Effects of lactation, energetic deficit and remating interval on reproductive performance of primiparous rabbit does.

Female rabbits (n = 151) were assigned at their first parturition (day 0) to one of three treatment groups (A: non-lactating does and ad libitum feeding, R: non-lactating does and restricted feeding, L: lactating does and ad libitum feeding). Additional females (n = 18) were slaughtered at parturition. Experimental females were presented to the male on days 3 (A3, L3 and R3 groups, n = 25, 26 and 26, respectively) or 10 (A10, L10 and R10 groups, n = 25, 25 and 24, respectively) and were slaughtered on day 28 after parturition. Compared to does slaughtered on day 0, adipose tissues were lighter in L (-66%) and R (-32%) females while they were heavier in A females (+40%; P < 0.01). These results suggest that both L and R females were in energy deficit. Receptivity (80% vs. 98%) and conception rate (51% vs. 83%) were lower in L compared to A females (P < 0.01) regardless the day of male presentation. Ovulation rate (-14%) and conception rate (-26%) were lower in R3 than in A3 does (P < 0.05). Ovulation rate was 24% lower in the L10 than in the A10 group (P < 0.01). The uterine contents were lighter (-25%) in L and R than in A does (P < 0.001) regardless the day of male presentation. These results suggest that the energy deficit associated with milk production can partly explain the negative influence of lactation on reproductive performance.     

Influence of metabolic status on oocyte quality and follicular characteristics at different postpartum periods in primiparous rabbit does

Low reproductive performance of high-yield primiparous animals is closely associated with the metabolic stress caused by a simultaneous gestation and lactation. The aim of this work was (1) to analyze body composition and metabolic environment at three time points along lactation (at parturition time; in the lactation period [Day 11 postpartum]; and in the postweaning period [Day 32 postpartum]) of primiparous rabbit does (Oryctolagus cuniculus) and (2) to investigate the ovarian status at insemination time and the possible link with metabolic environment and with their reproductive performance. To this end, does were either submitted to a semi-intensive reproductive rhythm (Group S, inseminated on Day 11 postpartum) or an extensive rhythm (Group E, inseminated on Day 32 postpartum). Body energy (P < 0.05) and protein content (P < 0.001) as well as serum leptin (P < 0.05) and protein concentrations (P < 0.001) increased significantly along the postpartum period. At parturition, body lipid content was significantly lower and serum nonesterified fatty acids concentrations were significantly higher than that on Days 11 postpartum and 32 postpartum. Concerning ovarian status at insemination time, no significant differences were found in mean follicular stages, serum estradiol, progesterone, and prolactin (PRL) concentrations or in prolactin receptor (PRL-R) immunostaining. However, follicles in Group S showed a significantly higher apoptosis index than that of Group E (P < 0.001). The nuclear and cytoplasmic oocyte maturation rates of Group S were also significantly lower than that in Group E. In addition, conception rate and prolificacy were improved in Group E (P < 0.001 and P < 0.05, respectively). In conclusion, in the early postpartum period, metabolic status seems to impact negatively on ovarian follicle and oocyte quality leading to a poor reproductive outcome in primiparous rabbit does.     

Energy balance and reproductive performance in rabbit does

The mortality and the culling rates of females are very high in rabbit breeding. In many cases, the dead or culled females show low reproductive performances and poor body conditions. Energy deficit leads to body mobilization and reduced reproductive performance. Consequently, energy balance and lifespan are closely linked. Two in vivo methods to estimate body composition were recently validated for rabbit does. Ultrasounds and TOBEC methods permitted the evaluation of the changes in energy balance and their relationship to reproductive performance of females. Influence of intrinsic (parity, litter size, genetic line, ...) and extrinsic (reproduction rhythm, temperature, ...) factors on the energetic balance of females are discussed. Energy deficit and depletion of body stores occurring during lactation lead to a decrease in reproductive performance and the physiological mechanisms implicated in these effects were presented. Interest and limitations of several strategies to reduce the body energy deficit in reproducing does and to improve their fertility and thus lifespan are discussed: rearing, feeding, management, genetic selection. A multi-facetted approach, combining these various strategies seems to be required to meet these objectives.     

