Concentrations of cholecystokinin (CCK) and secretin from neonatal guinea pig plasma were evaluated in relation to pancreatic growt, and secretion from dispersed pancreatic acini. Plasma CCK was low at birth (3.1±0.8 pmol/L) but rose markedly by day 15 (11.0±0.8 pmol/L,p<0.001). Plasma secretin was also low at birth (3.8±0.8 pmol/L) but peaked on day 4 (17.0±1.4 pmol/L,p<0.001) and remained elevated through d 15. Adult nonfasting plasma CCK and secretin levels were 12.3±0.8 and 8.9±1.5 pmol/L, respectively. Pancreatic weight more than doubled during the first week of life, with the greatest increase during the first 4 d (156±4 to 262±10 mg/100g body wt,p<0.001). Body weight increased most dramatically during the second week (126±9 to 190±7 gp<0.001). Amylase secretion from isolated acini stimulated by CCK-8, carbachol, phorbol ester, forskolin, and calcium ionophore (A23187) was present at birth. The percentage of total amylase content secreted in response to CCK, carbamylcholine, and secretin did not change during the first 2 wk of neonatal life, and was independent of surges in circulating CCK and secretin. These results indicate that functional maturity of the guinea pig pancreas for amylase secretion occurs early and is different from the rat, mouse, pig, and human. Since results can readily be compared between animals of different postnatal ages, the neonatal guinea pig is ideally suited for the study of hormonal effects on acinar cell
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