Characterisation and location of insulin-like-growth factor (IGF) receptors in the foetal bovine Semitendinosus muscle

We characterised IGFI and IGFII receptors and located them in bovine muscle during foetal growth. Semitendinosus muscle samples were taken from foetus es ranging from 80 to 270 days post-conception. The relative affinities of I-125-IGFII and I-125-IGFI mark the presence of typical type II and type I receptors in foetal muscle membranes. IGFII-specific binding is consistentl y five times greater than that of IGFI. The patterns of I-125-IGFII- and I- 125-IGFI-specific binding are similar. They increase up to 110 and 170 days post-conception, respectively (P < 0.05); thereafter, they decrease (P < 0 .05). This decrease was due to a fall in the number of receptors without an y change in affinity. At the adult stage the specific binding of both the I -125-IGF is very low. In foetal muscle, type II receptors are located both in the muscle bundles and in the connective tissue while type I receptors a re only located in the muscle bundles. (C) Inra/Elsevier, Paris.