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PubMed1986

Ultrastructural and metabolic changes associated with reproductive tract atrophy and adiposity in diabetic female mice.

The effect of progressive, diabetes-associated adiposity on reproductive tract structure and function was examined in 4- to 16-week-old C57BL/KsJ, control (+/?) and diabetic (db/db) mice. Uterine and ovarian tissues were analyzed by transmission electron microscopy for ultrastructural changes associated with increased intracellular lipid accumulation. In addition, the same tissues were analyzed for changes in activity of tissue lipoprotein lipase, an enzyme that hydrolyzes lipoprotein-associated triacylglycerols and supports the cellular uptake and storage of free fatty acids. Between 8 and 16 weeks of age, intracellular lipid deposits increased dramatically in the ovarian granulosa, thecal and stromal cell populations, as well as in the uterine epithelium, of diabetic mice compared to controls. By 16 weeks of age, the lipid deposits essentially occupied the entire cytoplasmic area of both the ovarian and uterine cell types in diabetics. The basal lamina underlying the uterine epithelium was expanded in the diabetics relative to controls, and the hyperglycemic condition induced an observable increase in endometrial intercellular space that was occupied by a hyaline type of ground substance of unknown composition and origin. In association with these structural changes, both ovarian and uterine lipase activities were greatly increased in the db/db mice compared with controls. These data suggest that the structural adiposity and functional decline in reproductive tract condition of the db/db mutants are related to the enhanced cellular lipid deposition observed in this species. These changes in structural and metabolic parameters are related to the reproductive incompetence characteristic of this murine model.

Animals↗

PubMed2001

The dependence of viral parameter estimates on the assumed viral life cycle: limitations of studies of viral load data.

Estimation of viral parameters, such as the basic reproductive number (R0) and infected cell life span, is central to the quantitative study of the within-host dynamics of viral diseases such as human immunodeficiency virus, hepatitis B or hepatitis C. As these parameters can rarely be determined directly, they are usually estimated indirectly by fitting mathematical models to viral load data. This paper investigates how parameter estimates obtained by such procedures depend on the assumptions made concerning the viral life cycle. It finds that estimates of the basic reproductive number obtained using viral load data collected during the initial stages of infection can depend quite sensitively on these assumptions. The use of models which neglect the intracellular delay before virion production can lead to severe underestimates of R0 and, hence, to overly optimistic predictions of how efficacious treatment must be in order to prevent or eradicate the disease. These results are also of importance for attempts at estimating R0 from similar epidemiological data as there is a correspondence between within-host and between-host models. Estimates of the life span of infected cells obtained from viral load data collected during drug treatment studies also depend on the assumptions made in modelling the virus life cycle. The use of more realistic descriptions of the life cycle is seen to increase estimates of infected cell life span, in addition to providing a new explanation for the shoulder phase seen during drug treatment. This study highlights the limitations of what can be learnt by fitting mathematical models to infectious disease data without detailed independent knowledge of the life cycle of the infectious agent.

Antiviral Agents↗

PubMed2001

Genetic parameters for cystic ovarian disease in dutch black and white dairy cattle.

Cystic ovarian disease (COD) is one of the most frequently diagnosed gynecological findings in dairy cattle. It causes temporary infertility and is likely to affect reproduction as well as production parameters in cows. The objectives of this study were to investigate the heritability of COD in a Dutch Black and White population and to estimate the genetic and phenotypic relationships with milk production traits. In the data set used, the overall incidence of COD was 7.7% (1204 COD diagnoses in 15,562 lactations). The farm incidence varied between 1.9 and 11.3%. The estimated heritabilities on the underlying and observable scales were 0.102 and 0.087, respectively. The genetic correlations between COD and 305-d milk, fat, and protein yields were 0.345, 0.379, and 0.441, respectively. We concluded that a genetic predisposition for COD exists in Dutch Black and White dairy cattle. The genetic correlations between COD and yield traits indicate that ongoing selection for production will increase the incidence of COD.

Animals↗

PubMed2006

An infertile couple suffering from oligospermia by partial sperm maturation arrest: can phytoestrogens play a therapeutic role? A case report study.

