Pancreatic insulin content of nonpregnant, pregnant and postpartum rats and the developing rat fetus.

Abstract

A study was made of the insulin content of pancreases of nonpregnant, pregnant and postpartum rats and of their developing fetuses. The insulin content of the extracts was measured by radioimmunoassay, using crystalline rat insulin as a standard. The mean concentration of insulin in the pancreas of nonpregnant animals was 43 ± 6 μg./gm. The insulin concentration did not change significantly during late pregnancy or on day 4 postpartum. However, the weight of the pancreas was significantly greater in the pregnant and the postpartum rats. Thus, the total insulin content of the pancreas was greater in the pregnant and postpartum rats, being 23 ± 1.4 μg. and 24 ± 1.9 ng. respectively, as compared to 15 ± 0.7 μg. in the nonpregnant rats. The fetal pancreases were obtained at five periods of gestation: daily from day 18 to day 22, and on day 4 after birth. The mean weight of the fetal pancreases progressively and significantly increased from 4.4 ± 0.3 mg. on day 18 to 14.1 ± 1.5 mg. on day 20. On day 4 after birth, the mean pancreatic weight was 15.1 ± 0.5 mg. The fetal pancreatic insulin concentration rapidly and progressively increased from 14 ± 2 μg./gm. on day 18, to 80 ± 9 μg./gm. on day 21, and by day 4 after birth was 621 ± 103 μg./gm. By day 21 the fetal pancreatic insulin concentration had reached the prenatal peak and was already twice that of the mother. The total fetal pancreatic insulin content showed a progressive increase during the fetal life from 0.07 ± 0.01 μg. on day 18, to 1.23 μg. on day 21, a seventeen fold increase.