Biomedical subjects

J E Parks

Publications and source records attributed to J E Parks.

At least 19 recordsLinked to original sources

PubMed2004

Effect of semen thaw method on conception rate in four large commercial dairy heifer herds.

Semen processed with procedures intended to permit a flexible thaw method is used to breed millions of cows yearly. One method of thawing straws, the "pocket thaw" is used extensively with semen prepared with these procedures. Published field data is lacking for thaw method comparisons with semen processed to permit flexible-thawing. The objective of the present study was to measure the effect of semen thaw method (warm-water or pocket thaw) over all seasons and its interaction with herds, inseminators, straw package size, and sperm number on conception rate in commercial dairy heifer herds using semen processed with procedures historically optimized for success with flexible-thawing. Professional inseminators performed 11,215 services over a 16-month period in four large herds, achieving a 67.6% conception rate. Thaw method was alternated weekly. Thaw effect on conception status, determined by 70 days non-return rate, was estimated by a generalized linear mixed model. Neither thaw method nor number of sperm per straw significantly affected probability of conception (P=0.658 and 0.769, respectively). No interactions of thaw method with herd, sperm number, season, straw size, and straw size by season were detected (P=0.297, 0.526, 0.365, 0.723, and 0.824, respectively). Bull, herd, inseminator within herd, year, season, and straw size affected conception rate (P=0.002, 0.000, 0.000, 0.000, 0.000, and 0.014, respectively). In conclusion, for semen processed with procedures that permit flexible-thawing, thaw method (pocket thaw versus warm-water thaw) did not affect conception rate under commercial conditions and with routine semen handling methods.

Animals↗

PubMed2003

Prospects for spermatogenesis in vitro.

In recent years, extraordinary progress has been made in a broad range of reproductive technologies, including spermatogonial transplantation in the male. However, effective procedures for the complete recapitulation of spermatogenesis in vitro, including meiosis, have remained elusive. Such procedures have the potential to facilitate (1) mechanistic studies of spermatogenesis, (2) directed genetic modification of the male germ line, and (3) treatment of male factor infertility. Early studies demonstrated the importance of germ cell-Sertoli association for germ cell survival in vitro. Recently, evidence for male germ cell survival and progression through meiosis has been reported for the rat, mouse, and man. We demonstrated the expression of spermatid-specific genes (protamine and transition protein 1) by alginate-encapsulate neonatal bull testis cells after 10 weeks in culture, suggesting that meiosis had occurred. Although identifiable germ cells in these cultures were very sparse, some indication of acrosome development was observed. Following round spermatid injection (ROSI) with presumptive spermatids produced in vitro, 50% of blastocysts produced were diploid and 37% were Y-chromosome positive. Improved culture conditions, which promote germ cell survival, differentiation, and proliferation, are essential for in vitro spermatogenesis (IVS) to become a useful technology. Other approaches to male germ cell manipulation and spermatid production are discussed.

Animals↗

PubMed2001

In vitro production of haploid germ cells from fresh or frozen-thawed testicular cells of neonatal bulls.

Improved methods for culturing spermatogenic cells will facilitate the study of spermatogenesis, treatment of male factor infertility, and genetic modification of the male germ line. The objective of this study was to develop a procedure for achieving male germ cell progression through meiosis in vitro. Testes from 3-day-old bulls were decapsulated and seminiferous tubules were dissociated enzymatically to recover Sertoli and germ cells. Dissociated cells were reaggregated by phytohemagglutinin and encapsulated by calcium alginate, then cultured for up to 14 wk in modified Dulbecco modified Eagle medium/F12 (32 degrees C, 5% CO(2) in air). At 2, 5, and 10 wk, cultured cells were examined and evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis for protamine-2 (PRM-2) and transition protein-1 (TP-1) mRNA, expressed specifically in round spermatids. Ploidy was characterized by flow cytometric analysis of DNA content of cultured cells. Only Sertoli cells and gonocytes were observed in seminiferous tubules of 3-day-old testes. By 10 wk of culture, small spherical cells (7-10 microm) were apparent at the margin of cell associations in culture. Following RT-PCR and Northern blot analysis, specific bands corresponding to PRM-2 and TP-1 were detected only in adult testis RNA or after 10 wk of culture. Based on flow cytometry, a haploid population of cells appeared in vitro that was not in 3-day-old bull testis. The novel culture system developed in this study is the first to promote differentiation of gonocytes to presumptive spermatids in vitro based on the expression of spermatid-specific genes.

