Endogenous digitalis-like factors in human milk.

Area of Science:

• Biochemistry
• Endocrinology
• Human Physiology

Background:

• Endogenous digitalis-like factors (EDLFs) are a group of compounds with structural and functional similarities to cardiac glycosides.
• These factors are found in various mammalian tissues and biological fluids, including plasma and breast milk.

Purpose of the Study:

• To quantify the concentration of EDLFs in human milk and colostrum.
• To compare EDLF levels in breast milk with those in healthy adults and pregnant women.
• To investigate the characteristics of EDLFs in milk, including their binding to milk proteins.

Main Methods:

• Measurement of EDLF concentrations using solid-phase radioimmunoassay (RIA) with antidigoxin antibodies.
• Assay of EDLF concentrations using a radioreceptor assay (RRA) involving human placenta Na+/K(+)-ATPase.
• Analysis of milk and serum samples after heating and/or Sep-Pak C18 cartridge extraction.

Main Results:

• Mean EDLF concentrations in milk (35.6 ng/L) and colostrum (61.3 ng/L) were measured by RIA.
• Mean EDLF concentration in milk was 573 ng/L by RRA, with a wide range (0-2098 ng/L).
• EDLF concentrations in milk were higher than in healthy adults but comparable to third-trimester pregnancy serum levels.
• Heating and extraction significantly altered EDLF values in milk and serum.
• EDLFs in milk appeared to be unbound or weakly bound to milk proteins.

Conclusions:

• Human milk and colostrum contain significant concentrations of EDLFs.
• The levels of EDLFs in milk suggest a potential physiological role during lactation.
• EDLFs in milk exhibit different properties compared to serum EDLFs, particularly regarding protein binding.