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PubMed1984

Use of exposure data in occupational reproductive studies.

Accurately characterizing worker exposure presents some unique problems in occupational reproductive studies. The latency period between exposure and the adverse event may be relatively brief - days, weeks, or months. Inaccurately identifying the specific exposure period which initiated the adverse event may then contribute to sizeable misclassification errors. This paper discusses different types of exposure models that can be used to help reduce misclassification and delineate the exposure-effect relationships more accurately. The advantages and disadvantages of exposure data sources are also discussed.

Female↗

PubMed2002

[The role of leptin in human reproduction].

The article reviews the current literature about leptin, a hormone produced mainly in the adipose tissue, in terms of its role in reproduction. The structure of leptin, its biological activity as well as its influence on secretion of their hormones has been discussed. The leptin concentrations during the ovulatory cycle, pregnancy puerperium and assisted reproduction have been presented. It has been suggested that leptin may have an advantageous effect not only on oocyte and zygote development in the early stages, but also on the process of implantation and therefore its evaluation may be useful for the clinical determination of embryo quality in IVF-ET program.

Adipose Tissue↗

PubMed1988

Gonadotropins--domestic animals.

The application of RIAs for the gonadotropins to the study of domestic animal reproduction has depended on the availability of sensitive and specific reagents, automated systems for increased throughput and an awareness of the assay errors. Illustrations are given on the measurement of seasonal, surge and episodic changes in LH secretion and the advantages gained by such investigation are outlined.

Animals↗

PubMed1987

[Structure of the inguinal gland in the mountain hare in various states of reproductive activity. I. The sebaceous glands].

Histology and ultrastructure of sebaceous glands of the integumental inguinal gland of the hare were studied during the periods of low and high reproductive activity (in winter and in spring breeding season). It was established that the glands were functioning continually (cells in acini of all the animals used contained numerous secretory granules). The expansion of agranular endoplasmic reticulum and Golgi complex in secretory cells of sexually active animals, especially of males, shows an increased intensity of gland secretory process during the breeding season.

Animals↗

PubMed1983

Endocrine changes associated with onset of spermatogenesis in Holstein bulls.

After birth, a bull enters a period of infancy during which the reproductive organs are relatively quiescent. This is followed by the prepubertal period, which starts at 10 to 12 wk in well-fed Holstein bulls, characterized by profound changes of hypothalamic, pituitary, and gonadal function that culminate in puberty. The prepubertal sequence of events probably is: a) initiation of spontaneous discharge of luteinizing hormone; b) hormone induced differentiation of Leydig cells with increased secretion of androstenedione in response to luteinizing hormone stimulation; c) further differentiation of Leydig cells resulting in luteinizing hormone-stimulated secretion of testosterone; d) testosterone-induced differentiation of indifferent supporting cells to Sertoli cells concomitant with testosterone-induced differentiation of gonocytes to prespermatogonia and A-spermatogonia; e) increased sensitivity of the hypothalamus-anterior pituitary to negative feedback of gonadal steroids; f) diminished frequency and amplitude of luteinizing hormone discharge; g) formation of junctional complexes between Sertoli cells and establishment of the blood-testis barrier; h) formation of primary spermatocytes and ultimately spermatids and spermatozoa; and i) continued increase of efficiency of spermatogenesis until sufficient sperm are produced to provide the first ejaculum around 37 to 38 wk. Following puberty, the reproductive capacity of a bull increases for several years until the male is sexually mature.

Animals↗

PubMed1999

Calls on reproductive and developmental toxicants to a regional poison center.