Animals↗

PubMed1999

Thermotolerance of IVM-derived bovine oocytes and embryos after short-term heat shock.

A series of experiments were designed to study the effect of elevated temperatures on developmental competence of bovine oocytes and embryos produced in vitro. In experiment 1, the effect of heat shock (HS) by a mild elevated temperature (40.5 degrees C) for 0, 30, or 60 min on the viability of in vitro matured (IVM) oocytes was tested following in vitro fertilization (IVF) and culture. No significant difference was observed between the control (39 degrees C) and the heat-treated groups in cleavage, blastocyst formation, or hatching (P > 0.05). In experiment 2, when the HS temperature was increased to 41.5 degrees C, neither the cleavage rate nor blastocyst development was affected by treatment. However, the rate of blastocyst hatching appeared lower in the HS groups (13% in control group vs. 3.9% and 5.6% in 30 min and 60 min, respectively; P < 0.05). When IVM oocytes were treated at 43 degrees C prior to IVF (experiment 3), no difference was detected in blastocyst and expanded blastocyst development following heat treatment for 0, 15, or 30 min, but heat treatment of oocytes for 45 or 60 min significantly reduced blastocyst and expanded blastocyst formation (P < 0.05). In experiment 4, the thermotolerance of day 3 and day 4 bovine IVF embryos were compared. When embryos were pre-treated with a mild elevated temperature (40.5 degrees C) for 1 hr, and then with a higher temperature (43 degrees C) for 1 hr, no improvement in thermotolerance of the embryos was observed as compared to those treated at 43 degrees C alone. However, a higher thermotolerance was observed in day 4 than day 3 embryos. In conclusion, treatment at 43 degrees C, but not 40.5 degrees C or 41.5 degrees C significantly reduced oocyte developmental competence. An increase in thermotolerance was observed from day 3 to day 4 of in vitro embryonic development, which corresponds to the maternal to zygotic transition of gene expression in bovine embryos.

Animals↗

PubMed1999

Effects of cryopreservation procedures on the cytology and fertilization rate of in vitro-matured bovine oocytes.

The survival and developmental capacity of bovine oocytes after cryopreservation are greatly impaired, possibly due to organelle damage caused by freezing procedures. Distributions of chromosomes, microtubules, and microfilaments in bovine oocytes matured in vitro were examined after cooling, ethylene glycol (EG) exposure, or freezing. Oocytes were incubated after treatment for 20 min or 1 or 3 h, fixed, and evaluated using specific fluorescent probes. Abnormal cytological features increased over control levels after cooling or EG exposure and rewarming. Changes observed in oocytes during prefreezing manipulations included chromosome dispersal and clumping, microtubule depolymerization and alteration of spindle structure, and formation of craters and discontinuity in cytoskeletal actin staining. Freezing also led to an increase in the occurrence of cytological abnormalities. Less than 31% of frozen-thawed oocytes contained a normal chromosome arrangement 3 h postthaw (versus 90% of controls). Only 7-14% of frozen-thawed oocytes had normal spindles (versus 59-71% of controls). Normal distribution of filamentous actin was observed in less than 30% of oocytes postthaw (versus 62-89% of controls). These results indicate that the steps in a conventional freezing procedure cause irreversible alterations in multiple cytological components of bovine oocytes, demonstrating the need for improved strategies for preventing cellular damage during cryopreservation procedures.

Actin Cytoskeleton↗

PubMed1997

Effects of dietary selenium and vitamin E concentrations on phospholipid hydroperoxide glutathione peroxidase expression in reproductive tissues of pubertal maturing male rats.

