BACKGROUND: The regulation of appetite and food intake in birds are implemented as complex homeostatic mechanisms at different levels of control. OBJECTIVES: The current research aimed to investigate the effects of glycine and strychnine-sensitive receptors on food intake induced with dopamine in neonatal broiler-type chickens. METHODS: This study was conducted in five experiments (each consisting of four treatment groups with 12 birds). In experiment 1, chickens in the control group received intracerebroventricular (ICV) injection of saline (with 0.1 % Evans Blue) and different doses of dopamine (10, 20, and 40 nmol) in treatments groups 2-4, respectively. Experiments 2 and 3 were designed similar to the experiment 1 except for the fact that chickens received different doses of glycine (50, 100, and 200 nmol) and strychnine (50, 100, and 200 nmol) instead of dopamine. Experiment 4 was performed to investigate the mediatory role of strychnine (100 nmol) on food intake induced with dopamine (40 nmol). Moreover, experiment 5 investigated the interaction between non-effective doses of glycine (50 nmol) and dopamine (10 nmol) and their interplay on food intake. Afterwards, cumulative food intake based on bodyweight percentage (BW %) was measured at 30, 60, and 120 minutes after the injection. RESULTS: The obtained findings revealed that effective doses of dopamine and glycine dose-dependently induced hypophagia in neonatal meat-type chickens (p < /em>≤0.05). In addition, injection of strychnine increased food intake and also inhibited the hypophagic effect induced by dopamine (p < /em>≤0.05). Furthermore, co-administration of non-effective doses of glycine and dopamine significantly decreased food intake compared to the groups which only received dopamine or glycine (p < /em>≤0.05). CONCLUSIONS: Our findings suggested that strychnine-sensitive receptors may have a mediatory role in food intake induced by dopamine. Additionally, it seems that glycine and dopamine probably have synergistic effects on food intake control in neonatal meat-type chickens.

We evaluated the effectiveness of 2 dopamine antagonists as treatments for fescue toxicosis in horses. Sixteen gravid mares were assigned by breed and expected foaling date to 1 of 3 treatment groups: endophyte-infested control 1.1 mg of domperidone/kg of body weight/d; and 3.3 mg of sulpiride/kg/d. Mares were pastured on endophyte-infected fescue and received 0.454 kg of a corn and dried molasses carrier containing the drug treatment. Treatment started 30 days prior to expected foaling date and continued until parturition. Blood samples were collected, and mammary gland scores were recorded every 5 days. Body weight and body condition scores were obtained every 28 days. Serum was analyzed for prolactin, progesterone, and estradiol-17beta concentrations. Domperidone-treated mares had shorter (P = 0.09) gestation duration and foaled closer (P = 0.07) to their expected parturition date than did control mares. Mammary gland scores were higher (P < 0.05) for domperidone-treated mares than for control mares. By 4 and 9 days after the start of treatment, serum prolactin concentration was higher P < 0.05) in domperidone-treated mares and sulpiride-treated mares, respectively, than in control mares. Domperidone- and and sulpiride-treated mares had higher (P < 0.05) serum progesterone and lower (P < 0.01) estradiol-17beta concentrations than did control mares. These results indicate that domperidone may offer considerable potential as a treatment for fescue toxicosis in horses.

We evaluated the effectiveness of 2 dopamine antagonists as treatments for fescue toxicosis in horses. Sixteen gravid mares were assigned by breed and expected foaling date to 1 of 3 treatment groups: endophyte-infested control 1.1 mg of domperidone/kg of body weight/d; and 3.3 mg of sulpiride/kg/d. Mares were pastured on endophyte-infected fescue and received 0.454 kg of a corn and dried molasses carrier containing the drug treatment. Treatment started 30 days prior to expected foaling date and continued until parturition. Blood samples were collected, and mammary gland scores were recorded every 5 days. Body weight and body condition scores were obtained every 28 days. Serum was analyzed for prolactin, progesterone, and estradiol-17beta concentrations. Domperidone-treated mares had shorter (P = 0.09) gestation duration and foaled closer (P = 0.07) to their expected parturition date than did control mares. Mammary gland scores were higher (P < 0.05) for domperidone-treated mares than for control mares. By 4 and 9 days after the start of treatment, serum prolactin concentration was higher P < 0.05) in domperidone-treated mares and sulpiride-treated mares, respectively, than in control mares. Domperidone- and and sulpiride-treated mares had higher (P < 0.05) serum progesterone and lower (P < 0.01) estradiol-17beta concentrations than did control mares. These results indicate that domperidone may offer considerable potential as a treatment for fescue toxicosis in horses.

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.

