Cryobiology of rat embryos II: A theoretical model for the development of interrupted slow freezing procedures

Current mammalian embryo cryopreservation protocols typically employ an interrupted slow freezing (ISF) procedure. In general, ISF consists of initial slow cooling, which raises the extracellular solute concentration, and results in cell dehydration. Permeating cryoprotective agents (CPAs), such as dimethyl sulfoxide (DMSO), are typically included in the medium to protect the cells against high solute concentrations. As this ISF procedure continues, slow cooling is terminated at an intermediate temperature (T(p)), followed by plunging into liquid nitrogen (LN(2)). If the slow cooling step allowed a critical concentration ([CPA](c)) of CPA to be reached within the cell, the CPA will interact with the remaining intracellular water during rapid cooling, resulting in the majority of the intracellular solution becoming vitrified and preventing damaging intracellular ice formation (IIF). This study presents a theoretical model to develop efficient ISF procedures, on the basis of previously developed data for the rat zygote. The model was used to select values of initial CPA concentrations and slow cooling rates (from initial estimated ranges of 0 to 4 molal DMSO and 0 to 2.5 degrees C/min cooling rates) that would allow the intracellular solute concentration to exceed the critical concentration. The optimal combination was then determined from this range based on minimizing the duration of slow cooling.

Fundamental cryobiology of rat immature and mature oocytes: hydraulic conductivity in the presence of Me(2)SO, Me(2)SO permeability, and their activation energies

The hydraulic conductivity in the presence of dimethyl sulfoxide Me(2)SO (L(p)(Me(2)SO)), Me(2)SO (P(Me(2)SO)) permeability and reflection coefficient (sigma) of immature (germinal vesicle; GV) and mature (metaphase II; MII) rat oocytes were determined at various temperatures. A temperature controlled micropipette perfusion technique was used to conduct experiments at five different temperatures (30, 20, 10, 4, and -3 degrees C). Kedem and Katchalsky membrane transport theory was used to describe the cell volume kinetics. The cell volumetric changes of oocytes were calculated from the measurement of two oocyte diameters, assuming a spherical shape. The activation energies (E(a)) of L(p)(Me(2)SO) and P(Me(2)SO) were calculated using the Arrhenius equation. Activation energies of L(p)(Me(2)SO) for GV and MII oocytes were 34.30 Kcal/mol and 16.29 Kcal/mol, respectively; while the corresponding E(a)s of P(Me(2)SO) were 19.87 Kcal/mol and 21.85 Kcal/mol, respectively. These permeability parameters were then used to calculate cell water loss in rat oocytes during cooling at subzero temperatures. Based on these values, the predicted optimal cooling rate required to maintain extra- and intracellular water in near equilibrium for rat GV stage oocytes was found to be between 0.05 degrees C/min and 0. 025; while for rat MII oocytes, the corresponding cooling rate was 1 degrees C/min. These data suggest that standard cooling rates used for mouse oocytes (e.g., 0.5-1 degrees C/min) can also be employed to cryopreserve rat MII oocytes. However, the corresponding cooling rate required to avoid damage must be significantly slower for the GV stage rat oocyte. J. Exp. Zool. 286:523-533, 2000.

Effect of osmotic stress on the developmental competence of germinal vesicle and metaphase II stage bovine cumulus oocyte complexes and its relevance to cryopreservation

The effects of osmotic stress on germinal vesicle (GV) and metaphase II (MII) stage bovine cumulus oocyte complexes (COCs) were evaluated by first exposing them to various anisotonic NaCl solutions (75, 150, 600, 1200, 2400, and 4800 +/- 5 mOsm/kg) for 10 min and then returning them to isotonic TL-Hepes solution (270 +/- 5 mOsm/kg) at 20 +/- 2 degrees C. Percentages of oocyte maturation, fertilization, polyspermy, cleavage, and blastocyst formation were measured as endpoints. Exposure to anisotonic conditions had a significant (P < 0.05) effect on the developmental competence of both GV and bovine MII COCs. Oocytes at the GV stage were more sensitive to anisotonic stress than MII oocytes (P < 0.05). None of the GV oocytes developed to the blastocyst stage after exposure to hypertonic conditions (2400 or 4800 mOsm solutions), while exposure to hypotonic conditions (75 or 150 mOsm solutions) resulted in significantly lower (P < 0.05) blastocyst formation (9% and 13%, respectively) compared to the isotonic control (25%). A dramatic decrease to 4% development to blastocyst was observed for MII oocytes following exposure to a 4800 mOsm solution. Blastocyst formation of MII oocytes which were exposed to 75, 150, 600, 1200, or 2400 mOsm solutions were similar (15%, 20%, 18%, 14%, and 13%, respectively; P > 0.05), but lower (P < 0.05) than those in the control group (29%). Exposing GV oocytes to anisotonic conditions increased polyspermic fertilization (P < 0.05), although MII oocytes were not similarly affected (P > 0.05). These data support the hypothesis that osmotic stress is detrimental to bovine oocytes and must be considered when developing optimized cryopreservation procedures for these cells. Mol. Reprod. Dev. 55:212-219, 2000.

Temperature-dependent osmotic behavior of germinal vesicle and metaphase II stage bovine oocytes in the presence of Me2SO in relationship to cryobiology

Plasma membrane permeability coefficients and their activation energies (Ea) for water (Lp) and dimethyl sulfoxide (PMe2SO) as well as the reflection coefficient (sigma) were determined for germinal vesicle (GV) and metaphase II (MII) bovine oocytes. A micropipette perfusion technique was used with a temperature controlled circulation chamber, which was adapted to a micromanipulator. Experiments were performed at five different temperatures (30, 20, 10, 4 and -3 degrees C). The Kedem and Katchalsky model was assumed and L(p), P(Me2SO) and sigma were estimated. Estimated permeability values from the experimental temperatures were then applied to Arrhenius plots In(Lp) or In(PMe2SO) vs 1/Temperature (K) to estimate the activation energies (Ea) for L(p)Me2SO and P(Me2SO). The estimated E(a) for L(p)Me2SO for GV and MII oocytes were 23.84 Kcal/mol and 8.46 Kcal/mol, respectively. The E(a) for P(Me2SO) were 21.0 Kcal/mol and 23.20 Kcal/mol, respectively. The correlation (r2) for these linear regression plots for GV oocytes were 0.83 and 0.95 for L(p)Me2SO and P(Me2SO), respectively. For MII oocytes, r2 values were 0.95 and 0.99 for L(p)Me2SO and P(Me2SO), respectively. There was a possible discontinuity detected in the Arrhenius plot for L(p)Me2SO for GV oocytes. A significant decrease of the reflection coefficient was observed at 10 degrees C compared to other experimental temperatures. These data provide a fundamental basis that should be taken into account for low temperature preservation of bovine oocytes in the presence of Me2SO.