Phospholipid hydroperoxide glutathione peroxidase (PHGPX) is the second intracellular selenium (Se)-dependent glutathione peroxidase (GSH-Px) identified in mammals. Our objectives were to determine the effect of dietary vitamin E and Se levels on PHGPX activity expression in testis, epididymis, and seminal vesicles of pubertal maturing rats, and the relationship of PHGPX expression with testicular development and sperm quality. Forty Sprague-Dawley male weanling rats (21-d old), were initially fed for 3 wk a torula yeast basal diet (containing 0.05 mg Se/kg) supplemented with marginal levels of Se (0.1 mg/kg as Na2SeO3) and vitamin E (25 IU/kg as all-rac-alpha-tocopheryl acetate). Then, rats were fed the basal diets supplemented with 0 or 0.2 mg Se/kg and 0 or 100 IU vitamin E/kg diet during the 3-wk period of pubertal maturing. Compared with the Se-supplemented rats, those fed the Se-deficient diets retained 31, 88, 67, and 50% of Se-dependent GSH-Px activities in liver, testis, epididymis, and seminal vesicles, respectively. Testes and seminal vesicles had substantially higher (5- to 20-fold) PHGPX activity than liver. Dietary Se deficiency did not affect PHGPX activities in the reproductive tissues, but reduced PHGPX activity in liver by 28% (P < 0.0001). Dietary vitamin E supplementation did not affect PHGPX activity in liver, whereas it raised PHGPX activity in seminal vesicles by 43% (P < 0.005). Neither dietary vitamin E nor Se levels affected body weight gains, reproductive organ weights, or sperm counts and morphology. In conclusion, expression of PHGPX activity in testis and seminal vesicles was high and regulated by dietary Se and vitamin E differently from that in liver.

Animals↗

PubMed1997

Relationship between androstenedione-induced myometrial contractions and platelet-activating factor acetylhydrolase in late gestation in pregnant rhesus monkeys.

An association between platelet-activating factor (PAF) and myometrial contractions has been established. Estrogens regulate PAF activity via reduction in the activity of plasma PAF acetylhydrolase (PAF-AH), the enzyme that catalyzes PAF inactivation. Administration of androstenedione to pregnant monkeys leads to sustained increases in maternal plasma estradiol (E2), with persistent nocturnal myometrial contractions. The present study tested the hypothesis that androstenedione-induced contractions are associated with a fall in maternal plasma PAF-AH activity in monkeys. Eight monkeys (132-136 days gestation, dGA) were instrumented under halothane anesthesia with maternal vascular catheters and uterine electromyogram electrodes. At 138-142 dGA, two baseline maternal arterial samples were taken for E2 and PAF-AH measurements. The following day a continuous i.v. androstenedione infusion was started in 4 monkeys while 4 control monkeys received i.v. infusions of vehicle alone. Arterial blood sampling was repeated 1 and 3 days after the start of either infusion. Despite an increase in maternal E2 to term levels and established myometrial contractions, no change in maternal plasma PAF-AH activity occurred after androstenedione treatment. Maternal plasma E2, PAF-AH activity, and contractions remained unchanged from baseline in control monkeys. In conclusion, androstenedione-induced increases in maternal plasma E2 and myometrial contractions are not associated with a fall in maternal plasma PAF-AH specific activity.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1997

Antibody directed against plasma membrane components of equine spermatozoa inhibits adhesion of spermatozoa to oviduct epithelial cells in vitro.

Before fertilization, equine spermatozoa adhere to oviduct epithelial cells (OEC) of the mare. The biochemical basis for this adhesion has not been determined. Our objective was to produce an antiserum to block this interaction. Ejaculated spermatozoa were subjected to nitrogen cavitation and spermatozoal plasma membranes enriched by sucrose density gradient centrifugation; membrane enrichment was confirmed by comparative alkaline phosphatase analysis, electron microscopy, and one- and two-dimensional PAGE. Periacrosomal plasma membrane was used as an immunogen for the production of an antiserum, which recognized several components of spermatozoal plasma membrane on Western blots. Antigen-binding fragments (Fab) were isolated by papain digestion from a specific antiserum and from nonimmunized rabbit IgG (control). The periacrosomal regions of epididymal and ejaculated spermatozoa were immunolabeled with antiserum Fab but not control Fab. The immunoneutralizing activity of antiserum Fab was tested in fluorescent cell-binding assays by competitive inhibition of the binding of spermatozoa to OEC monolayers or explants. In both assays, binding of spermatozoa to OEC was reduced as the concentration of specific Fab increased. These results suggest that one or more protein or glycoprotein components of the rostral spermatozoal plasma membrane mediate adhesion between spermatozoa and oviduct epithelium in vitro.