We sought to characterize calls received by a regional Poison Center concerning reproductive hazards and to assess the quality of the responses. Data was extracted for a 3 mo period from all calls regarding reproductive or in utero developmental effects. The Poison Center responses were evaluated based on completeness of information gathered and final recommendations made. Two hundred seventy-one calls regarding 335 products were received. Ninety-seven percent of the calls concerned exposures during a pregnancy. Fifty-nine percent of the substances of concern were drugs; 32% were other chemicals; 7% were biological agents. Eleven percent of the exposures were occupational; 22% were environmental. Thirty-four percent of the exposures had not yet occurred. Sixty-two percent were characterized as no or minimal risk. For 13% of exposures, callers were advised to avoid initiating or continuing the exposure. Callers were referred to physicians or specialty services for 11% of exposures. The majority of responses were felt to be appropriate. Problematic areas included inconsistent advice and lack of referral. Discussion of exposures in light of other risk factors for and background rates of adverse reproductive outcomes, as well as more frequent referral to a specialist with expertise in reproductive toxicology was recommended.

Adolescent↗

PubMed1985

The effect of pen density during rearing on subsequent reproductive performance in gilts.

A study involving 109 crossbred gilts of Duroc and Landrace breeding that were reared in equal-sized pens with 8 or 16 pigs/pen was initiated to determine the effects of pen density during rearing on subsequent reproductive and maternal performance. Gilts in pens of eight were allowed 1.06 m2/animal from 30 to 65 kg and 1.25 m2/animal from 65 to 100 kg, whereas those in pens of 16 were allowed only one-half as much floor area per animal. Gilts raised in groups of eight farrowed 1.0 more pigs/litter (P less than .05), and .7 more pigs/litter born alive (P = .15), than gilts reared in groups of 16 pigs/pen. There were no pen-density differences in the number of corpora lutea at 30 d of gestation (P = .33) or in litter birth weight (P = .26). After adjusting by covariance for the number of live pigs at the beginning of the lactation period, gilts from the pen density of 16 had more pigs per litter alive (P less than .01) and heavier litter weights (P less than .05) at 21 d postpartum and higher piglet survival rates to 21 d (P less than .02) than gilts that were reared in the low pen-density of eight pigs/pen. Results of this study indicate that pen density during the growing-finishing period may affect subsequent reproductive and maternal performance of gilts.

Animals↗

PubMed2004

Effect of bST and reproductive management on reproductive performance of Holstein dairy cows.

The objective was to determine the effects of bovine somatotropin (bST) and two artificial insemination (AI) protocols on reproductive performance of Holstein cows. Lactating cows (n = 840) were assigned at 37 d in milk (DIM) to one of four treatments in a 2 x 2 factorial arrangement. Treatments consisted of either bST (500 mg/14 d) starting at 63 +/- 3 DIM or no bST (control), with cows either submitted for timed AI following a synchronized ovulation (Ovsynch) protocol or assigned to receive AI based on estrus detection (ED). Two injections of PGF2, at 37 +/- 3 and 51 +/- 3 DIM were used to presynchronize estrous cycles. Cows then received an injection of GnRH at 63 +/- 3 DIM, followed 7.5 d later by PGF2. Cows assigned to ED treatments were inseminated after observed estrus during a 7-d period. Cows in Ovsynch treatments received a second GnRH injection 48 h after the last PGF2alpha and received timed AI 16 to 18 h later. Pregnancy was diagnosed by ultrasound at 31 d after AI and confirmed 14 d later. Frequency of anovulation (18.5%) at 63 DIM was similar across treatments, but proportions of anovulatory cows decreased quadratically as body condition at 70 DIM increased from 2.25 to 3.75. Estrus detection rate after PGF2alpha tended to be lower in multiparous cows receiving bST, and bST reduced returns to estrus in nonpregnant cows. Conception rates were higher in cows receiving AI after ED and bST improved conception rates to first AI in cyclic cows by reducing embryonic mortality. Pregnancy loss was similar for cows inseminated following ED or the Ovsynch protocol. There was a positive impact of bST on fertility of cyclic cows inseminated at fixed time or at detected estrus, but effective resynchronization protocols are needed to optimize reinsemination of non-pregnant bST-treated cows.

