Pathology of end-stage remodeling in a family of cats with hypertrophic cardiomyopathy.

End-stage hypertrophic cardiomyopathy (ES-HCM), affecting 5-10% of human hypertrophic cardiomyopathy (HCM) patients, is characterized by relative thinning of the ventricular walls and septum with dilation of the ventricular lumen, decreased fractional shortening, and progression to heart failure. C. J. Baty and others recently documented similar progressive changes to ES-HCM in a family of four cats through serial echocardiograms. At the time of heart failure, these cats exhibited changes similar to those exhibited by human ES-HCM patients. Our objectives were to describe the pathologic alterations associated with ES-HCM and investigate the pathogenesis in three of the four cats. Grossly, there was left atrial dilation with relative thinning of the interventricular septum (IVS) and left ventricular free wall (LVFW). The left atrium contained large thrombi in two of the three cats, and all three cats died following thromboembolization of the aortic bifurcation. Histologically, all three cats had subendocardial and myocardial fibrosis, predominantly of the IVS and LVFW, and one cat had acute, multifocal, myocardial infarcts with mononuclear inflammatory cell infiltrates. The pathogenesis of ES-HCM is uncertain, but theories implicate occlusion of the coronary blood flow by thickening of the coronary vessels, coronary vascular thromboembolism or coronary vessel spasm, apoptosis of myocytes, and myocardial hypertrophy beyond the ability of the vasculature to supply blood. Apoptosis assays did not reveal any apoptotic myocytes. Considering the hypercoagulative state of these cats, coronary vascular thromboembolism could be a major contributing factor. We cannot exclude apoptosis or coronary vessel spasm on the basis of the data presented.

Glucose-regulated protein 78 (GRP78) is elevated in embryonic mouse heart and induced following hypoglycemic stress.

This study investigates the distribution and heart levels of glucose regulated protein (GRP) 78 during normal development and in response to hypoglycemia in the mouse. Results demonstrate that GRP78 is strongly expressed with in the heart, neural tube, gut endoderm, somites, and surface ectoderm of mouse embryos during early organogenesis, and GRP78 staining remains prominent in the heart from gestational days 9.5 through 13.5. Cardiac myocytes are the primary site of GRP78 expression within the heart. GRP78 levels are highest in the heart during early organogenesis and levels decrease significantly by the fetal period. GRP78 expression is increased after 24 h of hypoglycemia in the early organogenesis-stage heart. Considering the tissue specific pattern of GRP expression and changes during development of the heart, GRPs may play significant roles in the normal differentiation and development of cardiac tissue. GRP induction may also be involved in hypoglycemia-induced cardiac dysmorphogenesis.

Glut-1 expression and its response to hypoglycemia in the embryonic mouse heart.

The embryonic heart depends on glucose during early organogenesis. Glut-1 functions in constitutive glucose uptake in adult tissues and is the predominant glucose transporter in embryonic and fetal tissues. This study focuses on Glut-1 expression in the heart during normal organogenesis using immunohistochemistry for Glut-1 distribution, Western analysis for Glut-1 protein levels, and reverse transcriptase polymerase chain reaction for Glut-1 mRNA levels. The role of Glut in glucose uptake response to hypoglycemia in the embryonic heart is evaluated using the Glut inhibitor cytochalasin B. Cardiac Glut-1 expression is also evaluated after in vitro hypoglycemic exposure. Glut-1 levels are highest on gestational days 9-10, intermediate on gestational day 10.5, and lowest on gestational days 11.5-13.5 in the normal embryonic heart. Cardiac Glut-1 mRNA levels similarly decline between gestational days 9.5 and gd 13.5. Cytochalasin B produces a dose-dependent decrease in glucose uptake in hearts exposed to hypoglycemia for 30 min or 6 h, implicating Glut in this response. Glut-1 protein expression is unchanged after 2 or 6 h but increased after 12 and 24 h of hypoglycemia in the gestational day 9.5 heart. Thus, Glut-1 expression is prominent in the embryonic heart and is correlated with changes in cardiac glucose requirements during normal organogenesis. Glut activity increases in response to acute hypoglycemia and the expression of Glut-1 increases in response to prolonged hypoglycemia. These results support the importance of Glut-1 during normal cardiogenesis and in response to hypoglycemia in the embryonic heart.

Hexokinase I expression and activity in embryonic mouse heart during early and late organogenesis.

