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PubMedDate not supplied

The role of energy availability in Mammalian hibernation: a cost-benefit approach.

Hibernation is widely regarded as an adaptation to seasonal energy shortage, but the actual influence of energy availability on hibernation patterns is rarely considered. Here we review literature on the costs and benefits of torpor expression to examine the influence that energy may have on hibernation patterns. We first establish that the dichotomy between food- and fat-storing hibernators coincides with differences in diet rather than body size and show that small or large species pursuing either strategy have considerable potential scope in the amount of torpor needed to survive winter. Torpor expression provides substantial energy savings, which increase the chance of surviving a period of food shortage and emerging with residual energy for early spring reproduction. However, all hibernating mammals periodically arouse to normal body temperatures during hibernation. The function of these arousals has long been speculated to involve recovery from physiological costs accumulated during metabolic depression, and recent physiological studies indicate these costs may include oxidative stress, reduced immunocompetence, and perhaps neuronal tissue damage. Using an optimality approach, we suggest that trade-offs between the benefits of energy conservation and the physiological costs of metabolic depression can explain both why hibernators periodically arouse from torpor and why they should use available energy to minimize the depth and duration of their torpor bouts. On the basis of these trade-offs, we derive a series of testable predictions concerning the relationship between energy availability and torpor expression. We conclude by reviewing the empirical support for these predictions and suggesting new avenues for research on the role of energy availability in mammalian hibernation.

Adipose Tissue↗
PubMed1980

Persistent infection of mouse fibroblasts (L cells) with Chlamydia psittaci: evidence for a cryptic chlamydial form.

When monolayers of mouse fibroblasts (L cells) were infected with enough Chlamydia psittaci (strain 6BC) to destroy most of the host cells, 1 in every 10(5) to 10(6) originally infected cells gave rise to a colony of L cells persistently infected with strain 6BC. In these populations, the density of L cells and 6BC fluctuated periodically and reciprocally as periods of host cell increase were followed by periods of parasite multiplication. Successive cycles of L-cell and 6BC reproduction were sustained indefinitely by periodic transfer to fresh medium. Isolation of L cells and 6BC from persistent infections provided no evidence that there had been any selection of variants better suited for coexistence. Persistently infected populations consisting mainly of inclusion-free L cells yielded only persistently infected clones, grew more slowly, and cloned less efficiently. They were also almost completely resistant to superinfection with high multiplicities of either 6BC or the lymphogranuloma venereum strain 440L of Chlamydia trachomatis. These properties of persistently infected L cells may be accounted for by assuming that all of the individuals in these populations are cryptically infected with 6BC and that cryptic infection slows the growth of the host cell and makes it immune to infection with exogenous chlamydiae. According to this hypothesis, the fluctuations in host and parasite density occur because some factor periodically sets off the conversion of cryptic chlamydial forms into reticulate bodies that multiply and differentiate into infectious elementary bodies in a conventional chlamydial developmental cycle.

Animals↗
PubMed1999

Multigeneration reproductive toxicity assessment of 60-Hz magnetic fields using a continuous breeding protocol in rats.

Male and female reproductive functions have been proposed as possibly sensitive targets for the biological effects of 60-Hz (power frequency) magnetic fields (MF). However, experimental data relevant to this hypothesized association are very limited. In the present study, the "reproductive assessment by continuous breeding" design was used to identify possible effects of MF exposure on reproductive performance, fetal development, and early postnatal growth in rats. Groups of age-matched Sprague-Dawley rats (40 breeding pairs/group) were exposed continuously (18.5 hr per day) to linearly polarized, transient-free 60-Hz MF at field strengths of 0 Gauss (G; sham control), 0.02 G, 2.0 G, or 10.0 G. An additional group of 40 breeding pairs received intermittent (1 hr on/1 hr off) exposure to 10.0 G fields. F0 breeding pairs were exposed to MF or sham fields for 1 week prior to mating, during a 14-week period of cohabitation, and during a 3-week holding period after cohabitation. The duration of the cohabitation period was selected to be sufficient for the delivery of five litters in the sham control group. Pups from the final F1 litter from each breeding pair were exposed to MF or sham fields until sexual maturity, were cohabitated in MF or sham fields for 7 days with nonsiblings from the same exposure group, and were held in the MF or sham fields for 22 days to permit delivery of F2 pups for evaluation. No evidence of exposure-related toxicity was identified in any rat in the F0, F1, or F2 generations. Fetal viability and body weights in all litters of groups exposed to MF were comparable to those of sham controls. No significant differences between sham controls and MF-exposed groups were seen in any measure of reproductive performance (litters/breeding pair, percent fertile pairs, latency to parturition, litter size, or sex ratio) in either the F0 or F1 generation. Exposure of Sprague-Dawley rats to 60-Hz MF strengths of up to 10.0 G either during their peak reproductive period (F0) or during gestation and throughout their life span (F1) has no biologically significant effects on reproductive performance. These results do not support the hypothesis that exposure to pure, linearly polarized 60-Hz MF is a significant reproductive or developmental toxicant.

