BOVINE MAMMARY EXPLANT VERSUS PRIMARY CELL CULTURES: EFFECT OF BOVINE SOMATOTROPIN AND INSULINLIKE GROWTH FACTOR-I ON DNA CONTENT AND PROTEIN SYNTHESIS

摘要

Cellular DNA, milk protein content, and protein secretion by bovine mammaiy 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, insulinlike growth factor-I, and somatotropin + insulinlike 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 G_0G_1 phase was increased by: (a) insulinlike growth factor-I in explant cells; (b) somatotropin, insulinlike growth factor-I, and their combination in confluent primary cells; and (c) the combination of somatotropin and insulinlike growth factor in growing primary cells. Approximately 65% of explant and confluent primary cells were in the G_0G_1 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 p-casein than primary cells but secretion trends for P-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.