Hexokinase (HK) catalyzes the first step in glucose metabolism, that is, the conversion of glucose to glucose-6-phosphate (G6P). Four HK isoforms have been identified, of which HK-I is predominant in embryonic and fetal tissues. HK-I has been studied in preimplantation embryos and in fetal stages, but little is known about its activity or expression in the early postimplantation embryo. We evaluated HK-I expression, HK-I activity, and glycolytic metabolism in the embryonic mouse heart during early [gestational day (gd) 9.5] and late (gd 13.5) organogenesis. Immunohistochemistry demonstrated that HK-I is localized mainly in the heart at both stages, with stronger expression on gd 13.5. Densitometry after SDS-PAGE/western analysis confirmed higher immunodetectable HK-I protein levels in hearts on gd 13.5 vs gd 9.5. By contrast, RT-PCR demonstrated higher HK-I mRNA expression on gd 9.5 vs gd 13.5. Similarly, cardiac HK-I activity (conversion of glucose to G6P) and glycolysis (conversion of glucose to lactate) were higher on gd 9.5 than on gd 13.5. These results suggest a complex regulation of HK-I expression and activity in the embryonic heart during organogenesis, involving a change in the intrinsic activity of the enzyme with development. HK-I appears to play an important role in glucose metabolism during this critical stage of cardiogenesis.

Expression of glucose-regulated proteins (GRP78 and GRP94) in hearts and fore-limb buds of mouse embryos exposed to hypoglycemia in vitro.

Hypoglycemia, the classic inducer of glucose-related protein (GRP) synthesis, is dysmorphogenic in rodent embryos and detrimentally affects the heart. This study compares GRP induction in a target vs non-target tissue by evaluating GRP expression in hearts and fore-limb buds of mouse embryos following exposure to hypoglycemia in vitro. Gestational day 9.5 embryos were exposed to 2, 6, and 24 h of either mild (80 mg/dl glucose) or severe (40 mg/dl glucose) hypoglycemia using the method of whole-embryo culture. GRP78 increased in a dose- and time-dependent fashion in embryonic hearts exposed to either 40 mg/dl or 80 mg/dl glucose, whereas GRP94 levels increased in hearts only after 24 h of hypoglycemia. In contrast to the heart, GRP induction in fore-limb buds occurred only with GRP78 following the most severe level and duration of hypoglycemia. RT-PCR analysis demonstrated an elevation in GRP78 and GRP94 message levels in embryonic hearts following severe hypoglycemia. However, mRNA levels did not increase in response to mild hypoglycemia. Overall, these data demonstrate the preferential induction of GRPs in the heart as compared to fore-limb buds in mouse embryos exposed to hypoglycemia. Increases in GRP protein levels may be a more reliable biomarker of stress than message levels. However, both tissues and methods should be examined for enhanced biomarker sensitivity.

Cromakalim: embryonic effects and reduction of tolbutamide-induced dysmorphogenesis in vitro.

Cromakalim is a K(+) channel opener that causes smooth muscle relaxation by activating ATP-sensitive K(+) (K(ATP)) channels and producing membrane hyperpolarization. Cromakalim counteracts sulfonylurea-induced K(ATP) channel inhibition in adult cells, but little is known regarding its embryonic effects, alone or in combination with sulfonylureas. K(ATP) channels have been demonstrated in the embryo, but their role in normal and abnormal development is unknown. Early-somite mouse embryos were exposed for 24 hr in vitro to cromakalim at concentrations of 0 (Cntl), 1, 10, 100, 200, or 500 microM in 0.125% DMSO. Embryos were also exposed for 24 hr in vitro to a dysmorphogenic tolbutamide concentration (110 microg/ml) combined with a subdysmorphogenic concentration of cromakalim (1 microM). Embryos were evaluated for somite number, heart rate, malformations, and embryonic and yolk sac protein content. Embryos exposed to 1 microM cromakalim were similar to controls. Cromakalim exposure increased malformation rates at concentrations >/=200 microM, decreased heart rates at >/=10 microM, and decreased somite and protein values at 500 microM. Defects involved cranial neural tube, optic vesicle, heart, and somites. A malformation rate of 59% in embryos exposed to 110 microg/ml tolbutamide was reduced to 13% by adding 1 microM cromakalim to the culture medium. Heart rate, somite number, and protein values were also improved by combined exposure to cromakalim and tolbutamide compared with exposure to tolbutamide alone. These results support previous findings with diazoxide (K(+) channel opener) and chlorpropamide (sulfonylurea) and further suggest a potential role for K(ATP) channel effects in sulfonylurea-induced dysmorphogenesis.

