Chung-Ja M. Cha

The cross-generation effect of neonatal macrosomia in rat pups of streptozotocin-induced diabetes.

ABSTRACT: To study the cross-generation effect of enhanced growth in macrosomic newborn rats, we induced mild hyperglycemia in 15 pregnant Sprague Dawley rats by intraperitoneal injection of streptozotocin, 35 mg/kg body weight, on the 5th d of gestation. As reported previously, we produced hyperinsulinemia and accelerated growth in the fetuses of hyperglycemic dams. We also showed that the macrosomic female pups (second generation) continued to have a higher growth rate through the first 12 wk of life. In this study, the second-generation female rats were mated with macrosomic second-generation males; they demonstrated glucose intolerance during late pregnancy and delivered pups (third generation) with higher birth weight and plasma insulin levels than the pups from control second-generation rats. When the macrosomic third-generation pups were raised under identical nutritional and environmental conditions as controls, the macrosomic rats showed accelerated growth and higher fat tissue weight during the first 12 wk of life. Furthermore, the macrosomia was associated with glucose intolerance and higher insulin to glucose ratios compared to controls. We also mated the offspring of second-generation streptozotocin-injected nonmacrosomic as well as the offspring of macrosomic pups of buffer-injected dams; none of the pups from these matings were significantly macrosomic. Therefore, we conclude that the perpetuation of obesity and possibly glucose intolerance across generations in this rat model is predominantly a result of abnormal intrauterine metabolic environment rather than genetic factor driven.

Glucose metabolism in adipocytes of obese offspring of mild hyperglycemic rats.

ABSTRACT: Six pregnant rats were made mildly hyperglycemic by intraperitoneal injection of streptozotocin on d 5 of gestation. Four control rats were injected with citrate buffer. Thirty pups born to experimental dams who had increased birth weight (birth weight >1.7 SD of mean birth weight of pups from control dams) maintained accelerated growth through 10 wk of age. At 10 wk, oral glucose tolerance tests showed higher glucose and insulin levels than the controls (n = 37). In addition to the higher body weight, the experimental rats also had higher fat weight to body weight ratios. Adipocytes of epididymal fat from obese males and periovarian fat from obese females had higher lipid content with significantly larger cell size than the adipocytes of the controls. The adipocytes of macrosomic rats showed attenuated response to insulin-stimulated glucose conversion to total lipid and fatty acid when compared with the responses seen in the adipocytes of the control rats. Interestingly, although the insulin-stimulated glucose conversion to CO2 was similar in macrosomic and control males, the response in the macrosomic female was blunted when compared with that of the control females. Insulin receptor binding capacities of the macrosomic rats were lower than those of the controls, which is consistent with a phenomenon of down-regulation. However, the receptor affinities were higher in the experimental animals than in controls. Therefore, a postreceptor defect may account for the abnormality in glucose metabolism in the obese rats. In conclusion, the abnormal response to oral glucose loading in these experimental obese, hyperinsulinemic rats is due to peripheral tissue insulin resistance that is probably postreceptor in nature.

Neonatal Sympathoadrenal Response to Acute Hypoxia: Impairment after Experimental Intrauterine Growth Retardation

ABSTRACT: Sympathoadrenal system function may be altered following intrauterine growth retardation (IUGR) We tested the hypothesis that the growth-retarded newborn rat pup has increased basal sympathoadrenal activity under normoxic conditions and a blunted sympathoadrenal response to acute hypoxia. IUGR was established by uterine artery ligation on d 18 of gestation in Sprague-Dawley rats. Growth-retarded pups were chosen as those whose birth wt was more than 2 × SD below the mean birth wt of control pups delivered to sham-operated dams. At 24 ± 12 h of age cardiac sympathetic neuronal activity (CSNA) was determined by 3H-norepinephrine tracer and α -methyltyrosine techniques. Adrenal medullary catecholamine synthesis (CAT SYN) was measured by 14C-tyrosine precursor methods, and adrenal catecholamine release (CAT REL) was determined using α-methyl-tyrosine. IUGR and control pups were studied over a 120-min period of normoxia or hypoxia (Fio2=0.09). Under normoxic conditions, the IUGR pups had increased CSNA and increased adrenal CAT SYN CAT REL compared to controls. Adrenal CAT REL in normoxic IUGR pups was selective for epinephrine. In response to acute hypoxia, control pups had increased CSNA and increased adrenal CAT SYN and CAT REL compared to normoxic controls, with the proportion of norepinephrine and epinephrine released mimicking the ratio of the two amines in the adrenal. In contrast, in hypoxic IUGR pups CSNA and adrenal CAT SYN did not increase, and norepinephrine alone was released from the adrenal medulla. It is speculated that IUGR in the rat may lead to an acceleration of cardiac sympathetic innervation and premature establishment of neural regulation of adrenomedullary function, resulting in impaired sympathoadrenal responses to acute stresses such as hypoxia. Compromised sympathoadrenal system function in the IUGR fetus or newborn may contribute to the pathogenesis of the perinatal morbidities and the increased perinatal mortality known to occur in this high risk population.

