Ontogeny of Immunoreactive Cholecystokinin, Vasoactive Intestinal Peptide, and Secretin in Guinea Pig Brain and Gut*

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Abstract
The ontogeny of cholecystokinin (CCK), vasoactive intestinal peptide (VIP), and secretin (SEC) as well as other brain and gut peptides has been extensively studied in the rat. However, since the guinea pig (GP) appears to be functionally more mature at birth than the rat, we hypothesized that the concentrations of brain peptides, but not necessarily of gut peptides, in GP neonates would be closer to adult concentrations than those in the rat. The concentration and organ content of these three peptides were determined at birth, at 7, 14, 21, and 28 days of age, and in the adult in various portions of the gastrointestinal tract and brain. VIP and CCK in the brain at birth are 75% of adult levels compared to less than 10% in the rat. VIP concentrations in the stomach, duodenum, and jejunum are relatively constant from birth through adult life, whereas in the rat, the intestinal VIP concentration increased 3- to 4-fold from birth to adulthood. SEC, which in the gut is found only in mucosal tissues, peaked at birth, remained low from 7-28 days of age, and rose again in the adult. CCK, which in the gut is found in both the mucosa and muscle wall, like SEC peaks at birth, then remains low from 7-28 days of age, and rises in the adult. It is concluded that the GP neuronal tissues are much more mature at birth than are those in the rat.