Prenatal exposure to dexamethasone in the mouse alters cardiac growth patterns and increases pulse pressure in aged male offspring

Abstract

Exposure to synthetic glucocorticoids during development can result in later cardiovascular and renal disease in sheep and rats. Although prenatal glucocorticoid exposure is associated with impaired renal development, less is known about effects on the developing heart. This study aimed to examine the effects of a short-term exposure to dexamethasone (60 hours from embryonic day 12.5) on the developing mouse heart, and cardiovascular function in adult male offspring. Dexamethasone (DEX) exposed fetuses were growth restricted compared to saline treated controls (SAL) at E14.5, but there was no difference between groups at E17.5. Heart weights of the DEX fetuses also tended to be smaller at E14.5, but not different at E17.5. Cardiac AT1aR, Bax, and IGF-1 mRNA expression was significantly increased by DEX compared to SAL at E17.5. In 12-month-old offspring DEX exposure caused an increase in basal blood pressure of ~3 mmHg. In addition, DEX exposed mice had a widened pulse pressure compared to SAL. DEX exposed males at 12 months had an approximate 25% reduction in nephron number compared to SAL, but no difference in cardiomyocyte number. Exposure to DEX in utero appears to adversely impact on nephrogenesis and heart growth but is not associated with a cardiomyocyte deficit in male mice in adulthood, possibly due to compensatory growth of the myocardium following the initial insult. However, the widened pulse pressure may be indicative of altered vascular compliance.

Figure 1. Maternal food and water consumption during pregnancy.

The food intake (A) and water intake (B) of the pregnant dams was measured daily from E10.5 to E16.5. The infusion of SAL (open bars) and DEX (closed bars) was for 60 h starting from E12.5. Data is presented as presented as mean ± SEM. N = 5–10 dams per group per day.

Figure 2. Fetal body weight, heart weight, heart to body weight ratio and IGF-1 mRNA expression.

The body weights (A and B), heart weights (C and D) and heart to body weight ratios (E and F) of male fetuses as measured at post mortem tissue collection at embryonic day (E) 14.5 or E17.5. The mRNA levels of insulin like growth factor 1 (IGF-1) at E14.5 (G) and E17.5 (H) are shown, as measured by real-time PCR using the comparative cycle threshold method. Data is presented as litter mean of sexed fetuses ± SEM. N = 7–8 litters (one animal per litter). * P<0.05 unpaired Student's t-test.

Figure 3. Basal heart rate, mean arterial pressure and the pulse pressure in aged male offspring.

The basal heart rate, mean arterial pressure (MAP) and pulse pressure of mice prenatally exposed to SAL (open circles) or DEX (closed circles) as measured by radio telemetry. Each data point represents the mean of the sampled data collected for 10 seconds every 15 minutes for each 12 h night (N) and day (D) cycle. Measurements were started after 10 days post surgical implantation of the radio transmitter to allow the mice to recover normal circadian variations. Data is presented as mean ± SEM. N = 6–7 litters (one animal per litter). * P<0.05 by Repeated measures one way ANOVA.

Figure 4. Heart rate, mean arterial pressure and pulse pressure responses to restraint stress.

The delta change heart rate (A), mean arterial pressure (MAP; B) and pulse pressure (PP; C) after exposing the aged male mice to a 15 minute restraint stress from baseline values. The data points represent the Δ value between the mean of the data sampled during the restraint stress (10 seconds every minute for 15 minutes) from the baseline value (mean of data sampled 10 seconds every 5 minutes in the hour immediately prior to the restraint stress). SAL (open circles), DEX (closed circles). Data presented as the mean ± SEM. N = 6–7 litters (one animal per litter).

Figure 5. Effects of dexamethasone exposure on nephron number and cardiomyocyte number.

The number of nephrons in the kidney (A), and the number of cardiomyocytes (B) in the heart from aged male mice were assessed by unbiased stereology. Open bar indicates SAL exposed animals and the closed bar DEX exposed animals. Data is presented as mean ± SEM. N = 6 kidneys per group and N = 5 hearts per group (one animal per litter). * P<0.05, # P<0.0001 by unpaired Student's t-test.