Animals↗
PubMed2006

Morphological and functional state of rat ovaries in the early and late periods after injection of vepesid.

Morphological and functional state of the ovaries in female Wistar rats was assessed in the early and late periods after administration of antitumor drug vepesid in a single maximum tolerated dose. In the early period, the drug pronouncedly decreased the number of primordial follicles, bi- and multilayer follicles, and the total number of generative elements. The number of graafian vesicles and corpora lutea did not decrease. In the late period, exhaustion of the reserved potencies of gonads was more pronounced than in the control. Morphological alterations in the ovaries were accompanied by inhibition of the functional state of the female reproductive system in the period corresponding to the action on mature and primordial follicles. This inhibition manifested in increased postimplantation mortality.

Animals↗
PubMed2003

Effect of the amount of body condition loss from the dry to near calving periods on the subsequent body condition change, occurrence of postpartum diseases, metabolic parameters and reproductive performance in Holstein dairy cows.

We investigated the effect of body condition loss from the dry to near calving periods on the subsequent body condition change, the occurrence of postpartum diseases, the serum metabolic parameters total cholesterol, triglyceride, glucose, and urea nitrogen and the number of days to first breeding after calving in Holstein dairy cows. Body condition scoring (using a 5-point scale with quarter-point divisions) was performed on 67 pregnant Holstein dairy cows. Cows were scored once for body condition during the dry period (prepartum day 35 +/- 16), near calving (postpartum day 5 +/- 4), and subsequently at months 1 (+/- day 4), 2 (+/- day 5), 3 (+/- day 5), and 4 (+/- day 4) of lactation. At the same time, blood samples were collected to evaluate serum total cholesterol, triglyceride, glucose and urea nitrogen concentrations. Cows were categorized based on body condition loss from the dry to near calving periods into two groups: the moderate condition loss group (0-0.75 points, n=41), or the marked condition loss group (1.0-1.5 points, n=26). Regular reproductive health examination was conducted by the same investigator once a week. The marked condition loss group lost more body condition (P<0.01) than the moderate condition loss group consistently until month 1 of lactation. The recovery of body condition in the marked condition loss group was more delayed (P<0.01) than in the moderate condition loss group from months 1 to 4 of lactation. The occurrence of metritis and metabolic diseases (including abomasal displacement, milk fever, ketosis) was greater (P<0.01) in the marked condition loss group (62 and 23%) than in the moderate condition loss group (27 and 2%), respectively. The total cholesterol concentration was lower (P<0.05) in the marked condition loss group (167 +/- 5.3 mg/dl) than in the moderate condition loss group (183 +/- 5.8 mg/dl) at month 1 of lactation, however, the cholesterol levels at the other periods were not different (P>0.05) between the two groups. The triglyceride, glucose, and urea nitrogen concentrations were not different (P>0.05) from the dry period to month 4 of lactation between the two groups. The number of days to first breeding after calving was longer (P<0.05) in the marked condition loss group (103 +/- 7.8 day) than in the moderate condition loss group (87 +/- 5.3 day). We conclude that marked body condition loss from the dry to near calving periods results in the increased occurrence of postpartum metabolic and reproductive diseases, decreased serum total cholesterol concentrations at month 1 of lactation and a longer interval to first breeding after calving in Holstein dairy cows, probably due to the more severe energy deficit reflected by unfavorable body condition score change during early lactation.

Animals↗
PubMed2006

Estrogen effects on fetal and neonatal testicular development.

