Concentrations of estrogen (ER) and progesterone (PR) receptors were measured by radioreceptor assay in tumor (n = 319) and normal (n = 166) mammary tissue from 248 bitches. Correlations between ER and PR and between receptor expression in tumor and normal mammary tissue from the same bitches were evaluated. The influence of tumor, clinical, or hormonal variables on receptor expression also was studied. Approximately 80% of tumor and 95% of normal mammary tissue expressed detectable concentrations of ER, PR, or both. Direct correlation was found between ER and PR concentrations in normal and tumor tissues. Median ER concentrations were significantly higher (46 +/- 47 fmol/mg of cytosolic protein vs 27 +/- 24 fmol/mg of cytosolic protein; P = 0.0002) in normal than in tumor tissue. On the other hand, PR concentrations were significantly higher (57 +/- 52 fmol/mg vs 77 +/- 99 fmol/mg; P = 0.03) in tumors (especially benign tumors) than in normal tissue. Poorly differentiated malignant tumors expressed lower concentrations of receptors than did benign or well differentiated malignant tumors. The ER and PR concentrations decreased with increasing size of the lesion. Hormonal status of the bitch significantly (P < 0.05) influenced receptor expression in normal tissue: bitches in the luteal phase of the estrous cycle had higher concentrations of ER (69 +/- 62 fmol/mg) than did ovariectomized bitches (24 +/- 19 fmol/mg) or bitches in anestrus (38 +/- 45 fmol/ mg) or the follicular phase (13 +/- 7 fmol/mg). For PR, higher concentrations were observed in normal tissue during anestrus than during pseudopregnancy or in bitches treated with medroxyprogesterone acetate. Similar, but nonsignificant, variations were seen in tumor tissue except in medroxyprogesterone acetate-treated bitches in which PR concentrations were high in tumors and low in normal tissue from the same bitches.

Neutrophils are present in milk of cows as a means of suppressing invading pathogens during mastitis. However, the manner by which neutrophils traverse the secretory epithelia is still not clear: do they diapedese between epithelial cells or do they kill epithelial cells to gain entry into milk? We investigated the process of bovine neutrophil diapedesis across bovine mammary gland epithelium in vitro. The bovine mammary epithelial cell line MAC-T, grown on collagen-coated filters, formed a confluent monolayer with characteristic tight junctions, basal-apical polarity, and functional barriers to the dye trypan blue. Neutrophils added on the apical surface of the monolayer were stimulated to diapedese across the epithelium by the addition of Staphylococcus aureus (10(7) colony-forming units/ml) to the basal compartment. Light and transmission electron microscopy revealed the series of events for neutrophil transmigration: accumulation of neutrophils on the surface of epithelial monolayer; projection of pseudopods into intercellular junctions and movement of neutrophils between adjacent epithelial cells; and reapproximation of the lateral epithelial cell membranes and reformation of the apical tight junctions after neutrophils crossed the epithelium. Morphologically, epithelial cell damage caused by neutrophil diapedesis was not evident. This in vitro model provides a two-dimensional epithelial sheet by which neutrophil diapedesis can be qualitatively studied under defined conditions. Results of the study suggest a major mode by which bovine neutrophils diapedese across the alveolar epithelia into milk during mastitis.

A method was developed to evaluate frequent milking as a means of controlling intramammary infection. An artificial intramammary environment was used to determine growth responses of Escherichia coli (P4) to natural changes in the mammary gland resulting from bacterial invasion. Physical conditions manipulated in this model were growth medium, temperature, and oxygen tension. Mathematical modeling was then incorporated to generate predictions concerning growth dynamics of the organism when milking frequency was changed. To test accuracy of the model, initial predictions were derived from bacterial growth data in which E coli was incubated in tryptose soy broth for 12 hours at 37 C and PO2 equal to 23.3 mm of Hg. These predictions matched closely with experimental data in which 12-, 4-, and 2-hour milking intervals were simulated in the artificial intramammary environment. The mathematical model was then used to characterize growth rate data from in vitro experiments in ultra-high temperature-treated milk and in vivo experimental infection data generated with E coli (P4). Predictions generated from this model suggested that increasing milking frequency to 4 or 6 times daily controls growth of E coli for a prolonged period and that 12 times daily milking may lead to elimination of the bacterium.

Eight Holstein cows, 4 inoculated intracisternally in 1 quarter of the mammary gland with Escherichia coli and 4 noninfected controls, were administered ceftiofur sodium (3 mg/kg of body weight, IV, q 12 hours) for 24 hours, beginning at 14 hours after inoculation of infected cows. All challenge-exposed cows became infected, with mean +/- SEM peak log10 bacterial concentration in milk of 5.03 +/- 0.69 colony-forming units/ml. The infection resulted in systemic signs (mean peak rectal temperature, 41.5 +/- 0.3 C; anorexia; signs of depression) and local inflammation (mean peak albumin concentration in milk, 7.89 +/- 1.71 mg/ml). Ceftiofur was detectable in milk from all challenge-exposed cows, compared with only 1 of 4 noninfected cows, and the mean period after inoculation that ceftiofur was detectable in milk was longer (P < 0.05) in infected (147.7 +/- 27.5 hours) than noninfected cows (1.3 +/- 1.3 hours). However, maximal ceftiofur concentration attained in milk for all cows was 0.28 micrograms/ml, and was 0.20 micrograms/ml or less for all but 2 milk samples collected for 10 days after challenge exposure. Mean serum concentration of ceftiofur peaked at 1.0 +/- 0.3 micrograms/ml and 0.7 +/- 0.1 micrograms/ml for infected and noninfected COWS, respectively. After each ceftiofur dose, mean peak and trough concentrations of ceftiofur in serum did not differ between groups; however, concentration of ceftiofur in serum was higher at 7 hours after each dose in noninfected cows, suggesting more rapid clearance of the drug in infected cows. Ceftiofur was not detected in serum (< 0.05 micrograms/ml) of any cow at or after 120 hours following inoculation of infected cows. Storage of serum samples at -20 C for 3 weeks resulted in a 98.8% decrease in ceftiofur activity, compared with that in fresh serum samples. Eighty-seven percent of this loss occurred 30 minutes after mixing serum and ceftiofur; thus, about 13% of the original activity was lost in storage. Storage of milk samples under similar conditions did not result in loss of ceftiofur activity. Despite acute inflammation, the dosage of ceftiofur used in this trial would not result in drug concentrations in milk above FDA safe concentrations, or above the reported minimum inhibitory concentration for coliform bacteria.