Blastocyst score affects implantation and pregnancy outcome: towards a single blastocyst transfer

OBJECTIVE

To determine the relationship between blastocyst score and pregnancy outcome.

DESIGN

Retrospective review of blastocyst transfer in an IVF clinic.

SETTING

Private assisted reproductive technology unit.

PATIENT(S)

107 patients undergoing blastocyst culture and transfer of two embryos.

INTERVENTION(S)

Culture of all pronucleate embryos in sequential media to the blastocyst stage (day 5), followed by transfer of two blastocysts.

MAIN OUTCOME MEASURE(S)

Implantation rates, pregnancy rates, and twinning were analyzed.

RESULT(S)

When a patient received two top-scoring blastocysts (64% of patients), implantation and pregnancy rates were 70% and 87%, respectively. The twinning rate in this group was 61%. When only one top-quality blastocyst was available for transfer (21% of patients), the implantation and pregnancy rates were 50% and 70%. The twinning rate for this group was 50%. In contrast, when only low-scoring blastocysts were available for transfer (15% of patients), implantation and pregnancy rates were 28% and 44%, and the twinning rate was 29%. No monozygotic twins were observed in this group of patients.

CONCLUSION(S)

The ability to transfer one high-scoring blastocyst should lead to pregnancy rates greater than 60%, without the complication of twins.

Evaluation of botulinum toxin A therapy in children with adductor spasm by gross motor function measure

Intramuscular injection of botulinum neurotoxin A is a relatively new method for treating spastic movement disorders in children. One major goal of any therapy for patients with movement disorders is to improve gross motor function. In this study, 18 patients with adductor spasm were treated with botulinum neurotoxin A. Treatment effect was determined with the Gross Motor Function Measure, a standardized, validated instrument designed to assist in assessment of gross motor function. Spastic muscle hyperactivity and joint mobility were evaluated by the modified Ashworth Scale and by range of motion, respectively. Compared to pretreatment values, significant improvement in gross motor function (P < .010), decrease in the modified Ashworth Scale, and increase in the range of motion (P < .010) were achieved. Patients with moderate impairment of gross motor function (classed at level III and level IV in the Gross Motor Function Classification System) benefited most from treatment. In patients with severe handicap (level V), only one of five treated patients showed improvement in gross motor function. Nevertheless, all patients in this subgroup benefited from improved ease in hygienic care. In conclusion, we have demonstrated that for most children with moderate functional impairment, the Gross Motor Function Measure is a useful instrument for objective documentation of improvements of gross motor function following treatment with botulinum neurotoxin A.

A single medium supports development of bovine embryos throughout maturation, fertilization and culture

Oocytes and embryos are typically exposed sequentially to varying culture media in standard in-vitro protocols. Expenditures of energy may be required following each medium change to adjust to the changing environment. Therefore, a single base medium was evaluated for its ability to support in-vitro maturation, fertilization and pre-implantation development (IVM/F/C) of bovine oocytes and embryos. Four treatments were examined: a standard maturation [tissue culture medium (TCM) 199 with bovine calf serum (BCS)], fertilization (modified Tyrode's medium with albumin, lactate and pyruvate) and culture (hamster embryo culture medium/TCM with BCS) system (control) and three synthetic oviductal fluid (SOF) treatments; maturation in SOF with bovine serum albumin (SOFBSA), SOF with bovine calf serum (SOFBCS) or the control maturation medium (TCM199 with BCS; SOF199), followed by fertilization and culture in SOF medium. The percentage of total inseminated oocytes successfully developing to the morula and blastocyst stage did not differ (P > 0. 05) between treatments (control, 30.5 +/- 3.5; SOFBSA, 24.6 +/- 3.2; SOFBCS, 22.4 +/- 4.7; SOF199, 27.3 +/- 3.2). Embryos cultured in SOFBCS (92.1 +/- 6.4) had significantly higher cell numbers (P < 0. 05) than those cultured in control (74.8 +/- 4.8) and SOFBSA (71.6 +/- 6.6) but not SOF199 (81.2 +/- 6.8). In conclusion, a single medium can be used successfully throughout maturation, fertilization and pre-implantation embryo development. Moreover, inclusion of serum during maturation in the single medium system resulted in significantly greater cell numbers, possibly reflecting increased quality of the embryos produced.

