Induction of inflammatory responses by endotoxin in the non-lactating ovine mammary gland

In non-lactating ewes, intramammary infusion of endotoxin provokes an intense but transient inflammatory response as assessed by mammary lavage. The variability of the method for sampling the leucocytes in mammary secretions was examined. Initial lavage with 20 ml pyrogen-free saline recovered 83.0 +/- 2.8 and 84.4 +/- 3.0% of the total leucocyte numbers harvested by three serial washes of quiescent and inflamed glands, respectively. Lavage of glands prior to infusion of endotoxin did not affect the magnitude of the subsequent inflammatory response. Three treatments at 3.5 day intervals with the glucocorticoid, dexamethasone, which inhibits the inflammatory response to intramammary infusion of antigen in systemically immunized ewes, did not affect the inflammatory response to endotoxin. However, the variability of the inflammatory response to activated complement was greatly increased in dexamethasone-treated ewes; this effect was attributed to the induction of lactation which results in loss of sensitivity of the gland to the inflammatory activity of activated complement. The results indicated that the macrophages and lymphocytes which are present in mammary secretions in large numbers, and dexamethasone-sensitive lymphocytes in the gland, played a trivial role in the induction of inflammatory responses to endotoxin.