The Development of Pancreatic and Gastrointestinal Somatostatin-Like Immunoreactivity and Its Relationship to Feeding in Neonatal Rats*

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Abstract
Using a specific RIA technique, we have determined the somatostatin-like immunoreactivity (SLI) concentrations in acid extracts of pancreatic and gastrointestinal tissues and studied their relationships to feeding in fed and 15-h-fasted immature (less than 24 days old) rats. Mean pancreatic SLI concentrations per unit of protein were low before and immediately after birth before the initiation of feeding. They increased 7-fold during the first 3 days and remained high for the next 2 weeks. Gastric SLI concentrations were also low before and immediately after birth and increased progressively with age up to day 21 (time of weaning), followed by an abrupt increase at day 24, especially in 15-h-fasted rats. The mean SLI concentrations in the duodenum and jejunum were 4.9–6.3 times higher than that in the gastric antrum 1 day before birth and were also significantly higher than those in the gastric antrum for the first 3–7 days. No significant difference was found by age in the gel filtration patterns of tissue extracts from the pancreas, gastric antrum, and duodenum in fetal and fasted 3- and 24-day-old rats. I conclude from these findings that: 1) the developmental patterns of pancreatic and gastointestinal SLI show a close relationship with feeding, suggesting the important role of somatostatin in the digestive functions and nutrition in immature rats, and 2) the quantitative distribution of somatostatin in the gastrointestinal tract markedly differs so that there is intestinal predominance in fetal or neonatal rats, and predominance in the stomach in adult rats.