Evaluation of Insulin Sensitivity in Obese Offspring of Diabetic Rats by Hyperinsulinemic-Euglycemic Clamp Technique

ABSTRACT: Young adult macrosomic offspring of streptozotocin-induced mildly hyperglycemic rats exhibit accelerated growth through the first 10 wk of age. At 10 wk, oral glucose loading resulted in elevated plasma insulin and glucose concentrations compared to controls. To assess the mechanism of the abnormal glucose tolerance in vivo, hyperinsulinemic-euglycemic clamp studies were performed. Ten-wk-old rats were fasted overnight, and porcine insulin was infused (2.4 mU.kg-1.min-1). Glucose was infused concurrently at varying rates to maintain euglycemia for 40–60 min. Insulin levels were raised from a baseline value of 163 ± 57 pmol/L (23 ± 8 μU/mL) (SD) to 476 ± 57 pmol/L (67 ± 8 μU/mL) at steady state for males and from 178 ± 43 pmol/L (25 ± 6 μU/mL) to 454 ± 43 pmol/L (64 ± 6 μU/mL) for females. The results showed that the macrosomic male and female animals were significantly less sensitive to the effects of insulin than were their respective controls; this was evident by a lower increment in glucose disposal rate per unit increase in insulin (0.04 ± 0.01 versus 0.11 ± 0.03 for males and 0.05 ± 0.03 versus 0.18 ± 0.07 mg.kg-1 per μU/mL for females). The endogenous glucose production by the liver in the basal (fasted) state in the macrosomic group compared to controls was higher, suggesting possible hepatic insulin resistance. However, endogenous glucose production was suppressed to the same degree between the experimental and control groups during the hyperinsulinemic period, suggesting that the hepatic insulin resistance can be overcome by high insulin levels. Thus, the reduced sensitivity to the effect of insulin on glucose disposal in the macrosomic animals provides additional in vivo evidence for peripheral insulin resistance as a contributing factor for the development of glucose intolerance in obese offspring of mildly hyperglycemic dams.

Postnatal growth and fatty acid synthesis in overgrown rat pups induced by fetal hyperinsulinemia

Fetal hyperinsulinemia in the rat results in increased body weight, lipid content, and enhanced lipogenesis in liver and carcass. The purpose of our study was to determine whether the macrosomia and enhancement of fatty acid (FA) synthesis and/or content persisted postnatally in this animal model. Fetal hyperinsulinemia was produced in Sprague-Dawley rats by injecting fetuses with 2 units of insulin at 20.5 days of gestation. Alternate pups in the same litter were injected with saline. Pups were delivered surgically at 22.5 days of gestation, were weighed daily and sacrificed on day 15. FA content and synthesis rates of liver and skeletal muscle were measured. We found: (1) At birth, insulin-treated pups were 12% heavier than saline littermates, (5.88 +/- 0.14 g v 5.26 +/- 0.14 g, P less than .01); and (2) The enhanced growth associated with prenatal insulin treatment persisted during the suckling period, ie, compared with saline-treated controls, insulin pups were 15.7% heavier at 15 days of age (P less than .01); growth velocity of insulin pups, beginning on day 3, significantly exceeded that of control pups (P less than .05). FA contents of liver and muscle in insulin pups, (62.6 +/- 5.7 mumol/g and 62.7 +/- 13.2 mumol/g) were significantly greater (P less than .05) than in saline littermates (45.1 +/- 5.6 mumol/g and 30.2 +/- 4.7 mumol/g, respectively). We conclude that.(ABSTRACT TRUNCATED AT 250 WORDS)

Accelerated growth and abnormal glucose tolerance in young female rats exposed to fetal hyperinsulinemia.

