Lipid synthesis by co-cultures of mammary, liver, and adipose tissue explants from sometribove (recombinant methionyl bovine somatotropin)-treated dairy cows

Bovine mammary explant versus primary cell cultures: effect of bovine somatotropin and insulin-like growth factor-I on DNA content and protein synthesis

Cellular DNA, milk protein content, and protein secretion by bovine mammary explants were compared to cultures of confluent and growing primary bovine mammary secretory cells over 4 d. Explants were obtained at slaughter from eight Holstein cows (120 +/- 35 d lactation). Primary cells were grown to confluence, cryopreserved, thawed, and cultured through five passages. Explants and cells were cocultured with liver and adipose tissue in the presence of somatotropin, insulin-like growth factor-I, and somatotropin + insulin-like growth factor-I. Cellular DNA and milk proteins were assayed using fluorescent probes and flow cytometry. Media proteins were assayed by densitometer scanning of electrophoresis gel bands. DNA content of explant, confluent, and growing primary cells increased similarly through the 96 h incubation. DNA content in G0G1 phase was increased by: (a) insulin-like growth factor-I in explant cells; (b) somatotropin, insulin-like growth factor-I, and their combination in confluent primary cells; and (c) the combination of somatotropin and insulin-like growth factor in growing primary cells. Approximately 65% of explant and confluent primary cells were in the G0G1 or differentiated phase compared to 47% for the growing primary cells. Whey protein content and secretion were similar among cell types. Explant cells contained and secreted more beta-casein than primary cells but secretion trends for beta-casein and k-casein were similar after 48 h for both cell types. Results suggest that primary cell cultures are comparable to explant cultures when used to study mechanisms of DNA and milk protein synthesis and secretion.

An in vitro approach to ruminant mammary gland biology

This review discusses both fundamental and applied in vitro studies on ruminant mammary gland biology and summarizes progress made over the last decade in development of in vitro techniques to study growth, function and pathology of the mammary gland. The advantages and limitations of different in vitro systems are considered including explant cultures, primary cell cultures and immortalized lines of mammary-derived cells from cow, sheep and goat. The cell growth, differentiation and response to lactogenic hormones and growth factors are discussed as well as the relevance of the cell behavior in different culture conditions.

Effect of somatotropin and insulin-like growth factor-I on milk lipid and protein synthesis in vitro

The objective of this research was to test the hypothesis that bST stimulates milk secretion through the action of IGF-I. Cocultures of bovine mammary, adipose, and liver tissues were incubated with increasing concentrations (0 to 1000 ng/ml) of bST, IGF-I, prolactin, or bST plus prolactin. In addition, cocultures of mammary and adipose tissues without liver tissue were incubated with IGF-I. The synthesis of milk lipids and proteins and the concentration of cellular DNA were measured. The addition of liver tissue depressed DNA concentration and the synthesis of lipids and proteins in mammary tissue. In mammary tissue, increasing bST concentration resulted in greater synthesis of FFA, total lipids, and proteins than that produced by increasing concentrations of IGF-I, and the effect on protein synthesis was linear. Conversely, in adipose tissue, increasing the concentration of IGF-I in the presence of liver resulted in greater synthesis of FFA than that obtained by bST, and the effect was linear. The results do not support the hypothesis that bST acts through the actions of IGF-I on mammary cells. Rather, bST alters the delivery of nutrients to the mammary cells from other tissues and affects milk component synthesis through a mechanism that may not involve IGF-I.

In vitro DNA synthesis as indicator of mammary epithelial cell division: [14C]thymidine uptake versus flow cytometry cell cycle analysis

Mammary and adipose explants from eight mid-lactation Holstein cows were co-cultured for 24 h in the presence or absence of liver explants, 1 microgram/ml pituitary bovine somatotrophin, or 100 ng/ml insulinlike growth factor-I. Liver explants in the media significantly depressed DNA and protein synthesis by mammary tissue as measured by [14C]-thymidine and amino acid incorporation. As measured by flow cytometry, the concentration of DNA in the G0G1 and G2M cells and the percentage of cells in the G0G1 population of mammary tissue was also significantly depressed by liver tissue. Changes in the percentage of cells in the S and G2M phases were not significant. Insulinlike growth factor-I in the presence of liver explants depressed protein synthesis, thymidine incorporation, and the concentration of DNA in the G0G1 and G2M cells compared to control but did not affect the percentage of cells in the G0G1, S, or G2M phases. Previously it was assumed that changes in [14C]thymidine incorporation indicated that changes in cell division were occurring. Flow cytometry revealed that changes in DNA content of mammary cells as a result of liver or hormonal stimulation were not due to changes in cell division. Indications are that differences in cellular DNA content result from changes in the rate of amplification of individual genes responsible for milk protein synthesis.