Abstract
Cerastes cerastes venom in low concentrations (0.8-2.5 micrograms/ml) inhibited the response of the rat vas deferens to field stimulation, while higher concentrations (4-8 micrograms/ml) causes a contracture that was reversed by washing and transiently blocked by phentolamine. The effect of the venom and guanethidine (10(-7) M) was reversed by tyramine (4.6 x 10(-8) M) but unaffected by hexamethonium (1.4 x 10(-7) M). When the response to field stimulation was inhibited by the venom the response to norepinephrine was either potentiated or unchanged.