Dietary phytosterols and phytostanols decrease cholesterol levels but increase blood pressure in WKY inbred rats in the absence of salt-loading.

BACKGROUND

There are safety concerns regarding widespread consumption of phytosterol and phytostanol supplemented food products. The aim of this study was to determine, in the absence of excess dietary salt, the individual effects of excess accumulation of dietary phytosterols and phytostanols on blood pressure in Wistar Kyoto (WKY) inbred rats that have a mutation in the Abcg5 gene and thus over absorb phytosterols and phytostanols.

METHODS

Thirty 35-day old male WKY inbred rats (10/group) were fed a control diet or a diet containing phytosterols or phytostanols (2.0 g/kg diet) for 5 weeks. The sterol composition of the diets, plasma and tissues were analysed by gas chromatography. Blood pressure was measured by the tail cuff method. mRNA levels of several renal blood pressure regulatory genes were measured by real-time quantitative PCR.

RESULTS

Compared to the control diet, the phytosterol diet resulted in 3- to 4-fold increases in the levels of phytosterols in plasma, red blood cells, liver, aorta and kidney of WKY inbred rats (P < 0.05). The phytostanol diet dramatically increased (> 9-fold) the levels of phytostanols in plasma, red blood cells, liver, aorta and kidney of these rats (P < 0.05). The phytosterol diet decreased cholesterol levels by 40%, 31%, and 19% in liver, aorta and kidney, respectively (P < 0.05). The phytostanol diet decreased cholesterol levels by 15%, 16%, 20% and 14% in plasma, liver, aorta and kidney, respectively (P < 0.05). The phytostanol diet also decreased phytosterol levels by 29% to 54% in plasma and tissues (P < 0.05). Both the phytosterol and phytostanol diets produced significant decreases in the ratios of cholesterol to phytosterols and phytostanols in plasma, red blood cells, liver, aorta and kidney. Rats that consumed the phytosterol or phytostanol diets displayed significant increases in systolic and diastolic blood pressure compared to rats that consumed the control diet (P < 0.05). The phytosterol diet increased renal angiotensinogen mRNA levels of these rats.

CONCLUSION

These data suggest that excessive accumulation of dietary phytosterols and phytostanols in plasma and tissues may contribute to the increased blood pressure in WKY inbred rats in the absence of excess dietary salt. Therefore, even though phytosterols and phytostanols lower cholesterol levels, prospective clinical studies testing the net beneficial effects of dietary phytosterols and phytostanols on cardiovascular events for subgroups of individuals that have an increased incorporation of these substances are needed.