Glucose metabolism in mouse embryos exposed to metformin in vitro.

Metformin is an oral hypoglycaemic agent used to treat patients with non-insulin-dependent diabetes mellitus, but its effect on embryonic tissues has not been well studied. Early-somite mouse embryos were exposed in whole embryo culture to metformin (0-2000mug/ml) and assayed for glucose uptake and glycolysis at 6, 12 and 24 hours. Embryos exposed to metformin for 6 hours were also evaluated for glucose uptake in the presence of 0 or 100 mum cytochalasin B. Glucose uptake was increased in embryos exposed to metformin at 2000mug/ml for 6 hours and 1000mug/ml or more for 12 hours. Glycolysis was increased in embryos exposed to metformin at 2000mug/ml for 6 or 24 hours and 1000mug/ml or more for 12 hours, producing lactate concentrations up to six times higher than controls. Glut-1 was increased in embryos exposed to 1000mug/ml or more for 6 hours, and metformin-stimulated glucose uptake was significantly decreased by cytochalasin B. Thus, glucose uptake and glycolytic metabolism are increased in early-somite mouse embryos in response to high concentrations of metformin in vitro, and the mechanism of increased glucose uptake appears to involve a cytochalasin B-sensitive glucose transporter.

Tolbutamide: placental transfer, tissue distribution, and metabolic effects in murine embryos.

Tolbutamide is a sulfonylurea oral hypoglycaemic agent with suspected teratogenicity in humans and demonstrated teratogenicity in laboratory animals, but the underlying mechanism is unknown. This study examined maternal-to-conceptus tolbutamide transfer on gestational days 9.5 and 10.5 and drug concentration in embryonic head, heart, and trunk regions on gestational day 10.5 after maternal dosing in mouse. Embryos exposed to tolbutamide in vitro on gestational day 8.5 were assayed for glucose uptake, glycolysis, and protein content after 6, 12, and 24 hr. Dose-dependent tolbutamide transfer from maternal serum to extraembryonic fluid occurred on gestational day 9.5 and 10.5, with highest tolbutamide levels in embryonic heart on gestational day 10.5. In vitro tolbutamide exposure on gestational day 8.5 decreased glycolysis at 6 hr, increased glycolysis at 24 hr, and had no effect on glucose uptake at 6, 12, or 24 hr. Embryonic protein content reflected growth retardation after 24 hr tolbutamide exposure. Thus, mouse embryos are directly exposed to tolbutamide after maternal dosing on gestational day 9.5 and 10.5, with concentration of drug within embryonic heart. Tolbutamide-induced changes in glucose metabolism are less apparent in whole embryos than reported in adult tissues.

Immunolocalization and heart levels of GRP94 in the mouse during post-implantation development.

Glucose-regulated proteins (GRPs), which belong to the highly conserved family of stress proteins, are resident to the endoplasmic reticulum and function as molecular chaperones. Heat shock proteins have been shown to be developmentally regulated, but little work has been done to investigate the expression of GRPs during embryogenesis. Therefore, this study examined the distribution of GRP94 within mouse embryos during the period of organogenesis and characterized levels of GRP94 within the developing heart during organogenesis and late fetal stages. Our results demonstrate that the GRP94 protein is constitutively expressed within mouse embryos during early stages of organogenesis and is localized particularly within the developing heart, neuroepithelium, and surface ectoderm tissues. Positive staining for GRP94 remains within developing heart tissues throughout organogenesis and is found primarily within the atrial and ventricular myocardial cells. Western blot analysis of GRP94 expression demonstrates a significantly higher level of GRP94 in embryonic hearts during early stages of organogenesis than in later stages of organogenesis or the fetal period. These results demonstrate that the stress protein GRP94 is constitutively expressed within specific tissues during post-implantation mouse development and suggest that GRPs may play an important role in the process of myocardial cell differentiation and heart development.

Chlorobutanol: maternal serum levels and placental transfer in the mouse.