Differences in the reproductive endocrine status of ewes in the early post-partum period and during seasonal anoestrus

More (P less than 0.05) post-partum acyclic ewes (8/9) showed evidence of pulsatile LH release than did seasonally anoestrous ewes (2/8). Mean plasma prolactin concentrations were higher (P less than 0.05) in the post-partum ewes than in the seasonally anoestrous ewes. Hypothalamic and pituitary cytosol oestrogen receptor number, median eminence GnRH content and pituitary LH, FSH and prolactin contents were similar in the two groups of ewes. The number of nuclear-bound oestrogen receptors was greater (P less than 0.01) in pituitaries from seasonally anoestrous ewes than in pituitaries from post-partum ewes. These data suggest that the basis of acyclicity in seasonally anoestrous ewes and in post-partum ewes is probably due to their inability to generate LH pulse frequencies similar to that in the follicular phase of the oestrous cycle. The higher LH pulse frequency in post-partum ewes, compared to that in seasonally anoestrous ewes, suggests that pregnancy may partly negate the reduction in LH secretion that is associated with photoperiod-induced acyclicity. The lower number of nuclear-bound oestrogen receptors in post-partum ewes suggests that there may be lower plasma oestrogen levels and less ovarian follicular growth than in non-suckling anoestrous ewes.     

Exercise distributed across day and night does not alter circadian period in humans

In rodents, increased activity due to running-wheel access is associated with a change in observed circadian period. In humans, exposure to exercise has failed to demonstrate similar effects on period. Methodological issues with prior studies such as light exposure during exercise, length of study, and method of measuring period confounded those evaluations of the effect of exercise on period in humans. In the present experiment, the authors examined the effect of exercise on period in 8 subjects using a 44-day within-subjects inpatient study. They used a 20-h forced desynchrony protocol, in which subjects were exposed to exercise across circadian phases under dim light conditions. Exercise consisted of three 45-min sessions per wake period on an ergometer. Target exercise intensity was ~65% of maximal heart rate. Intrinsic circadian period was measured using both core body temperature and hourly plasma melatonin samples. Consistent with previous reports, the authors find no effect of exercise on endogenous circadian period as measured by either core body temperature or melatonin. Exercise distributed across biological day and night does not appear to affect circadian period.     

Metabolic responses to xenin-25 are altered in humans with Roux-en-Y gastric bypass surgery

Xenin-25 (Xen) is a neurotensin-related peptide secreted by a subset of enteroendocrine cells located in the proximal small intestine. Many effects of Xen are mediated by neurotensin receptor-1 on neurons. In healthy humans with normal glucose tolerance (NGT), Xen administration causes diarrhea and inhibits postprandial glucagon-like peptide-1 (GLP‐1) release but not insulin secretion. This study determines (i) if Xen has similar effects in humans with Roux-en-Y gastric bypass (RYGB) and (ii) whether neural pathways potentially mediate effects of Xen on glucose homeostasis.Eight females with RYGB and no history of type 2 diabetes received infusions with 0, 4 or 12 pmol Xen/kg/min with liquid meals on separate occasions. Plasma glucose and gastrointestinal hormone levels were measured and insulin secretion rates calculated. Pancreatic polypeptide and neuropeptide Y levels were surrogate markers for parasympathetic input to islets and sympathetic tone, respectively. Responses were compared to those in well-matched non-surgical participants with NGT from our earlier study.Xen similarly increased pancreatic polypeptide and neuropeptide Y responses in patients with and without RYGB. In contrast, the ability of Xen to inhibit GLP-1 release and cause diarrhea was severely blunted in patients with RYGB. With RYGB, Xen had no statistically significant effect on glucose, insulin secretory, GLP-1, glucose-dependent insulinotropic peptide, and glucagon responses. However, insulin and glucose-dependent insulinotropic peptide secretion preceded GLP-1 release suggesting circulating GLP-1 does not mediate exaggerated insulin release after RYGB. Thus, Xen has unmasked neural circuits to the distal gut that inhibit GLP-1 secretion, cause diarrhea, and are altered by RYGB.     

