Effects of cooling and warming rate to and from -70 degrees C, and effect of further cooling from -70 to -196 degrees C on the motility of mouse spermatozoa

We have previously reported high survival in mouse sperm frozen at 21 degrees C/min to -70 degrees C in a solution containing 18% raffinose in 0.25 x PBS (400 mOsm) and then warmed rapidly at approximately 2000 degrees C/min, especially under lowered oxygen tensions induced by Oxyrase, a bacterial membrane preparation. The best survival rates were obtained in the absence of glycerol. The first concern of the present study was to determine the effects of the cooling rate on the survival of sperm suspended in this medium. The sperm were cooled to -70 degrees C at rates ranging from 0.3 to 530 degrees C/min. The survival curve was an inverted "U" shape, with the highest motility occurring between 27 and 130 degrees C/min. Survival decreased precipitously at higher cooling rates. Decreasing the warming rate, however, decreased survivals at all cooling rates. The motility depression with slow warming was especially evident in sperm cooled at the optimal rates. This fact is consistent with our current view that the frozen medium surrounding sperm cells is in a metastable state, perhaps partly vitrified as a result of the high concentrations of sugar. The decimation of sperm cooled more rapidly than optimum (>130 degrees C/min), even with rapid warming, is consistent with the induction of considerable quantities of intracellular ice at these rates. When glycerol was added to the above medium, motilities were also dependent on the cooling rate, but they tended to be substantially lower than those obtained in the absence of glycerol. The minimum temperature in the above experiments was -70 degrees C. When sperm were frozen to -70 degrees C at optimum rates, lowering the temperature to -196 degrees C had no adverse effect.     

Viability and Morphology of rat heart cells after freezing and thawing of the whole heart

Intact adult rat hearts were cooled in the presence of 10% DMSO according to an external cooling program which approximated the optimal external three-step cooling program for the isolated adult heart cells: 20 min at ?20 °C, 0.2 °C/min from ?20 to ?25, ?30, or ?50 °C, and rapid cooling to ?196 °C. Following rapid thawing, cells were isolated after perfusion with a 0.1% collagenase solution. Only cells which originated from the free wall of the right ventricle could be isolated, even after cooling to ?20 °C. Most cells from hearts cooled to ?196 °C did not survive. When the third cooling step was omitted and the end temperature of the second cooling step was ?30 °C, 38% of the cells excluded trypan blue, 29% were morphologically intact, and 30% showed spontaneous contractions after thawing, expressed as percentages of the control, A much lower survival was found after cooling to ?50 °C.Histological and electron microscopical study of the heart immediately after thawing revealed no differences between hearts cooled to ?20, ?30, or ?196 °C. Also no marked differences were observed between the morphological integrity after freezing and thawing of the atrium, the left and right ventricle walls, and the ventricular septum. The survival data suggest the presence of nonmorphologically detectable alterations in cells frozen to ?196 °C, compared to cells frozen to ?30 °C. The morphological investigations indicate no essential differences in resistance of atrial and ventricular cells to the freezing process.Experiments involving neonatal rat hearts cooled to ?196 °C, according to the method which gave optimal preservation of the isolated cells, revealed that after thawing cells are present from which growing and contracting cultures can be derived. It appears that cells in the neonatal rat heart are more resistant to freezing to ?196 °C than cells in the adult rat heart.     

Effects of cooling on meiotic spindle structure and chromosome alignment within in vitro matured porcine oocytes

Meiotic spindle structure and chromosome alignment were examined after porcine oocytes were cooled at metaphase II (M II) stage. Cumulus-oocyte complexes (COCs) collected from medium size follicles were cultured in an oocyte maturation medium at 39 degrees C, 5% CO(2) in air for 44 hr. At the end of culture, oocytes were removed from cumulus cells and cooled to 24 or 4 degrees C for 5, 30, or 120 min in a solution with or without 1.5 M dimethyl sulfoxide (DMSO). After being cooled, oocytes were either fixed immediately for examination of the meiotic spindle and chromosome alignment or returned to maturation medium at 39 degrees C for 2 hr for examination of spindle recovery. Most oocytes (65-71%) cooled to 24 degrees C showed partially depolymerized spindles but 81-92% of oocytes cooled at 4 degrees C did not have a spindle after cooling for 120 min. Quicker disassembly of spindles in the oocytes was observed at 4 degrees C than at 24 degrees C. Cooling also induced chromosome abnormality, which was indicated by dispersed chromosomes in the cytoplasm. Limited spindle recovery was observed in the oocytes cooled to both 4 and 24 degrees C regardless of cooling time. The effect of cooling on the spindle organization and chromosome alignment was not influenced by the presence of DMSO. These results indicate that the meiotic spindles in porcine M II oocytes are very sensitive to a drop in the temperature. Both spindle and chromosomes were damaged during cooling, and such damage was not reversible by incubating the oocytes after they had been cooled.     