Abortion, Spontaneous↗

PubMed2004

Effects of exposure to genistein during pubertal development on the reproductive system of male mice.

Genistein, a soybean-originated isoflavone, is widely consumed by humans for putative beneficial health effects but its estrogenic activity may affect adversely the development of the male reproductive system. Twenty-one days old ICR mice weaned from dams fed with a casein-based AIN-76A diet during gestation and lactation were exposed to genistein (2.5 and 5.0 mg/kg/day, p.o.) for 5 weeks. 17beta-Estradiol (7.5 microg/kg/day) and corn oil were used for the positive and negative vehicle controls, respectively. The animals were fed the casein-based AIN-76A diet throughout the experiment. There were no significant differences in body weights of mice between the genistein groups and the negative control group. No significant differences in relative reproductive organ weights were found among all experimental groups. Sperm counts in epididymis and testes were slightly decreased in the genistein-exposed groups compared with control group. Sperm motile characteristics in genistein-exposed groups were slightly higher than those of the control group. Levels of phospholipid hydroxide glutathione peroxidase mRNA in the testis, epididymis, and prostate of mice exposed to genistein or estradiol were significantly higher than those of the controls (P<0.05). Exposure to genistein caused hyperplasia of Leydig cells in the testis and a slight increase of interstitial fibroblasts in the epididymis, while estradiol treatment caused severe damage to the testis and epididymis. These results suggest that dietary uptake of genistein during the juvenile period may affect male reproductive development, resulting in a slight decrease in sperm count, but with an increase in sperm motion quality.

Animals↗

PubMed1995

Long term sequelae of sex steroid treatment in the management of constitutionally tall stature.

AIM: To evaluate possible long term side effects of high doses of sex steroids in the management of constitutionally tall stature, with special attention to hypothalamic-gonadal function. METHODS: Sixty four tall adult men and 180 tall adult women, who received supraphysiological doses of sex hormones during puberty, were interviewed in a standardised way at a mean follow up period of 10 years after cessation of treatment. Sixty one untreated tall adult men and 94 untreated tall adult women served as controls. RESULTS: The majority of the subjects were satisfied with their decision regarding hormone treatment. Seventy seven per cent of the women and 78% of the men reported one or more side effects during treatment. Most side effects were mild. In women, only 3% stopped treatment because of an adverse event; in men, the reported side effects never stopped treatment. The frequency of reported side effects in women was higher during treatment with high doses of oestrogens than during oral contraceptive use, indicating a dose dependent relationship. Amenorrhoea of longer than six months after cessation of therapy was found in 5%. Menstrual cycle characteristics of previously treated women were comparable with controls. Malignancy was not reported. Information about a total of 127 pregnancies was obtained and revealed no distinct differences in details and outcome between previously treated women and men, and controls. CONCLUSIONS: At a mean follow up of 10 years there is no evidence that pharmacological doses of sex hormones have a long term effect on reproductive function. However, this period is still too short to draw definite conclusions.

Adult↗

PubMed2001

Demography of the endangered North Atlantic right whale.

Northern right whales (Eubalaena glacialis) were formerly abundant in the northwestern Atlantic, but by 1900 they had been hunted to near extinction. After the end of commercial whaling the population was thought to be recovering slowly; however, evidence indicates that it has been declining since about 1990 (ref. 1). There are now fewer than 300 individuals, and the species may already be functionally extinct owing to demographic stochasticity or the difficulty of females locating mates in the vast Atlantic Ocean (Allee effect). Using a data set containing over 10,000 sightings of photographically identified individuals we estimated trends in right whale demographic parameters since 1980. Here we construct, using these estimates, matrix population models allowing us to analyse the causes of right whale imperilment. Mortality has increased, especially among mother whales, causing declines in population growth rate, life expectancy and the mean lifetime number of reproductive events between the period 1980-1995. Increased mortality of mother whales can explain the declining population size, suggesting that the population is not doomed to extinction as a result of the Allee effect. An analysis of extinction time shows that demographic stochasticity has only a small effect, but preventing the deaths of only two female right whales per year would increase the population growth rate to replacement level.