Temperature change does not affect force between single actin filaments and HMM from rabbit muscles

The temperature dependence of sliding force, velocity, and unbinding force was studied on actin filaments when they were placed on heavy meromyosin (HMM) attached to a glass surface. A fluorescently labeled actin filament was attached to the gelsolin-coated surface of a 1-microm polystyrene bead. The bead was trapped by optical tweezers, and HMM-actin interaction was performed at 20-35 degrees C to examine whether force is altered by the temperature change. Our experiments demonstrate that sliding force increased moderately with temperature (Q(10) = 1.6 +/- 0.2, +/-SEM, n = 9), whereas the velocity increased significantly (Q(10) = 2.9 +/- 0.4, n = 10). The moderate increase in force is caused by the increased number of available cross-bridges for actin interaction, because the cross-bridge number similarly increased with temperature (Q(10) = 1. 5 +/- 0.2, n = 3) when measured during rigor induction. We further found that unbinding force measured during the rigor condition did not differ with temperature. These results indicate that the amount of force each cross-bridge generates is fixed, and it does not change with temperature. We found that the above generalization was not modified in the presence of 1 mM MgADP or 8 mM phosphate.     

Metabolic and biochemical changes in plasma of the periparturient rabbit does with different litter size

The aim of this study was to investigate the metabolic and biochemical changes in plasma that occur in the reproductive rabbit doe close to the parturition, as well as if the number of offspring affects the metabolism and the health status of the doe. At −3, 4 and 12 days from parturition (–D3, D4, and D12, respectively) nine rabbit does at their third parity from a commercial hybrid line (HYPLUS PS 19) selected for high prolificacy were weighted and blood was collected for a wide inflammometabolic profile. According to the number of offspring the does were retrospectively divided in two groups: high litter size group (HI; n=5) and low litter size group (LO; n=4). BW was higher (P<0.01) at –D3 and had the lowest values at D4. At D12, the BW was lower (P<0.05) in LO compared with HI. Several metabolites significantly changed from dry to lactation period. Glucose and cholesterol had the lowest levels at –D3; non-esterified fatty acid (NEFA) and aspartate aminotransferase had the highest values before parturition (P<0.05); creatinine and β-hydroxybutyrate (BHBA) were higher at –D3 with respect to D4 (P<0.05). The lowest value of paraoxonase was observed in does at –D3 (P<0.05), whereas at this time ceruloplasmin and total bilirubin had the highest concentration (P<0.05). The differences for blood profile parameters between does grouped according to litter size were mainly evident before parturition (–D3). In particular, BHBA, NEFA and total bilirubin had higher concentrations (P<0.05) in HI v. LO group, whereas albumin and PON were lower in HI group (P<0.01). After parturition there were no significant differences for the metabolic parameters between the two groups. The results show that for reproductive rabbit doe the last days of gestation are very stressful from a metabolic and inflammatory point of view. The genetic selection of does for higher litter size has increased their ability to mobilize body reserves in order to guarantee the nutrients to a high number of kits. This exposes them to a more severe metabolic and inflammatory challenge during the transition period. Consequently, feeding and managerial strategies for high prolificacy periparturient rabbit does should be revised.     

Metabolic rate is negatively linked to adult survival but does not explain latitudinal differences in songbirds

Survival rates vary dramatically among species and predictably across latitudes, but causes of this variation are unclear. The rate‐of‐living hypothesis posits that physiological damage from metabolism causes species with faster metabolic rates to exhibit lower survival rates. However, whether increased survival commonly observed in tropical and south temperate latitudes is associated with slower metabolic rate remains unclear. We compared metabolic rates and annual survival rates that we measured across 46 species, and from literature data across 147 species of birds in northern, southern and tropical latitudes. High metabolic rates were associated with lower survival but survival varied substantially among latitudinal regions independent of metabolism. The inability of metabolic rate to explain latitudinal variation in survival suggests (1) species may evolve physiological mechanisms that mitigate physiological damage from cellular metabolism and (2) extrinsic rather than intrinsic sources of mortality are the primary causes of latitudinal differences in survival.     

Cocoa procyanidin chain length does not determine ability to protect LDL from oxidation when monomer units are controlled

Cocoa flavan-3-ols (catechin, epicatechin and oligomeric procyanidins) were tested for their ability to decrease LDL oxidative susceptibility and spare alpha-tocopherol (alpha-toc) in vitro. Physiologic concentration (0.10-0.50 &mgr;M) of flavanols were used. The flavanols increased LDL conjugated diene lag times dose-dependently from 23-207% and 15-143% in response to copper and AAPH oxidation, respectively, and delayed alpha-toc consumption. Sparing of LDL alpha-toc represents a possible mechanism for flavanols to enhance the resistance of plasma and LDL to oxidative stress. Procyanidins decreased LDL oxidative susceptibility with increasing chain length. However, when based on equivalent amounts of monomeric units, they inhibited LDL oxidation to a similar extent. This suggests that antioxidant activity of procyanidins with biologic substrates is not attributable to chain length or charge delocalization through polymeric linkages, but primarily to ring structures and catechol groups. Additionally, human plasma was analyzed for the presence of oligomeric procyanidins following consumption of a flavanol-rich cocoa product. Procyanidin dimers were detected in plasma concordant with the appearance of monomeric flavanols, with a peak of 0.08 +/- 0.01 &mgr;mol/L (n = 6) at two hours after consumption. Thus, this paper confirms the occurrence of procyanidins in human plasma, and extends previous structure-function observations regarding flavanoid protection of LDL.     