Chlorobutanol (CB) is a pharmaceutical preservative and the active ingredient in certain sedatives and anesthetics and produces adverse effects in adult tissues and mouse embryos in vitro. Chlorobutanol is slowly eliminated in humans, but little is known about its serum levels in other species or placental transfer in any species. Pregnant mice gavaged with 80 mg CB/kg on gestational day (gd) 9.5 provided serum at 10 min to 36 h post-dosing for a time course study. Additional mice gavaged with 0, 8, 40 or 80 mg CB/kg on gd 9.5 provided maternal serum and embryos 2 h post-dosing for a placental transfer study, and CB levels were measured using capillary gas chromatography with electron capture detection. Dosing with 80 mg CB/kg produced maternal serum levels between 30.8 micrograms/mL (10 min) and < 1 microgram/mL (36 h), with a half-life of 7.45 h. Embryonic CB levels increased with maternal dose and were correlated with maternal serum levels. Serum levels of CB in the mouse appeared to follow a time course similar to humans, with rapid absorption and slow elimination. Placental transfer, as demonstrated here in the mouse, may allow embryonic accumulation of CB to potentially toxic levels.

Comparison of effects of albendazole sulfoxide on in vitro produced bovine embryos and rat embryos.

OBJECTIVE: To evaluate and compare effects of albendazole sulfoxide (ABZSO) on rat embryos and bovine embryos produced in vitro. ANIMALS: In vitro produced bovine embryos. Rat embryos recovered from naturally bred Sprague-Dawley rats. PROCEDURE: 4- and 8-cell bovine embryos were randomly allocated to ABZSO or vehicle control groups. After 48 hours, embryos were evaluated for cell number and blastomere morphology. Rat embryos of similar stages, flushed from the uterine tube on gestational day 2-5, were randomly allocated to treatment or control groups. After 24 hours, embryos were evaluated as described previously. RESULTS: 44% of control bovine embryos divided in culture (> or = 16-cell stage). Fifteen percent of the controls had morphologic abnormalities, including disparity in blastomere size and cytoplasmic vacuoles and stippling. Treated (> or = 1 microgram of ABZSO/ml) bovine embryos differed (P < 0.0001) from controls, with 4% development and 93% abnormal morphology. Forty-five percent of control rat embryos divided in culture. Treated (> or = 500 ng of ABZSO/ml) rat embryos differed (P < 0.0003) from controls with regard to ability to divide. There were no consistent morphologic abnormalities in rat embryos. CONCLUSIONS: In vitro produced bovine embryos were susceptible to ABZSO at a concentration > or = 1 microgram/ ml, resulting in decreased ability to divide and presence of gross morphologic abnormalities. Rat embryos produced in vivo and exposed in vitro to ABZSO at a concentration > or = 500 ng/ml had decreased ability to divide in culture. CLINICAL RELEVANCE: Despite severe effects of ABZSO (> or = 1 microgram/ml) on bovine embryo development in vitro, it is beyond the scope of this study to speculate whether a therapeutic dosage of albendazole (10 mg/kg of body weight) would result in necessary concentrations of ABZSO in vivo to disrupt embryogenesis.

Brief hypoglycemia alters morphology, function, and metabolism of the embryonic mouse heart.

This study examined effects of brief embryonic exposure to hypoglycemia on the developing mouse heart during organogenesis. Mouse embryos were exposed in whole-embryo culture to brief periods (2, 4, or 6 h) of hypoglycemia (20, 40, or 80 mg/dL glucose) at three developmental stages (10, 20, or 30 somites), and hearts were examined for morphologic, functional, and metabolic effects. Hypoglycemia produced abnormal cardiac structure and expansion and pericardial edema, and it disrupted histologic integrity and growth of the heart, particularly at 20 somites. Embryonic heart rate was decreased by hypoglycemia at all three stages. Cardiac glucose uptake and glycolysis were increased by hypoglycemia, suggesting a compensatory response to glucose deficiency, with little effect on ATP levels. In summary, brief embryonic exposure to hypoglycemia affects the morphology, function, and metabolism of the developing heart. Mechanisms by which metabolic responses are related to morphologic and functional effects are currently unclear.

Persistent oropharyngeal membrane in a Hereford calf.

Persistent oropharyngeal membrane was found in a 6-day-old Hereford calf. The calf was unable to nurse and had not passed feces since birth. Physical examination revealed a fold of tissue spanning the caudal oral cavity, and a barium study demonstrated that food remained within the oral cavity despite a swallowing reflex. A thickened epiglottis was demonstrated radiographically but was not confirmed on necropsy. Necropsy revealed a complete soft-tissue partition between oral cavity and oropharynx with a central blind-ended diverticulum. Only a few cases of persistent oropharyngeal membrane have been reported previously, all in humans. This is the first report of this defect in domestic animals. Possible similarities to the more common persistent anal membrane are discussed.

Determination of chlorobutanol in mouse serum, urine and embryos by capillary gas chromatography with electron capture detection.

