Secretion of parathyroid hormone-related protein by bovine mammary cellsin vitro

Abstract

Mammary cells were isolated from lactating cows at 1 to 6 weeks after calving and evaluated for their ability to secrete PTHrP in vitro. The tissue was enzymatically digested to release glandular acini. The digested acini were cultured on thin (1.0 mm) or thick (2.5 mm) layers of collagen. The cultures containing thick collagen were detached and allowed to contract on day 6. The culture medium consisted of M199 with prolation (8 µg/ml), insulin (5 µg/ml), cortisol (5 µg/ml), and fetal bovine serum (15%). PTHrP production was measured by N-terminal RIA and bioassay (stimulation of adenylate cyclase in the ROS 17/2.8 cell line). Medium was collected at 2-day intervals for 14 days. The cells reached confluence at 4–6 days. PTHrP production was low at day 2 (<0.5 ng/ml), but increased to peak production (2–4 ng/ml) at approximately day 6–8 of culture and remained constant until day 14. Immunoreactive and bioactive PTHrP levels in the culture medium correlated well. The cultures produced high levels of lactoferrin (500 to 3000 ng/ml) and low levels of α_s1-casein (14 to 77 ng/ml).

Prolactin stimulated PTHrP production approximately 50% on days 6–14. PTHrP production was increased approximately 100% by treatment with EGF (10 ng/ml) for 2 to 4 days. Histologic evaluation of cultures on thick, contracted collagen revealed an inner layer of epithelial cells with and an outer layer of collagen containing stromal cells. These data demonstrated that mammary cells from lactating cows produced and secreted PTHrP in vitro in a regulated manner.