A characterization of immunoreactive somatostatin in human milk.

In the present work, somatostatin-like immunoreactivity (SLI) in human milk was characterized. In the early postpartum period, SLI levels were highest on the first day after delivery, and then gradually declined. From the fifth day postpartum, SLI levels in milk seemed unchanged. On the fifth day after delivery, milk SLI was significantly (p less than 0.01) higher than plasma SLI (126.3 +/- 11.7 vs. 17.6 +/- 1.1 pmol/L). The results indicate an active transport from blood or synthesis of somatostatin within the mammary gland. Gel filtration studies of skimmed milk, as well as milk exposed to urea and HCl, and aspirated milk from the human premature newborn, revealed that the main portion of milk SLI either represents somatostatin covalently bound to a larger protein, or more likely, a high molecular weight variant of somatostatin.