ABSTRACT: This study was designed to evaluate the relationship between fetal macrosomia and postnatal growth as well as the glucose homeostasis in young female rats. We produced fetal macrosomia by fetal insulin injection at 20 Vi days of gestation. The control subjects were injected with saline. The weights were recorded weekly from birth up to 12 wk. Only the female rats were studied. At 4, 6, 10, and 12 wk of age, oral glucose tolerance tests were performed. Also, at wk 6, 10, and 12, peri-renalovarian- salpingeal fat weights, the RNA, DNA, and protein contents of the abdominal muscle were determined. Onehundred seventeen control and 78 macrosomic rats were studied. The macrosomic rats showed a higher body weight (10-12%) than the control rats from birth up to 8 wk, but at 10 and 12 wk their weights were similar. The fat weights reflected the body weights, i.e. a higher fat weight in the macrosomic rats during the period of accelerated growth (from birth up to 8 wk), and a similar fat weight when the body weight of the two groups were similar at 10 and 12 wk. At 4 and 6 wk of age, the plasma glucose level measured in response to the oral glucose loading were similar in both groups. However, at 10 and 12 wk of age, the macrosomic rats had significantly higher fasting plasma glucose levels and exhibited consistently higher plasma glucose levels for the 3.5-h period of postglucose administration compared to the control rats. The plasma insulin levels rose significantly following glucose challenge. However, the values were similar in both groups at 10 and 12 wk. We conclude that the primary hyperinsulinemiainduced fetal macrosomia is associated with an increased fat deposition resulting in an increased weight gain during young adulthood. The increased fat deposition may manifest peripheral insulin resistance exhibiting the glucose intolerance at a later age. The mechanism involved in this development remains to be investigated.

Effect of respiratory acidosis on glucose homeostasis in experimental intrauterine growth retardation in rats

Hypoglycemia and asphyxia account for a significant proportion of morbidity in the infant with intrauterine growth retardation (IUGR). The purpose of this study was to evaluate changes in glucose homeostasis in IUGR rats during acute respiratory acidosis. IUGR was produced by bilateral uterine artery ligation at 17 days of gestation in 14 pregnant rats with 23 successfully delivered pups. The normal pups (n = 31) were those whose mothers were sham operated at the same gestational period. The IUGR and normal pups were studied at 2 days of age. One group of pups was studied under room air while another was subjected to 20 min of exposure to a gas mixture of 10% O2/15% CO2, balanced with N2. Gluconeogenesis in the liver and carcass, as well as plasma glucose and catecholamines were determined before and after the exposure to the gas mixture. The results showed that the 2-day-old IUGR rats have lower body weight (P less than 0.001), liver weight (P less than 0.001), plasma glucose (P less than 0.001), and rate of gluconeogenesis (P less than 0.01) when compared with the normally grown rats. During respiratory acidosis, the normally grown rats showed an increase in plasma epinephrine (P less than 0.005) without significant change in plasma glucose and rate of gluconeogenesis. The IUGR rats on the other hand, demonstrated a decrease in rate of gluconeogenesis (P less than 0.02), an increase in plasma glucose (P less than 0.001) while the plasma epinephrine level remained unchanged. We speculate that respiratory acidosis blunted cellular metabolism in the IUGR rat resulting in decreased peripheral glucose utilization.(ABSTRACT TRUNCATED AT 250 WORDS)

246 GROWTH AND FATTY ACID METABOLISM IN EXPERIMENTAL INTRAUTERINE GROWTH RETARDATION: EFFECTS OF POSTNATAL NUTRITION

Growth rate and fatty acid (FA) metabolism were evaluated in the first 3½ days of life in rats as a function of degree of intrauterine growth retardation (IUGR) and of postnatal nutrition. IUGR (mild, BW≤1 SD and severe, BW≤2 SD) was produced by uterine artery ligation on 18th day of gestation, and controls were sham operated. Food intake was manipulated by varying the litter size per dam; n=16 for underfeeding, n=10 for normal feeding and n=4 for overfeeding. The growth rate in the control pups was reduced by underfeeding while overfeeding and normal feeding resulted in the same rate. The mild IUGR responded the same way as in control. In severe IUGR group, the growth rate was similar regardless of the feeding protocol. The fatty acid content in carcass was reduced as a result of either prenatal or postnatal undernutrition in spite of a higher fatty acid synthesis rate (FASR) (tritiated water technique). In liver and lung, there was no difference in FASR between controls and IUGR and feeding did not influence the rate; the fat content was lower in under fed control and in IUGR rats. In the brain, FASR of normal fed IUGR was markedly higher and the rate almost doubled in underfed IUGR. This was accompanied by significantly less FA contents in both normal fed and under fed IUGR group. We conclude that postnatal undernutrition retards postnatal growth of normal and mildly affected IUGR rats, but no additional growth retardation was observed in the severely affected IUGR pups. The changes in fatty acid metabolism in various organs studied were consistent with the alterations in growth.