Alkaline extraction and characterization of cholecystokinin-immunoreactivity from rat gut

Generally some variation of neutral or acid extractants has been used to recover immunoreactive cholecystokinin (CCK) from gut as well as from brain. Recovery of CCK in 0.1 N NaOH extracts from gut mucosa, gut muscle, or whole gut ranged up to threefold higher than in similar water or 0.1 N HCl extracts, although the reverse was the case for the extraction of secretin from the same tissue. CCK-immunoreactive peptides from rat gut were found to resemble a CCK-33-like peptide, sulfated CCK-12 and CCK-8, as well as smaller COOH-terminal fragments, which are larger than the C-terminal tetrapeptide amide. The fraction of immunoreactivity in the form of a CCK-33-like peptide was greater, although the total recovery was less, in acid extractants of whole gut. Proper interpretation of dynamic changes in gut CCK in response to fasting, feeding, and other laboratory manipulations requires efficient extraction of total immunoreactivity.