A sensitive and specific method for the determination of chlorobutanol (1,1,1-trichloro-2-methyl-2-propanol) in mouse serum, urine, and embryos by capillary gas chromatography with electron capture detection is described. For sample preparation n-hexane was used to extract chlorobutanol and the internal standard 2,2,2-trichloroethanol (TCE) from each matrix. Following extraction chromatographic separation of the samples was achieved with a fused-silica capillary column (30 m x 0.25 mm I.D., 0.25 micron film thickness). The method as described has the required sensitivity to quantitate chlorobutanol in individual embryos following administration of a single oral dose of the drug to a pregnant mouse. The limit of detection was 1 pg on column and the detector response was linear from 1 to 100 micrograms/ml for serum, 0.2 to 20 micrograms/ml for urine, and 1 to 10 ng/embryo.

Embryopathic effects of diazoxide and the reduction of sulfonylurea-induced dysmorphogenesis in vitro.

Diazoxide is a benzothiadiazine used in oral and intravenous preparations to treat hypertension and hypoglycaemia, but its effect on embryonic development has not been well studied. Previous in vivo work has suggested placental transfer and teratogenicity of diazoxide in humans and laboratory animals, but this study represents the first in vitro investigation of the effect of diazoxide on the embryo. The in vitro method of whole-embryo culture was used to expose mouse embryos to specific levels of diazoxide (0-200 mug/ml) during organogenesis at well-defined (4-6 and 20-25 somite) stages of development. In addition, the combined effect of diazoxide [ATP-sensitive K(+) (K(ATP)) channel opener] and the sulfonylurea oral hypoglycaemic agent chlorpropamide (K(ATP) channel blocker), was evaluated in vitro in embryos with 4-6 somites. Diazoxide produced malformations and growth retardation in mouse embryos exposed to 100 mug/ml or more for 24 hr in vitro at both stages of organogenesis. In addition, a subteratogenic concentration of diazoxide (25 mug/ml) reduced the embryopathic effects of chlorpropamide (130 mug/ml) in embryos with 4-6 somites. A potential mechanism for these effects involves K(ATP) channels.

Embryopathic effects of the oral hypoglycemic agent chlorpropamide in cultured mouse embryos.

OBJECTIVES: The oral hypoglycemic agent chlorpropamide was evaluated for embryopathic effects in the mouse embryo model. STUDY DESIGN: Mouse embryos (n = 10 to 31 per group) were exposed in whole embryo culture to serum from chlorpropamide-treated rats or chlorpropamide-supplemented control rat serum. Hypoglycemic serum from chlorpropamide-treated rats was supplemented with glucose to control for effects of hypoglycemia. Differences in malformation rates were evaluated by Fisher's exact test and numerical differences by analysis of variance. RESULTS: Mouse embryos were malformed by > or = 24 micrograms/ml of chlorpropamide, embryonic protein content and somites were decreased by > or = 130 micrograms/ml of chlorpropamide, and visceral yolk sac protein was reduced by > 500 micrograms/ml of chlorpropamide. Similar development occurred in serum from chlorpropamide-treated rats and chlorpropamide-supplemented control serum, and growth was not improved by adding glucose. CONCLUSIONS: Chlorpropamide produces malformations and growth retardation in mouse embryos in vitro at concentrations overlapping therapeutic levels in humans. Chlorpropamide-induced defects are not mediated by hypoglycemia or by products of chlorpropamide metabolism.

Embryotoxic effects of chlorobutanol in cultured mouse embryos.

Chlorobutanol (CB) is a commonly used preservative which is added to numerous pharmaceutical preparations, and it is the active ingredient in certain oral sedatives and topical anesthetics. Chlorobutanol has demonstrated adverse effects in adult tissues, but CB has not been previously investigated for its effect on the developing whole embryo. The method of whole-embryo culture was used in this study to expose mouse embryos during two stages of organogenesis to CB at final concentrations of 0 (control), 10, 25, 50, 100, and 200 micrograms/ml. Embryos were evaluated for heart rate (HR), malformations, and somite number, and embryos and visceral yolk sacs (VYSs) were assayed for total protein content as a measure of overall growth. Neurulating (3-6 somite) embryos were malformed and growth retarded by exposure to CB concentrations > or = 25 micrograms/ml, with decreased VYS growth at > or = 50 micrograms/ml and decreased HR at > or = 100 micrograms/ml CB. Early limb-bud stage (20-25 somite) embryos were malformed at CB concentrations > or = 50 micrograms/ml and growth retarded at > or = 100 micrograms/ml, with decreased VYS growth at 200 micrograms/ml and decreased HR at > or = 100 micrograms/ml CB. Thus, CB produces dysmorphogenesis in mouse embryos in vitro, and neurulating embryos are somewhat less sensitive than early limb-bud stage embryos. The concentrations of CB that interfere with normal embryonic development are within the range of human blood levels measured following multiple doses of CB. Preparations containing CB should be used with caution during pregnancy, particularly when repeated dosing may allow accumulation of CB to potentially embryotoxic levels.

