Effects of dietary borage oil rich in gamma-linolenic acid on blood pressure and vascular reactivity

To assess the effects of dietary borage oil on blood pressure and vascular reactivity, male Sprague-Dawley rats were fed a purified diet with 11% wt of either sesame oil (SES) rich in oleic acid or borage oil (BOR) rich in gamma-linolenic acid for 7 weeks. Blood pressure measured by tail cuff method, intraarterial pressor response to graded intravenous infusion of angiotensin II (AII) and norepinephrine (NE) and vascular reactivity of isolated aortic segments to potassium chloride (KCL), NE, serotonin and AII were studied. BOR-fed rats had lower systolic blood pressure which was most marked at weeks 3, 5 and 6. Moreover, BOR-fed rats had attenuated in vivo pressor responses to both NE and AII. Maximal contractile force by aortic segments in vitro in response to NE and AII was significantly lower in BOR-fed rats. There was no difference in the contractile responses to KCL or serotonin. The results indicate that the blood pressure lowering effect of BOR may be mediated by alterations in the pressor responses and vascular reactivity to NE and AII.