Hydraulic conductivity (Lp) and its activation energy (Ea), cryoprotectant agent permeability (Ps) and its Ea, and reflection coefficients (sigma) for golden hamster individual pancreatic islet cell membranes

Long-term cryopreservation of islets of Langerhans would be advantageous to a clinical islet transplantation program. Fundamental cryobiology utilizes knowledge of basic biophysical characteristics to increase the understanding of the preservation process and possibly increase survival rate. In this study several of these previously unreported characteristics have been determined for individual islet cells isolated from Golden hamster islets. Using an electronic particle counting device and a temperature control apparatus, dynamic volumetric response of individual islet cells to anisosmotic challenges of 1.5 M dimethyl sulfoxide (DMSO) and 1.5 M ethylene glycol (EG) were recorded at four temperatures (8, 22, 28, and 37 degreesC). The resulting curves were fitted using Kedem and Katchalsky equations which describe water flux and cryoprotectant agent (CPA) flux based on hydraulic conductivity (Lp), CPA permeability (Ps), and reflection coefficient (final sigma) for the membrane. For Golden hamster islet cells, Lp, Ps, and final sigma for DMSO at 22 degreesC were found to be 0.23 +/- 0.06 microm/min/atm, 0.79 +/- 0.32 x 10(-3) cm/min, and 0.55 +/- 0.37 (n = 11) (mean +/- SD), respectively. For EG at 22 degreesC, Lp equaled 0.23 +/- 0.06 microm/min/atm, Ps equaled 0.63 +/- 0.20 x 10(-3) cm/min, and final sigma was 0.75 +/- 0.17 (n = 9). Arrhenius plots (ln Lp or ln Ps versus 1/temperature (K)) were created by adding the data from the other three temperatures and the resulting linear regression yielded correlation coefficients (r) of 0.99 for all four plots (Lp and Ps for both CPAs). Activation energies (Ea) of Lp and Ps were calculated from the slopes of the regressions. The values for DMSO were found to be 12.43 and 18.34 kcal/mol for Lp and Ps (four temperatures, total n = 52), respectively. For EG, Ea of Lp was 11.69 kcal/mol and Ea of Ps was 20.35 kcal/mol (four temperatures, total n = 58).

Antral follicles develop in xenografted cryopreserved African elephant (Loxodonta africana) ovarian tissue

The preservation of germ plasm from endangered species could augment captive breeding programs aimed at maintaining genetic diversity. Mammalian female germ plasm (oocytes) is extremely difficult to collect and cryopreserve; however, a promising alternative is the cryopreservation of ovarian tissue. In the present study, athymic nude (nu/nu) Balb/C mice were used to evaluate in vivo viability of cryopreserved ovarian tissue from Institute of Cancer Research genotype (ICR) mice or elephants. Female mice were ovariectomized prior to transplant of cryopreserved-thawed ovarian tissue from ICR mice (n=4) or elephants (n=6). Control mice were sham operated (n=4) or ovariectomized (n=5). Transplants were in the ovarian bursa, enabling in vivo ovulation and pregnancies from allografts. Vaginal cytology was monitored daily, and the intervals between and duration of epithelial cells present in smears were evaluated. Appearance of epithelial cells in sham-operated and allografted mice were at intervals of 4.3+/-0.6 and 3.3+/-0.5 days, lasting for 1.4+/-0.1 and 1.6+/-0.2 days, respectively. Sporadic incidence of epithelial cells in ovariectomized animals occurred at longer intervals (8.6+/-3.8 days). Females with xenografted elephant ovarian tissue demonstrated epithelial cells in vaginal smears at intervals of 4.5+/-1.0 days, for 2.5+/-0.5 days duration, which was significantly longer than the other groups (P < 0.05). Histological evaluation of tissues at the time of epithelial cells in smears demonstrated well-developed antral follicles, although oocytes were of poor morphological appearance or only cumulus-like complexes were seen. The nude mouse model is effective for assessing cryopreserved ovarian tissue xenograft function which can support the development of antral follicles.

Membrane permeability characteristics of metaphase II mouse oocytes at various temperatures in the presence of Me2SO

In this study, the hydraulic conductivity (Lp), Me2SO permeability (PMe2SO), and the reflection coefficients (sigma) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me2SO at temperatures of 30, 20, 10, 3, 0, and -3 degrees C. These data were then used to calculate the intracellular concentration of Me2SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 microliters of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me2SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me2SO were plotted against time. Mean (means +/- SEM) Lp values in the presence of Me2SO were (LpMe2SO) at 30, 20, 10, 3, 0 and -3 degrees C were determined to be 1.07 +/- 0.03, 0.40 +/- 0.02, 0.18 +/- 0.01, 7.60 x 10(-2) +/- 0.60 x 10(-2), 5.29 x 10(-2) +/- 0.40 x 10(-2), and 3.69 x 10(-2) +/- 0.30 x 10(-2) microns/min/atm, respectively. The PMe2SO values were 3.69 x 10(-3) +/- 0.3 x 10(-3), 1.07 x 10(-3) +/- 0.1 x 10(-3), 2.75 x 10(-4), +/- 0.15 x 10(-4), 7.83 x 10(-5) +/- 0.50 x 10(-5), 5.24 x 10(-5) +/- 0.50 x 10(-5), and 3.69 x 10(-5) +/- 0.40 x 10(-5) cm/min, respectively. The sigma values were 0.70 +/- 0.03, 0.77 +/- 0.04, 0.81 +/- 0.06, 0.91 +/- 0.05, 0.97 +/- 0.03, and 1 +/- 0.04, respectively. The estimated activation energies (Ea) for LpMe2SO, and PMe2SO, and sigma were 16.39, 23.24, and -1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.

Effect of developmental stage on bovine oocyte plasma membrane water and cryoprotectant permeability characteristics

Knowledge of bovine oocyte plasma membrane permeability characteristics at different developmental stages in the presence of cryoprotective agents (CPAs) is limited. The objective of this study was to determine the oolema hydraulic conductivity (Lp), cryoprotectant permeability (P[CPA]), and reflection coefficient (sigma) for immature (germinal vesicle stage, GV) and in vitro-matured (metaphase II, MII) bovine oocytes. Two commonly used cryoprotective agents, dimethyl sulfoxide (DMSO) and ethylene glycol (EG), were studied. Osmometric studies were performed using a micromanipulator connected to an inverted microscope at 22 +/- 2 degrees C. Each oocyte was immobilized via a holding pipette, and osmotically induced volume changes over time (dv/dt) were recorded. The Lp values for GV and MII oocytes in DMSO (L(p)DMSO) were 0.70 +/- 0.06 and 1.14 +/- 0.07 microm/min/atm (mean +/- SEM) and in EG (L(p)EG) were 0.50 +/- 0.06 and 0.83 +/- 0.07 microm/min/atm, respectively. Estimates of P(DMSO) for GV and MII oocytes were 0.36 +/- 0.03 and 0.48 +/- 0.03 microm/sec, and PEG values for GV and MII oocytes were 0.22 +/- 0.03, 0.37 +/- 0.03 microm/sec, respectively. The values for GV and MII oocytes in DMSO (sigma[DMSO]) were 0.86 +/- 0.03 and 0.90 +/- 0.04 and in EG (sigma[EG]) were 0.94 +/- 0.03 and 0.76 +/- 0.04, respectively. These data demonstrate that bovine oolema permeability coefficients to water and cryoprotectants change after in vitro maturation. Furthermore, the bovine oocyte P(DMSO) is higher than the P(EG). These results may provide a biophysical basis for developing criteria for choosing optimal CPAs and for minimizing damage during addition and removal of the CPAs. Additionally, these data support the hypothesis that different procedures may be required for optimal cryopreservation of different oocyte developmental stages.