In recent years, evidences have accumulated that exposure to environmental components with estrogenic activity causes reproductive disorders in human populations. Studies conducted over the past 50 years have clearly shown a continual decline in semen quality accompanied by an increase in male reproductive disorders during this period in industrial countries. As healthy gametes are a prerequisite for healthy children, such disorders are a significant problem not only for the current society, but also for future generations. These male reproductive disorders have been attributed to xenobiotics, and particularly to xenoestrogens, which have steadily increased in diversity and concentration in the environment and food. Epidemiological, clinical, and experimental studies have suggested that excessive exposure to estrogens and xenoestrogens during fetal and neonatal development may induce testicular developmental disorders, leading to alterations in the adult male fertility. Recently, we have clearly demonstrated that fetal and neonatal testes are very sensitive to estrogens, as the inactivation of estrogen receptor alpha increases steroidogenesis and the inactivation of estrogen receptor beta enhances development of the germ cell lineage in the male.

Androgens↗
PubMed1995

Endocrine basis of the reproductive pattern of the Gentoo penguin (Pygoscelis papua): winter breeding and extended laying period in northern populations.

Changes in plasma LH, prolactin, testosterone, estradiol, and progesterone were investigated throughout moult and reproduction in free-living male and female Gentoo penguins (Pygoscelis papua) at Crozet Island (46 degrees S, 51 degrees E), where this species is able to relay after a reproductive failure. In both sexes, LH, prolactin, and steroid hormones, remained at basal levels during the moult. LH level was highest at the time of arrival at the colony for breeding and, although it decreased after courtship, it did not drop at basal value by incubation and first chick brooding period. Prolactin peaked for both chick brooding periods; replacement clutch was associated with an increased secretion of LH, whereas high prolactin levels were maintained. Testosterone, in male, and estradiol, in female, peaked during courtship I and chick brooding II; progesterone, in female, peaked during courtship I and II. These hormonal patterns are consistent with those observed in passerine species which are also able to relay after a reproductive failure. Winter breeding observed at Crozet Island might reflect the extreme adaptive capacity of Gentoo penguin species.

Adaptation, Biological↗
PubMed2005

Effects of methyltestosterone on reproduction in the Japanese quail (Coturnix coturnix japonica).

Although the hormone-mediated effects of the synthetic androgenic hormone methyltestosterone (MT) are well characterized in mammals, little is known about endocrine and other toxic effects on reproduction in birds. In a one-generation study, MT was administered to adult Japanese quail (12 pairs per group) at dietary dose levels of 0, 10, 50, and 110 ppm for a period of 3 weeks. Reproductive performance was severely affected in the groups receiving 50 and 110 ppm MT. In females, the egg-laying rate was reduced not only related to the dose administered but also to the duration of treatment. The administration of 110 ppm, and to a lesser extent, of 50 ppm MT resulted in an immediate and dramatic decrease in the total number of eggs laid, which complicated reliable assessment of other reproduction-related parameters. In males, the findings suggested inhibition of spermatogenesis at dose levels of 50 ppm and above, resulting in a subsequent reduction in male fertility.

Anabolic Agents↗
PubMed1999

Abortion rates reflect the optimization of parental investment strategies.

Parental investment decisions in human beings, including infanticide, have usually been considered in relation to the postnatal survival probabilities of their children. A number of factors which influence parental ability and willingness to invest in offspring have been identified from these studies. Here we argue that at least some of the same factors which influence investment decisions postpartum also affect the decision to terminate a current pregnancy through voluntary abortion. We show that both female age and marital status influence the probability of abortion, with the key variable being the likelihood of future marriage. Thus, abortion procedures extend a woman's ability to manage her reproduction into the prenatal period.

Abortion, Induced↗
PubMedDate not supplied

[Medical aspects of adolescent sexuality].