Daunorubicin does not induce immunohistochemically detectable endothelial dysfunction in rabbit aorta and femoral artery

Anthracyclines are one of the most effective anticancer drugs ever developed, but their clinical use has been hampered by the risk of severe cardiotoxicity. In this study, we investigated whether rabbits exposed to a different cumulative dose of anthracycline suffer from immunohistochemically detectable vascular toxicity and endothelial dysfunction. Daunorubicin (3 mg/kg, i.e. 50 mg/m2) was administered i.v. to rabbits once weekly for 1-10 weeks to reach different cumulative doses of the drug (50-500 mg/m2), while control rabbits received saline. The rabbits were sacrificed either 24 hours or 7 days after reaching each particular cumulative dose, and aortas and right femoral arteries were collected for immunohistochemical analysis. Immunohistochemical analysis showed ICAM-1 staining in many aortas from both saline and daunorubicin-treated rabbits without any relationship to the anthracycline treatment. On the contrary, unlike in the lipopolysaccharide-treated or hypercholesterolemic rabbits, no distinct immunoreactivity for other markers of inflammation, oxidative and nitrosative stress (VCAM-1, 4-HNE, iNOS and nitrotyrosine) were detected in aortas and femoral arteries from either control or daunorubicin-treated animals. No relationship to the cumulative dose of the drug or post-expose set up of harvesting was found. In this study, we have demonstrated that daunorubicin does not induce gross histopathological changes in the studied arteries and it fails to induce immunohistochemically detectable endothelial dysfunction. Thus, we propose that endothelial cells are much less susceptible to anthracycline toxicity than cardiac myocytes. In addition, our data suggest that vascular toxicity of anthracyclines plays rather a minor role in the cardiovascular complications of anthracycline chemotherapy.     

Intracerebroventricular and septal injections of arginine vasopressin are not antipyretic in the rabbit

Arginine vasopressin (AVP) has been reported to have an antipyretic effect in the ewe and guinea pig near term. Perfusions with AVP of sites in the septal region also reduced fever in non-pregnant sheep. In the present experiments adult rabbits with third cerebral ventricular or septal cannulas were restrained in a 23°C environment, and rectal temperature was recorded every 10 min. Fever induced by IV administration of leukocytic pyrogen was not reduced by AVP (25–100 ng) given intraventricularly 20 min later. Doses of 1–5 μg AVP injected into the septum likewise were not antipyretic but actually caused an increase in fever. This augmentation of the febrile response is consistent with results of previous studies in this laboratory in which AVP increased hyperthermia in a hot environment and enhanced hyperthermic responses to PGE₂. The data from these experiments provide no evidence that central AVP is an endogenous antipyretic in rabbits; rather, it may be that central AVP augments fever in this species.     

To breed or not to breed: Physiological correlates of reproductive status in a facultatively biennial iguanid

It is unusual for seasonal breeders to frequently skip opportunities for reproduction. We investigated the relationship between physiological state and reproductive decision-making in Galápagos marine iguanas (Amblyrhynchus cristatus), a species in which females typically reproduce biennially, although the proportion of breeding individuals varies significantly across years. Nearly all adult-sized females initiated follicular development prior to the lekking period, but 38% of females resorbed all developing follicles 5-15 days before the start of copulations. Receptive and non-receptive females differed in reproductive hormones during the mate choice period. Testosterone peaked in receptive females immediately prior to copulation, indicating that testosterone or its derivative estradiol likely mediates female receptivity in Galápagos marine iguanas. Non-receptive females showed significant peaks in both testosterone and progesterone during follicular atresia, suggesting that these hormones may be involved in inhibiting vitellogenesis. Two to three weeks prior to the period of reproductive decision-making (and the onset of follicular atresia in non-receptive females) receptive females were in higher body condition, were developing larger follicles, and had lower levels of both baseline and stress-induced corticosterone. Reproduction is extremely costly in this long-lived species, and increases the likelihood of mortality in the year following breeding; females could therefore gain significant benefits from being attuned to indicators of reproductive success. We suggest that corticosterone may modulate reproductive decisions by altering individual sensitivity to both internal and external cues of the likelihood of successful reproduction.     

