The circulating insulin-like growth factors (IGF-I and -II) occur largely as components of a 140 kDa protein complex with IGF binding protein-3 and the acid-labile subunit (ALS). This ternary complex regulates the metabolic effects of the serum IGFs by limiting their access to tissue fluids. Since the tissue distribution of ALS gene expression has not been reported in humans or other primates, and the baboon has been developed as a model for human growth and metabolism, it was chosen for this study. A cDNA for baboon ALS was isolated by reverse transcriptase polymerase chain reaction and used to screen Northern blots of total RNA from the lung, liver, kidney, adrenal, muscle, intestine, and spleen of adult baboons. The expression of the single approximately 2.2 kb baboon ALS mRNA transcript was restricted to the liver, suggesting that serum ALS levels are controlled by regulation of hepatic expression of this peptide in primates.
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