Differential changes in the milk concentrations of epidermal growth factor and insulin-like growth factor-I during lactation in the tammar wallaby, Macropus eugenii.
Insulin-like growth factor-I (IGF-I) and epidermal growth factor (EGF) have been measured in milk during lactation of the tammar wallaby (Macropus eugenii) and related to the total growth-promoting activity of the milk as determined in cultured L6 rat myoblasts. EGF increased throughout lactation from 10 ng/ml at 99 days to 25 ng/ml at 263 days. As a greater increase occurred with total soluble proteins in the milk, the EGF content per milligram of protein was decreased slightly during lactation. That EGF is secreted in tammar milk at a relatively constant amount is consistent with data from eutherian mammals, even though actual EGF concentrations either decrease or increase during lactation in those species. A very different pattern of secretion was observed with IGF-I, which increased sixfold to a maximum of 1043 ng/ml at 205 days of lactation before falling to approximately 300 ng/ml toward the end of lactation. The protein synthesis-stimulating activity of the milk measured in myoblasts demonstrated a similar pattern to that obtained with IGF-I. The IGF-I changes are unlike the data reported in eutherian mammals in which this growth factor falls to low levels from high concentrations in initial colostrum. The highest concentration of IGF-I in tammar milk coincides with the changeover to a high fat, high protein, low hexose milk composition that is produced at an increased rate when the young leaves the pouch. IGF-I in tammar milk may be important for mammary gland maturation at this stage.
Ballard
F J
FJ
Cooperative Research Centre for Tissue Growth and Repair, Adelaide, Australia.
Grbovac
S
S
Nicholas
K R
KR
Owens
P C
PC
Read
L C
LC
D000818:Animals; D004815:Epidermal Growth Factor / Q000378:metabolism*; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007700:Kinetics; D007774:Lactation / Q000502:physiology*; D007614:Macropodidae; D008892:Milk / Q000378:metabolism*
D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I