The vesicular monoamine transporter (VMAT-2) inhibitor tetrabenazine induces tremulous jaw movements in rodents: implications for pharmacological models of parkinsonian tremor.

Tetrabenazine (TBZ) is a reversible inhibitor of vesicular monoamine storage that is used to treat Huntington's disease. TBZ preferentially depletes striatal dopamine (DA), and patients being treated with TBZ often experience parkinsonian side effects. The present studies were conducted to investigate the ability of TBZ to induce tremulous jaw movements (TJMs), which are a rodent model of parkinsonian tremor, and to determine if interference with adenosine A2A receptor transmission can attenuate TJMs and other motor effects of TBZ. In rats, TBZ (0.25-2.0mg/kg) significantly induced TJMs, which primarily occurred in the 3.0-7.5-Hz frequency range. The adenosine A2A antagonist MSX-3 (1.25-10.0mg/kg) significantly attenuated the TJMs induced by 2.0mg/kg TBZ in rats, and also significantly reduced the display of catalepsy and locomotor suppression induced by TBZ. In mice, TBZ (2.5-10.0mg/kg) dose dependently induced TJMs, and adenosine A2A receptor knockout mice showed significantly fewer TJMs compared to wild-type controls. MSX-3 (2.5-10.0mg/kg) also significantly reduced TBZ-induced TJMs in CD1 mice. To provide a cellular marker of these pharmacological conditions, we examined c-Fos expression in the ventrolateral neostriatum (VLS). TBZ (2.0mg/kg) significantly increased the number of c-Fos-positive cells in the VLS, which is indicative of reduced DA D2 receptor transmission, and 10.0mg/kg MSX-3 significantly attenuated the TBZ-induced c-Fos expression. These results indicate that TBZ induces tremor as measured by the TJM model, and that pharmacological antagonism and genetic deletion of adenosine A2A receptors are capable of attenuating this oral tremor.

Response to high-dose radioactive iodine administration in cats with thyroid carcinoma that had previously undergone surgery.

Seven cats with thyroid carcinomas that had previously undergone surgical removal of neoplastic tissue were treated with 30 mCi of radioactive iodine (131I). Six of the cats had clinical signs of hyperthyroidism; 1 did not. There were no complications associated with 131I treatment, and clinical signs resolved in all cats. Technetium scans of 4 cats made after treatment did not have evidence of isotope uptake. In the remaining 3 cats, small areas of isotope uptake, the intensity of which was equal to or less than the intensity of uptake in the salivary glands, were seen. All 7 cats became hypothyroid after treatment; 4 required L-thyroxine supplementation. One cat was alive 33 months after treatment. The other 6 cats were euthanatized because of unrelated diseases 10 to 41 months after treatment.

Confirmation of a pulmonary component of multicentric lymphosarcoma with bronchoalveolar lavage in two dogs.

Histologic examination of lung tissue has been the only definitive diagnostic procedure used to confirm pulmonary involvement with lymphosarcoma (LSA) in dogs. Lung involvement with LSA was diagnosed by cytologic examination of bronchoalveolar lavage fluid in 2 dogs with multicentric LSA. Both dogs had cough or dyspnea, in addition to peripheral lymphadenopathy or visceral organomegaly. Both dogs had nonspecific, abnormal thoracic radiographic findings, including diffuse pulmonary interstitial pattern, hydrothorax, and mediastinal and retrosternal lymphadenopathy. In these 2 dogs, postmortem lung histologic examination, performed immediately after bronchoalveolar lavage, confirmed the cytologic diagnosis of pulmonary infiltration with LSA.

Bromide toxicosis (bromism) in a dog treated with potassium bromide for refractory seizures.

