Because the secretory cells are located in the epidermis and are connected to the skin surface, stingray venom is easily transferred by direct contact through the laceration and into the body of the enemy (Pedroso et al., 2007). This venom is known to be heat sensitive, or thermolabile, becoming inactive at high temperatures (Magalhaes et al., 2008). This aspect of the venom will be discussed in more detail in the Treatment section of this website. The venom in stingrays also exhibits two-fold higher activity in freshwater, Potamotrygon falkneri, then in marine rays, Dasyatis guttata (Barbaro et al., 2007).
As shown by the table below, the LD50, the dose administered which results in at least 50% of the tested organisms dying, is around 100 mg kg-1 for the Himantura gerrardi ray which can be found in both freshwater and marine environments (Dehghani et al., 2009).
Table 1. Lethal activity of Himantura gerrardi epithelium extract when injected into mice. Used with permission from (Dehghani et al., 2009)
The venom of marine stingrays is made up of a number of components including polypeptides with large molecular mass, serotonin, and hyaluronidases. Hyaluronic acid forms a large part of the vertebrate extracellular matrix. The hyaluronidases found in the stingray venom are enzymes that cleave hyaluronic acid in order to increase absorption and diffusion rates of the venom through tissues in the victim. These enzymes are examples of spreading factors (Magalhaes et al., 2008). These proteins that help break down local tissues in victims are located in the stingray’s mucus layer which comes into direct contact with the laceration and wound (Magalhaes et al., 2006). Enzymatic degradation in the victim’s tissue is similar in both freshwater and marine envenomations. In both types of stingrays, the venom contains proteases which act as diffusion factors. These proteases have broad substrate specificity, allowing the venom to degrade multiple proteins and segments of the extracellular matrix resulting in extensive tissue damage. Marine and freshwater tissue extracts revealed that both types of venom are immunogenic, inducing significant amounts of antibodies (Barbaro et al., 2007). The toxin, itself, is made up of soluble proteins that are labile because of their natural instability and the fact that these proteins are inactivated by enzymatic activity and heating (Russell et al., 1958).