Mechanisms responsible for the positive inotropic effects of dopexamine were investigated in 8 halothane-anesthetized horses. The hemodynamic effects of increasing infusions of dopexamine (5, 10, 15 microgram/kg of body weight/min) were determined before and after sequential administration of specific antagonists. Using glycopyrrolate and chlorisondamine, and atenolol and ICI 118,551, muscarinic and nicotinic ganglionic, and beta, and beta-adrenergic receptor blockade, respectively, was induced. Dopexamine infusions induced increase in heart rate, cardiac output, systolic and mean arterial blood pressure, and maximal rate of left ventricular pressure development (+dP/dt(max)). Right atrial pressure and systemic vascular resistance decreased. Parasympathetic and ganglionic blockade attenuated cardiac output, systolic and mean aortic blood pressures, and +dP/dt(max) responses to dopexamine infusion. Dopexamine-induced increase in heart rate was potentiated by parasympathetic and ganglionic blockade. beta-Adrenergic receptor blockade decreased heart rate, cardiac output, arterial blood pressure, and +dP/dt(max) from baseline values and markedly reduced the response to dopexamine infusion. beta-Adrenergic receptor blockade induced further decrease in hemodynamic variables from baseline values and completely abolished the cardiostimulatory effects of dopexamine on +dP/dt(max) These data indicate that baroreflex activity, beta- and beta 2-adrenergic receptor stimulation may be an important cause of dopexamine's positive inotropic effects in horses.

Lateral cecal arterial blood flow, carotid arterial pressure, heart rate, and mechanical activity of the circular and longitudinal muscle layers of the cecal body were measured in 7 conscious healthy horses during IV infusion of physiologic saline solution for 60 minutes (control), during a 60-minute IV infusion of dopamine (at dosages of 1, 2.5, and 5 microgram/kg/min), and for 60 minutes after IV infusion of dopamine. The mean values for lateral cecal arterial blood flow during IV infusion of dopamine at a dosage of either 1 or 2.5 microgram/kg/min were not significantly different from the mean values for lateral cecal arterial blood flow during IV infusion of saline solution. The mean values for lateral cecal arterial blood flow, however, were significantly greater during IV infusion of dopamine at a dosage of 5 microgram/kg/min than the mean values for lateral cecal arterial blood flow during IV infusion of saline solution. Intravenous infusion of dopamine at 1 and 2.5 microgram/kg/min did not significantly change the mean values for carotid arterial pressure. In contrast, the mean values for carotid arterial pressure were significantly less during IV infusion of dopamine at dosages of 2.5 and 5 microgram/kg/min than during infusion of saline solution. The mean values for heart rate were not significantly altered by infusion of dopamine at a dosage of either 1 or 2.5 microgram/kg/min, but infusion of dopamine at a dosage of 5 microgram/kg/min significantly increased heart rate. Intravenous infusion of dopamine at dosages of either 1 or 5 microgram/kg/min did not significantly change the mechanical activity of the circular muscle layer of the cecal body, as measured by the area under the strain gauge deflection curve. Conversely, the mechanical avtivity of the circular muscle layer of the cecal body was significantly reduced by IV infusion of dopamine at a dosage of 2.5 microgram/kg/min. This reduction of circular muscle mechanical activity by dopamine infusion was attributable to a significant decrease in the total duration of contractions. The mechanical activity of the longitudinal muscle layer was not significantly altered by infusion of dopamine at any dose. These results suggest that IV infusion of dopamine at a dosage of 5 microgram/kg/min increased lateral cecal arterial blood flow by either increasing cardiac output or dilating the lateral cecal artery, an effect most likely mediated by dopaminergic or beta-adrenergic receptors. In addition, dopamine had a biphasic effect on contractile activity of the equine cecum.

The concentrations of dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole-3-acetic acid (5-HIAA) in CSF obtained from the cisterna magna of 21 nonneurologically compromised dogs were determined by high-pressure liquid chromatography and electrochemical detection. A rapid method of sample preparation, which involved single filtration through a deproteinizing membrane, was used. Canine CSF obtained in this manner contained 5.78 +/- 0.78 ng of DOPAC/ml, 72.19 +/- 4.09 ng of HVA/ml, and 29.95 +/- 1.67 ng of 5-HIAA/ml. Linear regression analysis between HVA and 5-HIAA yielded a correlation coefficient of 0.4804. The neurotransmitter index, HVA/5-HIAA, was found to be more indicative of the dopaminergic metabolite HVA than the acid metabolite of serotonin, 5-HIAA (correlation coefficient with HVA = 0.5529 vs a correlation coefficient with 5-HIAA = -0.4462). A poor relationship (correlation coefficient = -0.1715) was found to exist between the 2 dopaminergic metabolites DOPAC and HVA in the CSF.

