Cholecystokinin/gastrin receptors in the pancreas of newborn (3-day-old) rats are of type A, as in control mature rats, revealed by pharmacological analysis of specific ' 251-Bolton-Hunter-reagent- day-old rats, 90 -125 kDa in 10-day-old rats and 85 -100 kDa in 14-day-old and 21 -day-old rats, as found in control adult rats. Endo-a-N-acetylglucosaminidase F treatment yielded a core protein of 42 kDa in all developmental stages. These findings are consistent with an age-related postnatal expression of distinct glycoforms of pancreatic cholecystokinin receptors. Furthermore, it was observed that the period 2-3 weeks after birth, characterized by stabilization of the mass of the cholecystokinin receptor, precedes the dramatic increase in the receptor number.Cholecystokinin (CCK) and gastrin are hormonal peptides that share the same C-terminal pentapeptide amino acid sequence [I]. Pancreatic acinar cells from dog and guinea pig have been shown to possess two types of CCK receptor [2 -61. The CCKA receptor type, has a high affinity for CCK, and the pancreatic CCKn or gastrin receptor type has a high affinity for gastrin and poorly discriminates between CCK and gastrin peptides.The existence of specific CCK receptors in term foetus and neonatal rat pancreas was previously documented, although acini or lobules seem to be unresponsive to CCK stimulation near birth [7-91. It was also shown that the capacity of the high-affinity sites on rat pancreatic acini, as well as amylase secretion due to CCK stimulation, gradually increases with