We describe the case of a 30-year-old man with severe oligospermia, caused by partial sperm maturation arrest at spermatidic stage, who was given phytoestrogens. The couple had been trying to conceive for 3 years. The woman was normal at the clinical and endocrinological examination. No other parameters except sperm count, motility and morphology were altered in the male subject. Semen analysis was performed at baseline and after 3 and 6 months of therapy, which consisted of phytoestrogens 80 mg/day for 6 months. An additional semen analysis was performed 6 months after the termination of therapy (wash-out period). During the third month semen parameters improved drastically; therefore a reproductive technique (intrauterine insemination) was performed. This treatment resulted in pregnancy, and a healthy baby weighing 3300 g was born. After 6 months of treatment, sperm parameters ameliorated further. Conversely, after the wash-out period, they returned to baseline values. The appealing results strongly suggest a therapeutic role for phytoestrogens in the treatment of oligospermia. However, it is evident that a validation stage and randomized, controlled studies are essential in order to confirm this observation and verify that phytoestrogens can play an important role in male infertility.

Adult↗

PubMedDate not supplied

Effect of nutritional stress on the hypothalamo-pituitary-gonadal axis in the growing male rat.

BACKGROUND/OBJECTIVE: Nutritional dwarfing (ND) consists of a decrease in weight and height gain and delayed onset of puberty. The aim of the present investigation was to study the modifications induced in male rats by the nutritional stress of a mere 20% reduction in food intake which, however, started immediately after weaning. MATERIALS AND METHODS: At weaning, male Wistar rats were divided into two groups: Control (C) and ND. C rats were fed ad libitum with a balanced rodent diet. ND received 80% of the diet consumed by C for 4 weeks (T4); then they were fed ad libitum for another 4 (T8) and 8 weeks (T12). The rats were studied at T0, T4, T8 and T12 for the effects of nutritional stress and refeeding on nutritional status, body composition, hypothalamic-pituitary-gonadal axis, and sperm morphology and concentration. RESULTS: ND body weight and length diminished vs. C (p < 0.001). ND body fat percentage decreased 40% (p < 0.001) without change in the percentage of body protein content. The hypothalamic content of LHRH did not change. However, FSH, LH and testosterone serum levels had significantly decreased (p < 0.001) at T4 in ND rats. A 48.4 % decrease in serum leptin in the ND group was observed at T4 (p < 0.05). The absolute testicular and seminal vesicle weight was significantly decreased by ND at T4 (p < 0.001). At T4 the percentage of anomalies of caudal spermatozoa increased in about 64% (p < 0.001) of ND vs. C rats, despite the unchanged sperm concentrations. All parameters normalized during refeeding. CONCLUSION: In this model, a decrease in leptin due to nutritional stress could be responsible, at least in part, for the inhibition of reproductive function. Refeeding normalized all parameters studied.

Animals↗

PubMed2005

Biochemical characteristics and sperm production of turkey semen in relation to strain and age of the males.

The effect of turkey strain [BUT (Big-6), Hybrid Large White (HLW), and Nicholas (N-700)] on semen quantitative parameters (ejaculate volume, sperm concentration, and total number of sperm) and biochemical parameters (seminal plasma protein concentration, acid phosphatase activity in spermatozoa and seminal plasma, and antiproteinase activity of seminal plasma) was investigated over the reproductive period. The Big-6 strain had better quantitative parameters of semen compared with HLW and N-700 strains. Besides protein concentration, the Big-6 strain had the highest level of acid phosphatase activity in semen and antiproteinase activity in seminal plasma. The N-700 strain was characterized by reduced quantitative parameters and the lowest levels of all biochemical parameters in semen. While quantitative parameters of semen showed very little trend over the 21 wk of the reproductive season, the biochemical parameters increased several fold. Biochemical parameters of semen seemed to be more affected than quantitative parameters by age of the males. These changes may be related to decreasing semen quality with increasing age of male turkeys.

Aging↗

PubMed2006

Serum biochemical reference values for gestating and lactating sows.

Reference values have been established for serum biochemical parameters in sows from high producing pig herds. In total, 132 clinically healthy sows from eight breeding herds were serially sampled three weeks and one week before farrowing, and at one week and three weeks after farrowing. Fourteen serum biochemical parameters, focusing mainly on energy and protein metabolism, hepatobiliary and kidney function and inflammation, were investigated. The reproductive state significantly influenced the investigated parameters, other than for urea and non-esterified fatty acids. First parity sows showed higher concentrations of gamma-glutamyltransferase, phosphorus and haptoglobin, and higher albumin/globulin and haptoglobin/albumin ratios compared to sows with 2 parities. The concentrations of creatinine, globulin and total protein however were lower in first parity sows. Between-herd variations were especially high (>50%) for gamma-glutamyltransferase, alkaline phosphatase and non-esterified fatty acids. Serum biochemical parameters constitute an important diagnostic tool to assess the health status of sows, but to interpret the outcome properly, it is important to consider reproductive state and parity.

