What effect does bufotoxin, secreted by toads, have on the body?

Bufotoxin is a potent compound found in the secretions of certain toads, notably the Bufo species. Its primary physiological effect is on the heart and circulatory system. This toxin acts similarly to certain cardiac glycosides, which can influence heart rate and rhythm by inhibiting sodium-potassium ATPase. This inhibition leads to an increase in intracellular sodium and calcium levels, ultimately enhancing the contractility of the heart muscle. Consequently, bufotoxin can result in effects such as increased heart rate, changes in blood pressure, and even arrhythmias, which are critical considerations in toxicology.

The other options do not accurately represent the main action of bufotoxin. While substances that affect the liver or muscle contractions exist, bufotoxin primarily targets the cardiovascular system. Similarly, while nerve growth stimulation is a notable area of study in neurobiology, bufotoxin does not play a role in this process. Thus, the correct answer emphasizes the toxin's significant impact on cardiac function and the circulatory system.