[Characterization and physiological development of receptors for insulin-like growth factors I and II (IGFs) in the mammary gland of ewes].

Membrane preparations were obtained by differential centrifugations of ewe mammary gland homogenates. These membrane preparations contained specific receptors for IGF1 and IGF2 which possess high affinities for their specific ligands (Ka .5 to 1.5 10(9) M-1). Maximum binding of 125I IGF1 was obtained after 48 h at 4 degrees C. This binding was inhibited by unlabelled IGF1 (ED50 = 14 ng/ml), partially inhibited by high concentrations of insulin (50 micrograms/ml). Prolactin (oPRL), growth hormone (bGH) or relaxin (Rel) were without effect. Maximum binding of 125I IGF2 was obtained after 6 h at 20 degrees C. This binding was inhibited by unlabelled IGF2 (ED50 = 44 ng/ml), partially inhibited by IGF1 (ED50 = 200 ng/ml) and unmodified by INS, PRL, bGH or Rel. Receptor numbers for IGF1 were significantly higher (p less than 0.01) on day 100 of pregnancy (N = 480 +/- 17 fmoles/mg proteins) compared to day 20 of lactation (N = 174 +/- 21 fmoles/mg). The numbers of IGF2 receptors were always higher than those of IGF1 receptors. During pregnancy the numbers of IGF2 receptors (N = 1,860 +/- 157 fmoles/mg) were also higher than during lactation. These results suggest that the mammary gland may constitute a target organ for IGFs. These factors could be involved in the regulation of mammary gland development and during cell differentiation.