Animals↗

PubMed1998

Effects of dietary 17 beta-estradiol exposure on serum hormone concentrations and testicular parameters in male Crl:CD BR rats.

A 90-day/one-generation reproduction study was conducted in male and female Crl:CD BR rats using dietary levels of 0, 0.05, 2.5, 10, and 50 ppm 17 beta-estradiol. The goals of this study were to set dose levels and evaluate several mechanistic endpoints for inclusion in multigeneration reproduction and combined chronic toxicity/oncogenicity studies with 17 beta-estradiol. In this report we discuss the effects of dietary 17 beta-estradiol exposure on serum hormonal levels and sperm parameters from P1 and F1 male rats. Sperm parameters were also evaluated in recovery P1 and F1 male rats that were fed control diets for 105 and 103 days, respectively, following 97 and 86-94 days of estradiol exposure, respectively. Measurement of Sertoli cell number from F1 male rats was performed to test the hypothesis that in utero exposure to estrogens will decrease Sertoli cell number and sperm production. Other findings from this 90-day/one-generation reproduction study are summarized elsewhere. 17 beta-Estradiol produced a dose-dependent decrease in body weight in P1 male rats at > or = 2.5 ppm and in the F1 male rats at 2.5 ppm. This decrease in body weight was due to a combination or reduced food consumption and food efficiency. In the recovery P1 males, body weight increased in the affected groups, albiet not to control levels, due to food consumption returning to control levels accompanied by an increase in food efficiency. However, in F1 males there was no corresponding rebound in body weight. In the P1 rats, exposure to 17 beta-estradiol decreased testis and epididymis weights in the 10 and 50 ppm groups, while no effects were seen in the P1 2.5 ppm group. In contrast, epididymis weights in the F1 and F1 recovery 2.5 ppm groups were statistically decreased; however, there were no histopathological effects observed. The decreases in testis weights in the P1 generation correlated with histopathologic evidence of interstitial cell atrophy and seminiferous tubule degeneration and reduced sperm production. Correlative changes in the epididymides of P1 rats were characterized by oligospermia or aspermia, the presence of germ cell debris in the lumen of tubules, and atrophy of epididymal tubules. 17 beta-Estradiol decreased testicular spermatid numbers, epididymal sperm numbers, and sperm motility in the P1 males in the 10 and 50 ppm groups, but not in the 2.5 ppm group. Following a 105-day recovery period in the P1 males, all sperm parameters and reproductive organ weights returned to control values except for the epididymal sperm count. Overall, the decline in testicular spermatid and epididymal sperm numbers in the P1 rats correlated with the reduced organ weights and the observed histopathological changes and appeared primarily related to the decrease in serum testosterone levels. In the F1 rats, no significant decreases were noted in the testicular spermatid number but a slight decrease in epididymal sperm number was seen in the 2.5 ppm group, which showed no evidence of recovery. Using morphometric analysis, no change was seen in the number of Sertoli cell nuclei per testis in F1 males. The pattern of hormonal responses seen in this study was characteristic of an estrogen receptor agonist such as 17 beta-estradiol: increased serum prolactin and decreased testosterone, luteinizing hormone, and follicle stimulating hormone levels. The data demonstrate that in utero and postnatal dietary administration of 17 beta-estradiol at levels which increased serum estradiol levels to approximately 400% of control and decreased testosterone levels to 33% of control did not reduce the number of Sertoli cell nuclei per testis.

Animals↗

PubMed2001

Effects of long-term in vitro incubation of human spermatozoa: functional parameters and catalase effect.

Prolonged incubation of human spermatozoa can have deleterious effects on sperm function. The aim of this paper was to describe the effects of a prolonged in vitro incubation, under similar conditions to those employed in human assisted reproduction, on various sperm functional parameters, and to investigate the effect of an antioxidant (catalase) on this system. Freshly collected ejaculates from 20 healthy donors were studied. Samples were divided into two aliquots: the first was incubated with Ham's F10 containing 3.5% HAS, and the second was incubated in the same medium plus catalase (100 units ml-1). All experiments were carried out with spermatozoa isolated using the swim-up technique. Spermatozoa recovered from the supernatant after 1 h (T1) of incubation in 5% CO2 in air at 37 degrees C, and after 5 h (T6), 23 h (T24) and 47 h (T48), were evaluated for concentration, motion parameters including hyperactivation (computer-assisted analysis), viability, ATP concentration, reactive oxygen species (ROS) generation, DNA integrity (acridine orange), and acrosome reaction (AR). The major alteration observed in sperm function during the prolonged in vitro incubation was a reduction in the number of motile spermatozoa, together with an impairment in the quality of sperm movement. ROS levels increased with the incubation time. No substantial modifications of sperm viability, chromatin condensation and AR inducibility were observed. The addition of catalase to the medium, while keeping ROS values within baseline levels, did not prevent the loss of motility or the corresponding increase in ATP.