Allogeneic and xenogeneic transplantation of cryopreserved ovarian tissue to athymic mice

Cryopreserved ovarian tissue has major applications for female oncology patients and for the development of genome resource banks. The objective of the present study was to develop a bioassay of cryopreserved ovarian tissue function after allogeneic and xenogeneic transplantation to ovariectomized athymic nude (nu/nu) Balb/C mice. Transplant function was assessed by examination of vaginal smears, number of live births, and posttransplant histology. Animals were sham operated (group I; n = 4) or ovariectomized (group II; n = 5) or were given transplants of either fresh (group III; n = 3) or cryopreserved (group IV; n = 4) Institute of Cancer Research-strain mouse ovarian tissue or cryopreserved sheep ovarian tissue (group V; n = 7). Vaginal smears were examined 5-7 times per week; the number of days between visualizations of epithelial cells in smears was 4.3 +/- 0.6 for group I, 8.6 +/- 3.8 for group II, 3.4 +/- 0.4 for group III, 3.3 +/- 0.5 for group IV, and 4.6 +/- 0.6 for group V. Epithelial cells were seen for 1.2-1.7 consecutive days; this value was significantly different between groups III and V. Live births were recorded from 3 of 4 animals from group I, 0 of 5 animals from group II, 2 of 3 animals from group III, and 1 of 4 animals from group IV. In vivo function and long-term survival of cryopreserved ovarian tissue after allogeneic or xenogeneic transplant were confirmed by the examination of vaginal cytology, and offspring were derived from allografts.

Live births after autologous transplant of cryopreserved mouse ovaries

The fertility of mice after autologous transplantation of ovaries, before or after cryopreservation, was investigated in this study. Female mice were randomly assigned to either sham-operated (n = 14), ovariectomized (n = 11), fresh (n = 12) or cryopreserved (n = 11) ovarian transplant groups. Ovaries were cryopreserved in 1.4 M dimethyl sulphoxide (DMSO) by cooling to -55 degrees C at 0.5 degree C/min (ice nucleation at -7 degrees C), plunged in liquid nitrogen and then thawed at room temperature. Oestrous cyclicity was observed 7 days after sham operation or 15 days after fresh or cryopreserved ovarian transplant. Ovariectomized animals did not demonstrate oestrous cyclicity but were mated, and no pregnancies resulted. Live births were recorded from all sham-operated, all fresh transplant, and 8/11 (73%) cryopreserved transplant animals. Overall mean +/- SEM litter sizes from fresh (4.32 +/- 0.44) and cryopreserved (4.71 +/- 0.57) transplant groups were smaller (P < 0.05) than those of sham-operated animals (12.54 +/- 0.44), although the sizes were not significantly different (P > 0.05) from each other. Animals were mated at least four times, with four litters of live pups from 4/4 sham-operated, 1/10 fresh and 1/9 cryopreserved ovarian transplant animals. Litter sizes from pups of sham-operated and transplant animals were not significantly different from each other. Following autologous transplantation of mouse ovaries, before or after cryopreservation, offspring appeared normal, with high rates of fertility.

Use of endometrial measurement as an exclusion criterion for in vitro fertilization using clomiphene citrate

OBJECTIVE

Previous reports have indicated an association between endometrial development and pregnancy outcome for patients treated with clomiphene citrate (CC) in conjunction with intrauterine insemination or intercourse. We expanded the use of CC for ovulation induction in association with in vitro fertilization (IVF). This study was designed to determine if endometrial thickness should be used as an inclusion or exclusion criterion for CC-IVF.

STUDY DESIGN

One hundred twenty-eight patients were enrolled in an ovulation-induction regimen using CC for expected IVF-ET between January 1992 and December 1992. A total of 81 patients met inclusion criteria for CC-IVF and had endometrial measurement performed prior to human chorionic gonadotropin administration. Patients were categorized on the basis of endometrial measurement as follows: (A) > 4 - < 7 mm, (B) > or = 7 - < or = 10 mm, and (C) > 10 mm. Standard IVF was performed, and pregnancy rates for each category were evaluated.

RESULTS

A total of 23 pregnancies (28% per retrieval) were established. Pregnancy rates were not different by category (P > .10, Fisher's Exact Test): (A) 3/15 (20%), (B) 13/41 (32%), and (C) 7/25 (28%).

CONCLUSION

These data suggest that for CC-IVF. endometrial measurement should not be used as an exclusion criterion since pregnancies occurred at comparable frequencies in all the groups.

Development of a novel microperfusion chamber for determination of cell membrane transport properties

A novel microperfusion chamber was developed to measure kinetic cell volume changes under various extracellular conditions and to quantitatively determine cell membrane transport properties. This device eliminates modeling ambiguities and limitations inherent in the use of the microdiffusion chamber and the micropipette perfusion technique, both of which have been previously validated and are closely related optical technologies using light microscopy and image analysis. The resultant simplicity should prove to be especially valuable for study of the coupled transport of water and permeating solutes through cell membranes. Using the microperfusion chamber, water and dimethylsulfoxide (DMSO) permeability coefficients of mouse oocytes as well as the water permeability coefficient of golden hamster pancreatic islet cells were determined. In these experiments, the individual cells were held in the chamber and perfused at 22 degrees C with hyperosmotic media, with or without DMSO (1.5 M). The cell volume change was videotaped and quantified by image analysis. Based on the experimental data and irreversible thermodynamics theory for the coupled mass transfer across the cell membrane, the water permeability coefficient of the oocytes was determined to be 0.47 micron. min-1. atm-1 in the absence of DMSO and 0.65 microns. min-1. atm-1 in the presence of DMSO. The DMSO permeability coefficient of the oocyte membrane and associated membrane reflection coefficient to DMSO were determined to be 0.23 and 0.85 micron/s, respectively. These values are consistent with those determined using the micropipette perfusion and microdiffusion chamber techniques. The water permeability coefficient of the golden hamster pancreatic islet cells was determined to be 0.27 microns. min-1. atm-1, which agrees well with a value previously determined using an electronic sizing (Coulter counter) technique. The use of the microperfusion chamber has the following major advantages: 1) This method allows the extracellular condition(s) to be readily changed by perfusing a single cell or group of cells with a prepared medium (cells can be reperfused with a different medium to study the response of the same cell to different osmotic conditions). 2) The short mixing time of cells and perfusion medium allows for accurate control of the extracellular osmolality and ensures accuracy of the corresponding mathematical formulation (modeling). 3) This technique has wide applicability in studying the cell osmotic response and in determining cell membrane transport properties.

