Effects of dietary gamma-linolenic acid on blood pressure and adrenal angiotensin receptors in hypertensive rats

• Published in: Proceedings of the Society for Experimental Biology and Medicine Vol. 218; no. 3; p. 234
• Main Authors: Engler, M M, Schambelan, M, Engler, M B, Ball, D L, Goodfriend, T L
• Format: Journal Article
• Language: English
• Published: United States 01-07-1998
• Subjects: Adrenal Glands - drug effects; Adrenal Glands - metabolism; Aldosterone - blood; Angiotensin II - metabolism; Animals; Blood Pressure - drug effects; Corticosterone - blood; Dietary Fats, Unsaturated - pharmacology; gamma-Linolenic Acid - pharmacology; Hypertension - physiopathology; Male; Rats; Rats, Inbred SHR; Receptors, Angiotensin - metabolism; Renin - blood
• ISSN: 0037-9727
• DOI: 10.3181/00379727-218-44292

In a previous study, we showed that dietary gamma-linolenic acid (GLA), an omega-6 polyunsaturated fatty acid found in borage oil (BOR), attenuates the development of hypertension in young spontaneously hypertensive rats (SHR). The purpose of this study was to determine the effects of dietary GLA on established hypertension in adult rats, as well as its effects on components of the renin-angiotensin-aldosterone axis. For 5 weeks, male SHR (14-15 weeks old) were fed a basal fat-free diet to which 11% by weight of sesame oil (SES) or BOR was added. Systolic blood pressure (SBP), determined by the tail cuff method, and weight were measured weekly. Plasma renin activity (PRA), aldosterone (PA), and corticosterone (PC) levels were measured at the end of the dietary treatments. The adrenal glands were homogenized, and angiotensin II (ANG II) binding was measured and plotted according to Scatchard. Systolic blood pressure was 12 mmHg lower at Week 5 in SHR fed the BOR diet compared to SES-fed rats (P < 0.005). Weight gains were similar in both dietary groups. Plasma aldosterone was lower, PRA was higher, and the PA/PRA ratio was significantly lower (P < 0.05) in BOR-fed rats. Levels of PC were the same in both groups. The BOR-enriched diet reduced adrenal ANG II receptor density and affinity compared to the SES diet. Results suggest that BOR inhibits adrenal responsiveness to ANG II by an action on adrenal receptors. Our findings demonstrated that dietary GLA lowers SBP in adult SHR. This effect may be mediated, at least in part, by interference with the renin-angiotensin-aldosterone system at the level of adrenal ANG II receptors.