Nucleation and growth of ice crystals inside cultured hepatocytes during freezing in the presence of dimethyl sulfoxide.

A three-part, coupled model of cell dehydration, nucleation, and crystal growth was used to study intracellular ice formation (IIF) in cultured hepatocytes frozen in the presence of dimethyl sulfoxide (DMSO). Heterogeneous nucleation temperatures were predicted as a function of DMSO concentration and were in good agreement with experimental data. Simulated freezing protocols correctly predicted and explained experimentally observed effects of cooling rate, warming rate, and storage temperature on hepatocyte function. For cells cooled to -40 degrees C, no IIF occurred for cooling rates less than 10 degrees C/min. IIF did occur at faster cooling rates, and the predicted volume of intracellular ice increased with increasing cooling rate. Cells cooled at 5 degrees C/min to -80 degrees C were shown to undergo nucleation at -46.8 degrees C, with the consequence that storage temperatures above this value resulted in high viability independent of warming rate, whereas colder storage temperatures resulted in cell injury for slow warming rates. Cell damage correlated positively with predicted intracellular ice volume, and an upper limit for the critical ice content was estimated to be 3.7% of the isotonic water content. The power of the model was limited by difficulties in estimating the cytosol viscosity and membrane permeability as functions of DMSO concentration at low temperatures.     

Studies on cryopreservation of Cryptosporidium parvum

Neonatal BALB/c mice received oocysts or sporozoites of Cryptosporidium parvum pretreated by a variety of cryopreservation protocols. Histologic sections of infected and control mice were examined to determine if pretreated organisms established infection in the intestine. Sporozoites were inoculated rectally, oocysts orally. Freshly excysted sporozoites were frozen in Hanks' balanced salt solution (HBSS) containing dimethylsulfoxide (DMSO) or glycerol at concentrations of 5%, 10%, or 15% at cooling rates of -1 C and -10 C per min. Other sporozoites were frozen to -70 C in the absence of cryoprotectant without controlled reduction of temperature, others placed in HBSS with 10% DMSO but not subjected to freezing, whereas others were placed in vitrification media containing 5.5 M propylene glycol, 6.5 M glycerol, or 8 M ethylene glycol for 1 min before resuspension in fresh HBSS and inoculation into mice. Intact oocysts were frozen without controlled reduction of temperature directly to -70 C in HBSS containing no cryoprotectant or in HBSS that contained 10% DMSO. Others were cooled at -0.3 C per min from 4 C to -70 C in HBSS with 5% or 10% DMSO. Still others were cooled at a rate of -1 C per min until reaching -40 C and then cooled at -10 C per min until reaching -70 C in HBSS with 7.5% DMSO. Oocysts and sporozoites not exposed to cryoprotectants were inoculated into mice orally and rectally, respectively, for control purposes. Only unfrozen oocysts and sporozoites not exposed to cryoprotectant, and some of the unfrozen oocysts and sporozoites exposed to 10% DMSO, successfully established infections in mice.     

Survival of frozen mouse embryos after rapid thawing from -196 degrees C.