The effect of collection temperature, cooling rate and warming rate on chilling injury and cryopreservation of mouse spermatozoa

The experiments presented here identify several factors that affect survival (motility) of cryopreserved mouse spermatozoa after freezing and thawing. Among these factors are: (i) the temperature at which spermatozoa are collected, (ii) the cooling rate to 0 degrees C and (iii) the warming rate from -196 degrees C to ambient. When excised epididymides were cooled to near 0 degrees (1-4 degrees C) and spermatozoa collected and mixed with cryoprotectant at that temperature, motilities after subsequent freezing and thawing were 8-10 times higher than when the spermatozoa were collected from the epididymides at 22 degrees C. In addition, the survival rates of spermatozoa warmed at rates ranging from 150 to 2000 degrees C min-1 were about five times higher than those in suspensions warmed at about 7500 degrees C min-1. The combination of a low collection temperature and the lower warming rates resulted in approximately 50% motility relative to unfrozen controls. Motility was reduced to 6-8% when the collection temperature was 22 degrees C, and to approximately 10% when frozen suspensions of spermatozoa collected in the cold were rapidly warmed from -196 degrees C. When spermatozoa collected at 22 degrees C were abruptly cooled to 0 degrees C, 40-80% of the cells suffered an irreversible loss of motility after warming. In contrast, when spermatozoa were cooled to 0 degrees C at 1 degree C min-1 and warmed (either rapidly or slowly), motilities were similar to those of uncooled controls (75-90%).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth of mouse pups derived from biopsied blastocysts

OBJECTIVE

To test the hypothesis that removal of cells from the pre-embryo affects intrauterine growth, as reflected in birth weight or growth to weaning.

METHODS

ICR Swiss albino and C57Bl/6 mice served as embryo donors to provide two strains of distinct coat colors. Alternate strains were assigned to control treatment or blastocyst biopsy of trophectoderm. Embryos from both treatments were transferred to a different uterine horn within each pseudopregnant recipient. A total of 412 embryos (206 controls and 206 biopsied blastocysts) were transferred to 26 recipients, which resulted in the birth of 122 pups.

RESULTS

There was no significant difference (P > .1) in birth weight or growth to weaning, defined as [[(weaning weight-birth weight)/birth weight)] x 100], between male and female pups. There was a significant difference (P < .01) between pups derived from ICR (birth weight 1.9 +/- 0.02 g; growth to weaning 544 +/- 14%; n = 72) versus C57Bl/6 (birth weight 1.43 +/- 0.03 g; growth to weaning 460 +/- 14%; n = 50) embryos. However, there was no significant difference (P > .1) in birth weight or growth to weaning for pups derived from biopsied embryos (birth weight 1.70 +/- 0.03 g; growth to weaning 502 +/- 14%; mean +/- standard error of the mean; n = 67) or control embryos (birth weight 1.71 +/- 0.05 g; growth to weaning 520 +/- 17%; n = 55).

CONCLUSIONS

These data support the null hypothesis that embryo biopsy does not result in reduced birth weight or altered subsequent growth to weaning.

Prevention of osmotic injury to human spermatozoa during addition and removal of glycerol

Use of a cryoprotective agent is indispensable to prevent injury to human spermatozoa during the cryopreservation process. However, addition of cryoprotective agents to spermatozoa before cooling and their removal after warming may create severe osmotic stress for the cells, resulting in injury. The objective of this study was to test the hypothesis that the degree (or magnitude) of human sperm volume excursion can be used as an independent indicator to evaluate and predict possible osmotic injury to spermatozoa during the addition and removal of cryoprotective agents. Glycerol was used as a model cryoprotective agent in the present study. To test this hypothesis, first the tolerance limits of spermatozoa to swelling in hypo-osmotic solutions (iso-osmotic medium diluted with water) and to shrinkage in hyperosmotic solutions (iso-osmotic medium with sucrose) were determined. Sperm plasma membrane integrity was measured by fluorescent staining, and sperm motility was assessed by computer-assisted semen analysis before, during and after the anisosomotic exposure. The result indicate firstly that motility was much more sensitive to anisosmotic conditions than membrane integrity, and secondly that motility was substantially more sensitive to hypotonic than to hypertonic conditions. Based on the experimental data, osmotic injury as a function of sperm volume excursion (swelling or shrinking) was determined. The second step, using these sperm volume excursion limits and previously measured glycerol and water permeability coefficients of human spermatozoa, was to predict, by computer simulation, the cell osmotic injury caused by different procedures for the addition and removal of glycerol. The predicted sperm injury was confirmed by experiment. Based on this study, an analytical methodology has been developed for predicting optimal protocols to reduce osmotic injury associated with the addition and removal of hypertonic concentrations of glycerol in human spermatozoa.

High water permeability of human spermatozoa is mercury-resistant and not mediated by CHIP28

A novel integral membrane protein with an apparent molecular mass of 28 kDa (CHIP28) was first isolated from human erythrocytes and is now recognized as a water channel protein. The expression of this protein has been found in several other cell types that all require high water permeability for their functions. Recent studies have shown that the water permeability (Lp) of human spermatozoa is among the highest reported for mammalian cells. Together with the low activation energy of human spermatozoa for Lp, this suggests that CHIP28 water channel may be present in the plasma membrane of human spermatozoa. However, our current studies do not support this hypothesis. Results from Western blot analysis on human sperm plasma membrane proteins, performed through use of an antibody against human erythrocyte CHIP28 protein, indicated that human spermatozoa do not express CHIP28 protein on their cell surface (n = 10). Consistent with the Western blot finding, mercuric chloride (HgCl2), a known water channel blocker, failed to reduce the osmotic water permeability of human spermatozoa. The calculated Lp values were 1.30 +/- 0.29 micron/min/atm (n = 16; mean +/- SEM) for the control group and 1.31 +/- 0.29 (n = 9; mean +/- SEM), 1.04 +/- 0.27 (n = 11; mean +/- SEM), and 1.34 +/- 0.19 (n = 6; mean +/- SEM), respectively, for the 10 microM, 30 microM, and 50 microM HgCl2-treated groups. These Lp values are not different (p > 0.05). In contrast, the same concentration of HgCl2 significantly blocked the osmotic water transport across the membrane of human erythrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental potential of microbiopsied murine blastocysts

OBJECTIVE

To evaluate the frequency of mouse pups born following blastocyst biopsy and embryo transfer compared to nonbiopsied controls.

