Effects of bovine somatotropin on beta-casein mRNA levels in mammary tissue of lactating cows.
Bovine somatotropin (bST) increases milk production in lactating cows through its effect on nutrient partition and maintenance of mammary cell function. A positive relationship between bST treatment and abundance of beta-casein mRNA in mammary tissues from lactating cows was hypothesized. In mammary tissue isolated from 14 midlactation Holstein cows, beta-casein mRNA was 35.4% higher among 7 cows receiving continuous bST infusions at 29 mg/d for 63 d compared with tissue from 7 untreated control cows. To investigate whether increased beta-casein mRNA resulted from a direct effect of bST on the mammary gland, explants of mammary tissue from other lactating cows that had not received bST were incubated with bST and prolactin in 2 experiments. Mammary explant cultures taken from 2 lactating cows that had not been milked for 48 h were supplemented with either prolactin or bST. Both prolactin and bST stimulated higher levels of beta-casein mRNA in the mammary explants compared with their non-supplemented counterparts. Explant cultures from 4 additional lactating cows were prepared from rear quarter mammary tissue subjected to milking intervals of 6 h for right rear quarters or 20 h for left rear quarters. Both bST- and prolactin-mediated increases in beta-casein mRNA were dependent on milking intervals. That is, levels of beta-casein mRNA were increased by bST or prolactin supplementation in explants isolated from the mammary quarters biopsied 20 h after milking but not for those biopsied at 6 h after milking. Results are consistent with a potential role for bST in up-regulating or sparing beta-casein mRNA levels in lactating bovine mammary tissue in a manner similar to prolactin.
Yang
J
J
Department of Human Nutrition, Food and Animal Sciences, University of Hawaii, Honolulu 96822, USA. jinzeng@hawaii.edu
Zhao
B
B
Baracos
V E
VE
Kennelly
J J
JJ
D000818:Animals; D015152:Blotting, Northern; D002364:Caseins / Q000235:genetics*; D002417:Cattle / Q000502:physiology*; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D013006:Growth Hormone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D007774:Lactation; D008321:Mammary Glands, Animal / Q000737:chemistry* / Q000187:drug effects*; D011388:Prolactin / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis*; D046509:Tissue Culture Techniques
D002364:Caseins; D012333:RNA, Messenger; C073294:growth hormone, bovine; D011388:Prolactin; D013006:Growth Hormone