Decrease in insulin secretion in lactating rats.

Abstract

Changes in plasma insulin concentrations in the pregnancy, lactation and after-weaning period in female rats were investigated. Plasma insulin concentrations increased as pregnancy progressed, but there was a sharp decrease before parturition and the values remained at 20 to 30% of those in virgin rats throughout the lactation period. The concentrations again returned to the same levels as in virgin rats 3 days after completion of lactation. Decreased plasma insulin concentrations during the lactation period were seen in the portal and abdominal veins and in the carotid artery. Plasma insulin concentrations in lactating rats decreased in dose-dependent manner with increased litter sizes, but they returned to the values in the virgin rats when the litter sizes were decreased and lactation stopped. Since the same amounts of insulin secretion as in virgin rats were observed in lactating rats after administration of glucose, it was evident that insulin secretion from the pancreas is suppressed in lactating rats. Because plasma insulin concentrations were not decreased in rats with the galactophores sectioned beforehand even when a sucking stimulus was applied, and there were dose-dependent decreases in the blood glucose levels in abdominal vein and simultaneous stepwise decreases in the portal insulin levels in lactating rats as the litters become larger, it was assumed that drops in peripheral blood glucose levels with milk secretion have an effect on the decreased plasma insulin conccntrations in lactating rats.