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.
Proceedings of the New Zealand Society of Animal Production, Volume 51, , 197-202, 1991
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