Mucosal gastrin receptor. V. Development in newborn rats.

We determined the development of the oxyntic gland mucosal gastrin receptor in rats killed at various times from 5 to 60 days after birth. Rats were weaned on the 18th day after birth. Newborn animals had no detectable gastrin binding, high serum gastrin levels (800-1,200 pg/ml), low antral gastrin levels (0.5-2.0 micrograms/g tissue), or high pH of gastric contents (pH greater than 5.0) and did not respond to pentagastrin. At the time of weaning, serum gastrin dropped to 600 pg/ml and reached adult levels (300 pg/ml) on day 40. Antral gastrin increased to 7.5 micrograms/g tissue on day 20 and reached adult levels (20 micrograms/g tissue) on day 22. Specific binding of gastrin was first detected on day 20 and reached the adult level of 4 fmol/mg protein on day 60. Pentagastrin significantly stimulated acid secretion on day 20 and DNA synthesis on day 25. Prevention of weaning through day 25 decreased the magnitude but did not prevent or delay the onset of the above changes. These results indicate that 1) the absence of a gastrin response in newborn rats is due to a lack of gastrin receptors, 2) development of gastrin receptor and biological sensitivity to gastrin appear at the time of weaning, and 3) the development that occurs with weaning is enhanced but not triggered by the shift to solid food.