Did your parents ever tell you that eating oily fish would make you clever? If so, you are probably aware that this particular old wives tale has now come true. And what magical ingredients do oils contain? The simple answer is fatty acids – fat molecules that are either saturated or unsaturated. Of the unsaturated fats, long-chain polyunsaturated fatty acids (PUFAs) are the most magical of all. Essential to human health, PUFAs are needed for building cell membranes, regulating the body's response to pain and maintaining a strong immune system. However, our bodies are unable to make these essential nutrients and we have to eat the right foods in order to obtain them. By regularly forking down fish, for example, we gain enough PUFAs to promote eye and skin health, reduce the risk of cardio-vascular disease and improve long-term memory. Your parents were right.
But what does this have to do with hares? As fellow mammals, hares have a similar need for PUFAs and a similar inability to synthesise them. Diet has a big influence on the fatty acid composition of their cell membranes. Recent studies on rats and humans suggest that muscle performance is reduced if muscle membranes don't contain enough fatty acids. Quite a serious issue for hares, which avoid predators by sprinting at speeds of up to 80 km h–1.
Teresa Valencak and colleagues at the University of Veterinary Medicine in Vienna were intrigued by the idea that hares might safeguard their athleticism by keeping their muscles enriched with fatty acids. The researchers were particularly eager to discover if leg muscles contained especially high levels of PUFAs, and if PUFA contents varied with seasonal differences in diet.
Valencak and the team collected over 100 hares during one summer and two winters in Austria. The scientists dissected muscles from various locations in the hares' bodies and measured fatty acid contents in cell membranes. To their surprise, they discovered that cell membranes from both skeletal and heart muscles had a high degree of unsaturation with 66% PUFAs. Results from studies on other mammals report PUFA proportions between 36% and 54%. Valencak's work therefore reveals that hares boast the highest proportion of PUFAs reported in any mammalian tissue. The team also discovered remarkable consistency in the PUFA contents of different muscles and suggest that, by maintaining record levels of PUFAs in muscle cell membranes, hares ensure that PUFAs are available for all other body parts.
The team's work also revealed that the fatty acid composition of hare cell membranes changes with season. The proportion of PUFAs increased markedly in hares during winter months, largely at the expense of saturated fatty acids. The changes in the types of fats present at different times of the year indicate that hares have a specific winter need for certain types of PUFAs. The researchers suggest that high levels of these PUFAs may help the animals to keep warm in the winter cold.
Taken as a package, Valencak's study points to PUFAs as having a critical role to play in the functioning of hare muscle cells. In the knowledge that hares can run four times faster than similarly sized rodents, it will be fascinating to learn if their record PUFA content is linked to their swift speed. Could it be that fatty acids maketh the hare?
- © The Company of Biologists Limited 2004