Animals↗

PubMed1994

Resorption of unemitted gametes in Lithognathus mormyrus (Sparidae, Teleostei): a possible synergic action of somatic and immune cells.

The resorption of unemitted gametes during the post-spawning period of the male and female reproductive cycles in Lithognathus mormyrus was studied by histochemical, histological and cytological methods. The resorption of residual spermatozoa involved the phagocytotic activity of Sertoli cells bounding the seminiferous cysts of spermatozoa, and those associated with spermatogonia lining the lobular lumen. Spermatozoa remaining in the sperm duct were phagocytozed by the lining epithelial cells. Eosinophilic granulocytes and macrophages were identified in the vicinity of residual spermatozoa. The remnants of oocytes underwent an atretic phenomenon in which follicle cells were firstly involved, inducing a progressive fragmentation of the oocyte cytoplasm. Subsequently, eosinophilic granulocytes invaded oocyte degenerative areas and clung to the remaining vitelline inclusions ensuring their biotransformation into waste products (brown bodies). The analogy of the resorption processes of both male and female unemitted gametes during the post-spawning period of natural reproductive cycle, involving first the enveloping somatic cells and then immune cells, is emphasized.

Animals↗

PubMed1980

Environmental influences on the postpartum animal.

Environmental influences on postpartum reproduction of the ewe, cow and sow are quite evident. Photoperiod predominantly controls the reproductive cycle of ewes lambing in the spring season and presents little problem in ewes lambing in the fall. The effect of hot ambient temperature and high humidity on ewes bred during anestrus and those bred after estrous cycles resume (late summer) needs study. In the southern regions of the United States hot ambient temperature and high humidity severely impair postpartum reproduction in cattle of European breeding. In the postpartum postweaned sow from southern states such as Minnesota, a marked reduction in reproduction during late summer and early fall has been reported. Presently, the physiological mechanisms by which hot ambient temperature and high humidity influence postpartum reproduction are not fully understood in the ewe and cow, and even less so in the sow. Hot temperatures and high humidity at the time of breeding of the ewe and cow reduce conception rates and subsequent pregnancy rates. Ewes and cows exposed to hot temperatures have increased rectal and uterine temperatures that may cause lower pregnancy rates. Altered hormonal levels and uterine blood flow have been associated with increased environmental, rectal and uterine temperatures.

Animals↗

PubMed1992

High dietary taurine effects on feline tissue taurine concentrations and reproductive performance.

The reproductive performance and outcome of kittens was determined for female cats fed 0.05, 0.2 or 1% taurine. No adverse effects of high taurine diets were noted in the adults or offspring, and the reproductive performance was slightly better than that of females fed the normal (0.05% taurine) diet. Body weight at birth and brain weight at weaning were significantly greater in the very high taurine group than in the normal taurine group, although the greatest growth rate was achieved by the normal taurine group. The concentration of taurine in milk of lactating females was substantially higher in cats fed the higher taurine diets. Brain of adult cats was resistant to increases in brain taurine concentrations, as was brain of newborn cats. However, brain of juvenile cats responded to higher dietary taurine intake with increased taurine concentrations. These results indicate that the higher taurine content in cat foods recently introduced for prevention of feline dilated cardiomyopathy should have no adverse effects over a prolonged period on health and reproduction of cats.

Administration, Oral↗

PubMed1986

Acquisition of potential for sperm motility in rainbow trout and chum salmon.

