for 10 wk and exposed to long (16L:8D) or short (8L:16D) photoperiods at 21 degrees or 5 degrees C. Maintenance in short day lengths reduced testicular, epididymal, and seminal vesicle mass and also significantly depressed spermatogenic activity. Cold ambient temperature further suppressed gonadal size in voles exposed to short days. Several pelage characteristics were affected by photoperiod, but not by temperature. Increased fur density, fur depth, and length of guard hair and underhair were observed in voles exposed to short days. Intrascapular brown fat and gonadal fat pad mass as well as body mass were significantly less in voles housed in cold temperatures than in voles exposed to warm ambient temperatures; photoperiod did not affect these parameters. Approximately 30% of the male voles exposed to short days maintained their reproductive systems, yet they clearly processed photoperiodic information; all short-day males, regardless of reproductive condition, had comparable winter pelage development. Our results suggest that in prairie voles, photoperiod may be a predictive cue for reproductive function in nature; however, it appears that pelage development is a more obligatory response to photoperiod than is reproduction.

Animals↗
PubMed1992

Lack of reproductive photoresponsiveness and correlative failure to respond to melatonin in a tropical rodent, the cane mouse.

Cane mice (Zygodontomys brevicauda) are year-round breeders in Venezuela. As shown previously, these animals are not reproductively responsive to variation in photoperiod. In the present experiments, male cane mice were maintained on long or short day lengths (16L:8D or 8L:16D, respectively) and challenged with each of three experimental treatments known to "unmask" reproductive photoresponsiveness in laboratory rats: olfactory bulbectomy, prolonged food restriction, and exposure as neonates to a single injection of testosterone. Variation in photoperiod had no inhibitory effect on the responses of cane mice to any of these three treatments, as assessed by the weight of their testes and seminal vesicles. A fourth experiment demonstrated that cane mice are insensitive to 10 wk of continuous exposure to pharmacological levels of melatonin, again as assessed by reproductive organ weight. Likewise, a fifth experiment documented a lack of response to 10 wk of late-afternoon injections of massive amounts of melatonin. The cane mouse apparently is unique among the animals challenged so far in these ways in that it seems to have no vestige of reproductive photoresponsiveness.

Animals↗
PubMed2006

Stimulation of reproductive growth in rainbow trout (Oncorhynchus mykiss) following exposure to treated sewage effluent.

Rainbow trout (Oncorhynchus mykiss) were exposed to 1.5 and 15% v/v secondary treated sewage effluent for 32 weeks in flow-through mesocosms. The exposure encompassed the full period of reproductive development for rainbow trout. Trout did not show any evidence of a dose-dependent change in growth. Fish exposed to 15% effluent were the only group to show mortality (5%) over the duration of the experiment. Trout at the highest effluent concentration had significantly higher liver size than reference water fish. Both male and female trout in the 15% exposure group also exhibited significantly higher gonad weight than the reference group. In female trout, this gonad size increase could be explained by higher egg numbers. Female and male trout both displayed a significant increase in plasma 17 beta-estradiol levels after exposure to 15% effluent, while neither sex had dose-dependent differences in plasma testosterone. Male trout displayed elevated vitellogenin levels and reduced plasma 11-ketotestosterone concentration after exposure to 15% effluent. Chemical examination of steroidal compounds, including both estrogens and androgens, in the wastewater revealed that only estrone was detectable at a mean concentration of 4.5 ng/L. It is assumed that the effects observed in trout exposed to 15% effluent were consistent with stimulation of reproductive development due to very low levels of estrogens. Overall, long-term exposure to treated sewage effluent containing low levels of estrogen did not have significant negative implications for reproductive development in rainbow trout.

Animals↗