Secretion of insulin-like growth factor I and II from blood into
milk of lactating goats
C.G. Prosser, I.R. Fleet, A.J. Davis, R.B. Heap
Dairying Research Corporation, Ruakura Agricultural Centre,
Private Bag, Hamilton, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1991, 51: 245-248
Milk from normally lactating goats contains on average 11 ng/ml
IGF-I and 106 ng/ml IGF-II, as determined by specific radioimmunoassay.
The present study was an attempt to determine whether IGFs in milk could
have originated from the blood. 125 I labelled IGF-I or IGF-II was
infused directly into one gland via a pudic arterial catheter for 60
mins and their appearance in milk followed for 720 min. A total of
5.2% of [125 I]IGF-I infused and 10.0% of [125I]IGF-II was recovered
from milk from both glands. Radioactivity consisted of TCA precipitable
material, which eluted from Sephacryl S-200 as free and protein-bound
IGF, and TCA soluble material which probably represents degraded
products of the peptides. The amount and time course of secretion of
TCA soluble radioactivity in milk from both glands was similar,
indicating degradation of infused peptide at textra-mammary sites.
Maximum specific activity in milk from the infused gland occurred at
80-120 min for IGF-I and 120 min for IGF-II and was 2.5 fold higher than
milk from the non-infused gland. The lower milk/plasma ratio for
immunoreactive IGF-I compared with 125I labelled IGF-I suggests all milk
IGF-I might be derived from the circulation whereas similar calculations
with IGF-II suggests only 78% of milk IGF-II could be accounted for by
its transfer from blood.
Keywords: NZSAPAB;
Goats; IGF-I, IGF-II; milk
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Last Updated 25-01-1997