The male reproductive organ of rainbow trout and chum salmon consists of a pair of testes and sperm ducts. Spermatozoa in the distal portion of the sperm ducts exhibit full motility in the K+-free medium. However, spermatozoa from the testis were almost immotile in this medium. This suggests that the spermatozoa acquire a capacity for movement during their passage from the testis along the sperm duct. In chum salmon migrating into a bay, the sperm duct was almost empty. However, after the fish have travelled upstream for 1 km to their spawning ground in the river, the spermatozoa have left the testis, moved into the sperm duct and are capable of becoming motile. Thus it is probable that the process of acquiring the ability to move occurs within a relatively short period in this simple reproductive organ. Additionally, testicular spermatozoa demembranated with Triton X-100 exhibited motility, although the motility was less than that of demembranated spermatozoa from the sperm duct, suggesting that the acquisition of motility may correspond with the development of some function of the plasma membrane.

Animals↗

PubMed1997

Gonadotropin-releasing hormone neurons: their structure and function.

The gonadotropin-releasing hormone (GnRH) neurons are essential for reproduction. GnRH neurons must release GnRH in a pulsatile pattern for optimal secretion of LH and FSH. In some species, GnRH surges actively evoke the preovulatory LH surge, while in others, GnRH secretion may be permissive. The GnRH neurons have a unique anatomy. The neurons develop, not from the ventricular epithelium like other CNS neurons, but migrate from the olfactory epithelium during fetal life. This feature provides a basis for the clinical link between olfactory and reproductive function and helps explain the atypical distribution of cells and variations in GnRH cell location noted across species. The diffuse organization of GnRH neurons has made the task of understanding the control of GnRH neurons by other CNS neurons more difficult. Recent evidence has helped discriminate influences that are permissive for GnRH release from those that direct changes in GnRH release.

Animals↗

PubMed1985

The effect of the brain and dorsal bodies of Helisoma duryi (mollusca: pulmonata) on albumen gland synthetic activity in vitro.

Albumen gland explants from Helisoma duryi can be maintained in a liquid culture medium for at least 96 hr. This allows measurement of incorporation of [14C]glucose into newly synthesized polysaccharides both retained in the tissue and released into the medium. The albumen gland basal synthetic activity is much higher in reproductively active than in reproductively inactive snails (maintained in constant darkness, virgin, or without dorsal bodies). The presence of the whole brain or cerebral ganglia (with dorsal bodies) of reproductively active snails in the culture medium stimulates polysaccharide synthesis in albumen gland explants from snails in constant darkness. Addition of dorsal body homogenate to the culture medium stimulates polysaccharide synthesis in albumen gland explants from snails without dorsal bodies. These results show that an endocrine factor from the dorsal bodies and possibly a neuroendocrine factor(s) from the cerebral ganglia directly stimulate polysaccharide synthesis in the albumen gland.

Albumins↗

PubMed1993

Seasonal reproduction in flying foxes, reviewed in the context of other tropical mammals.

Megachiroptera inhabit the Old World tropics and most are seasonal breeders having defined times of testis growth, mating and parturition. In Pteropus scapulatus, the little red flying fox, the robust rhythm of testis cycles is resistant to modification by photoperiod. P. poliocephalus, the greyheaded flying fox, can be manipulated by photoperiod but responds slowly and incompletely. Most mammals live in the tropics, many in seasonally harsh climates, and many breed seasonally. However, few long-lived tropical mammals have been investigated for photoperiodic entrainment of annual reproductive cycles, and only animals from the edge of the tropics have responded. Thus, in long-lived tropical mammals, factors that regulate seasonal breeding have not yet been identified. Endogenous oscillators may generate circannual rhythms centrally. Downstream pathways (reproduction, metabolism, antlers, etc.) may derive their rhythm directly from the oscillator or may be modified by environmental cues. Plasticity of the circannual oscillator resolves confusion from previous contrasts between circannual rhythms and environmentally cued patterns. Plasticity may continue throughout life (species responsive to zeitgebers), but the oscillator may be 'set' in utero in some tropical species. Feedback effects from temperature, nutrition, hormones, etc. can be readily tested in this model of an oscillator generating an endogenous circannual rhythm.

Animals↗