Acrosome↗

PubMed1994

Effects of cooling and rewarming on the meiotic spindle and chromosomes of in vitro-matured bovine oocytes.

The purpose of this study was to evaluate effects of cooling and rewarming on the meiotic spindle apparatus of bovine oocytes. In experiment 1, in vitro-matured bovine oocytes were either maintained at 39 degrees C or cooled abruptly to 4 degrees C or approximately 25 degrees C. Immunohistochemical and DNA staining for visualization of microtubules and chromosomes, respectively, revealed an anastral, barrel-shaped spindle in bovine oocytes. Exposure to 4 degrees C for 10-20 min caused complete disappearance of the spindle. Some chromosome dispersion occurred after 60 min at 4 degrees C. After exposure to approximately 25 degrees C for 30 min, 90% of oocytes appeared abnormal, having either an abnormal spindle or no spindle. In experiment 2, oocytes cooled to either approximately 25 degrees C or 4 degrees C for 30 min were rewarmed directly or in steps for 15 or 60 min. Spindles did not return to normal in most oocytes regardless of cooling temperature or rewarming scheme. Step-wise rewarming was no more beneficial than direct rewarming. More of the oocytes rewarmed directly contained dispersed chromosomes as time at 39 degrees C increased.

Animals↗

PubMed1994

Platelet-activating factor acetylhydrolase activity in seminal plasma from the bull, stallion, rabbit, and rooster.

Platelet-activating factor (PAF) acetylhydrolase, which inactivates PAF, has been detected in human and bovine seminal plasma and may represent a mechanism for regulating sperm-derived PAF. This study was designed to characterize further PAF acetylhydrolase in seminal plasma from domestic animal species. Sperm-free seminal plasma from the bull, stallion, rabbit, and rooster was assayed for acetylhydrolase activity based on the release of [3H]acetate from PAF. As reported previously for bull seminal plasma, activity in stallion, rabbit, and rooster seminal plasma was linear with both time and protein concentration, with specific activities of 97.4, 1.2, and 0.33 nmol PAF hydrolyzed/mg protein/min, respectively. Activity in seminal plasma from the bull, rabbit, and rooster was calcium-independent whereas activity in stallion seminal plasma increased with added calcium (p < 0.01). Addition of EDTA partially inhibited acetylhydrolase activity in stallion seminal plasma but increased the specific activity in rabbit seminal plasma (p < 0.01). Enzyme activity in bull seminal plasma was nondialyzable (50,000 molecular weight cutoff), stable at pH 5.0, and heat-labile (> or = 60 degrees C). Very little activity was associated with bull seminal plasma lipoproteins isolated by KBr flotation or by precipitation with polyanions. These results demonstrate that PAF acetylhydrolase activity is present in seminal plasma from different species, with large differences in specific activity among species. These differences may be related to species differences in the physiological role of PAF and its regulation in sperm and male tract fluids.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗

PubMed1993

Structural characterization of the early indoleacetic acid-inducible genes, PS-IAA4/5 and PS-IAA6, of pea (Pisum sativum L.).