Acrosome Reaction↗

PubMed1989

On the role of long incubation periods in the dynamics of acquired immunodeficiency syndrome (AIDS). Part 1: Single population models.

In this study, we investigate systematically the role played by the reproductive number (the number of secondary infections generated by an infectious individual in a population of susceptibles) on single group populations models of the spread of HIV/AIDS. Our results for a single group model show that if R less than or equal to 1, the disease will die out, and strongly suggest that if R greater than 1 the disease will persist regardless of initial conditions. Our extensive (but incomplete) mathematical analysis and the numerical simulations of various research groups support the conclusion that the reproductive number R is a global bifurcation parameter. The bifurcation that takes place as R is varied is a transcritical bifurcation; in other words, when R crosses 1 there is a global transfer of stability from the infection-free state to the endemic equilibrium, and vice versa. These results do not depend on the distribution of times spent in the infectious categories (the survivorship functions). Furthermore, by keeping all the key statistics fixed, we can compare two extremes: exponential survivorship versus piecewise constant survivorship (individuals remain infectious for a fixed length of time). By choosing some realistic parameters we can see (at least in these cases) that the reproductive numbers corresponding to these two extreme cases do not differ significantly whenever the two distributions have the same mean. At any rate a formula is provided that allows us to estimate the role played by the survivorship function (and hence the incubation period) in the global dynamics of HIV. These results support the conclusion that single population models of this type are robust and hence are good building blocks for the construction of multiple group models. Our understanding of the dynamics of HIV in the context of mathematical models for multiple groups is critical to our understanding of the dynamics of HIV in a highly heterogeneous population.

Acquired Immunodeficiency Syndrome↗

PubMed2004

Laboratory investigation into the development of resistance of Daphnia magna to the herbicide molinate.

Daphnia magna (F0 generation) was exposed to different sublethal molinate concentrations (0, 3.77, 4.71, 6.28, 9.42, and 18.85 mg/L) during 21 days. Chronic toxicity tests, using the same herbicide concentrations, were also carried out during 21 days using neonates of F1 first brood (F1-1st) and F1 third brood (F1-3rd) offspring generations from the parentals (F0) preexposed to the herbicide. Finally, offspring (from F1-1st and F1-3rd broods) were transferred to herbicide-free medium during a 21-day recovery period. The alga Nannochloris oculata (5 x 10(5) cells/mL) was used as food in all the experiments. The effect of molinate on survival, reproduction, and growth was monitored for the selected daphnid generations. The parameters used to evaluate herbicide effect on reproduction were mean total young per female, mean brood size, time to first reproduction, mean number broods per female, and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to molinate. Reproduction was significantly reduced when molinate concentration was increased in the medium. This effect was higher in the parental (F0) daphnids than in the F1-1st and F1-3rd offspring. In the recovery study, reproduction was still reduced in F1 generation daphnids (1st and 3rd), but only in those animals from parentals exposed to the highest molinate concentrations. The decreased with increasing concentrations of molinate in daphnids from the parental generation (F0). Significant differences were also found in daphnids from the F1 generation (exposure). The growth of the exposed organisms (F0 and F1) decreased, although the greatest decrease was found in the parental animals (F0) (25%) exposed to 9.42 mg/L molinate. F1 daphnids (1st and 3rd broods) from the recovery period did not show any significant difference in their growth after 21 days of study. Finally, survival was not affected after exposure to the selected molinate concentrations except in those daphnids from the F0 generation in which survival decreased 51% and 78% at the highest herbicide concentrations tested (9.42 and 18.85 mg/L). Our results suggest that the offspring daphnids seem to be adaptated to the herbicide molinate, showing more longevity and reproduction than their parentals.

Adaptation, Physiological↗

PubMedDate not supplied

Aging and responses to toxins in female reproductive functions.

