Beavers and drug discovery

The eighth season of BBC2’s Springwatch is upon us. As usual, I am not watching it live but recording it so that I can skip through the inane witterings of the presenters and the repetitive footage of creatures with which the programme-makers are obsessed — playful otters, noble red deer, cute seal pups, etc.

With the more recent series, and the spin-offs we now get in autumn and winter, I have also found myself fast-forwarding through blurry infrared footage of ripples in nocturnal streams, as the presenters gush about reintroducing the Eurasian beaver (Castor fiber) to Britain after an absence of 800 years.

The beaver’s extinction from these islands in about 1300 was mainly due to hunting. Trappers not only sought the animals’ pelts but also collected castoreum, a resin-like exudate from the mature beaver’s castor sacs. Both sexes have these sacs, which are often called scent glands although they are not true glands.

The trappers would retain some castoreum to smear on bait so as to lure more animals into their traps. But most was sold, mainly for medicinal purposes.

The Romans believed that the fumes of burning castoreum could induce abortion. Medieval medics employed it for various complaints, including headache, cramps, hysteria, nervousness and impotence. Paracelsus used it to treat epilepsy. It remained in the materia medica until about 1700.

Castoreum still has a reputation in some cultures as an aphrodisiac. It is also used in perfumery and to add flavour and odour to cigarettes. Even now, a pair of castor sacs can be worth more than the animal’s pelt.

Castoreum may have helped in some medical conditions because it contains salicylic acid, which the beavers ingest by dining on willow bark. But it also has a complex and diverse range of minor components, known as nupharamine alkaloids. Researchers have recently begun beavering away to investigate these alkaloids as possible lead compounds in drug discovery.