The effect of the rate of rewarming on the survival of 8-cell mouse embryos and blastocysts was examined. The samples were slowly cooled (0.3--0.6 degrees C/min) in 1.5 M-DMSO to temperatures between -10 and -80 degrees C before direct transfer to liquid nitrogen (-196 degrees C). Embryos survived rapid thawing (275--500 degrees C/min) only when slow cooling was terminated at relatively high subzero temperatures (-10 to -50 degrees C). The highest levels of survival in vitro of rapidly thawed 8-cell embryos were obtained after transfer to -196 degrees C from -35 and -40 degrees C (72 to 88%) and of rapidly thawed blastocysts after transfer from -25 to -50 degrees C (69 to 74%). By contrast, for embryos to survive slow thawing (8 to 20 degrees C/min) slow cooling to lower subzero temperatures (-60 degrees C and below) was required before transfer to -196 degrees C. The results indicate that embryos transferred to -196 degrees C from high subzero temperatures contain sufficient intracellular ice to damage them during slow warming but to permit survival after rapid warming. Survival of embryos after rapid dilution of DMSO at room temperature was similar to that after slow (stepwise) dilution at 0 degrees C. There was no difference between the viability of rapidly and slowly thawed embryos after transfer to pseudopregnant foster mothers. It is concluded that the behaviour of mammalian embryos subjected to the stresses of freezing and thawing is similar to that of other mammalian cells. A simpler and quicker method for the preservation of mouse embryos is described.     

Interaction of rate of latent heat removal during freezing and rates of subsequent cooling and warming on survival of the blood protozoan, Babesia rodhaini

Babesia rodhaini parasites in murine blood containing 1.5 m DMSO were frozen at two rates, as judged by the duration of the “freezing plateau”, then cooled to ?196 °C and rewarmed at two rates to detect interactions between the duration of the plateau and rates of subsequent cooling and rewarming. Infectivity tests showed that fast and slow freezing (plateau times of about 1 sec and 30 sec, respectively) had similar effects on parasite survival when cooling was at 130 °C/min and warming was at 800 °C/min. However, when either the cooling rate was increased to 3500 °C/min or the warming rate was decreased to 2.3 °C/min, fast freezing decreased parasite survival more than did slow freezing. It is suggested that fast freezing accentuated the damaging effects of fast cooling and slow warming by increasing intracellular ice formation.     

Optimal conditions for the preservation of mouse lymph node cells in liquid nitrogen using cooling rate techniques

The factors that affect the survival of mouse lymphocytes throughout a procedure for storage at ?196 °C have been studied both for the improvement of recovery and the possible extension to the mouse system of cell selection by freezing. After thawing, the survival of cells cooled at different rates in dimethyl sulphoxide (DMSO, 5 or 10%, $\text{v}\text{v}$) was assessed from the [³H]thymidine incorporation in response to phytohaemagglutinin and concanavalin A. Before freezing the protection against freezing damage increased with time (up to 20 min) in DMSO (5%, $\text{v}\text{v}$) at 0 °C. Superimposed upon this effect was toxicity due to the DMSO. During freezing and thawing the cooling rate giving optimal survival was 8 to 15 °C/min for cells in DMSO (5%) and 1 to 3 °C/min for DMSO (10%). Omission of foetal calf serum was detrimental. Rapid thawing (>2.5 °C/min) was superior to slow thawing. After thawing dilution at 25 or 37 °C greatly improved cell survival compared with 0 °C; at 25 °C survival was optimal (75%) at a moderate dilution rate of 2.5 min for a 10-fold dilution in FCS (10%, $\text{v}\text{v}$) followed by gentle centrifugation (50g).Dilution damage during both thawing and post-thaw dilution may be due to osmotic swelling as DMSO and normally excluded solutes leave the cell. The susceptibility of the cell membrane to dilution damage may also be increased during freezing. The need to thaw rapidly and dilute at 25 °C after thawing is probably due to a decrease in dilution stress at higher temperatures. Optimisation of dilution procedures both maximised recovery and also widened the range of cooling rates over which the cells were recovered. These conditions increase the possibility of obtaining good recovery of a mixed cell population using a single cooling procedure. Alternatively, if cell types have different optimal cooling rates, stressful dilution may allow their selection from mixed cell populations.     

Optimizing conditions for cryopreservation of an insect cell line

A cell line (UM-BGE-2) derived from embryos of the cockroach Blattella germanica was frozen to ?196 °C under a variety of conditions and cell viability was assayed after warming. It was found that cell viability was affected by the cooling rate, the warming rate, the controlled cooling endpoint temperature, and the type and concentration of cryoprotectant. The best survival for cells suspended in Grace's tissue culture medium containing 1 M Me₂SO was obtained when cells were cooled at 1 °C/ min to at least ?90 °C before being placed in liquid nitrogen and warmed at more than 900 °C/min. Cultures initiated from these frozen cells produce typical growth curves and appear normal after several passages.     

