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■科學家發現，受到壓力的老鼠的抗癌能力較普通老鼠高。資料圖片
有研究發現指，實驗鼠在受壓時(例如與其他老鼠打鬥)，都較在普通情況下的同類更能對抗癌症。科學家表示，結果有助發現潛在的神經抗癌治療。
負責是次研究的神經科學系教授杜林表示：「我們的生活方式對診斷癌症的影響，遠較我們之前想像的大。」
杜林的小組為實驗鼠注入會迅速擴散的皮膚癌—黑色素瘤，並讓癌細胞生長。他們將部分實驗鼠放在大籠，內有很多玩具、空間和其他同伴，其他的實驗鼠則放在普通的小籠。
3個星期後，在大的「刺激籠」內，實驗鼠的腫瘤縮少差不多一半，6星期後更縮少77%，其中17%實驗鼠的腫瘤在沒有癌症治療下完全消失。
杜林相信，在「刺激籠」的老鼠並非受到普通刺激，而是受了壓力。杜林說：「你可在一些老鼠身上找到咬過或打鬥的痕跡。」
雖然傳統智慧認為壓力是不健康的，但身體對壓力的回應是很複雜的，針對壓力釋出的荷爾蒙可有正面作用。
為了凸顯成效並非源自運動，研究員在小籠放入滾輪，小籠的老鼠比大籠的老鼠跑多3倍以上，但前者並沒有更強的抗癌能力。
實驗顯示，老鼠在受壓下會產生一種名為「腦源性神經營養因子」的大腦化學物質，這種物質會減少瘦素的製造，而瘦素是一種與胃口、黑色素瘤、前列腺癌和乳癌有關的荷爾蒙。科學家認為，瘦素越多，腫瘤便越少。瘦素在老鼠和人類身上的效用不同，而癌症的生長速度在被注射腫瘤的老鼠和人類身上亦各異；然而杜林相信，研究仍能在人類身上應用。 ■路透社 ■資深翻譯員 羅國偉
Stress Curbs Cancer in Mice
Experiments with mice showed that animals put into a stressful situation, even fighting with other mice, did a better job of fighting tumors than mice left to chill out. They said their findings point to a possible neurological treatment for cancer.
"The way we live, and how we live, may well have a much bigger impact on the prognosis of cancer than we recognized previously," Dr. Matthew During, a professor of neuroscience who worked on the study said.
During's team injected mice with melanoma, a type of fast-growing skin cancer, and let the tumors grow. They put some of the mice in a large cage, with lots of toys, space and many more other mice than usual. Other mice stayed in ordinary lab cages.
After 3 weeks, tumors shrank almost in half in the mice in the "stimulating" cage and they shrank 77 percent after 6 weeks. The tumors completely disappeared in 17 percent of the mice, with no other cancer treatment.
During believes that more than simple stimulation is at work in the mice. The mice in the "enriched" cages were a little stressed out. "You find some of them with little bite marks and fight marks," said During.
Although common wisdom holds that stress is not healthful, the body's response to stress is complex, and hormones released in response to stress can have positive effects.
To show the benefits were not simply due to exercise, the researchers placed running wheels in the smaller cage. The mice ran up to 3 times as far as the mice in the large cage, but were not more resistant to cancer.
Experiments to see what was happening biologically in the mice showed the stressed mice were producing more of a brain chemical called brain-derived neurotrophic factor. This compound reduces the production of leptin, a hormone linked with appetite and also associated with melanoma, prostate and breast cancer. The more leptin the mice produced, the smaller their tumors were.
Leptin acts differently in mice than it does in humans, and cancer grows differently in mice injected with tumors than it does in people. But During believes the findings may nonetheless apply to people. ■Reuters
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