Cryopreservation reduces the ability of hamster 2-cell embryos to regulate intracellular pH

Vitrification of hamster 2-cell embryos impairs the activity of both the Na(+)/H(+) antiporter and HCO(3)(-)/Cl(-) exchanger; the two transport proteins responsible for the regulation of intracellular pH (pHi). The activities of both the Na(+)/H(+) antiporter and HCO(3)(-)/Cl(-) exchanger were significantly reduced at 4 h following warming compared to freshly collected embryos. Normal levels of activity of both transporters were not restored until 6 h after warming. Thus, cryopreservation of cleavage stage hamster embryos has a detrimental effect on their ability to maintain intracellular ionic homeostasis. Impairment of these pHi regulatory proteins resulted in the pHi of embryos being significantly elevated from the control values of 1.2 to 7.35 for approximately 4 h after warming. In addition, an elevated pHi value significantly impaired oxidative metabolism. Therefore, the loss in developmental competence of embryos following cryopreservation may in part be explained by a reduced ability to regulate intracellular pH that results in perturbations in metabolism and disruption of energy production.

Ondansetron versus placebo for prophylaxis of nausea and vomiting in patients undergoing ambulatory laparoscopic cholecystectomy

BACKGROUND

Postoperative nausea and vomiting is a common problem in patients undergoing laparoscopic cholecystectomy (LC). The purpose of this study was to evaluate the efficacy of ondansetron given at the induction of anesthesia in patients scheduled for ambulatory LC.

METHODS

A total of 84 patients undergoing ambulatory LC were enrolled in a randomized, prospective, double-blinded study in which the subjects received either placebo or 4 mg ondansetron intravenously at induction of anesthesia. A nausea scoring system was employed utilizing a 5-point linear scale, with 1 point given for no nausea and a maximum of 5 points for an episode of emesis. Each patient received a total of four scores postoperatively.

RESULTS

The patients receiving placebo had significantly more episodes of nausea (53 versus 32; P <0.009) and emesis (11 versus 2; P <0.02), higher mean total nausea scores (7.2 versus 5.4; P <0.006), and need for additional postoperative antiemetics (23 versus 14; P <0.05) than those receiving ondansetron.

CONCLUSIONS

In patients undergoing ambulatory laparoscopic cholecystectomy, ondansetron at induction was highly effective in decreasing postoperative nausea and vomiting and should become the standard.

Lactate regulates pyruvate uptake and metabolism in the preimplantation mouse embryo

This study was an investigation of the interaction of lactate on pyruvate and glucose metabolism in the early mouse embryo. Pyruvate uptake and metabolism by mouse embryos were significantly affected by increasing the lactate concentration in the culture medium. In contrast, glucose uptake was not affected by lactate in the culture medium. At the zygote stage, the percentage of pyruvate taken up and oxidized was significantly reduced in the presence of increasing lactate, while at the blastocyst stage, increasing the lactate concentration increased the percentage of pyruvate oxidized. Lactate oxidation was determined to be 3-fold higher (when lactate was present at 20 mM) at the blastocyst stage compared to the zygote. Analysis of the kinetics of lactate dehydrogenase (LDH) determined that while the V(max) of LDH was higher at the zygote stage, the K(m) of LDH was identical for both stages of development, confirming that the LDH isozyme was the same. Furthermore, the activity of LDH isolated from both stages was reduced by 40% in the presence of 20 mM lactate. The observed differences in lactate metabolism between the zygote and blastocyst must therefore be attributed to in situ regulation of LDH. Activity of isolated LDH was found to be affected by nicotinamide adenine dinucleotide(+) (NAD(+)) concentration. In the presence of increasing concentrations of lactate, zygotes exhibited an increase in autofluorescence consistent with a depletion of NAD(+) in the cytosol. No increase was observed for later-stage embryos. Therefore it is proposed that the differences in pyruvate and lactate metabolism at the different stages of development are due to differences in the in situ regulation of LDH by cytosolic redox potential.

