Pancreatic insulin-, glucagon-, and somatostatin-positive islet cell populations during the perinatal development of the rat. II. Changes in hormone content and concentration.

Insulin, glucagon and somatostatin concentration were determined in the developing pancreas between 16 days post coitum and 10 days postnatal. Plasma insulin and glucagon concentrations were also measured. Pancreatic insulin content increased rapidly during the perinatal period and peaked in concentration on day 6 postnatal. Glucagon content also increased rapidly with the largest percentage increase occurring around the time of birth. The largest increase in somatostatin also occurred postnatally. Plasma insulin and glucagon concentrations were very high during the late fetal period. the insulin concentraton fell immediately after birth and rose slowly toward adult levels during the remainder of the period examined. Plasma glucagon was high during the entire neonatal period. The degree of differentiation of the islet cells, as estimated by their content of specific hormone products, is discussed in relation to the changes in cell volume reported n the preceding paper.