Mechanisms of Prenatal High-Salt "Fetal Programming" Resulting in Stress Hyperresponsiveness in The Adult Female Offspring in The Sprague Dawley Rat.

• Main Author: Johnson, Clinton L.
• Format: Others
• Published: BYU ScholarsArchive 2011
• Subjects: soluble epoxide hydrolase; glucocorticoid receptor; hypertension; methylation; Cell and Developmental Biology; Physiology
• Online Access: https://scholarsarchive.byu.edu/etd/2830; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=3829&context=etd

Female offspring of Sprague-Dawley rats fed a high-salt diet (HS) during pregnancy show an enhancement of mean arterial pressure (MAP) and heart rate (HR) response to acute stress in adulthood compared to offspring whose mothers were fed a normal-salt diet (NS) [1]. In the present study, we first examined the expression of soluble epoxide hydrolase (SEH) protein in brain tissue. Whole brains were collected and SEH gene (EPHX2) mRNA and SEH protein expression were analyzed using RT-PCR and Western blot, respectively. mRNA levels were relatively decreased in high-salt rats (1.0 ± 0.32 NS vs 0.39 ± 0.07 HS, n=6). However, the relative expression of SEH protein was significantly increased in HS rats (0.97 ± 0.06 NS vs. 1.72 ± 0.32 HS, n=10). SEH is an enzyme that inactivates epoxyeicosatrienoic acids (EETs), which can increase the level of oxygen free radical production and potentially produce an increase in blood pressure. Tempol, a free radical scavenger, was administered ntracerebroventricularly to HS (n=12) and NS (n=11) offspring to determine if the stressinduces cardiovascular hyperresponsiveness could be reversed. We were unable to conclusively show that this was the case. Hence, the expression of SEH protein in the brains of HS offspring was increased, but a role, if any, for this change in explaining the exaggerated response to acute stress remains elusive. Second, the expression of the glucocorticoid receptor (GR) gene was investigated. We focused on the methylation patterns of the exon 17 GR promoter and 17 CpG dinucleotide sites that include the NGFI-A transcription factor binding site. Female rats (HS n=8, NS n=8) were sacrificed and brains were immediately extracted. Tissue from the pituitary, hypothalamus, and hippocampus was removed and DNA was extracted from each of these areas. CT conversion was performed on the DNA samples followed by cloning and sequencing. Methylation patterns between HS and NS in the pituitary, hypothalamus, and hippocampus did not vary. RT-PCR and Western blot were performed to investigate differences in the levels of GR transcription and/or translation. There were no significant differences found. However, the trends found may suggest different levels of GR mRNA and protein between HS and NS female rats. DNA methylation may play a role in the regulation of GR in prenatal high-salt female offspring. Additional studies will be needed to pinpoint the mechanisms responsible for the exaggerated cardiovascular response to acute stress in HS offspring.