Vitrification of mouse and human blastocysts using a novel cryoloop container-less technique

OBJECTIVE

To vitrify mouse and human blastocysts with use of the cryoloop procedure and to assess subsequent development.

DESIGN

Controlled study of vitrification of mouse and human blastocysts.

SETTING

Research department of a private assisted reproductive technology unit.

PATIENT(S)

Blastocysts that were not suitable to be frozen were donated from patients.

INTERVENTION(S)

Culture of pronucleate embryos in sequential media to the blastocyst stage.

MAIN OUTCOME MEASURE(S)

Survival of the vitrification procedure was assessed by reexpansion, hatching, and outgrowth in culture. In addition, the viability of mouse blastocysts was assessed after transfer to pseudopregnant recipients.

RESULT(S)

Vitrification of mouse blastocysts did not affect the ability to reexpand, hatch, or outgrow in culture. Furthermore, implantation rates and fetal development were equivalent for nonfrozen and vitrified blastocysts. Vitrified human blastocysts were able to hatch and outgrow in culture at rates similar to nonfrozen controls.

CONCLUSION(S)

Cryoloop vitrification was able to cryopreserve mouse and human blastocysts without any reduction in the ability to reexpand and hatch in culture. Furthermore, viability was not reduced by the cryoloop vitrification of mouse blastocysts.

Regulation of intracellular pH in bovine oocytes and cleavage stage embryos

This study investigated the mechanisms for the regulation of intracellular pH in bovine oocytes and embryos. Na(+)/H(+) antiporter activity for the regulation of intracellular pH in the acid to neutral range was detected in both in vitro matured bovine oocytes and in vitro produced embryos. However, the activity of the antiporter was significantly reduced in oocytes compared to 2-cell, 4-cell, and 8-cell embryos. HCO(3)(-)/Cl(-) exchanger activity could be detected in oocytes and embryos using the chloride removal method, however the ability of this transporter to regulate intracellular pH against an alkaline load was poor and intracellular pH could not be re-established. The inability of the HCO(3)(-)/Cl(-) exchanger to adequately regulate intracellular pH was further highlighted by the arrest of embryos at the 8-16 cell stage when challenged with a small alkaline load. Therefore, bovine embryos are extremely sensitive to alterations in intracellular pH above the resting value of around 7.2. This sensitivity could account in part for impaired development and viability of bovine embryos produced in vitro.

Phosphate induced developmental arrest of hamster two-cell embryos is associated with disrupted ionic homeostasis

Culture of hamster embryos with 0.35 mM inorganic phosphate results in developmental arrest at the 2-cell stage. These arrested 2-cell embryos were found to have significantly elevated levels of both intracellular pH and intracellular free calcium. Culture of 2-cell embryos with both glucose and phosphate did not further alter intracellular ionic homeostasis. Developmental arrest of 2-cell embryos was dependent on the concentration of phosphate used. Culture with 1.25 microM phosphate did not alter development, while concentrations of 2.5 microM and 5.0 microM resulted in a percentage of embryos arresting development at the 2-cell stage. Analysis of intracellular levels of pH and calcium after culture with different phosphate concentrations revealed a significant negative correlation between intracellular calcium levels and development beyond the 2-cell stage. There was no correlation between the increase in intracellular pH and embryo development in the presence of phosphate. The increase in intracellular calcium levels after culture with phosphate appears to be derived from intracellular pools, as preventing the influx of extracellular calcium did not alter development beyond the 2-cell stage. Therefore, it is apparent that a disruption in ionic homeostasis is associated with developmental arrest of hamster embryos cultured with phosphate.

Blastocyst culture and transfer: analysis of results and parameters affecting outcome in two in vitro fertilization programs

OBJECTIVE

To determine whether previously described advanced blastocyst development and high implantation rates are confirmed in an expanded multicenter trial.

DESIGN

Retrospective review.

SETTING

Two private assisted reproductive technology units.