Reproductive senescence in laboratory rodents has been well characterized using vaginal smear analysis, a relatively simple and inexpensive technique to monitor changes in estrous cyclicity. Although some differences exist, laboratory animal models are available to study most aspects of age-related changes in human reproductive physiology (4,13). Thus presumptive reproductive toxins can be tested on laboratory rodents using the qualitative and quantitative parameters for estrous cyclicity described here to assess damage. Before implementing such tests, however, certain limitations must be considered. Quantitative changes in estrous cycles, for example, cycle length distribution, which indicate more subtle impairments in reproductive function, require more refined data analysis. In particular, baseline data for at least one month is required before exposure to the presumptive toxin. In addition, the period of maximum cycling regularity is fairly short (three to four months duration) so long-term exposures to presumptive toxins would not be applicable. Longer term exposure (greater than or equal to six months) would be permissible if qualitative changes in cyclicity (i.e., acyclic vs. cyclic) were the dependent variable used to assess toxicity. Finally, if other parameters of reproductive function (e.g., fertility, litter size) are used to assess reproductive toxicity, we urge that cycling characteristics of the offspring be carefully monitored to assess possible cryptic damage to later neuroendocrine functions that occurred to the fetuses in utero.

Aging↗

PubMed2006

Regional variations in semen quality of community-dwelling young men from Flanders are not paralleled by hormonal indices of testicular function.

Epidemiological studies of sperm quality are hampered by problems such as low participation rates and poor comparability of results due to methodological differences in semen analysis. More objective sperm quality-related serum markers would facilitate worldwide comparisons of male reproductive status. Our objectives were to investigate to what extent a set of hormonal indices of testicular function, previously established in a clinical setting, could predict regional variations in seminal parameters in men from the general population. We recruited 101 men aged 20-40 years from two regions in Flanders, and assessed their sperm parameters and levels of serum reproductive hormones. In one region compared to another, the participants had lower sperm counts (by 34%; P=.06), lower total sperm counts (by 41%; P=.02) and poorer sperm morphology (by 32%; P<.001), which were paralleled by significantly lower levels of free testosterone (by 11%; P=.03), while for total testosterone (T) and follicle-stimulating hormone (FSH), the differences were not significant (both P=.09) at 10% and 17%, respectively. There were no differences in inhibin B and the T to luteinizing hormone (LH) ratio, which are markers of testicular function. Receiver operating characteristic curve analysis revealed that T:LH, inhibin B, and the inhibin B/FSH ratio had significant discriminatory power between men with sperm concentrations below or above 13.5x10(6)/mL. Regional variations in the semen quality of community-dwelling individuals are not necessarily reflected in altered hormonal indices of testicular function and thus, these markers, validated in clinical settings, are not valid substitutes for the traditional semen quality assessment used in epidemiological population studies.

Adult↗

PubMed1990

[The genetic-demographic approach in anthropological research. VII. The influence of the social environment on the indices of the reproductive function in Khakass women].

The biodemographic parameters showing the influence of social factors upon the different elements of population and family structure are considered. It has been shown that the semi-generation time interval which corresponds to the duration of the active reproductive period of the generation is worth using to reveal the mechanisms of the social adaptation of the population. It has been found that socially determined differential fertility of families and genetically determined mortality in perinatal period are now the main components of the potential selection (index Crow).

Adult↗

PubMed2001

Overview of studies on rat sperm motion analysis using a Hamilton-Thorne Sperm Analyzer--collaborative working study.