METHODS

ICR Swiss albino and C57B1/6 mice served as embryo donors. Pregnant mare serum gonadotropin treatment was followed 46-52 hours later by hCG, when donors were paired with fertile males. Mating was confirmed the following day and embryos were collected on the afternoon of day 4. After overnight culture, hatching trophoblast was excised by micromanipulation with a fine-pulled glass pipette. Embryos (206 controls, 206 biopsied) were transferred to 26 pseudopregnant recipients. Alternate mouse strains were used to identify pups born from control or biopsied embryos.

RESULTS

The end point was percentage of pups born ((number born/number transferred) x 100), using angular transformation before analysis. There was no significant difference (P > .1) between percent live-born in control (27.7%) or biopsied (34.5%) embryos, nor were there any strain differences.

CONCLUSION

These data support the hypothesis that the developmental potential of murine blastocysts is not affected adversely by the biopsy procedure.

Membrane transport properties of mammalian oocytes: a micropipette perfusion technique

A perfusion technique using micropipette methodology was developed to determine quantitatively the membrane transport properties of mammalian oocytes. This method eliminates modelling ambiguities inherent in microdiffusion, a closely related technology, and should prove to be especially valuable for study of the coupled transport of water and cryoprotectant through mammalian oocytes and embryos. The method is described and evidence given for validity of the method for the simple case of uncoupled flow of water through the mouse oocyte membrane. The zona pellucida of a mouse oocyte was held by a micropipette with an 8-10 microns diameter tip opening and perfused by hyperosmotic media. The kinetic volume change of the cell was videotaped and quantified by image analysis. Experimental data and mathematical modelling were used to determine the hydraulic conductivity of the oocyte membrane (Lp) found to be 1.05, 0.45 and 0.26 microns min-1 atm-1 at 30 degrees C, 22 degrees C and 12 degrees C, respectively. The corresponding activation energy, Ea, for Lp was calculated to be 13.0 kcal mol-1. These values are in agreement with data obtained by other techniques. One of the major advantages of this technique is that the extracellular osmotic condition can be changed readily by perfusing a single cell with a prepared medium. To study the response of the same cell to different osmotic conditions, the old perfusion medium can be removed easily and the cell reperfused with a different medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the acrosomal status and viability of human spermatozoa simultaneously using flow cytometry

Acrosomal status and viability were evaluated simultaneously on human spermatozoa using flow cytometry. Samples were divided into three aliquots and randomly assigned to one of three treatments: (i) cryopreservation; (ii) 10 microM calcium ionophore [A23187 in dimethylsulphoxide (DMSO)] or (iii) DMSO alone (control). Acrosomal status was evaluated using monoclonal antibodies recognizing MH61 and CD46, respectively. Fluorescein-conjugated goat anti-mouse immunoglobulin (IgG) was used as a second antibody. Sperm viability was assessed using Hoechst 33258 (H258) exclusion. The following factors were analysed: (i) the specificity of the monoclonal antibodies for the human acrosome; (ii) the relative effectiveness of flow cytometry and direct fluorescent microscopy scoring and (iii) the acrosomal status and viability of the control, ionophore-treated, and cryopreserved spermatozoa. Across all treatments, the MH61 and CD46 monoclonal antibodies resulted in acrosomal status values (acrosome-reacted/viable spermatozoa) which were not significantly different (P > 0.05): control, 1.0 +/- 0.3% and 1.5 +/- 0.6% (mean +/- SEM); A23187, 42.8 +/- 3.5% and 38.1 +/- 3.5%; cryopreserved, 8.2 +/- 2.0% and 9.9 +/- 1.3%; respectively. However, acrosomal status among treatments differed significantly (P < 0.01). Flow cytometric and direct fluorescent microscopy assessments were significantly correlated (r2 = 0.96, P < 0.01). These results indicate that flow cytometry, using an acrosome-specific monoclonal antibody and a supravital dye, provides an objective and efficient method to evaluate human sperm acrosomal and viability status simultaneously.

Determination of the osmotic characteristics of hamster pancreatic islets and isolated pancreatic islet cells

The ability to store pancreatic islets using cryopreservation methodology would greatly assist the application of clinical islet transplantation to Type 1 (insulin-dependent) diabetics. It is our working thesis that the illumination of fundamental biophysical characteristics of these cells will lead to increased cryosurvival rates through theoretically predicted and experimental testing of optimal freezing protocol; as has been found for cells and tissues such as mammalian and Drosophila embryos. Pancreatic islets were isolated from Golden hamsters and their osmometric behavior, including inactive cell volume (Vb), was determined for either whole islets or isolated individual islet cells. When islets or islet cells were exposed to various concentrations of NaCl, they were found to exhibit a "classic" "Boyle-Van't Hoff" osmometric response. The Boyle-Van't Hoff representation of the volume curve (relative cell volume vs. 1/osmolality) yields a linear response with r values of .99 for each curve. Extrapolations to the normalized osmotically inactive volumes (Vb) were .43 and .22 for whole islets and individual islet cells, respectively. These data regarding the fundamental cryobiological characteristics of islets and islet cells should provide the foundation upon which to further the investigation of osmotic parameters of these cells and eventually lead to the determination of optimal freezing protocols.

Evaluation of mouse sperm acrosomal status and viability by flow cytometry

A procedure was developed to evaluate mouse sperm acrosomal status and viability simultaneously utilizing flow cytometry. Four fluorescein isothiocyanate (FITC)-conjugated lectins, peanut agglutinin (PNA), concanavalin agglutinin (ConA), Pisum sativum agglutinin (PSA), and soybean agglutinin (SBA), were investigated, with PNA providing the greatest sensitivity and specificity in distinguishing acrosome-present and acrosome-absent mouse spermatozoa. To expose lectin binding sites, digitonin (20 microM at room temperature for 10 min) was used to permeabilize sperm plasma membranes. Sperm cell viability was determined by Hoechst 33258-(H258) exclusion. To prevent permeabilized cells from staining with H258, salmon sperm DNA (SS-DNA) was applied to bind excess dye in the solutions after supravital staining. Calcium ionophore (A23187; 5 or 20 microM) was used to induce acrosome reactions. The results of flow cytometric analyses were compared with epifluorescence microscopic observation and were highly correlated (r = 0.999; P < 0.001). The method developed provides an objective and efficient procedure to estimate simultaneously both acrosomal status and viability of mouse spermatozoa.

Preimplantation genetics. An overview

Advances in methods used to detect specific genes or gene products have contributed to the development of methods to identify genetic disorders in preimplantation embryos. A variety of strategies have been developed, including polar body biopsy, removal of cells from multicell stage embryos, and biopsy of the polar trophectoderm from expanded blastocysts. These embryos are derived primarily from oocyte retrievals and in vitro fertilization procedures, although blastocysts could be obtained by uterine lavage. A number of animal models have been evaluated that demonstrate the feasibility of such techniques in the diagnosis of genetic disease. Clinical trials are under way in a number of clinical centers and current outcomes with human embryos are cited.

