Plant-Derived Gamma-Linolenic Acid Found to Suppress Contraction of a Major Artery Supplying the Brain

Research Background and Findings

The basilar artery supplies blood to vital regions of the brain, including the brainstem. Excessive contraction of this artery can narrow the blood vessel and reduce blood flow to the brain. Therefore, understanding the mechanisms that regulate vascular contraction is important for investigating cerebrovascular disorders.

GLA is an omega-6 polyunsaturated fatty acid found in plant oils such as evening primrose oil and borage oil. The research team previously demonstrated that GLA inhibits TP receptor-mediated contraction in coronary arteries, which supply blood to the heart. However, its effects on cerebral arteries remained unclear.

In the present study, the researchers investigated the effects of GLA on isolated pig basilar arteries. GLA inhibited contractions induced by U46619, a selective TP receptor agonist, and prostaglandin F_2α (PGF_2α). Pharmacological analysis suggested that GLA acts as an antagonist of the TP receptor.

Interestingly, GLA also inhibited contractions induced by PGF_2α even when TP receptors were blocked. Furthermore, it suppressed contractions induced by endothelin-1 (ET-1), another potent vasoconstrictor. These findings suggest that GLA also acts through mechanisms independent of TP receptor antagonism. In contrast, GLA had no apparent effect on contractions induced by high extracellular K⁺, suggesting that direct inhibition of voltage-dependent Ca²⁺ channels is unlikely to be a major mechanism.

To investigate these additional mechanisms, the researchers examined the involvement of K⁺ channels, which regulate vascular smooth muscle activity. They found that barium ions (Ba²⁺), which block certain types of K⁺ channels, attenuated the inhibitory effects of GLA on PGF_2α-induced contractions during TP receptor blockade and on ET-1-induced contractions. These findings suggest that activation of Ba²⁺-sensitive K⁺ channels, potentially including inwardly rectifying potassium (K_ir) channels, contributes to the TP receptor-independent inhibitory effects of GLA.

Taken together, the findings suggest that GLA inhibits basilar artery contraction through TP receptor antagonism and possible activation of Ba²⁺-sensitive K⁺ channels (Figure 1).

However, because the experiments were performed using isolated pig arteries, further studies are needed to determine whether dietary intake of GLA can improve cerebral blood flow or help prevent cerebrovascular disorders in humans.

Figure 1. Proposed Mechanisms Underlying the Inhibitory Effects of GLA on Basilar Artery Contraction
GLA may suppress basilar artery contraction through TP receptor antagonism and possible activation of Ba²⁺-sensitive K⁺ channels. K_ir channels and subsequent membrane hyperpolarization may contribute to the latter mechanism.