The increase of sexual activity among the adolescents has become a danger to their reproductive health. The goal of this study was to explore sexual behaviour of young people, to establish risks that endanger their reproductive health, and to find out the ways to reduce the consequences of adolescent sexuality. The study was conducted in the Mother and Child Health Care Institute of Serbia over a 2-year period. The sexual and reproductive behaviour, attitudes toward sexuality and contraception, as well as the prevalence rates of unintended pregnancy and Chlamydia trachomatis genital infections were analyzed in 300 sexually active adolescent females, aged 19 years. The first sexual intercourse was in 16.9 years, in average. Less than one-third of the total number (31.3%) of these persons had contraceptive protection at the first intercourse; condom was most frequently used (28.3%). Motives for the initiation of sexual activity were: love (45.7%), curiosity (35.7%), physical attraction and passion (8.3%), peer pressure (5.0%), on the boyfriend's insistence (4.7%), need for love (0.3%) and without answer (0.3%). Two-thirds of adolescent females (63.7%) reported more than one partner, 21.7% more than three and 10.2% more than five sexual partners. Almost half of girls (40.7%) experienced sexual intercourse in casual acquaintance, and 10.3% with a 10 or more years older partner. Use of contraceptive methods during each sexual encounter was inconsistent and sporadic. More than half of adolescent females (54.3%) relied on traditional forms of contraception, like withdrawal of the phallus. Condom was the method of contraceptive choice in one-third (34.3%) of girls, "birth-control pill" in 10.7% and spermicides in 0.7% of subjects. With a new sexual partner condom was used regularly by 55.6% of adolescents; and the remaining percentage of girls used condom irregularly (24.7%), or never (19.7%). The time interval between the initiation of sexual activity and the first gynaecological examination was more than 6 months in 56.7% of cases, and from one to three years in 31.0% of tested adolescent females. The reasons for the first gynaecological visit were as follows: fear of getting pregnant (22.0%), suspicion of contracting a sexually transmitted disease (22.0%) and symptoms indicating a pelvic inflammatory disease (18.3%). Only one-third of girls (37.7%) had their first gynaecological examination as a regular control examination or to get some contraceptive advice. During the adolescence unwanted pregnancy was noted in 16.0% of examined girls. One legal abortion had 14.4% of girls, two 1.3% and three 0.3% of adolescent females. Chlamydia trachomatis genital infection was found in 30.3% of girls. In the girls' opinion the improved knowledge about sexuality, reproduction and contraception is the best way of popularizing contraception among youth. This could be done by introduction of sexual education in school programmes (51.0%) or through mass media (33.3%). A successful health care service for young people should include: a gynaecologist who will have enough time and patience for an adolescent patient (91.3%); a female gynaecologist (36.7%); and a kind other health care workers (21.3%). In order to increase the number of adolescents who will use a condom, the following measures are necessary: a better quality of condoms (54.0%), installation of condom machines (15.6%), mass media education programmes on the significance of the condom role in the prevention of sexually transmitted diseases (10.0%), attractive design of condoms (7.0%), free condoms (6.7%), and universal accessibility of condoms (1.0%). The reproductive health of adolescent girls in Belgrade has been endangered by: their sexual behaviour, poor acceptance of healthy life styles, lack of responsibility in sexual relationships and high prevalence rates of unintended pregnancy and sexually transmitted diseases. Improvement of adolescent reproductive health could be achieved by: educational programmes for adolescents about sexuality, reproduction and contraception; appropriate adolescent advisory health care services; and a better condom quality.

Adolescent↗
PubMed2002

Food intake and body measurements of Atlantic bottlenose dolphins (Tursiops truncates) in captivity.

The food consumption (recorded in kg of individual fish species), body length and mass of 11 Atlantic bottlenose dolphins kept first at Windsor Safari Park, UK (1979-1993/1994), and later at Harderwijk Marine Mammal Park, The Netherlands (1993/1994-1995) are reported. This broad-scale, longitudinal study is based on historical data that were originally recorded for short-term husbandry purposes. The chemical composition and caloric value of the diet were variable and were not recorded. The food intake quantities should therefore be viewed as rough weight estimates of what wild conspecifics might eat (depending on their diet). The average annual food consumption of adult males and non-pregnant, non-lactating females was approximately 2000 kg of fish (estimated at 176 x 10(5) kJ). Food consumption showed little increase during gestation, but was 58-97% higher during lactation than during similar periods in non-reproductive years. All six calves began to eat solid food within a year of birth although suckling continued for 14-37 months after birth. The pattern of food intake of mothers and calves varied substantially between suckling periods. No seasonal changes in food consumption were detected, although there were small seasonal changes in water temperature. Births occurred at various times of year, since the timing of mating varied between years. The animals' body length increased rapidly during the first 3 years of life after which the growth rate decreased. Body length reached asymptote at approximately 270 cm. Adults of both sexes weighed around 260 kg. The relationship between standard body length (in cm) and body mass (in kg), although based on a small sample size (n = 16), can be expressed as body mass = 17.261e(0.0156(body length-100)). Animals weighing 155-225 kg consumed between 2 and 4% of their body mass per day.

