AJP - Endocrinology and Metabolism, Vol 244, Issue 3 253-E261, Copyright © 1983 by American Physiological Society
Cortisol and its possible role in regulation of sodium and potassium in human milk
B. S. Keenan, S. W. Buzek and C. Garza
Cortisol (F), Na, and K were measured in human milk samples taken every 4 h
during 28 24-h cycles in 19 subjects. F in milk, measured by
radioimmunoassay of unchromatographed extracts, demonstrated a circadian
variation similar to that of plasma F and was dexamethasone-suppressible.
Values ranged from 220 +/- 41 (SE) ng/dl at 2300 h to 1,214 +/- 210 at 0700
h. When milk extracts were chromatographed, a similar circadian variation
was seen, and F ranged from 87 +/- 27 (SE) ng/dl at 2300 h to 784 +/- 164
at 700 h. The morning values of F exceeded previous estimates of
corticosteroid binding capacity in milk, indicating the possibility of
significant levels of unbound F. The subjects were divided into three
groups according to time postpartum: I, 3.5-6 wk; II, 8-18 wk, and III,
20-32 wk. In milk, normalized values of F (unchromatographed) and
electrolytes (x/means) were compared, with x the value at time t and means
the mean value for a 24-h cycle. A significant circadian variation was seen
in milk for (x/means)Na, (x/means)K, (x/means)Na/K, and x/means)F.
Correlation of (x/means)F with (x/means)Na 4 h later was negative in all
three groups (r = -0.36 to -0.56, P less than 0.10-0.001) as was (x/means)F
vs. (x/means)Na/K (r = -0.33 to -0.61, P less than 0.10-0.001); (x/means)F
vs. (x/means)K 4 h later was positive (r = 0.38 to 0.52, P less than
0.05-0.001). Dexamethasone administration caused a significant decrease in
milk means Na and an increase in meansK in all five subjects (P less than
0.01). Thus, milk Na and K concentrations appeared regulated by adrenal
corticosteroids.