Pregnancy rates after peritoneal ovum-sperm transfer

We present the technique of peritoneal ovum-sperm transfer as an option for treatment in couples with unexplained infertility factors. In 1989 we reported the first successful pregnancy, in the United States, after transferring sperm and oocyte into the peritoneal cavity. We now report the results of a prospective study of this procedure. Twelve women with unexplained infertility underwent 23 cycles of peritoneal ovum-sperm transfer. Ovulation stimulation was achieved with human menopausal gonadotropin. Ultrasonographically directed oocyte recovery was performed by the transvaginal route with the patient under local anesthesia and sedation. After oocyte recovery, 4.5 +/- 0.4 (mean +/- SE) oocytes and 13.3 +/- 1.0 (mean +/- SE) x 10(6) motile spermatozoa were transferred into the pouch of Douglas. Six clinical pregnancies occurred in 23 stimulated cycles for a pregnancy rate of 26% per cycle. This value compares with the overall pregnancy rates of 16% for in vitro fertilization and 27% for gamete intrafallopian transfer reported by the In Vitro Fertilization Registry. Thus these preliminary data suggest that peritoneal ovum-sperm transfer is at least as successful as in vitro fertilization and gamete intrafallopian transfer. Advantages of peritoneal ovum-sperm transfer over gamete intrafallopian transfer include its being an office nonsurgical procedure not necessitating a general anesthetic and decreased cost. Therefore peritoneal ovum-sperm transfer is a reasonable first approach in couples with unexplained infertility.

Cloning of a gap junctional protein from vascular smooth muscle and expression in two-cell mouse embryos

Gap junctional proteins (connexins) form aqueous channels that enable direct cell-cell transfer of ions and small molecules. The distribution and conductance of gap junction channels in cardiac muscle determine the pattern and synchrony of cellular activation. However, the capacity for smooth muscle to restrict contractile events temporally and spatially suggests that cell-cell coupling or its regulation may be decidedly different in this tissue. We isolated a cDNA from vascular smooth muscle which encodes a connexin (Mr 43,187) structurally homologous to cardiac connexin43. Vascular smooth muscle connexin43 mRNA was expressed prominently in smooth muscle tissues, cultured vascular myocytes, and arterial endothelial cells. A model for functional expression of connexins was developed in two-cell B6D2 mouse embryos. Microinjection of in vitro transcribed vascular smooth muscle connexin43 mRNA was shown to be sufficient to induce intercellular coupling in previously uncoupled blastomeres. Through the construction of two deletion mutants of connexin43, we also show that the formation of cell-to-cell connections does not depend upon a predicted cytoplasmic region within 98 residues of the carboxyl terminus. Finally, the identification of connexin43 in smooth muscle and endothelial cells provides supporting evidence for the existence of heterocellular coupling between cells of the vascular intima.

Evaluation of circulating anti-sperm antibodies in fertile and patient populations

Several reports have demonstrated the presence of anti-sperm antibodies (ASA) in infertile populations; however there is a paucity of information regarding ASA in fertile populations. The purpose of this study was to establish objective criteria for the interpretation of the Immunobead Binding Test (IBT) based on values obtained from fertile individuals. Sera from 20 fertile couples (n = 40) were assayed by using a modification of the IBT previously described by Clarke et al. An initial lower limit of binding for positivity (lower limit) of 14% was used based upon the mean value for each isotype plus 2 standard deviations (SD) of 4 negative control sera assayed 4 to 7 times each. One-way ANOVA or chi-square analyses were used to analyze these data. There was no difference in percent immunobead binding between males and females in the fertile population (P greater than 0.1); therefore the data were pooled. Percent binding for fertile controls was: IgG, 21.7 + 31.9% (mean + SD); IgA, 19.5 + 25.8%; IgM, 16.9 + 14.9%. Initial analysis indicated no significant difference (P greater than 0.10) in percent binding between fertile and infertile individuals. The corresponding frequency of positive values (for at least one isotype) using a 14% lower limit was 23/40 (57.5%). This was not significantly different (P greater than 0.1) from the frequency observed in the patient population (140/242, 57.8%). New lower limits of positivity for each isotype were established based upon the mean plus 2 SD from the fertile control data: IgG, 85.4%; IgA, 71.1%; IgM, 46.7%.(ABSTRACT TRUNCATED AT 250 WORDS)

Sperm antibodies after intraperitoneal insemination of sperm: a preliminary report

To test the hypothesis that intraperitoneal insemination of sperm induces the expression of anti-sperm antibodies a prospective study was designed. Fifteen women undergoing intraperitoneal insemination (with or without oocyte transfer) were studied with 11 women having evaluation of anti-sperm antibodies. Sperm antibodies were detected by the immunobead test prior to intraperitoneal insemination and after each treatment cycle. Two criteria were used to assess positivity: the first based upon negative controls and the second based upon the evaluation of 20 fertile control couples. Using the first criteria, of 11 of the women undergoing IPI for the first time, 7 were initially negative and 4 were initially positive for at least 1 isotype. After treatment, 3 additional patients were positive (for a total of 7) and 4 patients remained negative. This alteration in sperm antibody frequency was not different (P = .4) as determined by the Fisher's Exact Test. Four of the 11 patients underwent a second cycle of IPI. All 4 patients were negative prior to the first treatment and 3 were negative prior to the second treatment. Subsequent to the second exposure, all 4 of these women were positive for at least 1 isotype. This shift in frequency distribution after 2 cycles was significant (P = .01). The frequency of antisperm antibodies for the same 11 patients was evaluated by using fertile control values as the basis of positivity. Two patients (18%) were positive for anti-sperm antibodies prior to intraperitoneal insemination. There was no change in the frequency of positivity after 1 cycle of IPI.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration in platelet count during early pregnancy in the mouse

Published reports of pregnancy associated thrombocytopenia in mice have utilized the Quackenbush strain. The inability of some laboratories to verify this observation in other mouse strains prompted us to report our findings by using Swiss Albino ICR mice. In Exp. 1, pregnant and pseudopregnant mice were bled prior to mating (time 0) and daily on day 1 (vaginal plug) through day 7. In Exp. 2, media from 24 hr cultures of 2-cell mouse embryos or media from unfertilized oocytes were injected into splenectomized mice. Animals were bled at time 0 (before injection) and at 30, 60, and 120 min after injection. In Exp. 3, splenectomized mice were treated with either media from 2-cell stage embryos or with media supplemented with synthetic platelet-activating factor (PAF: 0.05, 0.1 or 0.2 micrograms). Animals were bled as in Exp. 2. Platelet numbers were determined in duplicate from each blood sample by using a hemacytometer. In Exp. 4, antagonist (SRI 63-441) or vehicle was administered to mated mice on days 1 through 4 of pregnancy. Animals were examined on day 8 to determine number of developing conceptuses. In Exp. 1-3, data were analyzed by using ANOVA for repeated measures, and in Exp. 4 data were analyzed by chi-square analysis. In Exp. 1, there was a treatment x time interaction (P less than .06) due to transient thrombocytopenia in pregnant but not pseudopregnant mice.(ABSTRACT TRUNCATED AT 250 WORDS)