PATIENT(S)

One hundred seventy-four patients who underwent blastocyst culture and transfer.

INTERVENTION(S)

Culture of all pronucleate embryos in sequential media to the blastocyst stage (day 5) followed by ET.

MAIN OUTCOME MEASURE(S)

The number and percentage of blastocysts developed, implantation rates, pregnancy rates, and parameters that affected outcome were analyzed.

RESULT(S)

Only 3 of 174 patients failed to achieve blastocyst-stage ET. The mean blastocyst development rate was 48%. The ongoing pregnancy rate was 66.3% per oocyte retrieval, with a mean (+/-SE) of 2.2 +/- 0.05 blastocysts transferred and an implantation rate of 48% per blastocyst transferred.

CONCLUSION(S)

Blastocyst culture and transfer is an effective means of treating patients who respond well to gonadotropins. High pregnancy rates can be accomplished with low numbers of embryos transferred. Patients who failed to achieve ET were rare.

Fetal development after transfer is increased by replacing protein with the glycosaminoglycan hyaluronan for mouse embryo culture and transfer

The effect of macromolecules on mouse embryo development and viability after culture in sequential media was investigated. It was found that high rates of viable blastocysts could be obtained in the absence of any macromolecule. Blastocyst cell numbers were increased when bovine serum albumin was present in the culture medium, although this benefit was not manifest after blastocyst transfer. Rather, the highest rates of implantation and fetal development after blastocyst transfer were observed when hyaluronan was the macromolecule in the culture media. Subsequent analysis revealed that the beneficial effects of hyaluronan were due to its presence in the transfer medium. As the highest cell numbers and hatching rates obtained in this study occurred when both serum albumin and hyaluronan were present in the same medium, it is proposed that embryo culture media should contain both serum albumin and hyaluronan, while the transfer medium need only contain hyaluronan.

Bicarbonate/chloride exchange regulates intracellular pH of embryos but not oocytes of the hamster

The ability to regulate intracellular pH (pH(i)) is essential for normal cell development and differentiation. This study was an investigation of the regulatory system used by the hamster oocyte and preimplantation embryo to regulate pH(i) in the alkaline range. Recovery from alkalosis by late 1-cell and 2-cell embryos was rapid, and physiological pH(i) levels could be restored within 10 min. Recovery from an induced alkaline load was dependent on the chloride concentration in the external medium and sensitive to a stilbene derivative 4,4'-diisothiocyanatostilbene-2,2'-di-sulfonic acid that inhibits bicarbonate and chloride exchange. Therefore the recovery from alkalosis by hamster embryos appears to be via activity of the HCO(3)(-)/Cl(-) exchanger that was activated above a pH(i) set point of 7.24. In contrast, hamster oocytes and early 1-cell embryos (collected 3-4 h post-egg activation) could not recover from an intracellular alkalosis, and pH(i) remained elevated. Therefore, the hamster oocyte and the early 1-cell embryo still undergoing pronuclear formation lack an active HCO(3)(-)/Cl(-) exchanger for the restoration of pH(i). Inability to restore pH(i) from an alkali challenge resulted in a reduced ability of embryos to develop to the morula/blastocyst stages in culture, indicating that HCO(3)(-)/Cl(-) exchange is involved in physiological regulation of pH(i).

Developmental competence and metabolism of bovine embryos cultured in semi-defined and defined culture media

Development of in vitro-produced bovine embryos was studied in 3 two-step culture media: synthetic oviduct fluid (SOF), Gardner's G1/G2, and control (hamster embryo culture medium with 11 amino acids [HECM-6] followed by tissue culture medium 199 + 10% bovine calf serum). Modifications were made to reduce or eliminate protein. Glycolysis and Krebs cycle activity of morulae and blastocysts developed from selected immature oocytes were measured. There were no differences in development to the morula and blastocyst stages between SOF, G1/G2, or control (41%, 36%, and 46%, respectively), although more blastocysts developed in control medium than in G1/G2 (46%, 30%, respectively). Reducing or removing BSA during the initial culture period did not significantly reduce development to blastocyst (31%, 33%, respectively), although development was reduced in SOF with BSA removed from the final culture period (19%). There were no differences in development to the blastocyst stage between SOF, SOF with BSA removed during the initial culture period, and control (44%, 32%, 49%, respectively), but development was reduced in chemically defined protein-free medium throughout the culture period (21%). Krebs cycle activity did not differ between treatments; however, glycolysis was highest in the control embryos and lowest in embryos cultured in protein-free medium. Embryos that developed in the presence of serum appeared dark and granular and had elevated glycolytic rates compared to embryos developed in completely defined medium. This study shows that both metabolism and blastocyst development of embryos are altered by different culture media, implying a functional linkage between these two indicators of successful embryogenesis.