Maturation of porcine oocytes after cooling at the germinal vesicle stage

Maturation of porcine oocytes was examined after oocytes were cooled at the germinal vesicle stage. Cumulus-oocyte complexes (COCs) collected from medium-sized follicles were cooled at 24 degrees C or 4 degrees C for 5, 30 or 120 min in a solution with or without 1.5 M dimethylsulfoxide (DMSO). After rewarming, COCs were cultured in maturation medium at 39 degrees C, 5% CO2 in air for 44 h. Meiotic spindle organisation (by immunostaining and confocal microscopy), nuclear maturation (by orcein staining) and cytoplasmic maturation (by intracellular glutathione assay) of oocytes were examined after maturation. When COCs were cooled at 24 degrees C for various times in the medium without DMSO, a tendency to decreased spindle formation, nuclear maturation and cytoplasmic maturation was observed, but there was no statistical difference compared with controls. Addition of DMSO during cooling inhibited subsequent nuclear maturation and spindle formation. When COCs were cooled at 4 degrees C, both nuclear and cytoplasmic maturation as well as spindle formation were inhibited in most oocytes in a time-dependent manner. DMSO during cooling did not have any beneficial effect on subsequent oocyte maturation and spindle formation. These results suggest that porcine oocytes are very sensitive to a drop in the temperature before exposure to culture. Cooling oocytes before maturation inhibits their subsequent spindle organisation, nuclear and cytoplasmic maturation. Addition of DMSO to the cooling solution did not protect porcine oocytes from cooling-induced damage.     

Cryoinjury in endothelial cell monolayers

Developing successful cryopreservation strategies for corneas have proven to be more difficult than anticipated, because of the resulting loss of viability and detachment of endothelial cells from Descemet's membrane following cryopreservation of corneas. The objectives of this study are to develop a more detailed understanding of cryoinjury in human corneal endothelial cell (HCEC) monolayers and to examine the effects of storage temperature, cryoprotectant type and concentration, and cooling/warming rates on HCEC monolayers. Monolayers of endothelial cells attached to collagen-coated glass, immersed in an experimental solution (with and without cryoprotectant) were cooled at 1 degrees C/min to various temperatures (-5 to -40 degrees C), then thawed directly or cooled rapidly to -196 or to -80 degrees C before thawing. Cryoprotectants used were dimethyl sulfoxide and propylene glycol in concentrations of 1 and 2M. Monolayers were assessed for membrane integrity and detachment using SYTO/ethidium bromide fluorescent stain. The presence of cryoprotectants resulted in high recovery of membrane integrity and low monolayer detachment in monolayers thawed directly from temperatures down to -40 degrees C. In contrast, there was excessive detachment and loss of membrane integrity in monolayers cooled to -196 degrees C compared to monolayers cooled to -80 degrees C. Also, increasing cryoprotectant concentrations did not improve recovery of the monolayers. The higher recovery and lower detachment after storage at -80 degrees C compared to storage at -196 degrees C suggest that storage temperatures for corneas should be re-evaluated.     

Three-step cooling: A preservation method for adult rat heart cells

Adult rat heart cells were exposed to two-step cooling to ?196 °C with different holding periods at different subzero temperatures between both steps. The highest survival based on the percentage of trypan blue-excluding cells was 25% with 10% DMSO and a holding period of 6 min, and 21% with 15% DMSO and a holding period of 30 min. The highest survival based on morphological intactness was about 10%; there was no difference in results after cooling with 10 and 15% DMSO, and after holding between 2 and 30 min. The optimal survival based on the percentage of contracting cells was 52%, with 15% DMSO and a holding period of 2 min.When the holding period was replaced by a programmed cooling stage, the results could be improved. With this threestep cooling method, the optimal values, based on the number of trypan blue-excluding, intact, and contracting cells, were 40, 32, and 60%, respectively. It appeared that in the presence of 10% DMSO, which provided better survival than 5 and 15%, no significantly different results were obtained when the starting temperatures of the second cooling step varied between ?10 and ?20 °C, when the end temperatures varied between ?30 and ?60 °C, or when the cooling rates of the second cooling step varied between 0.1 and 1 °C/min. Three-step cooling provided similar results as linear cooling from 0 to ?100 °C, followed by rapid cooling to ?196 °C.     

