Complex sentence: It stimulates the acinar cells of the pancreas to release a juice rich in pancreatic digestive enzymes (hence the original name "pancreozymin") that catalyze the digestion of fat, protein, and carbohydrates.
Split into simpler sentences: It stimulates the acinar cells of the pancreas to release a juice rich in pancreatic digestive enzymes, hence the old name "pancreozymin". Together these enzymes catalyze the digestion of fat, protein, and carbohydrates.