AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 6 1461-R1466, Copyright © 1994 by American Physiological Society
Circadian and ultradian rhythms of peripheral prolactin concentrations in lactating dairy cows
A. M. Lefcourt, R. M. Akers, D. L. Wood and J. Bitman
Milk Secretion and Mastitis Laboratory, United States Department of Agriculture, Beltsville, Maryland 20705.
To investigate possible circadian and ultradian periodicities for
peripheral prolactin in lactating dairy cows, integrated 15-min blood
samples taken sequentially over 48 h from six cows were analyzed by
radioimmunoassay. Cows were housed in an environmental chamber at 19
degrees C with lights on 0700 to 2300, fed daily at 0900, and milked at
0800 and 2000. Peripheral concentrations exhibited sinusoidal circadian
rhythms. For two cows, a nadir of 15 ng/ml occurred around 1900 and a
zenith of 29 ng/ml around 0730. For four cows, circadian rhythms were 180
degrees out of phase, with a nadir of 28 ng/ml around 0840 and a zenith of
40 mg/ml around 1920. Ultradian peaks, which varied in amplitude within and
among animals, showed no consistent relationship with either milking or
feeding. Spectral analyses indicated rhythms around 100 min for the first
two animals and 150 min for the four animals. In conclusion, there were no
simple relations between prolactin rhythms and lights on or lights off.
Further, results suggest that changes in the phase of circadian rhythms may
be associated with changes in the periods of ultradian rhythms.
