This regulates the enzymatic quantity in pancreatic juice

The correct option is Pancreozymin.

To understand why this is the correct answer, let us break down the physiological regulation of pancreatic secretions step-by-step:

1. Composition of Pancreatic Juice: Pancreatic juice is composed of two main fractions: an aqueous bicarbonate component (rich in water and bicarbonate ions) and an enzymatic component (rich in digestive enzymes like amylase, lipase, and trypsinogen).

2. Hormonal Regulation: The secretion of these components is regulated by hormones released by the enteroendocrine cells of the duodenum in response to food entering from the stomach.

3. Secretin vs. Pancreozymin (CCK):
- Secretin primarily stimulates the duct cells of the pancreas to secrete a large volume of watery fluid rich in bicarbonate ions (${\mathrm{HCO}}_3^{-}$) to neutralize stomach acid.
- Pancreozymin (which is now known to be the same hormone as Cholecystokinin or CCK, often referred to as CCK-PZ) acts on the acinar cells of the pancreas to stimulate the secretion of a juice rich in digestive enzymes (the enzymatic quantity).

4. Conclusion: Historically and in specific contexts, Pancreozymin is the designated term that highlights the hormone's role in stimulating the release of pancreatic enzymes (hence "pancreo-" for pancreas and "-zymin" for enzyme). Therefore, it regulates the enzymatic quantity in pancreatic juice.