Regular Black Bean Consumption Is Necessary to Sustain Improvements in Small-Artery Vascular Compliance in the Spontaneously Hypertensive Rat

Abstract

Edible legume seeds, such as lentils, have been shown to modulate the structural and functional properties of hypertensive blood vessels, however, the effects of dried beans have not been similarly evaluated. To determine whether beans could attenuate hypertension-induced vascular changes (remodeling and stiffness) in relation to their phytochemical content, spontaneously hypertensive rats (SHR) were fed diets containing black beans (BB; high phytochemical content as indicated by their dark seed coat colour) or navy (white) beans (NB; low phytochemical content) for eight weeks. An additional follow-up phase was included to determine how long the alterations in vascular properties are maintained after bean consumption is halted. Assessments included blood pressure (BP), pulse wave velocity (PWV), vessel compliance (small-artery) and morphology (large-artery), and body composition. Neither BBs nor NBs altered BP or PWV in SHR. SHR-BB demonstrated greater medial strain (which is indicative of greater elasticity) at higher intraluminal pressures (80 and 140 mmHg) compared to SHR-NB. BB consumption for 8 weeks enhanced vascular compliance compared to SHR-NB, as demonstrated by a rightward shift in the stress–strain curve, but this improvement was lost within 2 weeks after halting bean consumption. BB and NB increased lean mass after 8 weeks, but halting BB consumption increased fat mass. In conclusion, regular consumption of BBs may be appropriate as a dietary anti-hypertensive strategy via their positive actions on vascular remodeling and compliance.

Processing method modulates the effectiveness of black beans for lowering blood cholesterol in spontaneously hypertensive rats

“…19 Thus, the absence of changes in blood pressure or aorta morphology in the present 4 week study with beans are in agreement with previous findings. 18,19…”

“…For example, direct assessments of blood vessel health by employing pulse wave velocity to determine arterial elasticity / stiffness could be an acceptable alternative to evaluate the cardiovascular benefits of pulses based on studies performed with other dietary formulations. [35][36][37][38] With respect to duration, changes in aorta morphology (elastin and collagen content) have been observed at 8 weeks but not 4 weeks with black beans or mixed beans (combination of black, navy, red kidney, pinto) in SHR, 18,19 and interestingly, the changes in vascular structure and function (improved compliance of resistance arteries) observed with black beans at 8 weeks occurred in the absence of blood pressure lowering. 19 Thus, the absence of changes in blood pressure or aorta morphology in the present 4 week study with beans are in agreement with previous findings.…”

“…In other studies, we observed lower total cholesterol and HDL cholesterol in SHR rats fed a mixed bean diet for 4 weeks compared to the pulse-free diet, 18 and that lowering of total cholesterol after an 8 week intervention with black beans was abolished after a 2-4 week washout period with a bean-free diet. 19 In the context of cardiovascular health, future studies need to examine the effects of pulse processing on vascular function as we have observed in both humans and animals that the benefits of pulse consumption on blood vessel health are due to alterations in vascular structure and function, [18][19][20]34 and are not necessarily explained by cholesterol-lowering per se as elevated cholesterol is only a risk factor for cardiovascular disease. As regulatory agencies move towards hard endpoints (e.g.…”

“…The bean powders were incorporated into semi-purified diets at an inclusion level of 30% (wt/wt) based on animal studies by us 18,19 and others. 22 The diets were formulate to be isocaloric and isonitrogenous, based on the proximate analysis of the processed beans ( Table 1).…”

“…Black beans (Phaseolus vulgaris L.) and spontaneously hypertensive rats (SHR) were chosen for this study because published data from our group shows that black beans lower total blood cholesterol in this model. 18,19…”