Two early auxin-inducible genes (PS-IAA4/5 and PSIAA6) from pea were cloned using previously isolated complementary DNA sequences. They are present in single copy per haploid genome, and are members of a large divergent multigene family that encodes similar proteins. The genes were structurally characterized and sequence analysis of their 5'-flanking regions revealed the presence of several highly conserved sequences found in various auxin-regulated genes from other plant species. Their coding regions are interrupted by three and two introns, respectively. Introns two and three of PS-IAA4/5 and introns one and two of PS-IAA6 are located in identical positions. These genes encode proteins of 189 (21,036 Da) and 179 (20,330 Da) residues that are 46% identical. They also share a significant degree of identity (42 to 80%) with other proteins encoded by auxin regulated genes in soybean, mungbean and Arabidopsis thaliana. All proteins contain four conserved domains ranging in size from 9 to 43 amino acids. Their most prominent feature is the presence of a highly charged N terminus consisting of two clusters of acidic residues separated by a cluster of basic amino acids.

Amino Acid Sequence↗

PubMed1993

Osmometric behavior, hydraulic conductivity, and incidence of intracellular ice formation in bovine oocytes at different developmental stages.

Bovine oocytes that were immature (IMM), matured in vitro (IVM) or in vivo (MAT), or matured and fertilized in vitro (IVF) were studied using a microscope diffusion chamber to estimate osmotic parameters and a cryomicroscope to characterize intracellular ice formation (IIF). Linear Boyle van't Hoff relationships were observed with all four types of oocytes between 0.265 and 0.799 osm NaCl. At 20 degrees C, estimates of hydraulic conductivity (Lp) were significantly higher for IVM oocytes than IMM and MAT oocytes (0.84 micron/(min.atm) vs 0.45 and 0.47, respectively). IVM oocytes also tended to have higher Lp values than IVF oocytes (0.55 micron/(min.atm)). At 5 degrees C, the Lp of IVM oocytes decreased to 0.36 micron/min.atm) corresponding to an Arrhenius activation energy of 7.84 kcal/mol. The incidence of IIF in MAT oocytes suspended in salt solution and subjected to linear cooling to -60 degrees C was 45% at 4 degrees C/min, 75% at 8 degrees C/min, and 93% at 16 degrees C/min; with IVF oocytes, the incidence of IIF was 40% at 4 degrees C/min, 92% at 8 degrees C/min, and 100% at 16 degrees C/min. Comparisons involving median IIF temperatures (TIIF50s) and the distributions of the observed IIF temperatures for IMM (Myers et al., Cryo-Lett. 8, 260), IVM (Chandrasekaran et al., Cryobiology 27, 676), MAT and IVF oocytes indicated that the IIF incidence in IMM oocytes cooled at 4 degrees C/min was greater than that of oocytes at the other developmental stages cooled at the same rate. The TIIF50s of IVM and IVF oocytes were lowered by equilibration in 1.5 M ethylene glycol (EG), glycerol, or propylene glycol (PG) prior to cooling, with EG tending to lower the TIIF50s more than glycerol or PG. For all three cryoprotectants, the TIIF50s and IFF temperature distributions were cooling-rate dependent. The Weibull probability distribution was fitted to the distributions of the IIF temperatures of oocytes suspended in salt solutions with and without cryoprotectants yielding R2 values ranging from 0.70 to 0.98.

Animals↗

PubMed1993

Factors affecting preservation and fertility of bull sperm: a brief review.

This paper is a brief review of the factors that determine the number of sperm required for insemination to obtain high fertility and ways that sperm viability might be prolonged. Damage to sperm during freezing results in a requirement, after thawing, of about 6 x 10(6) motile sperm (> 10 x 10(6) total) per insemination to achieve near-maximal fertility, whereas 2.5 x 10(6) motile fresh sperm result in high nonreturn rates. Multiple inseminations to bracket the time of ovulation are usually not economical except in superovulated cows. Earlier unpublished work on sperm packaging for slow release in the cow and methods for stabilizing membranes to increase sperm survival time in the cow are discussed. Current studies are directed towards reducing catabolic metabolism of sperm and studying membrane changes during freezing and thawing and during incubation with bovine oviduct epithelial cells. Studies with bull sperm indicate that the choline and ethanolamine phosphoglyceride components of their membranes represent an unstable configuration. Exposure of sperm to liposomes with the sterol cholesterol can alter the phospholipid bilayer and increase capacitation time. Similar approaches may produce sperm with a longer fertilizing life following insemination. New procedures in vitro permit low cost modelling of fertilization, which will facilitate research by reducing the cost of studies in vivo.