Animal Husbandry↗
PubMed2004

Energy-based modeling as a basis for the analysis of reproductive data with the midge (Chironomus riparius).

We propose a biologically based approach to analyze reproductive data for the midge (Chironomus riparius). We showed in a previous study that its larval development can be divided in two distinct phases regarding the use of energy: The somatic growth period and the gametic growth period. We hypothesize here the gametic period to be a crucial period for the energetic investment for reproduction. To test this, we performed several assays with different feeding programs. Our results confirmed that energetic investment for reproduction mainly occurs during the gametic growth period. We could then propose energy-based models to analyze reproductive data. We assumed the effects to result from a perturbation in the use of energy. Two models corresponding to different physiological modes of actions--decreased efficiency of feeding (i.e., feeding decrease model) or increased cost of egg production (i.e., egg-cost increase model)--were built and used for the analysis of data obtained after an exposure to an artificially copper-spiked sediment. During this experiment, different exposure patterns were performed to investigate whether effects on reproduction resulted mainly from an exposure that occurs during the gametic growth period or from an exposure that occurs during the somatic growth period. These exposure patterns led to similar effects on reproduction, which suggests that the toxicant-induced stress persists during the whole life cycle, even in case of exposure occurring only during part of it. Both the feeding decrease model and egg-cost increase model were able to describe the data. We showed that addition of copper in the sediment, even in low quantity (<6.5 mg/kg), might affect reproduction at the individual level. If no-effect concentrations were derived from these results, this may lead to an overprotective value. A relevant no-effect concentration could be derived from further investigations at the population level.

Animals↗
PubMed1990

Teleost model for studying the effects of chemicals on female reproductive endocrine function.

The effects of several mammalian reproductive toxins on reproductive endocrine function in female Atlantic croaker (Micropogonias undulatus) were examined. Croaker were exposed to sublethal concentrations of lead, cadmium, benzo[a]pyrene (BaP), or a polychlorinated biphenyl mixture (Aroclor 1254) for 1 month during the period of ovarian recrudescence. Reproduction was altered after exposure to all four chemicals. The plasma levels and secretion rates of reproductive hormones were augmented after exposure to cadmium resulting in precocious ovarian growth. In contrast, treatment with lead, BaP, or Aroclor 1254 caused a decline in circulating steroid hormone levels and ovarian growth. Changes in hormone secretion rates from isolated pituitary and ovarian tissues incubated in vitro were also observed after exposure to several of the reproductive toxins. It is concluded that the Atlantic croaker is a sensitive model for examining the effects of reproductive toxins on female reproductive endocrine function. Our results indicate that these chemicals may act at various sites on the hypothalamus-pituitary-gonadal axis to alter reproductive endocrine function.

Animals↗
PubMed1992

Effects of thyroxine on the photoperiodic control of energy balance and reproductive status in Siberian hamsters.

Siberian hamsters (Phodopus sungorus sungorus) exhibit a variety of seasonal responses when exposed to short days (SD), including decreases in body weight and fat, gonadal regression, and changes in several nonsteroid serum hormone concentrations. One such SD-induced hormonal change is a modest decrease in serum thyroxine (T4) concentrations. In an attempt to determine any underlying hormonal influences for the SD-induced decreases in body weight and fat, we investigated the possible role of T4 and triiodothyronine (T3). This potential paradoxical effect of these hormones on body weight and fat, as compared with most other rodent species, is not without precedent in Siberian hamsters. Specifically, changes in the gonadal steroids have opposite effects on body weight and fat in Siberian hamsters compared with laboratory rats and mice, and Syrian hamsters. SD serum thyroid hormone concentrations were elevated to long-day (LD) levels via subcutaneous T4 injections. Vehicle- and noninjected controls were included, as well as three similar LD-housed groups. Although we found a trend towards decreased T4 serum concentrations in noninjected control hamsters following 9 weeks of SD exposure, this effect did not reach statistical significance. SD-housed, T4-injected hamsters had similar decreases in body, fat pad, and paired testes weights compared to the SD-housed, vehicle- and noninjected controls despite having LD-like serum T4 and T3 concentrations. Thus, no paradoxical effect of the thyroid hormones on body weight (fat) was found, nor do these hormones appear to play a role in the effects of SDs on reproductive status in this hamster species.

Adipose Tissue↗