An evaluation of the accuracy of screening antisperm antibodies using the combined GAM immunobead

A simplified method of screening for antisperm antibodies has been previously described using rabbit antihuman immunoglobulin immunobeads (GAM beads). These reports have indicated a high correlation between the GAM bead and maximal individual isotype binding. However, preliminary data in our laboratory (using a 14% cut-off criterion) indicated a high frequency of samples with positive GAM bead, but negative individual isotype results. This study was conducted to evaluate more critically the use of the GAM bead for initial antisperm antibody screening. Immunobead binding tests were performed on 98 undiluted sera. The maximal binding of the individual isotype beads (IgG, IgA, or IgM) and the GAM beads were significantly correlated (r = 0.94, P = 0.0001). However, when results were categorized as positive or negative, there was a significantly lower frequency (P less than 0.05) of positive samples using the individual isotype (46.9%) than using the GAM approach (58.2%). These data support the hypothesis that, based on continuous percent binding, the GAM bead method produces results similar to individual isotype testing. However, when data are interpreted categorically, the results may differ significantly.

Pregnancy resulting from peritoneal ovum sperm transfer procedure

This is the first reported transvaginal ultrasound-guided POST pregnancy in the United States. Advantages over the GIFT procedure include it being an office procedure done under local anesthesia and IV sedation, and decreased cost. Larger series are needed to compare pregnancy rates.

Divergent selection for in vitro developmental capacity of preimplantation mouse embryos

Replicated divergent selection was conducted for two generations in ICR mice for in vitro developmental capacity (IVDC; percentage of fertilized one-cell zygotes developing to blastocysts in vitro per female donor). Realized heritabilities based on high and low selection were 0.03±0.08 and -0.11±0.09 in replicate 1, and 0.10±0.11 and 0.08±0.10 in replicate 2. No differences were detected between selection lines (P>0.2) or replicates (P>0.1). Estimate of heritability in the base population based on 332 daughter-dam pairs was 0.14±0.18. These results indicate that additive genetic variance contributes little to the phenotypic variance in this trait. Considerable phenotypic variation in IVDC was observed (mean=49.3; SD=31.0), with a range of IVDC from 0%-100%. Utilization of donor female as a blocking factor is suggested for designs of experiments with preimplantation embryos to increase precision and power of statistical analyses.

Lower sodium lactate in Whitten's medium improves in vitro developmental capacity of one-cell mouse embryos

A modification of Whitten's medium, involving a reduced content of Na-lactate syrup (0.2 ml/100 ml; 11.65 mM) and osmolarity (251 mOsm), was compared with normal Whitten's medium (0.37 ml/100 ml; 21.6 mM) for ability to support mouse embryonic development in vitro from one-cell to the blastocyst stage. In a pilot study utilizing 10 ICR donor female mice, in vitro developmental capacity (IVDC; percentage of fertilized one-cell embryos developing to blastocysts in vitro per female donor) was significantly enhanced by the modified medium (68.0 versus 24.0%; P<0.001). In the main study, utilizing 134 ICR and 17 ICR x C57BL/6J F(1) donor females, the modified medium supported increased IVDC for both ICR (67.9 versus 51.1%; P<0.001) and F(1) females (98.5 versus 89.4%; P<0.05). A large degree of among donor-female variation in IVDC was observed for both media in the ICR stock (SD = 30.0). The beneficial role of the reduction of Na-lactate in Whitten's medium may be related to an improved provision of energy requirements for first cleavage and/or a more suitable osmolarity for development.

Development potential of bovine oocytes matured in vitro or in vivo

Bovine oocytes matured in vivo or in vitro were evaluated after sperm-oocyte incubation for frequency of sperm penetration, frequency of male pronuclei formation, and embryonic development. The frequency of sperm penetration was not different for in vitro matured oocytes (216/295, 73%) vs. in vivo matured oocytes (119/176, 70%). However, formation of male pronuclei was reduced (p less than 0.05) for oocytes matured in vitro (149/216, 69%) vs. in vivo (104/119, 88%). Early embryonic development was evaluated 48 h after the onset of sperm-egg incubations. In vitro matured and fertilized oocytes failed to develop to the 2-cell stage (3/88, 3%), whereas oocytes matured in vivo showed normal development (23/56, 40%) to the 2- and 4-cell stage. Development to the blastocyst stage was evaluated after 5 days in ovine oviducts (in vivo). Morulae and blastocysts were obtained only after in vitro fertilization from oocytes that were in vivo-matured (recovered from oviduct, 14/56, 25%; recovered from follicle, 36/80, 45%). Oocytes that were matured in vitro and fertilized in vitro failed to develop to morulae (0/33) in vivo.

Effects of fetal calf serum and bovine serum albumin on in vitro maturation and fertilization of bovine and hamster cumulus-oocyte complexes

Bovine serum albumin (BSA) and fetal calf serum (FCS) were evaluated as protein supplements for in vitro maturation and fertilization of oocytes from cows and hamsters. BSA and low doses of FCS (0.1 or 1.0%) did not support viability or maturation of the cumulus-oocyte complex as well as higher doses of FCS (5, 10, or 20%) for either species. BSA failed to support cumulus expansion for bovine or hamster cumulus-oocyte complexes. All doses of FCS examined supported cumulus expansion in bovine cumulus-oocyte complexes, whereas the hamster complexes required at least 1.0% FCS to induce cumulus expansion. The addition of a serum filtrate, Solcoseryl, with BSA improved viability of the cumulus in the bovine but did not support cumulus expansion or completion of Meiosis I in bovine complexes. In vitro fertilization could be accomplished in media containing FCS by increasing the heparin concentration in the bovine system or reducing FCS for the hamster system. Polyspermy was increased when FCS was the protein supplement. It is not known whether this is an interaction of FCS with the sperm or oocyte. In conclusion, FCS was found necessary for follicle-stimulating-hormone (FSH)-induced cumulus expansion. It also improved cumulus cell viability and completion of the first meiotic division in complexes of both species compared with BSA.

Nuclear transplantation in mouse embryos: assessment of recipient cell stage

Enucleated zygotes were compared with enucleated two-cell embryos as recipients for donor nuclei from eight-cell embryos. Only one or two cleavage divisions were observed when eight-cell nuclei were transplanted to enucleated zygotes. Development of enucleated two-cell embryos containing a transplanted eight-cell nucleus was appreciably better with 51% (45/89) of the embryos forming blastocysts in vitro and 42% (25/60) initiating implantation. Of these, eleven implantation sites on Day 10 of gestation were examined histologically and two contained normally developing embryos. No development was observed beyond Day 12 of gestation. These observations indicate that a major transition occurs between the zygote and two-cell stage that results in the two-cell recipient being more compatible with the eight-cell nucleus than with the zygote.