Mutation from guanine to adenine in 25S rRNA at the position equivalent to E. coli A2058 does not confer erythromycin sensitivity in Sacchromyces cerevisae

The macrolide erythromycin binds to the large subunit of the prokaryotic ribosome near the peptidyltransferase center (PTC) and inhibits elongation of new peptide chains beyond a few amino acids. Nucleotides A2058 and A2059 (E. coli numbering) in 23S rRNA play a crucial role in the binding of erythromycin, and mutation of nucleotide A2058 confers erythromycin resistance in both gram-positive and gram-negative bacteria. There are high levels of sequence and structural similarity in the PTC of prokaryotic and eukaryotic ribosomes. However, eukaryotic ribosomes are resistant to erythromycin and the presence of a G at the position equivalent to E. coli nucleotide A2058 is believed to be the reason. To test this hypothesis, we introduced a G to A mutation at this position of the yeast Saccharomyces cerevisiae 25S rRNA and analyzed sensitivity toward erythromycin. Neither growth studies nor erythromycin binding assays on mutated yeast ribosomes indicated any erythromycin sensitivity in mutated yeast strains. These results suggest that the identity of nucleotide 2058 is not the only determinant responsible for the difference in erythromycin sensitivity between yeast and prokaryotes.     

Cold stress does not induce stress proteins SP 25 and SP 72 in rat skeletal muscle.

Cryotherapy is a common treatment for musculoskeletal injuries, yet the mechanism(s) underlying its effects remain unclear. Since cryotherapeutic treatment often involves temperatures that are known to induce the protective stress proteins (SPs), we determined whether SP 25 and SP 72 expression was altered following a 20-min cold stress to the hindlimb muscles of Sprague-Dawley rats. The right hindlimb of anesthetized animals was placed in an ice bath until muscle temperature decreased to either 8.4 +/- 0.4 degrees C or 19.7 +/- 0.3 degrees C for 20 min. After a 24-h recovery, the white and red gastrocnemius, plantaris, soleus, extensor digitorum longus, and tibialis anterior muscles from both legs were removed and rapidly frozen in liquid nitrogen. Portions of the muscles were homogenized and SP 25 and SP 72 content was assessed by SDS-PAGE/Western blot analyses. Quantification of SP 25 and SP 72 by densitometric scanning of blots demonstrated no significant increases in SP 25 or SP 72 content in any of the muscles exposed to either the 8 or the 20 degrees C cold stress compared to muscles from the unstressed contralateral limbs. These results suggest that a 20-min cold stress of 8 degrees C or 20 degrees C does not increase muscle SP 25 or SP 72 content.     

Lifespan and age,but not residual reproductive value or condition,are related to behaviour in wild field crickets

Individuals frequently show long‐term consistency in behaviour over their lifetimes, referred to as “personality.” Various models, revolving around the use of resources and how they are valued by individuals, attempt to explain the maintenance of these different behavioural types within a population, and evaluating them is the key for understanding the evolution of behavioural variation. The pace‐of‐life syndrome hypothesis suggests that differences in personalities result from divergent life‐history strategies, with more active/risk‐taking individuals reproducing rapidly but dying young. However, studies of wild animals provide only limited support for key elements of this and related hypotheses, such as a negative relationship between residual reproductive value and activity. Furthermore, alternative models make divergent predictions regarding the relationship between risk‐taking behaviours and variables consistent in the short‐term, such as condition. To test these predictions, we regularly measured willingness to leave a shelter and the activity level of wild adult field crickets (Gryllus campestris) at both short and long intervals over their entire adult lives. We found some support for a pace‐of‐life syndrome influencing personality, as lifespan was negatively related to willingness to leave the shelter and activity. Crickets did not appear to protect their “assets” however, as estimates of residual reproductive value were not related to behaviour. Although there was considerable variance attributed to the short‐term consistency, neither trait was affected by phenotypic condition, failing to support either of the models we tested. Our study confirms that behaviours may covary with some life‐history traits and highlights the scales of temporal consistency that are more difficult to explain.