Bioassay to measure effects of cooling and warming rates and protection by dimethyl sulphoxide on survival of frozen Babesia rodhaini

The percentages of Babesia rodhaini parasites that survived different rates of cooling to −79 °C were determined by titrating infectivity in CBA mice before freezing and after thawing. The cryoprotective effect of DMSO and the effect of warming rate were also assessed.When parasitized blood containing 1.5 DMSO was cooled at nominal rates of 2.5 °, 265 °, and 2785 °C/min and warmed at 4320 °C/min, the respective survival rates were 0.075, 4.9, and 0.1%, indicating the existence of an optimal cooling rate. Blood without DMSO cooled and warmed under the same conditions was over 1000 times less infective. When parasitized blood containing DMSO was cooled at 2785 °C/min and warmed at 4320 °, 24.5 °, and 1.84 °C/ min, infectivity decreased progressively with the warming rate. The degrees of haemolysis in frozen and thawed blood indicated that cooling rate was more important than an intact host cell to survival of the parasite.The growth rate of B. rodhaini in CBA mice, estimated to be one binary fission in 8.5 hr, was not affected by the addition of DMSO followed by freezing and thawing.     

Cryoprotection of murine lymphocyte subpopulations using a microprocessor-controlled cooling system

Single-cell suspensions of splenic lymphocytes from 5- to 6-month-old C57BL/6 mice were cryopreserved using cooling rates ranging from ?0.25 to ?10.0 °C/min with the microprocessor-controlled cooling system developed in our laboratory. The cells (30 × 10⁶ cells/ml) were suspended in RPMI 1640 containing 10% FCS and 10% DMSO, and a total volume of 1.75 ml was frozen. Fluorescein-diacetate staining identified viable cells in unfrozen controls and frozen-thawed suspensions. Functional capacity was assessed in vitro by the incorporation of [³H]thymidine by dividing cells activated with graded concentrations of the T-lymphocyte mitogens, PHA-P and Con A, and the B-lymphocyte mitogen, LPS. High percentages of viable cells were recovered after cooling at rates ranging from ?0.5 to ?5.0 °C/min, as compared with those of unfrozen control suspensions. Incorporation of [³H]thymidine by T and B cells reached similar levels after cooling at rates ranging from ?0.25 to ?5.0 °C/min, and the percentage incorporation of [³H]thymidine as compared with that of unfrozen cells was 80–100%, except for T lymphocytes activated with PHA-P after cooling at ?5.0 °C/min. The relative response of cell suspensions to T- and B-cell mitogens, the relative mitogenic index, was unchanged from that of unfrozen controls in suspensions cooled at all rates including two (?0.25 and ?10.0 °C/min), which permitted recovery of only 55% of unfrozen cells. The importance of the constant cooling rates and rapid compensation for heat released at the phase change using the microprocessor-controlled system and of precise determinations of cellular viability and function are discussed and related to the apparent protection conferred on subpopulations of murine lymphocytes using cooling rates ranging from ? 0.25 to ?10.0 °C/min.     

Survival of 16-celled and morula stage rabbit embryos frozen to -196 degrees C,.

Preimplantation stage (16-celled and morula) rabbit embryos were successfully frozen to -196 degrees C. The cooling rate (from a room temperature to 0 degrees C), the presence of the mucin layer surrounding embryos, the ice-seeding treatment and the thawing procedure were examined to determine their effects on the survival of the frozen embryos of Japanese white, New Zealand white and Dutch-Belted rabbits. A high proportion (51%; 16-celled, 69%; morula) of Dutch-Belted rabbit embryos developed in vitro, when they were frozen to -196 degrees C, applying the ice-seeding at -4 degrees C in the presence of 12.5% DMSO, after being cooled to 0 degrees C at the rate of 7-9 degrees C/min, and were diluted by a stepwise addition of 4 different strength PBS on thawing. The highest rate of in vitro development (81%; Japanese white, 75%; New Zealand white, 82%; Dutch Belted embryos) was obtained when the morula stage embryos were frozen to -196 degrees C applying seeding at -4 degrees C after being cooled to 0 degrees C at the rate of 1 degrees C/2.5 min and were diluted, on thawing, by stepwise addition of 6, 3 and 1% DMSO solution and a culture medium. No great difference was found in the survival rate between the embryos covered with the mucin layer and those which had not the coat. All the embryos frozen without applying seeding treatment failed to develop in vitro after being thawed and diluted. Nine out of 27 does each of which received 6 reimplantations of the embryos frozen-thawed became pregnant and were found to be carrying 37 normal fetuses on the 12th day of pregnancy.     

