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.

OBJECTIVE To assess the possible impact of medetomidine on concentrations of alfaxalone in plasma, when coadministered as a constant rate infusion (CRI) to dogs, and to determine the possible impact of medetomidine on the cardiopulmonary effects of alfaxalone during CRI. ANIMALS 8 healthy adult Beagles. PROCEDURES 3 treatments were administered in a randomized crossover design as follows: 1 = saline (0.9% NaCl) solution injection, followed in 10 minutes by induction of anesthesia with alfaxalone (loading dose, 2.4 mg/kg; CRI, 3.6 mg/kg/h, for 60 minutes); 2 = medetomidine premedication (loading dose, 4.0 μg/kg; CRI, 4.0 μg/kg/h), followed by alfaxalone (as in treatment 1); and, 3 = medetomidine (as in treatment 2) and MK-467 (loading dose, 150 μg/kg; CRI, 120 μg/kg/h), followed by alfaxalone (as in treatment 1). The peripherally acting α2-adrenoceptor antagonist MK-467 was used to distinguish between the peripheral and central effects of medetomidine. Drugs were administered IV via cephalic catheters, and there was a minimum of 14 days between treatments. Cardiopulmonary parameters were measured for 70 minutes, and jugular venous blood samples were collected until 130 minutes after premedication. Drug concentrations in plasma were analyzed with liquid chromatography–tandem mass spectrometry. RESULTS The characteristic cardiovascular effects of medetomidine, such as bradycardia, hypertension, and reduction in cardiac index, were obtunded by MK-467. The concentrations of alfaxalone in plasma were significantly increased in the presence of medetomidine, indicative of impaired drug distribution and clearance. This was counteracted by MK-467. CONCLUSIONS AND CLINICAL RELEVANCE The alteration in alfaxalone clearance when coadministered with medetomidine may be attributed to the systemic vasoconstrictive and bradycardic effects of the α2-adrenoceptor agonist. This could be clinically important because the use of α2-adrenoceptor agonists may increase the risk of adverse effects if standard doses of alfaxalone are used.

OBJECTIVE To quantify plasma fentanyl concentrations (PFCs) and evaluate antinociceptive and respiratory effects following application of transdermal fentanyl patches (TFPs) and assess cerebrospinal μ-opioid receptor mRNA expression in ball pythons (compared with findings in turtles). ANIMALS 44 ball pythons (Python regius) and 10 turtles (Trachemys scripta elegans). PROCEDURES To administer 3 or 12 μg of fentanyl/h, a quarter or whole TFP (TFP-3 and TFP-12, respectively) was used. At intervals after TFP-12 application in snakes, PFCs were measured by reverse-phase high-pressure liquid chromatography. Infrared heat stimuli were applied to the rostroventral surface of snakes to determine thermal withdrawal latencies after treatments with no TFP (control [n = 16]) and TFP-3 (8) or TFP-12 (9). Breathing frequency was measured in unrestrained controls and TFP-12–treated snakes. μ-Opioid receptor mRNA expression in brain and spinal cord tissue samples from snakes and turtles (which are responsive to μ-opioid receptor agonist drugs) were quantified with a reverse transcription PCR assay. RESULTS Mean PFCs were 79, 238, and 111 ng/mL at 6, 24, and 48 hours after TFP-12 application, respectively. At 3 to 48 hours after TFP-3 or TFP-12 application, thermal withdrawal latencies did not differ from pretreatment values or control treatment findings. For TFP-12–treated snakes, mean breathing frequency significantly decreased from the pretreatment value by 23% and 41% at the 24- and 48-hour time points, respectively. Brain and spinal cord tissue μ-opioid receptor mRNA expressions in snakes and turtles did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In ball pythons, TFP-12 application resulted in high PFCs, but there was no change in thermal antinociception, indicating resistance to μ-opioid-dependent antinociception in this species.

