Protodioscin is a steroidal saponin found in Tribulus terrestris and other plants. It has been found to trigger the release of nitric oxide in corpus cavernosum tissue and also produce statistically significant increases in hormonal levels. Protodioscin is a steroidal saponin found in Tribulus terrestris and other plants. It has been found to trigger the release of nitric oxide in corpus cavernosum tissue and also produce statistically significant increases in hormonal levels. A steroidal saponin found in tribulus terrestris.