Insulin and insulin-like growth factor-I stimulate DNA synthesis in bovine mammary tissue in vitro.
Effects of insulin and insulin-like growth factor I (IGF-I) on [3H]thymidine incorporation, in vitro, by mammary tissue slices obtained from prepartum and lactating cows were investigated. Both insulin and IGF-I induced up to a 10-fold increase in [3H]thymidine incorporation in the mammary slices cultured in serum-free media. The effect of insulin-stimulated [3H]thymidine incorporation occurred at a threshold of greater than 1.75 pmol/ml and appeared to reach maximum at greater than 8.8 nmol/ml. The response to IGF-I occurred at greater than 6.5 pmol/ml and reached the equivalent of maximal insulin-stimulated incorporation at 39 pmol/ml. No synergistic or additive effects were observed between these two factors. The in vitro response took 3 to 4 d to reach maximum and was inhibited by cytarabine. Mammary tissue obtained from lactating cows incorporated more [3H]thymidine per microgram DNA in response to insulin (175 pmol/ml) than mammary tissue from pregnant cows. Culture of mammary tissue slices with growth hormone, cortisol, prolactin, or triiodothyronine showed no stimulation of [3H]thymidine incorporation over control. Autoradiography of the cultured lactating tissue showed incorporation of [3H]thymidine by 51, 24 and 29% of the ductal epithelial, secretory alveolar epithelial and myoepithelial cells, respectively. All alveolar epithelial cells that incorporated [3H]thymidine contained secretory products. Among nonsecretory cells, 25 and 28% of the fibroblasts and white blood cells, respectively, were labeled. Insulin-like growth factor I, but not bovine somatotropin, stimulated [3H]thymidine uptake into DNA in lactating bovine mammary tissue. Thus, our data support the concept that bovine somatotropin acts through IGF-I to increase DNA synthesis in mammary cells.
Baumrucker
C R
CR
Dept. of Dairy and Anim. Sci. Pennsylvania State University, University Park 16802.
Stemberger
B H
BH
D000818:Animals; D001345:Autoradiography; D002417:Cattle / Q000235:genetics / Q000378:metabolism*; D046508:Culture Techniques; D004247:DNA / Q000096:biosynthesis*; D005260:Female; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007774:Lactation / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D013002:Somatomedins / Q000494:pharmacology*; D013936:Thymidine / Q000378:metabolism
D007328:Insulin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D004247:DNA; D013936:Thymidine