This collaborative study was conducted to determine the utility and sensitivity of nine sperm motion parameters generated by a Hamilton-Thorne Sperm Analyzer (HTM-IVOS) for detecting adverse effects of chemicals on sperm motion in rats. The efficacy of sperm motion parameters was investigated using nine reproductive toxicants: adriamycin, alpha-chlorohydrin (3 different studies were carried out), dinoseb, ethylene glycol monoethyl ether, 2,5-hexanedione, sulfasalazine, trimethyl phosphate, and ornidazole. The percentage of motile sperm (% motile sperm), the only parameter expressing the status of semen containing non-motile sperm, detected adverse effects on sperm motion in 9 out of 10 studies. However, weak effects on sperm motion were not detected by this parameter in 4 out of 7 studies in which sperm motion disorders were noted at medium or low dosages. The percentage of progressively motile sperm (% progressive sperm) and the sperm velocity parameters (average path velocity, straight line velocity, and curvilinear velocity) detected adverse effects on sperm motion in all studies. In 7 studies which noted sperm motion disorders at medium or low dosages, weak effects on sperm motion were detected by the % progressive sperm in 5 studies and by the sperm velocity parameters in 6 studies. In 10 studies, amplitude of lateral head displacement (ALH) did not detect adverse effects on sperm motion in 4 studies, and beat cross frequency (BCF) failed to detect adverse effects on sperm motion in 3 studies. Because ALH and BCF show the swimming pattern of spermatozoa as head movement, the characteristics of these parameters are different from the % progressive sperm and the sperm velocity parameters. Straightness (STR) and linearity (LIN), which are secondary parameters calculated from sperm velocity parameters, could not detect adverse effects on sperm motion when the sperm velocity parameters did not detect adverse effects. On the basis of these results, we concluded that the % progressive sperm and sperm velocity parameters are useful and sensitive indicators for detecting adverse effects on sperm motion. However, in the % progressive sperm, setting up a suitable threshold of VAP and/or STR is important to gain further sensitivity for detecting adverse effects on sperm motion. The % motile sperm is useful for assessment of sperm motion disorder, and ALH and BCF are useful for evaluating the swimming pattern of sperm. STR and LIN are not very useful for detecting adverse effects on sperm motion.

Animals↗

PubMed1994

Assessment of within-group variation in CYP1A mRNA inducibility in environmentally exposed and chemically treated Atlantic tomcod.

CYP1A gene expression has been implicated in the processing of environmental procarcinogens and levels of variation in CYP1A mRNA expression are high in both environmentally exposed and chemically treated Atlantic tomcod. The objective of this study was to evaluate the effects of physical and biological parameters such as temperature, sex, and reproductive state on within-group variation in CYP1A mRNA induction. Levels of variation in CYP1A mRNA expression were directly correlated with mean levels of gene induction. Our results indicate that sex and reproductive state, but not temperature, had significant effects on CYP1A mRNA inducibility in tomcod; however, these parameters did not account for all interindividual variation in CYP1A inducibility. Other intrinsic biological factors, such as genetic polymorphisms in molecular pathways leading to CYP1A induction, may contribute to the high levels of interindividual variation in CYP1A inducibility in Atlantic tomcod.

Animals↗

PubMed2006

[Differential-diagnostic features of clinical development of urogenital mycoplasmosis].

Every year urogenital mycoplasma draws the increasing attention, as serious pathological disease of women of reproductive age. During the urogenital mycoplasmosis, parameters of clinical semiology are expressed more significantly than without this disease. Among women with a reproductive pathology on a background of urogenital mycoplasmosis most often took place pathological discharge with a putrefactive smell, irritation, an itch and burning of genitals. Though frequency of such clinical symptoms as the painful sexual intercourse, pain conceded the pathological discharge. It is established, that during urogenital infections among pregnant women and women with a reproductive pathology the wide scale of specific symptoms are peculiar for the mycoplasmosis.

Adult↗

PubMed1997

Influence of temperature on the regulation and toxicity of zinc in Folsomia candida (Collembola).

To generate reproducible and reliable results, most protocols for standardized toxicity tests prescribe strict limits for test conditions such as temperature and relative humidity. In the field, however, variability of climate can influence the functioning of organisms and induce changes in sensitivity. To evaluate the influence of temperature on the ecotoxicity of zinc, the springtail Folsomia candida was exposed to zinc-contaminated soil at different temperatures. In one experiment, the toxicity of ZnCl2 was determined at a constant temperature and under alternating temperature conditions. Although control performance of F. candida was influenced by the temperature treatment, effect concentrations for reproduction were not significantly different between treatments. Levels of internal zinc regulation were higher in animals exposed to alternating temperatures. Based on the observed influence of temperature on the accumulation of zinc, a second experiment was performed to determine the sensitivity of F. candida to zinc at four different exposure temperatures. A decrease in temperature led to an increase in sensitivity when sublethal parameters such as growth and reproduction were considered. However, animals were less sensitive at lower temperatures where mortality was concerned. Internal zinc concentrations in the animals increased with decreasing temperatures, and when the effect on reproduction was based on internal zinc levels, differences between temperature treatments were not significant. From the results of this study it is concluded that for F. candida, constant temperature conditions form a good basis for the extrapolation of toxicity levels to fluctuating temperature conditions. Since the average exposure temperature can alter the sensitivity of F. candida for zinc, and changes in sensitivity are parameter dependent, exposure temperature should be chosen carefully.

Animals↗