Survival of carnation (Dianthus caryophyllus L.) shoot apices frozen to the temperature of liquid nitrogen

Effects of cooling and rewarming rates on the survival of carnationshoot apices frozen to the temperature of liquid nitrogen wereinvestigated. Ten percent dimethyl sulfoxide (DMSO), alone orin combination with 5% glucose, sucrose or sorbitol was mosteffective as a cryoprotectant for carnation shoot apices. Theshoot apices survived slow freezing at about –70?C inthe presence of 10% DMSO. About 80% of the shoot apices survivedfreezing at the temperature of liquid nitrogen after prefreezingat –50?C or below, regardless of the rewarming rates.Shoot apices in the presence of 10% DMSO were cooled at differentrates then rewarmed rapidly. The survival rate gradually decreasedto zero as the cooling rate increased from about 0.5?C/min to50?C/min. At cooling rates higher than 50?C/min, no survivalwas observed even at 5?10⁴?C/min. However, in apices prefrozenat –15?C or below then cooled ultrarapidly at 10⁴?C/min,all remained alive with subsequent rapid rewarming. These apicesdeveloped normal young plants. This ultrarapid cooling methodcombined with prefreezing seems to be useful for the cryopreservationof shoot apices from various plants. ¹Contribution No. 2207 from the Institute of Low TemperatureScience, Hokkaido University. This work was supported in partby a Grant-in-Aid (No. 434035) for Scientific Research fromthe Ministry of Education, Science and Culture. (Received November 13, 1979; )     

Membrane transport properties of equine and macaque ovarian tissues frozen in mixtures of dimethylsulfoxide and ethylene glycol

The rate at which equine and macaque ovarian tissue sections are first cooled from +25 degrees C to +4 degrees C has a significant effect on the measured water transport when the tissues are subsequently frozen in 0.85 M solutions of glycerol, dimethylsulfoxide (DMSO), or ethylene glycol (EG). To determine whether the response of ovarian tissues is altered if they are suspended in mixtures of cryoprotective agents (CPAs), rather than in solutions of a single CPA, we have now measured the subzero water transport from ovarian tissues that were suspended in mixtures of DMSO and EG. Sections of freshly collected equine and macaque ovaries were suspended either in a mixture of 0.9 M EG plus 0.7 M DMSO (equivalent to a mixture of approximately 5% vv of EG and DMSO) or in a 1.6M solution of only DMSO or only EG. The tissue sections were cooled from +25 degrees C to +4 degrees C and then frozen to subzero temperatures at 5 degrees C/min. As the tissues were being frozen, a shape-independent differential scanning calorimeter technique was used to measure water loss from the tissues and, consequently, the best fit membrane permeability parameters (L(pg) and E(Lp)) of ovarian tissues during freezing. In the mixture of DMSO+EG, the respective values of L(pg) and E(Lp) for equine tissue first cooled at 40 degrees C/min between +25 degrees C and +4 degrees C before being frozen were 0.15 microm/min atm and 7.6 kcal/mole. The corresponding L(pg) and E(Lp) values for equine tissue suspended in 1.6M DMSO were 0.12 microm/min atm and 27.2 kcal/mole; in 1.6M EG, the values were 0.06 microm/min atm and 21.9 kcal/mole, respectively. For macaque ovarian tissues suspended in the mixture of DMSO+EG, the respective values of L(pg) and E(Lp) were 0.26 microm/min atm and 26.2 kcal/mole. Similarly, the corresponding L(Lg) and E(Lp) values for macaque tissue suspended in 1.6M DMSO were 0.22 microm/min atm and 31.4 kcal/mole; in 1.6 M EG, the values were 0.20 microm/min atm and 27.9 kcal/mole. The parameters for both equine and macaque tissue samples suspended in the DMSO+EG mixture and first cooled at 0.5 degrees C/min between +25 degrees C and +4 degrees C were very similar to the corresponding values for samples cooled at 40 degrees C/min. In contrast, the membrane parameters of equine and macaque samples first cooled at 0.5 degrees C/min in single-component solutions were significantly different from the corresponding values for samples cooled at 40 degrees C/min. These results show that the membrane properties of ovarian cells from two species are different, and that the membrane properties are significantly affected both by the solution in which the tissue is suspended and by the rate at which the tissue is cooled from +25 degrees C to +4 degrees C before being frozen. These observations suggest that these variables ought to be considered in the derivation of methods to cryopreserve ovarian tissues.     

