Milk insulin, GH and TSH: relationship to changes in milk lactose, glucose and protein during lactogenesis in women.

Changes in concentration of insulin, growth hormone (GH) and thyroid stimulating hormone (TSH) in the whey fraction of mammary secretion of women during late pregnancy and lactogenesis were determined by radioimmunoassay. The milk hormone changes were compared to changes in the concentration of milk lactose, glucose and proteins which reflect the transition from colostrum to milk production during lactogenesis. During late pregnancy the average concentrations of insulin, GH and TSH in the colostrum of 2 women were 114.6 microU ml-1, 21.7 microU ml-1 and 14.1 microU ml-1, respectively. The concentrations of these hormones fell from high to low levels between day 1 and day 2 post partum concomitantly with the changes in the concentration of milk lactose, glucose and protein. On day 5 post partum the average milk concentrations of insulin, GH and TSH were 21.0 microU ml-1, 4.0 microU ml-1, and 5.0 microU ml-1, respectively. Similar milk hormone changes occurred in non breast feeding women during the first 11 days post partum. During 2 to 13 months of lactation one woman, the average concentration of milk insulin was 12 microU ml-1. In another woman, from 0 to 22 days after termination of breast feeding, the concentration of insulin increased from 19 to 56 microU ml-1. There were significant positive correlations between hormones and total protein and negative correlations between hormones and lactose, and hormones and glucose in women during lactogenesis and involution. The results showed that the changes in insulin, GH and TSH in milk were closely related to changes in secretory activity and permeability of the breast.