Na l-14C Stearate and Na 2-14C Acetate Metabolism and Morphological Analysis of Late Prepartum Bovine Mammary Tissue

Nonlactating mammary tissue from two cows, approximately 1 to 2 weeks (A) and 2 days (B) prepartum, actively utilized Na 1-a4C stearate and Na 2-z4C acetate for lipid synthesis. Tissue B incorporated significantly more of the radioactive substrates into triglycerides than Tissue A. Tissue B possessed steary] desaturase which was not detected in Tissue A. Tissue B utilized about six times more acetate for fatty acid synthesis than did Tissue A, and this was preponderantly acylated into triglycerides. Fatty acid synthetase from Tissue B synthesized short chain fatty acids. Microscopic analyses revealed that the alveoli of tissue B were distended, had a low epithelium and abundant lumenal protein and lipid whereas A showed little alveolar distention and a taller epithelium. Tissue B had 30% more lumenal area than A whereas the reverse was true for connective tissue. Epithelial, adipose, and vascular tissue areas were similar in both cows. Cellular lipid inclusions were more abundant and larger in. B than in A. In some instances secreted lipid had coalesced to form a single droplet filling an alveolar lumen. Protein secretion was evident in B but not as apparent in A.