A 4-year-old German Shepherd Dog was evaluated because of chronic hind limb lameness and recurrent seizures. Diagnostic evaluation of the dog confirmed rheumatoid arthritis and idiopathic epilepsy. The rheumatoid arthritis was treated with prednisone and piroxicam. The seizures were treated with phenobarbital plus clonazepam. The seizures were refractory and potassium bromide was substituted for clonazepam. The dog was reevaluated 4 months after initiation of potassium bromide treatment because of recurrence of arthritis signs. During hospitalization, the dog had neurologic signs, which progressed from depression to recumbency and stupor. Anisocoria, muscle pain, and hyporeflexia were noticed. Bromide toxicosis was diagnosed on the basis of toxic serum bromide concentration (2.7 mg/ml; therapeutic range, 1.0 to 2.0 mg/ml). Following cessation of potassium bromide treatment, the neurologic signs resolved. The seizures recurred 6 weeks after potassium bromide was discontinued. Bromide treatment was reinitiated at half the initial dosage. After 6 weeks, the serum bromide concentration was 1.9 mg/ml, and no seizures had been reported by the dog's owners. Therapeutic serum bromide concentrations in dogs has been reported to be 0.5 to 2.3 mg/ml. The serum bromide concentration at which toxic signs are expected is variable in human beings because individuals differ in their tolerance of the drug. Clinical trials are necessary to determine the toxic serum bromide concentrations in dogs. This case of bromism in a dog suggests that the dosage of potassium bromide should be based on serial measurement of serum bromide concentrations.

An antifibrotic agent reduces blood pressure in established pulmonary hypertension in the rat.

We have shown that administration of the antifibrotic agent cis-4-hydroxy-L-proline (cHyp) to rats at the onset of exposure to hypoxia prevents collagen accumulation in pulmonary arteries and the rise in pulmonary blood pressure. In this experiment, we tested whether cHyp is effective when administered after hypertension was already established. Rats were exposed to hypoxia (10% O2) for 21 days. Groups were hypoxic animals treated with cHyp (200 mg/kg sc twice daily) on days 10-21 (hypoxic cHyp) and saline-injected hypoxic animals (hypoxic). On day 21, we measured mean right ventricular pressure, hematocrit, collagen content of main and intrapulmonary arteries, and wall thickness of arterioles. Treatment reduced right ventricular pressure from 21 +/- 1 to 17 +/- 1 mmHg (P less than 0.05), hematocrit from 66 +/- 1 to 56 +/- 1% (P less than 0.05), hydroxyproline content of intrapulmonary arteries from 30 +/- 3 to 11 +/- 2 micrograms/vessel (P less than 0.05), and wall thickness from 27 +/- 3 to 16 +/- 2 microns (P less than 0.05). These results show that vascular collagen content is increased in established pulmonary hypertension and that cHyp treatment is effective in partially preventing the hemodynamic, structural, and biochemical changes if started after pulmonary hypertension is established. cHyp may also affect the rheological properties of blood.

Collagen and elastin metabolism in hypertensive pulmonary arteries of rats.

We evaluated the processes controlling the accumulation of collagen and elastin in main pulmonary arteries of rats during an episode of hypoxic pulmonary hypertension. Explant cultures of main pulmonary arteries were incubated with [3H]proline to measure collagen and protein synthesis and percent collagen synthesis. Elastin synthesis was measured by [14C]valine incorporation into insoluble elastin. Relative collagen synthesis increased twofold (from 1.1 +/- 0.2 x 10(3) to 2.0 +/- 1.0 x 10(3) disintegrations per minute [14C]hydroxyproline/vessel/hr/mg protein), relative collagen synthesis doubled (from 2% to 4-5% of total protein synthesis), and elastin synthesis increased ninefold (from 0.4 +/- 0.2 x 10(4) to 3.6 +/- 0.6 x 10(4) dpm [14C]valine/vessel/hr/mg protein) in early hypertension. The level of pro alpha l(I) collagen RNA paralleled the relative collagen synthetic rate during the study period. Within 7 days of recovery from hypoxia, collagen and elastin contents were normal. We conclude that collagen and elastin in main pulmonary arteries are synthesized rapidly during an episode of hypoxic pulmonary hypertension and that collagen and elastin are rapidly removed from the hypertensive vessel during normoxic recovery.