Immunolocalization and expression of insulin-like growth factor I (IGF-I) in the ovine mammary gland during mammogenesis, lactation and involution

Abstract

The Insulin-like growth factor I (IGF-I) is growth stimulating factor of mammary epithelial cells in vivo and in vitro, and in synergism with mammogenic hormones, IGF-I regulates the mammary development. IGF-I was identified by immunohistochemistry in sheep mammary glands during mammogenesis, lactogenesis, and involution to establish differences in IGF-I expression during mammary development. Mammary biopsies were conducted during prepuberty, puberty, pregnancy, lactation and involution periods. The “quoin” incising technique was used and IGF-I was detected by immunohistochemistry using the streptavidin–biotin–peroxidase method. Immunostaining for IGF-I was seen in every studied period, ranging from weak to intense, mainly associated with the structures of the mammary parenchyma. The highest expression of IGF-I was observed in the lactating ewes group from 1 to 10 days postpartum, and the lowest expression was found in ewes with more than 120 days of lactation. No significant difference of IGF-I expression was found between prepubertal and pubertal ewes. Ewes in the 1–10 lactation days group had a significantly higher IGF-I expression than those in the 95–105 lactation days group, and both had significantly higher IGF-I expression than those in the more than 120 lactation days group. The expression of IGF-I differed significantly in pregnant ewes with regard to the group from 1 to 10 lactation days and the one of more than 120 lactation days. The results lead us to conclude that there are differences in the expression of ovine mammary IGF-I during mammogenesis, lactogenesis, galactopoiesis and involution, and the IGF-I expression is associated with parenchyma, fundamentally with the alveolar epithelium.