OBJECTIVE To evaluate the antinociceptive efficacy of IM morphine sulfate or butorphanol tartrate administration in tegus (Salvator merianae). ANIMALS 6 healthy juvenile (12- to 24-month-old) tegus (mean ± SD body weight, 1,484 ± 473 g). PROCEDURES In a crossover study design, tegus were randomly assigned to treatment order, with a minimum washout period of 15 days between treatments. Each of 5 treatments was administered IM in a forelimb: saline (0.9% NaCl) solution (0.5 mL), morphine sulfate (5 or 10 mg/kg), or butorphanol tartrate (5 or 10 mg/kg). A withdrawal latency test was used to evaluate antinociception, with a noxious thermal stimulus applied to the plantar surface of the hind limb before (0 hours; baseline) and 0.5, 1, 2, 3, 4, 6, 12, and 24 hours after each treatment. Observers were unaware of treatment received. RESULTS With saline solution, mean hind limb withdrawal latencies (interval to limb withdrawal from the thermal stimulus) remained constant, except at 12 hours. Tegus had higher than baseline mean withdrawal latencies between 0.5 and 1 hour and at 12 hours with morphine at 5 mg/kg and between 1 and 12 hours with morphine at 10 mg/kg. With butorphanol at 5 and 10 mg/kg, tegus maintained withdrawal responses similar to baseline at all assessment points. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that morphine, but not butorphanol, provided antinociception at 5 and 10 mg/kg in tegus as measured by thermal noxious stimulus testing. These data supported the hypothesis that μ-opioid (but not κ-opioid) receptor agonists provide antinociception in reptiles.

Objective: To investigate effects of various imidazoline and nonimidazoline α-adrenergic agents on aggregation and antiaggregation of bovine and equine platelets. Sample: Blood samples obtained from 8 healthy adult cattle and 16 healthy adult Thoroughbreds. Procedures: Aggregation and antiaggregation effects of various imidazoline and nonimidazoline α-adrenergic agents on bovine and equine platelets were determined via a turbidimetric method. Collagen and ADP were used to initiate aggregation. Results: Adrenaline, noradrenaline, or α-adrenoceptor agents alone did not induce changes in aggregation of bovine or equine platelets or potentiate ADP- or collagen-induced platelet aggregation. Adrenaline and the α2-adrenoceptor agonist clonidine had an inhibitory effect on ADP- and collagen-induced aggregation of bovine platelets. The α2-adrenoceptor antagonists phentolamine and yohimbine also inhibited collagen-induced aggregation of bovine platelets. Noradrenaline, other α-adrenoceptor agonists (xylazine, oxymetazoline, and medetomidine), and α-adrenoceptor antagonists (atipamezole, idazoxan, tolazoline, and prazosin) were less effective or completely ineffective in inhibiting ADP- and collagen-induced aggregation of bovine platelets. The imidazoline α2-adrenoceptor agonist oxymetazoline submaximally inhibited collagen-induced aggregation of equine platelets, and the α2-adrenoceptor antagonist idazoxan, along with phentolamine and yohimbine, also inhibited collagen-induced aggregation of equine platelets. The imidazoline compound antazoline inhibited both ADP- and collagen-induced aggregation of equine platelets. Conclusions and Clinical Relevance: Several drugs had effects on aggregation of platelets of cattle and horses, and effective doses of ADP and collagen also differed between species. The α2-adrenoceptor agonists (xylazine and medetomidine) and antagonists (tolazoline and atipamezole) may be used by bovine and equine practitioners without concern for adverse effects on platelet function and hemostasis.

Objective—To develop an antibody-based flow cytometric assay to detect coated platelets in dogs and to characterize the interaction of recombinant human coagulation factor VIIa with activated platelets from dogs with hemophilia A. Sample—Platelets from 4 dogs with hemophilia A, 4 dogs with hemophilia B, 4 dogs with von Willebrand disease, and 6 hemostatically normal dogs. Procedures—Freshly isolated platelets were activated with thrombin, convulxin, or a thrombin-convulxin combination. Resulting platelet phenotypes were resolved on the basis of P-selectin and fibrinogen expression, and binding of recombinant human coagulation factor VIIa to these distinct platelet subpopulations was measured by use of a flow cytometric assay. Results—Coated platelets were identified on the basis of expression of α-granule fibrinogen and were generated in response to stimulation with the thrombin-convulxin combination but not to stimulation with either agonist alone. Approximately 70% of the platelets from dogs with hemophilia A, hemophilia B, and von Willebrand disease and from the control dogs had the coated platelet phenotype. Recombinant human coagulation factor VIIa bound preferentially to coated platelets with a mean ± SD binding equilibrium constant of 2.6 ± 0.5μM. Conclusions and Clinical Relevance—Formation of coated platelets in dogs was similar to that in humans. Recombinant human coagulation factor VIIa bound preferentially to coated platelets from dogs. Impact for Human Medicine—A similar mechanism of action for recombinant human coagulation factor VIIa may exist in dogs and humans. The potential for use of dogs in the study of bleeding disorders in humans was strengthened.