Teratogenic effects of tolbutamide on early-somite mouse embryos in vitro.

The present study investigated the teratogenicity of the oral hypoglycemic agent, tolbutamide, using an in vitro approach, and evaluated the role of its main metabolic effect, hypoglycemia. Teratogenesis was evaluated by culturing early-somite mouse embryos for 24 h in serum from rats treated with tolbutamide (79-117 micrograms/ml) or normal rat serum supplemented with tolbutamide (110-152 micrograms/ml). Tolbutamide-treated serum was then supplemented with glucose to control for potential effects of hypoglycemia. Mouse embryos demonstrated high malformation rates following exposure to serum from tolbutamide-treated rats (79%) or normal rat serum supplemented with tolbutamide (85%) compared with controls (4%), and defects included cardiac, ocular, neural tube, and somite abnormalities. Overall growth was reduced in treated embryos and yolk sacs, as determined by total protein contents. Embryonic growth and malformation rates were not improved by glucose supplementation of hypoglycemic tolbutamide-treated serum. Thus, tolbutamide produces malformation in mouse embryos in vitro at concentrations comparable to those in human serum, and the effects do not appear to be mediated by hypoglycemia. The potential risk of tolbutamide on the developing embryo must be considered in the therapy of pregnant diabetic patients.

Hypothermia: teratogenic and protective effects on the development of mouse embryos in vitro.

Hypothermia often occurs in association with clinical conditions involving severe hypoglycemia, but its effect on embryonic development has not been well evaluated. Thus, the whole embryo culture method was used to expose day 9 (neurulating) and day 10 (early limb bud stage) mouse embryos to physiologic levels of hypothermia (35 degrees C and 32 degrees C) for 4 and 24 hr. Embryos were evaluated after 24 hours for growth and malformations and compared with controls grown at 37 degrees C. Lactate production was measured in embryos cultured for 4 hr at 32 degrees C and compared with those cultured at 37 degrees C. A 4-hr exposure to hypothermia produced little effect morphologically but reduced the rate of lactate production at both embryonic stages. A 24-hr exposure to hypothermia at 35 degrees C or 32 degrees C produced growth retardation and dysmorphogenesis in embryos undergoing neurulation. Early limb bud stage embryos were less sensitive to this treatment, with growth retardation produced only at the lower temperature. Since hypothermia is commonly associated with severe hypoglycemia in cases of diabetic insulin overdose, day 9 (neurulating) mouse embryos were exposed concurrently to short periods of hypothermia and hypoglycemia and compared with embryos cultured in hypoglycemic medium at normal temperature. The results demonstrate that hypothermia partially protects embryos against the dysmorphogenic effects of hypoglycemia. A balance of metabolic rate and available substrate is discussed as a possible mechanism for this protective effect.

Embryopathic effects of short-term exposure to hypoglycemia in mouse embryos in vitro.

The effect of short-term hypoglycemia was studied at two stages of development in postimplantation mouse embryos in vitro. Day 8 (gastrulating) mouse embryos were placed in hypoglycemic medium (60, 80, 100, or 110 mg/dl glucose) for 4 hours in which normoglycemia (120 to 150 mg/dl glucose) was restored for the remaining 44 hours of culture. Day 9 (neurulating) mouse embryos were exposed to hypoglycemia (20, 40, 60, or 80 mg/dl glucose) for 2, 4, 6, or 24 hours followed by normoglycemia for the remainder of 24 hours. At the end of culture embryos were evaluated for growth and malformations and compared with controls grown in normoglycemic medium. The results show that a 50% reduction in glucose for as little as 2 hours causes dysmorphogenesis in neurulating mouse embryos, whereas longer exposure times, more severe levels of hypoglycemia, or both are required to affect growth. Furthermore, gastrulating embryos are more sensitive to short periods of hypoglycemia than those undergoing neurulation.