Na+/H+ antiporter activity in hamster embryos is activated during fertilization

This study characterized the activation of the regulatory activity of the Na+/H+ antiporter during fertilization of hamster embryos. Hamster oocytes appeared to lack any mechanism for the regulation of intracellular pH in the acid range. Similarly, no Na+/H+ antiporter activity could be detected in embryos that were collected from the reproductive tract between 1 and 5 h post-egg activation (PEA). Activity of the Na+/H+ antiporter was first detected in embryos collected at 5.5 h PEA and gradually increased to reach maximal activity in embryos collected at 7 h PEA. Parthenogenetically activated one-cell and two-cell embryos demonstrate Na+/H+ antiporter activity, indicating that antiporter activity is maternally derived and initiated by activation of the egg. The inability of cycloheximide, colchicine, or cytochalasin D to affect initiation of antiporter activity indicates that antiporter appearance is not dependent on the synthesis of new protein or recruitment of existing protein to the cell membrane. In contrast, incubation of one-cell embryos with sphingosine did inhibit the appearance of Na+/H+ antiporter activity, showing that inhibition of normal protein kinase C activity is detrimental to antiporter function. Furthermore, incubation of oocytes with a phorbol ester which stimulates protein kinase C activity induced Na+/H+ antiporter activity in oocytes in which the activity was previously absent. Incubation with an intracellular calcium chelator also reduced the appearance of antiporter activity. Taken together, these data indicate that the appearance of Na+/H+ antiporter activity following egg activation may be due, at least in part, to regulation by protein kinase C and intracellular calcium levels.

Distribution of pre-pro-glucagon and glucagon-like peptide-1 receptor messenger RNAs in the rat central nervous system

Glucagon-like peptide-1 (GLP-1) is derived from the peptide precursor pre-pro-glucagon (PPG) by enzymatic cleavage and acts via its receptor, glucagon-like peptide-1 receptor (GLP-1R). By using riboprobes complementary to PPG and GLP-1R, we described the distribution of PPG and GLP-1R messenger RNAs (mRNAs) in the central nervous system of the rat. PPG mRNA-expressing perikarya were restricted to the nucleus of the solitary tact or to the dorsal and ventral medulla and olfactory bulb. GLP-1R mRNA was detected in numerous brain regions, including the mitral cell layer of the olfactory bulb; temporal cortex; caudal hippocampus; lateral septum; amygdala; nucleus accumbens; ventral pallium; nucleus basalis Meynert; bed nucleus of the stria terminalis; preoptic area; paraventricular, supraoptic, arcuate, and dorsomedial nuclei of the hypothalamus; lateral habenula; zona incerta; substantia innominata; posterior thalamic nuclei; ventral tegmental area; dorsal tegmental, posterodorsal tegmental, and interpeduncular nuclei; substantia nigra, central gray; raphe nuclei; parabrachial nuclei; locus ceruleus, nucleus of the solitary tract; area postrema; dorsal nucleus of the vagus; lateral reticular nucleus; and spinal cord. These studies, in addition to describing the sites of GLP-1 and GLP-1R synthesis, suggest that the efferent connections from the nucleus of the solitary tract are more widespread than previously reported. Although the current role of GLP-1 in regulating neuronal physiology is not known, these studies provide detailed information about the sites of GLP-1 synthesis and potential sites of action, an important first step in evaluating the function of GLP-1 in the brain. The widespread distribution of GLP-1R mRNA-containing cells strongly suggests that GLP-1 not only functions as a satiety factor but also acts as a neurotransmitter or neuromodulator in anatomically and functionally distinct areas of the central nervous system.

