Effect of Insulin-Like Growth Factor I on Deoxyribonucleic Acid Synthesis and Galactopoiesis in Bovine Undifferentiated and Lactating Mammary Tissuein Vitro*

Abstract

We have demonstrated that insulin-like growth factor I (IGF-I), at physiological concentrations, is a potent mitogen of bovine undifferentiated mammary epithelial cells cultured in collagen in serum-free medium. Its activity is independent of insulin, although at pharmacological concentrations insulin may substitute for IGF-I. The maximal [3H]thymidine incorporation stimulated by either IGF-I or insulin was only 25-40% of that in medium supplemented with 10% fetal calf serum (FCS) only. Epidermal growth factor (EGF) exhibited low mitogenic activity which was not synergistic with IGF-I in serum-free medium. IGF-I and EGF had low synergistic activity when added separately to 10% FCS-supplemented medium. Strong synergism (100% or more) was observed, however, when both factors were added simultaneously, indicating that their maximum mitogenic effect is dependent on a simultaneous presence of other factors existing in FCS. The galactopoietic effect of IGF-I was tested in organ culture of bovine lactating mammary gland. Neither fatty acid synthesis nor alpha-lactalbumin secretion was stimulated by IGF-I, even at 2000 ng/ml. These results indicate that, at least in our in vitro system, galactopoiesis is not affected by IGF-I.

Contribution of insulin-like growth factor (IGF)-I and IGF-binding protein-3 to mitogenic activity in bovine mammary extracts and serum

“…Mammary epithelial cells were prepared from mammary parenchymal tissue from a prepubertal Friesian heifer (200 kg body weight, 242 days of age) essentially according to Shamay et al (1988). Within 10 min of slaughter, mammary parenchyma was excised aseptically from the outer margin of the parenchyma and minced finely with scissors.…”

“…Collagen gels were prepared essentially as described by Shamay et al (1988). A collagen solution prepared from rat tail tendons was neutralized using a neutralizing solution (10 M-199 without bicarbonate and 0·33 M NaOH at a 2:1 ratio) at a ratio of about 6:1.…”

“…3 H]thymidine was determined essentially according to Shamay et al (1988). On day 3 of culture, 50 µl basal medium containing 20 mCi/l [methyl-3 H]thymidine were added to each well.…”

“…However, much evidence indicates that bST functions by an indirect mechanism of action, mediated at least in part by insulinlike growth factor (IGF)-I (Akers 1985, Kleinberg 1997. The mitogenic effect of IGF-I on mammary explants (Baumrucker & Stemberger 1989, or mammary organoids of bovine (Shamay et al 1988, McGrath et al 1991 and ovine (Winder et al 1989) origin in collagen gel culture, and in mammary tissue of pregnant heifers (Collier et al 1993) has been documented. In the mammary gland, IGF-I is synthesized locally by stromal tissue and is considered to act on adjoining epithelial cells via a paracrine mechanism of action (Cullen et al 1992).…”

DNA synthesis by ovine mammary alveolar epithelial cells: effects of heparin, epidermal growth factor-related peptides and interaction with stage of pregnancy

“…Expression of both the insulin-like growth factor and epidermal growth factor families has been reported in mammary gland (see Forsyth 1996, for references) and both are mitogens for mammary epithelial cells. In ruminants, IGF-I and IGF-II are potent mitogens (Shamay et al 1988, Baumrucker & Stemberger 1989, Winder et al 1989, McGrath et al 1991, Peri et al 1992 thought to act via the type 1 IGF receptor and stimulating a 5-to 10-fold increase in DNA synthesis. Amphiregulin and TGF-, members of the EGF family, approximately double DNA synthesis (Fig.…”