Nutritional and somatotropin regulation of the mitogenic response of mammary cells to mammary tissue extracts

Our objective was to investigate the mitogenic response of primary mammary epithelial cells to extracts of mammary parenchyma from 24 prepubertal Frie sian heifers treated with placebo or growth hormone at either a low or a hi gh feeding level. The mitogenic responses to mammary extracts were tested b y using primary mammary epithelial organoids obtained from prepubertal heif ers cultured for 4 to 5 d in collagen gels in serum-free medium supplemente d to 5% concentration of the mammary extracts. Cell proliferation was deter mined using [methyl-H-3]thymidine incorporation as a measure of DNA synthes is. High feeding level reduced DNA synthesis in response to mammary extract s. At low feeding level, growth hormone treatment decreased DNA synthesis i n response to mammary extracts whereas, at high feeding level, growth hormo ne increased DNA synthesis in response to mammary extracts. These results s uggest that locally produced growth factors are involved in the regulation of mammary development when mammary growth is modulated by feeding level an d growth hormone treatment. (C) 2000 Elsevier Science Inc. All rights reser ved.