OBJECTIVE To determine the cardiopulmonary effects of progressively increasing infusion rates of dopamine hydrochloride and phenylephrine hydrochloride in healthy adult New Zealand White rabbits anesthetized with isoflurane. ANIMALS 6 New Zealand White rabbits. (Oryctolagus cuniculus). PROCEDURES Each rabbit was anesthetized on 2 occasions (≥ 2 weeks apart) with isoflurane in oxygen at 1.5 times the published isoflurane minimum alveolar concentration of 2.07%. Carotid artery and pulmonary artery catheters were placed. During each anesthetic episode, each rabbit received 5 progressively increasing doses of either dopamine (5, 10, 15, 20, or 30 μg/kg/min) or phenylephrine (0.125, 0.25, 0.5, 1.0, and 2.0 μg/kg/min). Blood gas and cardiopulmonary measurements were obtained after a 20-minute equilibration period prior to administration of the first drug dose (baseline) and after each subsequent dose administration. RESULTS Dopamine increased stroke index at the highest infusion rate of 30 μg/kg/min; however, cardiac output and mean arterial blood pressure remained unchanged from baseline values. Administration of phenylephrine at a rate of 2 μg/kg/min increased mean arterial blood pressure to 62 mm Hg from the baseline value of 45 mm Hg. This was a result of an increase in systemic vascular resistance with a concomitant decrease in heart rate and no change in cardiac output. Blood lactate concentration increased with time when rabbits received either treatment. CONCLUSIONS AND CLINICAL RELEVANCE Within the dose range of 5 to 30 μg/kg/min, dopamine was not an effective treatment for isoflurane-induced hypotension in rabbits and phenylephrine was only minimally effective at a dose of 2 μg/kg/min.

Objective-To determine the effects of domperidone on in vivo and in vitro measures of gastrointestinal tract motility and contractility in healthy horses. Sample-18 adult horses and tissue samples from an additional 26 adult horses. Procedures-Domperidone or placebo paste was administered to healthy horses in a 2-period crossover study. Gastric emptying was evaluated after oral administration of domperidone paste (1.1 or 5.0 mg/kg) or placebo paste by means of the acetaminophen absorption test in 12 horses. Frequency of defecation, weight of feces produced, fecal moisture, and stomach-to-anus transit time of microspheres were evaluated after administration of domperidone paste (1.1 mg/kg) or placebo paste in 6 horses. The effect of domperidone on smooth muscle contractile activity in samples of duodenum, jejunum, ileum, or colon obtained from 26 horses immediately after euthanasia (for nonsystemic medical problems) was investigated. Results-Oral administration of 5.0 mg of domperidone/kg increased peak plasma acetaminophen concentration and area under the curve, indicating increased gastric emptying. Administration of 1.1 mg of domperidone/kg had no effect on gastric emptying, transit time, defecation frequency, or amount and moisture of excreted feces. Contractile activities of circular and longitudinal muscle strips from the duodenum, jejunum, ileum, or colon were not altered by domperidone. Dopamine increased contractile activity of longitudinal muscle strips but not that of circular muscle strips from the midjejunum. Domperidone decreased the dopamine-induced contractile activity of midjejunal longitudinal muscle strips. Conclusions and Clinical Relevance-The potential beneficial effects of domperidone in horses with ileus need to be evaluated in horses with decreased gastric emptying or adynamic ileus.

Objective: To determine cardiopulmonary effects of incremental doses of dopamine and phenylephrine during isoflurane-induced hypotension in cats with hypertrophic cardiomyopathy (HCM). Animals: 6 adult cats with severe naturally occurring HCM. Procedures: Each cat was anesthetized twice (once for dopamine treatment and once for phenylephrine treatment; treatment order was randomized). Hypotension was induced by increasing isoflurane concentration. Cardiopulmonary data, including measurement of plasma concentration of cardiac troponin I (cTnI), were obtained before anesthesia, 20 minutes after onset of hypotension, and 20 minutes after each incremental infusion of dopamine (2.5, 5, and 10 μg/kg/min) or phenylephrine (0.25, 0.5, and 1 μg/kg/min). Results: Mean ± SD end-tidal isoflurane concentration for dopamine and phenylephrine was 2.44 ± 0.05% and 2.48 ± 0.04%, respectively. Cardiac index and tissue oxygen delivery were significantly increased after administration of dopamine, compared with results after administration of phenylephrine. Systemic vascular resistance index was significantly increased after administration of phenylephrine, compared with results after administration of dopamine. Oxygen consumption remained unchanged for both treatments. Systemic and pulmonary arterial blood pressures were increased after administration of both dopamine and phenylephrine. Acid-base status and blood lactate concentration did not change and were not different between treatments. The cTnI concentration increased during anesthesia and infusion of dopamine and phenylephrine but did not differ significantly between treatments. Conclusions and Clinical Relevance: Dopamine and phenylephrine induced dose-dependent increases in systemic and pulmonary blood pressure, but only dopamine resulted in increased cardiac output. Hypotension and infusions of dopamine and phenylephrine caused significant increases in cTnI concentrations.