Control of venom production and secretion by sympathetic outflow in the snake Bothrops jararaca.
Many studies have examined the morphological and biochemical changes in the secretory epithelium of snake venom glands after a bite or milking. However, the mechanisms of venom production and secretion are not yet well understood. The present study was undertaken to evaluate the role of the sympathetic nervous system in the control of venom production and secretion. Venom glands were obtained from Bothrops jararaca (Viperidae) snakes, either unmilked previously or milked 4, 7 or 15 days before they were killed. Levels of tyrosine-hydroxylase-like immunoreactivity were higher in venom glands collected 4 days after milking, coinciding with the maximal synthetic activity of the secretory cells. The only catecholamine detected by high-performance liquid chromatography was noradrenaline, indicating the presence of noradrenergic fibres in these glands. In reserpine-treated milked snakes, no venom could be collected, and electron microscopic analysis showed narrow rough endoplasmic reticulum cisternae, instead of wide cisternae, and less well-developed Golgi apparatus compared with milked untreated snakes, indicating impairment of protein synthesis and secretion. The administration of isoprenaline or phenylephrine (beta- and alpha-adrenoceptor agonists, respectively) to reserpine-treated milked snakes promoted the widening of the rough endoplasmic reticulum and restored venom production, but only phenylephrine restored the development of the Golgi apparatus and the formation of many secretory vesicles. These results provide the first evidence that the sympathetic nervous system plays an important role in venom production and secretion in the venom glands of Bothrops jararaca. Understanding the importance of noradrenergic stimulation in venom production may provide new insights for research into the treatment of snakebites.