Abstract
In the solitary tract nucleus (NTS), angiotensin (Ang) II attenuates whereas Ang‐(1‐7) enhances baroreflex sensitivity (BRS) for control of heart rate. Hypertensive (mRen2)27 rats have low medullary Ang‐(1‐7) relative to Ang II associated with impaired BRS that is restored by CB1 receptor blockade in the NTS, consistent with elevated 2‐arachidonylglycerol (2‐AG) in dorsal medulla relative to SD rats. Sprague‐Dawley (SD) rats develop elevated systolic blood pressure as they age, which is associated with impaired BRS resulting from reduced NTS Ang‐(1‐7). We now report that older SD rats exhibit higher 2‐AG at ~70 versus ~15 wks of age (3.9 ± 0.6 vs 1.8 ± 0.3 ng/mg tissue; p < 0.02, n = 4 ‐ 6 each group). Anandamide also tended to be higher in older rats; however, levels were 1000‐fold lower than 2‐AG. Consistent with the elevated endocannabinoids (EC) in dorsal medulla, CB1R antagonist SR141716 (36 pmol/120 nl) microinjection into NTS of older SD rats increased BRS (0.53 ± 0.08 baseline vs 1.06 ± 0.6 msec/mm Hg 60 min after SR141716; p < 0.05, n = 3). In conclusion, elevated ECs within the NTS appear to contribute to the BRS impairment observed in older SD rats.Grant Funding Source: Supported by NIH: P01‐HL51952, R01‐DA03690, and RTI International
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