During the breeding season, the effect of constant administration of an agonist analog of gonadotropin-releasing hormone (GnRH; goserelin acetate) on reproductive activity of mares was determined. Twenty-four mares undergoing estrous cycles were allocated at random to 6 groups (n = 4/group) and, on May 29 (day 0), received no treatment (group 1, controls), 120 micrograms (group 2), 360 micrograms (group 3), 600 micrograms (group 4), or 1,200 micrograms (group 5) of GnRH agonist/d for 28 days via a depot implanted subcutaneously. The final group of mares (group 6) was treated with 120 miocrograms of GnRH agonist/d for 84 days (3 occasions at 28-day intervals). During a pretreatment period (April 19 to May 29) and for 90 days after initiation of GnRH agonist treatment, follicular development and ovulation were monitored by transrectal ultrasonography of the reproductive tract at 2- to 3-day intervals. On each occasion a blood sample was collected for determination of luteinizing hormone (LH) and progesterone. Estrous behavior was monitored by teasing of mares with a stallion. Initiation of agonist treatment was random, relative to the stage of the estrous cycle, and all mares ovulated within 11 days before or after implantation. in 3 of 4 nontreated control mares, estrous cycles were observed throughout the study, with interovulatory intervals ranging from 18 to 26 days. In the remaining mare, concentration of progesterone was high after asynchronous double ovulation during the pretreatment period, suggestive of persistent corpus luteum. In group-2 mares, ovulation occurred in all mares 7 days before and 2 days after initiation of treatment; however, the next anticipated ovulation was delayed in 3 of 4 mares (interovulatory interval, 33 to 70 days). Estrous cycles were not disrupted in the remaining mare. At higher doses (groups 3-5), 1 mare each from groups 3 and 5 ovulated between days 0 and 2 of treatment initiation.

Effect of estrogen (E2) and progesterone (P4) on uterine antibacterial activity and immunoglobulin concentrations in mares was studied. In 2 in vitro experiments, 6 mixed-breed mares were ovariectomized, and uterine fluid and blood serum were analyzed. Antibacterial assay methods were used to determine inhibitory effects on Streptococcus zooepidemicus of uterine fluid samples collected on days 3, 5, and 8, and serum obtained on day 8 of treatment. Single radial immunodiffusion methods were used to quantify amounts of IgA and IgG in uterine fluid and serum on days 3, 5, 8, and 14 of treatment. Neither E2 nor P4 increased activity of serum and uterine fluid against S zooepidemicus. Numbers of colony-forming units per milliliter of bacteria were significantly (P < 0.01) lower in control Hanks' balanced salt solution with 1.0% gelatin (HBSSG) than in uterine fluids. Bacterial numbers were significantly (50%) greater in uterine fluids and serum than in HBSSG controls for both treatments. Both fluids, especially serum, supported significantly (P < 0.01) more growth of S zooepidemicus than did HBSSG when incubated for 0, 2, and 4 hours. These findings are in contrast to previous reports of antibacterial activity in the uterus of sexually intact mares undergoing an estrous cycle: great reduction of bacterial count in uterine fluid from mares in diestrus, and significant increases in bacterial numbers in uterine fluid or serum from mares in estrus. Treatment comparisons between serum and uterine fluid IgA and IgG concentrations were not significantly different, although overall IgA concentration in the uterus was higher than concentration in serum. The IgG concentration in uterine fluid was higher in P4- than E2-treated mares. However, IgG concentration was significantly (P < 0.01) higher in uterine fluid on day 8 in P4-treated mares than on day 3 or 5. Results of this study indicate that neither immunoglobulin concentration nor hormone treatment has a direct effec.

The antibiotic polymyxin B sulfate is a cationic polypeptide with a unique cyclical configuration and distinct cationic characteristics. In this investigation, polymyxin B was evaluated to determine its ability to prevent synthesis of lactic acid and tumor necrosis factor-alpha (TNF-alpha) by lipopolysaccharide-stimulated strain RAW 2647 macrophage-like cell populations. In this context, gradient concentrations of polymyxin B were formulated in the presence of fixed concentrations of lipopolysaccharide fractions from Escherichia coli (B4:0111), E. coli (J5), Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella minnesota, and S. typhimurium (Re). Quantitation of TNF-alpha was established by the application of a tissue culture-based biological assay system, using the WEHI 164 clone 13 indicator cell line. Investigations also included evaluation of the ability of gradient concentrations of lipopolysaccharide fractions from E. coli (B4:0111), E. coli (J5), K. pneumoniae, P. aeruginosa, S. minnesota, and S. typhimurium (Re) to form a complex with polymyxin B. This was established through application of high-performance thin-layer chromatography techniques. On the basis of the known molecular characteristics of lipopolysaccharide, its lipid A-core subfractions, and polymyxin B, these results imply that cytoprotective properties of polymyxin B are attributable to direct interaction and subsequent complex formation. More specifically, the mechanism by which polymyxin B exerts affinity for lipopolysaccharide fractions is proposed to occur through attractive ionic interactions established between the cationic diaminobutyric acid residues of polymyxin B and the mono- or diphosphate group(s) of the lipid A-core moiety. It is highly probable that this molecular phenomenon is accompanied by hydrophobic interactions established between the terminal methyloctanoyl or methylheptanoyl groups of polymyxin B and the saturated carbon chains of the lipid A-core subfraction of lipopolysaccharide fractions.

