Most vipers don't waste their venom on any old mouthful. It takes time and energy to produce a gland-full of venom, so profligacy isn't an option. But just what triggers toxin synthesis wasn't clear until Norma Yamanouye and her colleagues began testing the response of Bothrops jararaca's venom glands to noradrenaline. The venom gland's adrenoceptor became desensitised to noradrenaline after venom was extracted from the snake, but after a month the receptor had regained its sensitivity. So once venom production was triggered,it didn't seem possible to stimulate the adrenoceptor again until the gland was recharged with venom 30 days later().
But was noradrenaline triggering the toxin's synthetic cycle? Yamanouye tested the gland's toxin-secreting cells by first depleting the gland's own noradrenaline and then giving the cells a dose of phenylephrine, to stimulate the adrenoceptor and see whether the stimulated cells began producing venom. While the team watched, the cells appearance changed, in preparation for making the snake's venomous protein `suggesting that stimulation of theα-adrenoceptor during or shortly after biting is essential for the onset of the venom production cycle' says Yamanouye.