Bovine in vitro fertilization with frozen-thawed semen

A procedure to obtain high and repeatable fertilization frequencies for bovine in vitro fertilization (IVF) with frozen-thawed sperm was developed. IVF frequency of in vitro matured oocytes was increased by a swimup sperm separation procedure (P=0.01) or treatment of sperm with the glycosaminoglycan heparin (P=0.0001), but the two factors did not interact (P=0.23). Heparin was the most important factor in increasing IVF frequencies. The fertilization frequency was not affected by the batch of oocytes used (P=0.38), but bull effects were present (P<0.05). Within a bull, the IVF system was highly repeatable and varied between trials no more than +/- 12% in fertilization frequency with an overall fertilization frequency of 299 379 (79%) on four trials over four bulls. In vivo matured oocytes fertilized in vitro were transferred to ewe or heifer oviducts. Morulae or blastocysts were recovered from ewes after four to five days, while conceptuses were present in the bovine after 25 days (diagnosed by ultrasound). Embryonic development from the IVF system either pre- or postimplantation was normal.

Use of a fluorescent stain for visualization of nuclear material in living oocytes and early embryos

Hoechst dyes 33342 and 33258 were used to visualize pronuclei and nuclei of early preimplantation embryos. Murine one-cell zygotes exposed to dye stained rapidly over a range of concentrations (0, 0.02, 0.04, 0.1 or 0.2 micrograms/50 microliter of media). Development to morula and blastocyst in vitro was reduced (39/70, 56%; p less than 0.05) compared to controls (44/57, 77%) but not completely blocked. Porcine and bovine zygotes and embryos could also be stained but required incubation times up to 4 hr. Porcine embryos exposed to Hoechst 33342 had limited (p less than 0.01) in vitro development (29/74, 39%) compared to unstained controls (49/64, 76%). Hoechst dyes stain embryos from different species but suitably adjusted incubation times are required. Limited preimplantation development in vitro may be expected following staining and exposure to ultraviolet light.

Fertilization potential of follicular oocytes classified by stage of cycle and size of follicle

Bovine follicular oocytes, collected from two sizes of vesicular follicles and from donor animals from three stages of the estrous cycle, were matured and fertilized in vitro. Frequency of fertilization and ability to form male pronuclei after in vitro maturation were found to be independent of both estrual stage and follicular size.

Developmental potential of isolated blastomeres from early murine embryos

Experiments were designed to evaluate the effect of blastomere separation on blastocoele formation and development of viable fetuses. Two-cell and four-cell murine embryos were dissociated into individual blastomeres and cultured to the blastocyst stage. For embryos of both stages, zona removal and blastomere separation reduced (P<0.05) the number of viable embryos at the onset of culture and reduced (P<0.01) the frequency of continuation of development of blastomeres to the blastocyst stage. Attempts to repeatedly split two-cell stage embryos decreased in vitro development to blastocysts. The number of cells in two-cell embryos that were cultured to blastocyst was not different for control (64.8 +/- 11.5) or for two-cell embryos cultured without the zona pellucida (60.9 +/- 10.1) but was reduced (P<0.01) for one-half embryos that were cultured to blastocysts (35.6 +/- 10.6). The cell number of blastocysts obtained from dissociated four-cell (1/4) embryos (17.4 +/- 1.4) was similarly reduced (P<0.01). In vivo development was assessed after cultured embryos were transferred to the uteri of day 3 pseudopregnant females. Zona free intact embryos (2/36, 6%) and zona free half embryos (7/36; 19%) developed less frequently (P<0.05) than intact controls (45/100). Noncultured morula briefly exposed to pronase to thin the zona had similar impaired development. Embryos with thinned zona or no zona developed less frequently (21/82, 2/72 respectively, P<0.05) than nonpronase-treated controls (50/83).

The effect of semen extension, cAMP and caffeine on fertilization of bovine oocytes

A previously reported in vitro system that used epididymal spermatozoa for fertilizing bovine follicular oocytes (1) has been expanded to include ejaculated semen as the sperm source. Frequency of fertilization was higher when semen was extended 1:1 prior to transport to the laboratory rather than transport as neat semen. Pretreatment of spermatozoa with cAMP, caffeine or both prior to insemination of oocytes did not increase frequency of either acrosome reactions or fertilization after sperm/oocyte incubation.

Control of luteal function during pregnancy: antiluteolytic and luteotropic properties of the developing mouse conceptus

Eight experiments were conducted to examine the influence of the conceptus on luteal function in mice. In uterine intact pseudopregnant mice, exogenous treatment with placental extracts or pregnant mouse plasma from Day 8 or Day 10 of gestation did not prolong the life span of the corpora lutea (CL). The interestrous interval (IEI) of hysterectomized pseudopregnant mice was extended by treatment with Day 10 placental extract and was accompanied by elevated plasma progesterone, consistent with the luteotropic nature of the Day 10 conceptus. The IEI of uterine intact pseudopregnant mice was prolonged by the presence of ectopically developing blastocysts and was further extended by a treatment with Day 10 placental extracts but not by treatment with Day 8 placental extracts. Although the ectopic blastocyst delayed the effect of the uterine luteolytic mechanism, there was no indication of luteotropic activity: the ectopic blastocysts were unable to activate the CL of the estrous cycle. In addition, plasma progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were measured in pseudopregnant, hysterectomized pseudopregnant and pregnant mice on Day 2 through 13 post-mating. The results of these experiments suggest a two-step mechanism in prolonging luteal function during pregnancy which involves two different substances. This mechanism involves an initial signal from the conceptus which blocks the uterine luteolytic mechanism and a subsequent luteotropic stimulus from the Day 10 conceptus which extends luteal life span to approximately the length of gestation.

Plasma concentrations of progesterone and 13,14-dihydro-15-keto prostaglandin F-2 alpha in pregnant, pseudopregnant and hysterectomized pseudopregnant mice

Hysterectomized pseudopregnant mice had plasma progesterone concentrations on Days 6, 8, 10 or 12 after mating that were greater (P less than 0.05) than those of intact pseudopregnant mice and lower (P less than 0.01) than those of pregnant mice. Concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha on Days 6, 7, 8, 9 or 10 after mating were lower (P less than 0.05) in pregnant and higher (P less than 0.01) in intact pseudopregnant mice than in hysterectomized pseudopregnant mice. The results support the conclusion that there are uterine and extra-uterine luteolytic mechanisms which are mediated by prostaglandin and are perhaps functional by Day 6 of pregnancy.