In our laboratory we are using a rat animal model to determine the consequences of prenatal stress against a high fat diet background. Pregnant female Sprague-Dawley (SD) rats are maintained on standard chow (CHOW) or 60% high fat (HF) diet throughout gestation and lactation. In addition, half of each diet group was subjected to a variable stress paradigm (STRESS) to determine the short- and long-term metabolic effects of maternal stress during the last week of gestation on offspring (). Details have been described previously [37
Schedule of variable stress during gestation.
In this model we find that prenatal variable stress is non-habituating and has a significant effect in elevating baseline glucocorticoid levels in dams. HF diet feeding results in greater caloric consumption during the first 2 weeks of gestation and produces greater weight gain in HF fed dams than CHOW fed dams. STRESS in the 3rd
week of gestation suppresses maternal weight gain. Thus, although maternal HF feeding accelerates weight gain during the first two weeks of gestation, a combination of lower caloric consumption among the HF dams and less weight gain in STRESS dams results in no difference in body weight among the groups by gestation day 21, immediately prior to parturition. HF diet consumption increased plasma leptin levels, but had no effect on blood glucose or plasma insulin indicating that the dams had not developed a diabetes, a condition that by itself produces offspring with gestational diabetes show increased adiposity, impaired pancreatic function, impaired glucose tolerance, and altered hypothalamic development [38
At birth, both male and female pups from STRESS dams weighed more than those from CON moms irrespective of maternal diet. There were no differences in litter sizes or male to female ratios at birth and thus these factors could not account for the differences in birth weight among the groups. From birth on, both prenatal stress and HF diet conditions had significant effects on the pups’ weight gain. Pups from dams’ that were stressed and/or on HF diet weighed more as early as postnatal (PND) 7 compared to those from dams on CHOW diet and the difference in body weight persisted until weaning on PND 21 (). Using whole body NMR after the animals were sacrificed, we determined that the increase in body weight among STRESS and HF offspring was associated with greater adiposity in both male and female pups from HF dams () with no difference in visceral vs. subcutaneous distribution (data not shown). Although the HF-STRESS group is heavier than HF-CON, the amount of body adiposity and lean mass appears to be lower in the HF-STRESS group. This non-significant difference is likely due to the fact that body composition analysis was done post-mortem and we also separated the subcutaneous from the visceral fat depot thus introducing some degree of error.
Fig. 1 Body weight of male and female offspring through PND 21. Left: Male offspring in each litter were weighed on postnatal days (PND) 1, 7, 14, and 21. Right: Female offspring in each litter were weighed on PND 1, 7, 14, and 21. CHOW-CON (n = 11 litters), (more ...)
Body composition of male offspring on PND 21.
We challenged male and female offspring to an oral glucose tolerance test to assess their ability to clear glucose. Pups from HF dams cleared glucose more slowly and required a greater amount of insulin compared to CHOW pups suggesting that they may be developing insulin resistance. Together these data suggest that maternal HF diet during gestation and lactation has significant metabolic effects on the offspring by the time they are weaned.
Hormones leptin, insulin and corticosterone are critical in the proper development of neural circuitry during the early postnatal period [41
]. We collected blood from pups on PND 1, 7, 14 and 21 and the endocrine profile of male offspring is shown in . On PND 1, male pups from the HF-STRESS group already had significantly elevated plasma leptin levels. From PND 7 on both HF-CON and HF-STRESS groups had elevated plasma leptin compared to those pups from CHOW fed dams. Plasma insulin was not different until PND 21 when pups from HF diet fed dams had significantly higher levels of insulin regardless of whether or not they were subject to prenatal stress. Corticosterone levels were lower in both CHOW- and HF-STRESS groups on PND 1 but did not differ through the rest of the suckling period.
Fig. 2 Endocrine profile in male offspring PND 1-21. Top: Plasma leptin. Middle: Plasma insulin. Bottom: Plasma corticosterone. CHOW-CON (n = 11), CHOW-STRESS (n = 10), HF-CON (n = 11), HF-STRESS (n = 10). * P < 0.05 vs. CHOW-CON, CHOW-STRESS, HF-CON; (more ...)
When weaned onto CHOW diet, the in utero experience did not affect offspring body weight at 70 days of age. However, when weaned onto HF diet, both male and female pups from dams that were stressed and/or on HF diet gained more body weight and this was attributable to greater adiposity. Males weaned on CHOW diet showed no difference in glucose clearance or insulin secretion in an OGTT. However, males weaned on HF diet had impaired glucose tolerance if their dams were stressed or on HF diet.
We had originally hypothesized that prenatal stress against a background of HF diet feeding would result in an additive or synergistic effect on the metabolic profile of the offspring. However, the data at the time points examined suggest that there is no increased effect of the combination of stress and HF diet. There may have been a ceiling effect of either stress or HF diet or both that masked evidence of additivity or synergism. In particular, the HF diet that we used had a 60% fat content and lowering this to 40% would maintain a fat content that is comparable to a standard Western diet. An alternative possibility is that maternal HF diet would have a “beneficial” effect in attenuating the stress response of the dam and, in turn, lessen its impact on the developing fetus. Dallman and colleagues have demonstrated that high fat diet can attenuate the HPA axis response to stress [42
]. We did not note either a detrimental or beneficial effect of HF diet on top of the effects of stress.