The effect of oxytetracycline (OTC) on bovine blood mononuclear cells and neutrophil functions was examined in vitro. Neutrophil functions tested include respiratory burst, peroxidase, and antibacterial activities. Neutrophils were treated with OTC (10 to 1,500 > microgram/ml) before exposure to either opsonized zymosan or bacteria. A dose-response inhibition of antibacterial activity to high concentrations of OTC (500 to 1,000 microgram/ml) was observed. Beginning at a concentration of 15 microgram/ml, OTC treatment of neutrophil Iysates resulted in decreased peroxidase activity. A dose response was not observed. In contrast, respiratory burst, measured by nitroblue tetrazolium dye reduction, increased after OTC exposure, but only at high concentrations (500 and 1,000 microgram/ml) of OTC. Mitogen-induced proliferation of blood mononuclear cells cocultured with OTC and concanavalin A, phytohemagglutinin-P, or pokeweed mitogen was inhibited at an OTC concentration of 100 microgram/ml at 48 and 72 hours of culture. These results indicate that blood mononuclear cells are more sensitive to the inhibitory effects of OTC than are neutrophils. Furthermore, the OTC-mediated inhibition of neutrophil antimicrobial activity is inversely related to the increase in nitroblue tetrazolium reduction. This suggests that OTC is uncoupling the hexose monophosphate shunt from production of secreted oxygen radicals. These results also suggest that the peroxidase enzyme system has a large biological reserve capacity.

A rifampicin-resistant Pasteurella haemolytica serotype 1 with 2 added plasmids was used as a colonization-challenge strain in calves to test the resistance to colonization elicited by vaccination. Nine calves were vaccinated with a tissue culture-derived P haemolytica serotype-1 vaccine which, in a prior study, had elicited a serotype-specific inhibition of nasal and tonsillar colonization by the homologous serotype under field conditions. The vaccinates and 9 nonvaccinated control calves were exposed by tonsillar instillation with the challenge strain. The P haemolytica were enumerated in nasal secretion and tonsil wash specimens collected biweekly for 3 weeks. Rifampicin-supplemented agar medium inhibited growth of other bacterial species in the specimens and, thus, increased the sensitivity of detection of the challenge P haemolytica by 100-fold. The challenge strain retained its plasmids during the period of colonization. Inhibition of colonization was evidenced by lower frequency of isolations and fewer isolations of the challenge strain from nasal secretion and tonsil wash specimens of the vaccinates than from those of the nonvaccinates.

A murine monoclonal antibody (MAB) 6G7 generated against tachyzoites of Neospora caninum recognized 8 major and several minor antigens, as observed by western blot analysis. Relative rate of migration of the 8 major antigens ranged from 31 to 97.4 kd. In addition, MAB 6G7 recognized a Toxoplasma gondii tachyzoite antigen with a relative rate of migration of 107 kd. Immunogold labeling of N caninum tachyzoites grown in human foreskin fibroblast cells indicated that MAB 6G7 binds to micronemes, dense granules, basal portions of rhoptries, and intravacuolar tubules within the parasitophorous vacuole. Monoclonal antibody 6G7 also bound to micronemes and basal portions of rhoptries within tachyzoites of T gondii. Monoclonal antibody 6G7 did not significantly inhibit development of tachyzoites in vitro.

The cause of species difference in the susceptibility of erythrocytes to L-sorbose, and the difference in the hemolytic effect of sorbose on high potassium-containing (HK) and low potassium-containing (LK) canine erythrocytes were examined. L-sorbose was phosphorylated in canine erythrocytes, but not in human erythrocytes. Furthermore, sorbose-1-phosphate, a metabolite of L-sorbose, strongly inhibited the hexokinase of LK canine erythrocytes, but not that of HK canine erythrocytes. These results strongly indicated that inhibition of hexokinase by sorbose-1-phosphate in LK erythrocytes induced severe glycolytic limitation in these cells, resulting in hemolysis, and that HK erythrocytes are resistant to sorbose-induced hemolysis because these cells have a high hexokinase activity.

