SAN DIEGO, CA (American Physiological Society) -- The simple sunflower seed may hold the key to reducing hypertension and associated loss of cognitive ability, and preventing debilitating strokes. A new research study may be an opening salvo in a new front in the war against strokes, the nation's third leading killer.

Background

This year, about 600,000 Americans will have a stroke and 160,000 of them will die. Many strokes are the consequence of atherosclerotic plaques that occur in one or more of the feeder arteries to the brain. The plaque activates a mechanism that triggers the clotting of the blood, a clot develops and blocks the artery, thereby leading to acute loss of brain function in a localized area.

One of the leading contributors to a stroke is hypertension. Before a stroke occurs, prolonged hypertension has been associated with a range of impairments and cognitive ability. Presently, evidence indicates that reduction of hypertension reduces the incidence and the susceptibility of patients to brain damage.

Now a researcher suggests that linoleic acid, a doubly unsaturated fatty acid, which is essential in nutrition in mammals. It cannot be produced in animals, the sources of this needed nutrient are vegetable seed oils, such as: safflower, sunflower, and hemp seed.

The Study

The objectives of the current investigation were to assess the effects of linoleic acid on the contraction of aortic rings, blood pressure levels, spatial reference memory and brain dopamine receptors in spontaneously hypertensive rats (SHRs). The hypothesis to be tested is that linoleic acid does not only help in controlling hypertension, but may also help in decreasing hypertension-induced cognitive decline by increasing dopamine D1 binding in specific rat brain regions.

To achieve these objectives the researchers set out to determine: the effects of linoleic acid administration on the contraction of aortic rings; the consequences of administering linoleic acid on the systolic blood pressure; the effects of linoleic acid administration on spatial reference memory; the impact of linoleic acid administration on the D1 receptor binding kinetics in specific regions of the rat brain.

The author of the study, "Effects of early nutritional supplementation of linoleic acid in Hypertension," is Vallie Holloway PhD, Loyola University Medical Center, Maywood, IL. She is presenting her findings at the upcoming scientific conference, "The Power of Comparative Physiology: Evolution, Integration and Application" an American Physiological Society (APS) intersociety meeting scheduled for August 24-28, 2002, at the Town & Country Hotel, San Diego, CA. To learn more about the conference and presentations go to: http://www.the-aps.org/meetings/aps/san_diego/home.htm

Dr. Holloway set out to contribute to the effort to find a possible mechanism by which linoleic acid is associated with hypertension-induced cognitive impairment. These findings may assist in formulating a strategy or treatment to control cognitive decline associated with hypertension.

Methodology

Rats were randomly divided into two groups. One group was used as control and the second group was treated with linoleic acid. In these experiments, spontaneously hypertensive rats (SHRs) were divided into three groups: SHRs of various ages were used: the three month old group, where the genes that trigger hypertension are fully expressed. This is then called the early hypertensive stage; the six month age group, labeled the mid-hypertensive stage; and the nine month age group, called the late hypertensive stage and drug solutions were administered.

Results

The principal findings of this study were as follows:

• Linoleic acid significantly improved the vasodilatory responses within the rat thoracic artery rings in the four and five month treated spontaneously hypertensive rats.

• Linoleic acid administration seems to significantly decrease the systolic blood pressures of SHRs at three and six months. The concurrent ingestion of linoleic acid seemed to be inversely related to elevated blood pressure levels.

• The memory of Spontaneously hypertensive rats (SHRs) at three, four, and five months were assessed with a maze and the results indicate that the latency period to find the platform was consistently significantly higher in the spontaneously hypertensive rats as compared to their controls. These findings clearly indicate that hypertension is associated with decline in spatial reference memory, consistent with those reported by other researchers in the field.

• In the three month-old SHRs, the effects of linoleic acid on spatial reference memory indicated no significant difference in the latency period. However, LA administration to six and nine month old SHRs, resulted in significant decline in spatial memory. This indicates that linoleic acid administration produced a significant improvement of spatial reference memory in these rats.

• Dopamine plays an important role in learning and memory. The D1 receptor in the hippocampus facilitates acquisition and retention of different working memory tasks In addition, D1 receptors are located on blood vessels. Activation of D1 results in widening of the arteries. Dopaminergic D1 binding kinetics were evaluated in the hippocampus, thalamus, hypothalamus and cortex of the control and SH rats. Results obtained indicate that controls had significantly higher D1 receptor density in all brain areas studied as indicated by higher Bmax as compared to the Spontaneously Hypertensive rats. Since SHRs exhibited a deficit in spatial reference memory, this suggests that D1 receptor density may be positively linked to spatial reference memory. This further supports the assertion that administering linoleic acid to SHRs did not only result in improvement of spatial reference memory but also significantly increased Bmax of D1 dopamine receptors.

Linoleic acid administration improved endothelial-dependent vasodilation in spontaneously hypertensive rats, associated with significant decline in blood pressure. In addition, linoleic acid administration resulted in the improvement in the observed hypertension-induced decline of spatial reference memory in SHRs which may be due to an increase expression of dopamine D1 receptors in rat brain regions. In conclusion, the current findings strongly suggest that the early incorporation of linoleic acid in the diet, may not only help in controlling hypertension, but may also improve hypertension-induced cognitive impairment.