Animals↗

PubMed1993

Rapid determination of sperm cell concentration in bovine semen by flow cytometry.

A flow cytometric technique is described for determining sperm concentration in fresh or extended semen with improved accuracy, precision, repeatability, ease of conduct, and rapidity. The technique is designed to measure the ratio of a known number of fluorescent beads admixed with sperm stained with either acridine orange or propidium iodide. A significant advantage of the technique is the distinct resolution between sperm and other particles (e.g., somatic cells, fat droplets, and bacteria in the semen or extender) that interfere in other counting protocols. Field testing of this protocol over the past 3 yr has demonstrated its superiority over the Coulter counter, hemacytometer, and spectrophotometer for accuracy in counting sperm in extended semen and the accuracy of counting sperm in straws based on preextension spectrophotometric determination of sperm concentration. Sperm chromatin quality can be determined simultaneously with this sperm counting procedure. This approach to counting sperm provides an excellent procedure for quality control of sperm numbers in processed semen.

Acridine Orange↗

PubMed1992

Lipid composition and thermotropic phase behavior of boar, bull, stallion, and rooster sperm membranes.

Composition and thermotropic phase behavior of sperm membrane lipids from species ranging in sensitivity to cold shock were determined. Lipids from whole sperm and sperm plasma membrane were fractionated into neutral lipid, glycolipid, and phospholipid fractions. Compositional analyses were completed for free sterols, phospholipids and phospholipid-bound fatty acids. Phase transition temperatures were determined for phospholipid and glycolipid fractions using differential scanning calorimetry. Cholesterol was the major sterol in sperm lipids of all species. Cholesterol to phospholipid molar ratios were 0.26, 0.30, 0.36, and 0.45 for sperm plasma membrane of the boar, rooster, stallion, and bull, respectively. Choline and ethanolamine phosphoglycerides and sphingomyelin were the major phospholipid classes in sperm and their proportions differed across species. Phospholipid-bound fatty acyl compositions of choline and ethanolamine phosphoglycerides were characterized by a high proportion of docosapentanoyl and docosahexanoyl groups in mammalian sperm and shorter, more saturated groups in rooster sperm. Glycolipids represented less than 10% of total polar lipids for all species. Thin-layer chromatographic analysis indicated that the major glycolipid component of rooster sperm was different from that of mammalian sperm. Peak phase transition temperatures (Tm) for sperm membrane phospholipids were 24.0, 25.4, 20.7 and 24.5, for the boar, stallion, and rooster, respectively. Corresponding Tm's for glycolipids were 36.2, 42.8, and 33.4 with no exotherm for rooster sperm glycolipids. These results demonstrate a difference in both composition and thermotropic phase behavior of glycolipids between rooster and mammalian sperm which may be related to the greater tolerance of rooster sperm to rapid cooling.

Animals↗

PubMed1992

Performance of a kinetic model for intracellular ice formation based on the extent of supercooling.