Effect of warming rate on mouse embryos frozen and thawed in glycerol

Mouse embryos (8-cell) fully equilibrated in 1.5 M-glycerol were cooled slowly (0.5 degrees C/min) to temperatures between - 7.5 and - 80 degrees C before rapid cooling and storage in liquid nitrogen (-196 degrees C). Some embryos survived rapid warming (approximately 500 degrees C/min) irrespective of the temperature at which slow cooling was terminated. However, the highest levels of survival of rapidly warmed embryos were observed when slow cooling was terminated between -25 and -80 degrees C (74-86%). In contrast, high survival (75-86%) was obtained after slow warming (approximately 2 degrees C/min) only when slow cooling was continued to -55 degrees C or below before transfer into liquid N2. Injury to embryos cooled slowly to -30 degrees C and then rapidly to -196 degrees C occurred only when slow warming (approximately 2 degrees C/min) was continued to -60 degrees C or above. Parallel cryomicroscopical observations indicated that embryos became dehydrated during slow cooling to -30 degrees C and did not freeze intracellularly during subsequent rapid cooling (approximately 250 degrees C/min) to -150 degrees C. During slow warming (2 degrees C/min), however, intracellular ice appeared at a temperature between -70 and -65 degrees C and melted when warming was continued to -30 degrees C. Intracellular freezing was not observed during rapid warming (250 degrees C/min) or during slow warming when slow cooling had been continued to -65 degrees C. These results indicate that glycerol provides superior or equal protection when compared to dimethyl sulphoxide against the deleterious effects of freezing and thawing.     

The effect of cooling rate and of dimethyl sulfoxide concentration on low temperature preservation of neonatal rat heart cells

The effect of five cooling rates, 1, 5, 10, 30, and 50 °C/min, and of four DMSO concentrations, 2.5, 5, 7.5, and 10%, on the survival of neonatal rat heart cells after freezing and thawing were studied. Growth area, contracting area and contraction frequency were used as viability parameters. Growth area and contracting area were measured in a number of fields in statistically adjusted locations of the culture dish on the second and on the fifth day of culturing.Without freezing, DMSO concentrations higher than 5% caused a considerable decrease of the growth area and of the contracting area. After freezing and thawing, biphasic survival curves were found with a narrow optimum at 2.5, 5, and 10% DMSO and a broad optimum at 7.5% DMSO. The survival based on the growth area and the survival based on the contracting area were about the same on the second day of culturing but differed on the fifth day. On the second day of culturing the highest survival was 73%, at a cooling rate of 5 °C/min and with 5% DMSO. On the fifth day of culturing the highest survival based on the growth area was 100%, at a cooling rate of 10 °C/min with 7.5% DMSO; the contracting area was the same as on the second day. The cooling rate of 5 °C/min was optimal at all DMSO concentrations tested. There was no correlation between the contracting area and the spontaneous contraction frequency after freezing and thawing when both were expressed as percentages of the control. The contraction frequency after freezing and thawing was independent of the cooling rate and was maximally 50% of the control value.     

Cooling of embryonic cells,isolated blastoderms,and intact embryos of the zebra fish Brachydanio rerio to −196 °c

Single cells from the developing embryo of the zebra fish survive freezing when protected with 1 M DMSO and cooled to ?196 °C in two steps. Cell survival drops from 85 to 26% when clumps of 5–10 cells are similarly frozen, and to 2% when isolated blastoderms are treated in the same way. This drastic decrease in survival is interpreted as an example of the “scale-up problem,” in which diffusional barriers prevent cryoprotectant equilibration and osmotic dehydration in large cell assemblanges.Isolated blastoderms develop considerably in culture, and retain some of this ability following cooling to ?25 °C after protection with DMSO or glycerol.Intact embryos protected with high concentrations of glycerol (2.8 M) tolerate slow cooling to ?196 °C surprisingly well, with most of the embryonic cells morphologically intact and actively extruding lobopodia. Glycerol could, however, only be removed from cells by disrupting the embryo so that diffusional barriers were removed. DMSO (2.8 M) was ineffective in preserving embryos or cells cooled to ?196 °C.