We defined methods for use of luminol-dependent chemiluminescence (LDCL) and superoxide anion (O2-) production as parameters of the oxidative metabolism of neutrophils isolated from 1.5- to 5-week-old neonatal calves. We determined how variations in blood sample handling, agonist preparation, individual variability, and age of calves influenced the LDCL and O2- responses to certain agonists, and defined concentrations of soluble and particulate agonists that maximally stimulated the oxidative metabolism of bovine neutrophils. Oxidative responses, particularly LDCL, were characterized by marked dayto-day variability, differed greatly within and between calves, were partially age-dependent, and were partially dependent on the individual agonist. Superoxide anion production had substantially less variability. We compared the in vitro oxidative (LDCL and O2-) responses of neutrophils isolated from neonatal calves stimulated by defined concentrations of the agonists-latex, phorbol myristate acetate, calcium ionophore, and opsonized zymosan-with responses to formylated oligopeptides and zymosan-activated serum, and to live, dead, live opsonized, and dead opsonized Pasteurella haemolytica organisms. Opsonization of particulates, pathogenic or nonpathogenic, enhanced the LDCL and O2- responses of stimulated neutrophils although P haemolytica was a less potent stimulant of oxidative functions than were nonbiological agonists. We conclude that the generation of reactive oxygen species by bovine neutrophils in response to P haemolytica is highly dependent on the presence of opsonins and is greatly enhanced in live vs killed bacteria. Futhermore, the in vitro generation of reactive oxygen species, including O2- by stimulated neutrophils, may be of biologic importance if similar events occur in vivo, and could have a major role in the pathogenesis of the acute lung injury associated with pneumonic pasteurellosis.

The potential of a gonadotropin-releasing hormone (GnRH) agonist (goserelin acetate), delivered constantly for 28 days via a subcutaneous depot, to induce ovulation in seasonally anestrous mares, was investigated. Two experiments were conducted, in which a range of doses (30 to 240 micrograms/mare/d) was examined. Mares were selected on the basis of lack of substantial follicular development (follicle diameter < 20 mm determined ultrasonically) and low serum concentrations of luteinizing hormone (LH) and progesterone. Constant administration of the GnRH agonist-induced ovulation in anestrous mares, but a dose-response relation was not observed. Furthermore, with identical doses tested in consecutive or alternate years, considerable variation was observed in the ovulatory response. In general, ovulation in all treated mares was accompanied by increased circulating concentrations of LH and a decrease in follicle-stimulating hormone values. Ovulation was preceded by an increase in estradiol and LH concentrations. In mares in which ovulation did not occur, concentration of LH increased during agonist treatment, whereas that of follicle-stimulating hormone either increased or did not change. It was concluded that constant administration of GnRH agonists may induce ovulation in mares during seasonal anestrus; however, percentage of mares ovulating and the lack of reproducibility of effect indicate that this approach is inappropriate for use as a reliable method to manipulate breeding activity in commercial broodmares.

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, but faded to ovulate during the remainder of the study (anovulatory for > 88 days). Similarly, an additional 2 mares of groups 2 and 3 ovulated within 2 days of GnRH agonist treatment. A second ovulation occurred in these mares 32 to 35 days later, thereafter, both mares were anovulatory for the remainder of the study. In the remaining 8 mares, interovulatory intervals were either lengthened (n = 6 mares, range, 32 to 82 days) or were unaffected (n = 2) by treatment. One group-6 mare had a lengthened interovulatory interval, 1 was anovulatory for > 90 days, and the remaining 2 mares were unaffected by treatment. During the 28-day treatment period, serum concentration of LH decreased (P < 0.05) only in mares of groups 3-5. In group-6 mares, concentration of LH was unchanged during each 28-day period after depot GnRH agonist administration. Thus, constant administration of a GnRH agonist to mares during the breeding season disrupted their estrous cycles. Anovulation or lengthening of the interovulatory interval by GnRH agonist treatment was associated with persistence of a corpus luteum or an extended follicular phase.