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Vitamin D analogues have an antiproliferative effect on prostate cancer cells in vitro and thus have been proposed as candidates for chemoprevention of prostate cancer. Insulin-like growth factor (IGF)-I has been shown to protect cells from apoptosis and plays an essential role in normal prostate physiology. We have studied the effects of the 1,25-dihydroxyvitamin D3 analogue EB1089 on the IGF system in the prostate in vivo. Treatment of rats with EB1089 for 14 days caused a 25% decrease in ventral prostate weight. Apoptosis was detected in prostate sections of EB1089-treated rats by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling(TUNEL) assay and histologic examination of hematoxylin/eosin stained tissue sections indicated that secretory epithelial cells were flattened, a characteristic of cells undergoing pressure-induced atrophy. Ventral prostate regression was associated with 15- to 25-fold increases in gene expression of IGF-binding proteins (IGFBPs)-2,-3,-4 and -5. We also observed a 40-fold increase in prostatic IGF-I mRNA levels in response to EB1089. Although we have previously shown that castration of rats leads to upregulation of IGFBPs in the ventral prostate, EB1089 treatment had no effect on serum levels of dihydrotestosterone or free testosterone. These results suggest that prostate regression induced by EB1089 may be related to alterations in availability of IGF-I as a result of increased production of IGFBPs.
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Mammary explants from two heifers pretreated with oestradiol and progesterone were cultured for 96 h with various combinations of hormones and calf plasma to identify the complement causing mammary tissue development in vitro in the cow. Initial tissue histology, determined by quantitative morphological analysis, was maintained by incubation with insulin, cortisol, oestrogen and progesterone; enlarged lumina were observed after treatment with insulin and cortisol. Lactogenesis was induced in vitro by insulin, cortisol and prolactin, enhanced by adding oestrogen and progesterone at the doses used here and further stimulated by the addition of plasma. The most highly developed mammary alveoli were characterized by an increased luminal area with lipid and stainable secretion, epithelia with large lipid droplets in the apical cytoplasm and a limited stromal area. In a second experiment, samples of plasma were collected from two cows, successfully induced to lactate, on days 6, 15, 17, 19 and 21 after treatment with oestradiol and progesterone. Mammary gland explants from five heifers pretreated with oestradiol and progesterone in vivo were cultured with insulin and cortisol plus these plasma samples (30%, v/v) to test for changes in lactogenic activity. All plasma samples were found equally beneficial in promoting tissue differentiation. These experiments show that low concentrations of ovarian steroids synergize with prolactin at the level of the mammary epithelium and suggest that other plasma components aid the development of bovine mammary epithelium in vitro.
