Fish Oil Supplementation Attenuates Blood Pressure Response but Not Renal Vasoconstrictor Response to Orthostatic Stress in Healthy Older Humans
Authors: Drew Rachel C , Clark Christine M , Monahan Kevin D 
Published: November 2023

During orthostatic stress, sympathetically mediated renal vasoconstriction redirects blood flow from the kidneys to the systemic circulation to maintain blood pressure (BP) (Momen et al., 2006). Healthy older people exhibit an augmented renal vasoconstrictor response to lower body negative pressure (LBNP) compared to healthy young people (Clark et al., 2015). Dietary intake of omega‐3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oil (FO), can attenuate (Carter et al., 2013) or augment (Monahan et al., 2004) sympathetic responses to neural and physiological stressors. However, the effect of FO on the renal vasoconstrictor response to orthostatic stress is unknown. Therefore, ten healthy young (5 men; mean ± SEM 25 ± 1 y) and ten healthy older (3 men; 66 ± 2 y) subjects ingested 4 g FO daily for 12 weeks, and underwent graded LBNP (−15 and −30 mmHg) pre‐ and post‐FO supplementation. Renal blood flow velocity (RBFV; Doppler ultrasound), mean, systolic, and diastolic BP (photoplethysmographic finger cuff), and heart rate (HR; electrocardiogram) were recorded during both trials. Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as mean BP/RBFV, and pulse pressure (PP) was calculated as systolic BP ‐ diastolic BP. Statistical analysis involved repeated measures analysis of variance. Baseline values were similar between age groups for RVR (older: 2.0 ± 0.2 AU; young: 1.7 ± 0.1 AU), RBFV (older: 51 ± 6 cm.sec−1; young: 53 ± 3 cm.sec−1), SBP (older: 125 ± 3 mmHg; young: 118 ± 3 mmHg), PP (older: 53 ± 3 mmHg; young: 52 ± 3 mmHg), and HR (older: 63 ± 3 b.min−1; young: 58 ± 2 b.min−1). The older group had higher baseline diastolic BP than the young group (older: 72 ± 1 mmHg; young: 66 ± 2 mmHg; P < 0.05). FO supplementation did not affect baseline cardiovascular values, but did increase erythrocyte EPA (older: pre‐FO 0.6 ± 0.1 % vs. post‐FO 3.2 ± 0.6 %; young: pre‐FO 0.5 ± 0.0 % vs. post‐FO 1.9 ± 0.5 %; P < 0.05) and DHA content (older: pre‐FO 3.6 ± 0.3 % vs. post‐FO 7.0 ± 0.6 %; young: pre‐FO 4.3 ± 0.2 % vs. post‐FO 6.0 ± 0.6 %; P < 0.05) in both age groups. FO did not affect responses to LBNP in either age group of RVR (older −30 mmHg: pre‐FO 20 ± 5 %, post‐FO 22 ± 3 %; young −30 mmHg: pre‐FO 6 ± 2 %, post‐FO 13 ± 6 %) or RBFV (older −30 mmHg: pre‐FO −10 ± 2 cm.sec−1, post‐FO −9 ± 1 cm.sec−1; young −30 mmHg: pre‐FO −6 ± 1 cm.sec−1, post‐FO −8 ± 2 cm.sec−1). However, FO attenuated the mean BP response to LBNP in the older but not the young group (older −30 mmHg: pre‐FO −4 ± 1 mmHg vs. post‐FO 0 ± 1 mmHg, P < 0.05; young −30 mmHg: pre‐FO −5 ± 1 mmHg vs. post‐FO −5 ± 2 mmHg). FO tended to attenuate the HR response to LBNP in the older group (older −30 mmHg: pre‐FO 9 ± 2 b.min−1, post‐FO 5 ± 1 b.min−1, P = 0.06; young −30 mmHg: pre‐FO 9 ± 3 b.min−1, post‐FO 10 ± 2 b.min−1). FO did not affect systolic or diastolic BP, or PP, responses to LBNP in either age group. In conclusion, FO supplementation attenuates the mean BP response but does not affect the renal vasoconstrictor response to LBNP in healthy older humans. These findings suggest that FO affects factors involved in the BP response but not the renal vasoconstrictor response to orthostatic stress in older people.Support or Funding InformationSupported by National Institutes of Health grants HL092309, AG024420, UL1 TR000127, and P01 HL096570.