Cryomicroscopy was used to study the incidence of intracellular ice formation (IIF) in protoplasts isolated from rye (Secale cereale) leaves during subfreezing isothermal periods and in in vitro mature bovine oocytes during cooling at constant rates. IIF in protoplasts occurred at random times during isothermal periods, and the kinetics of IIF were faster as isothermal temperature decreased. Mean IIF times decreased from approximately 1700 s at -4.0 degrees C to less than 1 s at -18.5 degrees C. Total incidence of IIF after 200 s increased from 4% at -4.0 degrees C to near 100% at -15.5 degrees C. IIF behavior in protoplasts was qualitatively similar to that for Drosophila melanogaster embryos over the same temperature ranges (Myers et al., Cryobiology 26, 472-484, 1989), but the kinetics of IIF were about five times faster in protoplasts. IIF observations in linear cooling of bovine oocytes indicated a median IIF temperature of -11 degrees C at 16 degrees C/min and total incidences of 97%, 50%, and 19% at 16, 8, and 4 degrees C/min, respectively. A stochastic model of IIF was developed which preserved certain features of an earlier model (Pitt et al. Cryobiology 28, 72-86, 1991), namely Weibull behavior in IIF temperatures during rapid linear cooling, but with a departure from the concept of a supercooling tolerance. Instead, the new model uses the osmotic state of the cell, represented by the extent of supercooling, as the independent variable governing the kinetics of IIF. Two kinetic parameters are needed for the model: a scale factor tau 0 dictating the sensitivity to supercooling, and an exponent rho dictating the strength of time dependency. The model was fit to the data presented in this study as well as those from Myers et al. and Pitt et al. for D. melanogaster embryos with and without cryoprotectant, and from Toner et al. (Cryobiology 28, 55-71, 1991) for mouse oocytes. In protoplasts, D. melanogaster embryos, and mouse oocytes, the parameters were estimated from IIF times in the early stages of isothermal periods, while the osmotic state of the cell was relatively constant. In bovine oocytes, the parameters were estimated from linear cooling data. Without further calibration, the model was used to predict total IIF incidence under different cooling regimes. For protoplasts, D. melanogaster embryos, and bovine oocytes, the model's predictions were quite accurate compared to the actual data. In mouse oocytes, adjustment of the hydraulic permeability coefficient (Lp) at 0 degree C was required to yield realistic behavior.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Effects of cryopreservation procedures on sperm membranes.

Empirical approaches to semen cryopreservation have resulted in the production of young in a broad range of species. However, acceptable levels of fertility in most domestic animal species has not been achieved. In this review, an attempt has been made to describe the complexity of the sperm plasma membrane and the many steps in a cryopreservation procedure where membrane perturbations can occur. Improvement in sperm cryopreservation procedures will require a careful consideration of the complexity of the sperm plasma membrane, the interaction of its components and the influence of cooling, freezing and thawing on these interactions.

Journal Article↗

PubMed1992

Persistent free-running circannual reproductive cycles during prolonged exposure to a constant 12L:12D photoperiod in laboratory woodchucks (Marmota monax).

Serum levels of gonadal steroid were assayed at approximately 3-month intervals in groups of 5 to 8 male or female woodchucks which were exposed to a natural photoperiod for 1 year as yearlings or 3 years as adults (Study 1), or a constant photoperiod of 12L:12D from birth for 4.5 years (Study 2). After 4.5 years of 12L:12D, food intake was measured in November and compared with that in natural photoperiod animals (Study 3). Other groups of 11 males and 3 females were housed in 12L:12D for 2.5 years after capture at 2 months of age, and gonadal structure and serum steroid levels in November were compared with those of animals at selected times in the normal annual cycle (Study 4). All animals were provided food and water ad libitum and were not induced to hibernate. In Study 1, normal circannual breeding season elevations in testosterone in males and in progesterone in females were detected in most animals maintained in natural photoperiod. In Study 2, similar cycles persisted for 4.5 years in animals exposed to 12L:12D. However, based on quarterly blood samples, obvious asynchrony relative to natural light animals appeared to develop after 2, 3, or 4 years, with apparent free-running intervals of about 10 to 11 months. In Study 3, mean daily food consumption in late autumn for woodchucks in the 12L:12D group was 72% greater than animals in the natural photoperiod. In Study 4, some woodchucks exposed to 12L:12D for only 2.5 years had prematurely increased spermatogenic activity, Leydig tissue development, and elevated serum testosterone levels in November. They were similar in November to those in natural photoperiod animals in March, and significantly greater than those in natural photoperiod animals in November when normal regression and repair of the testis was complete. Likewise, females in the 12L:12D group had luteinized follicles and elevated progesterone in November which were not noted in natural photoperiod animals and which were similar to those observed during the spring in unbred females under normal conditions. The results suggest that circannual cycles of metabolic and reproductive activity in woodchucks persist in the absence of normal changes in photoperiod, are entrained to seasonal changes in the natural photoperiod, and can recede to a periodicity of less than 12 months within 2.5 to 4 years of laboratory maintenance in 12L:12D.

Animals↗