Heparin and high-density lipoprotein mediate bovine sperm capacitation by different mechanisms

Capacitation is an important process in bovine sperm maturation and is an obligatory step prior to fertilization. Two capacitating agents, namely heparin and high-density lipoprotein (HDL), have been shown to induce sperm capacitation. A family of major proteins of bovine seminal plasma designated BSP-A1/A2, BSP-A3, and BSP-30 kDa (collectively called BSP proteins) bind to the sperm surface upon ejaculation via their membrane choline phospholipids. Our previous studies with bovine epididymal sperm showed that BSP proteins potentiate sperm capacitation induced by heparin and HDL. This study was undertaken to clarify the mechanism of capacitation induced by heparin and HDL in the presence of BSP proteins. Washed bovine ejaculated sperm were incubated with heparin (12 microg/ml) or HDL (10-160 microg/ml) in the presence of polyclonal antibodies against purified BSP proteins (anti-BSP proteins). The percentage of capacitated sperm was evaluated after the induction of the acrosome reaction (AR) with lysophosphatidylcholine. When sperm were incubated for 5 h with heparin and anti-BSP proteins (40 microg/ml), the AR level was not significantly different from control levels (16. 8 +/- 0.9% vs. 12.9 +/- 0.9%). In contrast, incubation of sperm for 8 h with HDL and anti-BSP proteins did not inhibit the AR (42.4 +/- 1.1% vs. 17.1 +/- 1.6 for the control samples). We also investigated the effect of heparin and HDL on protein tyrosine phosphorylation associated with capacitation. The tyrosine phosphorylation of a group of proteins was increased in the presence of heparin. However, HDL did not significantly stimulate protein phosphorylation. The increase in phosphorylation was correlated with an increase in the AR after the incubation with heparin but not with HDL. These results indicate that heparin and HDL mediate capacitation via different mechanisms.

Regulation of intracellular pH in hamster preimplantation embryos by the sodium hydrogen (Na+/H+) antiporter

This study was an investigation of the mechanisms for the regulation of intracellular pH (pHi) by hamster preimplantation embryos. The resting pH values of hamster embryos were similar at the 1-cell (7. 19 +/- 0.34), 2-cell (7.21 +/- 0.21), and 8-cell (7.22 +/- 0.41) stages. Cleavage-stage hamster embryos alleviated intracellular acidosis by activity of the Na+/H+ antiporter. The rate of recovery from acidosis was similar for embryos at 1-cell, 2-cell, and 8-cell stages. When Na+/H+ antiporter activity was inhibited by either incubation in Na+-free medium or the presence of an inhibitor, pHi was unable to recover to initial levels. Instead, pHi remained acidic. The Na+/H+ antiporter was also found to contribute to baseline pH regulation, as incubation in Na+-free medium resulted in an immediate intracellular acidification. The set point for Na+/H+ antiporter was pH 7.14. There was no evidence at any developmental stage for activity of either Na+-dependent HCO3-/Cl- exchanger or H+-ATPase in the regulation of pHi. Inhibition of the Na+/H+ antiporter by an amiloride derivative significantly reduced the ability of 2-cell embryos to develop in culture when challenged with acidosis, indicating that the Na+/H+ antiporter is an essential regulator of pHi.