Cultured rat pituitary cells were studied to: determine the effects of ergovaline and loline on in vitro prolactin release; delineate the agonistic activity of these alkaloids at the D2 dopamine receptor, using 2 selective D2 dopamine receptor antagonists; and compare the efficacy of 2 dopamine receptor antagonists in reversing effects of the treatments on in vitro prolactin secretion. Ergovaline reduced in vitro prolactin release by at least 40% (P < 0.05) at concentrations of 10(-4),10(-6), and 10(-8) M. However, loline reduced (P < 0.05) prolactin release only at the highest concentration, 10(-4) M. Two standard dopamine agonists, dopamine and alpha-ergocryptine, were used to verify that the inhibitory control mechanisms of in vitro prolactin release were intact. Both compounds reduced prolactin release by at least 40% for concentrations of 10(-4), 10(-6), or 10(-8) M. Selective D2 dopamine receptor antagonists 10(-6) M, domperidone and sulpiride, reversed (P < 0.05) the effect of loline on in vitro prolactin release. However, only domperidone (10(-6) M) was able to reverse (P < 0.05) the effect of ergovaline and only at the lowest ergovaline concentration (10(-8) M). Domperidone was more effective (P < 0.05) in reversing the prolactin-suppressing effect of alpha-ergocryptine than was sulpiride. The dose-response curve for domperidone (cubic fit, P < 0.0001) indicated a threshold concentration (10(-7)M) for reversal of alpha-ergocryptine's (10(-8)M) effect on prolactin release. However, at similar concentration of sulpiride (quadratic fit, P < 0.007), a threshold level was not obtained. These data indicate that ergovaline and loline mayact as D2 dopamine receptor agonists. Additionally, domperidone seems to be a more potent drug for reversal of the alkaloids hypoprolactinenic effect in vitro than does sulpiride.

Bovine whey samples were evaluated by use of lymphocyte-transformation tests to determine their effect on lymphocyte blastogenesis. Whey samples from mammary glands with clinical mastitis strongly inhibited DNA synthesis and blastogenesis in lymphocytes stimulated with mitogens or dividing because of bovine leukemia virus infection. Whey samples from apparently healthy glands either did not inhibit lymphocyte DNA synthesis or inhibited it to a lesser degree than did whey from mastitic glands. Degree of inhibition was dose-dependent. The molecules causing inhibition were noncytotoxic and underwent minimal binding to the lymphocytes. Inhibitory molecules were susceptible to various proteolytic and glycolytic enzymes, indicating a glycoprotein-like structure. Whey inhibited incorporation of thymidine if it was in the cell cultures during the early stages of stimulation. Incubation of lymphocytes in whey that inhibited thymidine incorporation did not affect DNA synthesis in subsequent culturing of the same cells without whey. Degree of inhibition was affected by the method of whey preparation.

Disposition kinetics of cloxacillin were examined in calves after topical administration of benzathine cloxacillin and single IV administration of sodium cloxacillin, and the susceptibility of 17 field isolates of Moraxella bovis was measured. For the IV pharmacokinetic phase, sodium cloxacillin was administered at dosage of 10 mg/kg of body weight to male Holstein calves (n = 6, weighing 146 to 170 kg), and serum concentration of cloxacillin was measured thereafter for 10 hours. For the ocular pharmacokinetic phase, 6 calves were given either of 4 benzathine cloxacillin topical formulations consisting of 50-, 125-, 250-, or 375-mg doses. Treatment was repeated every 10 days until all 4 benzathine cloxacillin dosages were tested in the same 6 calves. Blood and tears were collected for 72 hours after each benzathine cloxacillin formulation was administered, and the concentration of cloxacillin in each specimen was measured, using a bioassay. The minimal inhibitory concentration of cloxacillin for 17 field isolates of M bovis was determined by use of an agar pour-plate dilution assay. After single IV administration of sodium cloxacillin, its half-life, body clearance, and volume of distribution were 19.5 +/- 12.8 minutes, 18.3 +/- 2.2 ml/min.kg, and 496 +/- 290 ml/kg, respectively. After topical administration of benzathine cloxacillin, cloxacillin concentration in lacrimal fluid peaked between 30 and 45 minutes and ranged between 963 microgram/ml and 3,256 microgram/ml for the 125- and 375- mg doses, respectively. There was no detectable cloxacillin activity in the lacrimal fluid of any calf by 36 hours after topical administration of benzathine cloxacillin, and cloxacillin was not detected in the serum at any time. The mean lacrimal fluid cloxacillin concentration for the 4 groups during the first 8 hours was not significantly different; however, by 12 hours, the cloxacillin concentration in tears from calves of the 250- and 375-mg groups was significantly (P < 0.05) greater than that in calves of the 50- and 125-mg groups. Cloxacillin concentration greater than or equal to 3.13 microgram/ml was maintained for a significantly (P < 0.05) longer time after treatment, using the 375-mg dose, compared with the 50-mg dose of benzathine cloxacillin. The minimal inhibitory concentration of cloxacillin for 1 isolate was 6.25 microgram/ml, but was less than or equal to 3.13 microgram/ml for 16 other M bovis isolates.