Evaluating motor function in children with Down syndrome: validity of the GMFM

The Gross Motor Function Measure (GMFM) was developed and validated originally by Russell and colleagues as an evaluative assessment of gross motor function in children with cerebral palsy (CP). The present study reports the results of reliability and validity testing of the GMFM for use with children with Down syndrome (DS). One hundred and twenty-three children with DS were assessed twice over a 6-month period, using the GMFM and the motor scale of the Bayley Scales of Infant Development - second edition (BSID-II). In addition to the usual method of scoring the GMFM using only observed motor behaviours (standard score), parent reports of children's activities not seen by the assessor on the day of testing were also obtained and a second score (reported score) was calculated for each GMFM assessment. Test-retest and interrater reliabilities were excellent (all >0.90). Observed correlations between change on GMFM and judgements of change made independently by parents, intervenors, and masked video raters were lower than hypothesized. However, the pattern of change scores in predefined age and severity subgroups supported the contention that the GMFM was able to detect differential amounts of change as predicted. The GMFM was shown to be relatively more responsive to change in gross motor function than the motor scale of the BSID-II. The 'reported' scores on the GMFM demonstrated better evidence of reliability, validity, and responsiveness than the standard scoring method and this approach is recommended for use when assessing children with DS.

Calcium homeostasis in early hamster preimplantation embryos

The development in culture of 1-cell hamster embryos prior to the completion of fertilization is not well understood. In this study it was observed that culture for only 6 h of these early 1-cell embryos collected before pronuclei formation (3 h post-egg activation; PEA) significantly increased intracellular free calcium levels (194.3 +/- 3.1 nM) compared to levels in similarly aged 1-cell embryos collected from the oviduct at 9 h PEA, after pronuclei formation is complete (134.2 +/- 6.8 nM). Not only was the developmental competence of cultured 3-h PEA embryos with elevated intracellular free calcium levels compromised as compared with that of embryos collected from the oviduct at 9 h PEA; these embryos also had impaired cytoplasmic mitochondrial distribution (ratio of 0.62 +/- 0. 06 for cultured embryos compared to 0.44 +/- 0.04 for in vivo-developed embryos) and decreased lactate metabolism (2.93 +/- 0. 22 pmol/embryo per 3 h for cultured embryos compared to 5.37 +/- 0. 36 for in vivo-developed embryos). This impairment in mitochondrial distribution and function and reduced development in culture by 3-h PEA embryos appears related to the ability to regulate intracellular calcium homeostasis. Intracellular free calcium levels were reduced by culture with increased medium magnesium concentrations, calcium channel inhibitors nifedipine or verapamil, or an intracellular calcium chelator. All of these treatments also stimulated development of 3-h PEA embryos to the morula/blastocyst stages and prevented impairment in mitochondrial organization and function. Conversely, culture with low medium magnesium and high calcium concentrations that increased intracellular free calcium levels resulted in low development and reduced mitochondrial function. Therefore, it appears that removal of the early embryo from the oviduct results in an inability to regulate intracellular calcium levels. As increased magnesium concentrations, nifedipine, and verapamil inhibit L-gated calcium channels, it may be a loss of regulation of these channels that alters calcium homeostasis resulting in impaired developmental competence.

Intracellular divalent cation homeostasis and developmental competence in the hamster preimplantation embryo

The intracellular magnesium and calcium ion concentrations of in vivo-developed 2-cell hamster embryos were measured using ratiometric fluorometry. Intracellular magnesium and calcium ion concentrations were found to be 0.369 +/- 0.011 mM and 129.3 +/- 7.5 nM respectively. Culture of 1-cell hamster embryos for 24 hr to the 2-cell stage in control medium containing 0.5 mM magnesium and 2.0 mM calcium resulted in approximately a threefold increase to 343.5 +/- 8.0 nM in intracellular calcium ion concentration, while magnesium ion levels were not altered (0.355 +/- 0.007 mM). Increasing medium magnesium concentrations to 2.0 mM significantly increased intracellular magnesium ion concentrations of cultured 2-cell embryos with a concomitant reduction in intracellular calcium ion concentrations. Furthermore, increasing the medium magnesium concentration to 2.0 mM significantly increased development of 1-cell embryos collected at either 3 or 9 hr post-egg activation to the morula/blastocyst and blastocyst stages. Resultant blastocysts had an increased total cell number and increased development of the inner cell mass. Most important, however, culture with 2.0 mM magnesium increased the fetal potential of cultured 1-cells twofold. Therefore, because highest rates of development were observed in a medium that resulted in reduced intracellular calcium ion concentrations, it appears that altered calcium homeostasis is associated with impaired developmental competence of 1-cell embryos in culture.