Analysis of equine cisterna magna cerebrospinal fluid for the presence of some monoamine neurotransmitters and transmitter metabolites.

Small volumes (0.05 ml) of cisterna magna cerebrospinal fluid (CSF) from 23 neurologically normal horses were analysed for the monoamine neurotransmitters dopamine, norepinephrine, epinephrine, serotonin and their metabolites using high pressure liquid chromatography and electrochemical detection. Two metabolites, homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were present in all CSF samples. The deaminated and methylated metabolite of dopamine, HVA, was present at a mean concentration of 42.33 +/- 3.14 ng/ml of CSF. The deaminated metabolite of serotonin, 5-HIAA, was present at a mean concentration of 45.52 +/- 3.65 ng/ml of CSF. A positive correlation was found between the CSF concentrations of HVA and 5-HIAA (r = 0.72, p = 0.0003). The mean ratio of HVA to 5-HIAA concentrations was 1.07 +/- 0.05. The ratios of HVA to 5-HIAA concentrations were found to be more indicative of the serotonergic metabolite 5-HIAA (r = -0.62, p = 0.0016) than the dopaminergic metabolite HVA (r = 0.11, p = 0.60). There was a stronger relationship between the concentrations of 5-HIAA and the ratios of HVA to 5-HIAA in male CSF (r = -0.85, p = 0.0006) than in female CSF (r = -0.54, p = 0.01). Concentrations of CSF neurotransmitter metabolites were evaluated in horses grouped by age (0-4, 5-9 and 10-13 years). The youngest group of horses had a significantly (p = 0.003) greater CSF concentration of HVA than of 5-HIAA. The 10-13-year-old horses had a significantly (p = 0.02) lower mean CSF HVA concentration than the 0-4-year-old horses. No age-related differences in CSF 5-HIAA concentrations were detected.

Determination of homovanillic acid, 5-hydroxyindoleacetic acid and pressure in the cerebrospinal fluid of collie dogs following administration of ivermectin.

Twelve adult Collie dogs were studied to determine the effects of ivermectin on neurotransmitter metabolites released from the brain into the cerebrospinal fluid (CSF) and on CSF pressure. Ten of the 12 Collies were given ivermectin orally at a concentration of 200 micrograms/kg body weight. Three of these 10 Collies showed clinical signs of ivermectin-induced toxicosis which progressed into a state of unresponsive recumbency in 2 dogs. Cerebrospinal fluid pressures and neurotransmitter metabolite concentrations in cisterna magna CSF were analysed 49 to 50 hours after administration of ivermectin in 6 of the 10 treated dogs, and in the 2 untreated control Collies. Cerebrospinal fluid pressures were within normal limits in all dogs. However, compared to the CSF concentrations in the 2 untreated and 3 non-reactive Collies, the 2 ivermectin-reactive Collies still in recumbency had elevated CSF concentrations of homovanillic acid (HVA), a metabolite of dopamine, and 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of serotonin. These findings suggest an association between altered neurotransmission and severe ivermectin-induced neurological abnormalities. No evidence of elevated intracranial pressure was found.

Analysis of cat retina for dopamine, dihydroxyphenylacetic acid, 3-methoxytyramine and homovanillic acid.

Twenty retinas from 10 cats were evaluated for dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT) and homovanillic acid (HVA) by high pressure liquid chromatography and electrochemical detection. Dopamine was present in all 20 retinas at a mean concentration of 3.00 +/- 0.54 ng/mg protein. Dihydroxyphenylacetic acid, 3-MT and HVA were detected in 16, 14 and 9 retinas respectively. In retinas in which these metabolites were detectable, they were present in the following mean concentrations: DOPAC, 1.07 +/- 0.21 ng/mg protein; 3-MT, 3.44 +/- 0.97 ng/mg protein and HVA, 4.54 +/- 1.05 ng/mg protein. Significantly higher concentrations of 3-MT (p = 0.0108, paired t test) and HVA (p = 0.0166, paired t test) than DOPAC were present in cat retina. Linear correlation analysis between DA and its metabolites indicated that the 3-MT and DOPAC concentrations correlated well with each other and with the amount of DA in cat retina. The concentrations of the end product metabolite, HVA, had poor correlations with the concentrations of 3-MT, DOPAC or DA. These data indicated that once DA is released in cat retina it can be metabolized to 3-MT, DOPAC and HVA.

Synthesis and aldose reductase inhibitory activity of substituted 2-oxoquinoline-1-acetic acid derivatives.

A number of 2-oxoquinoline-1-alkanoic acids that contain the N-acylglycine fragment found in several known inhibitors of aldose reductase were synthesized and tested in the rat lens assay. All of the target compounds were prepared by alkylation of the appropriate 2-oxoquinoline intermediates with a halo ester, followed by hydrolysis of the intermediate esters. In the rat lens assay, the 1-acetic acid derivatives 9a-e display the highest level of aldose reductase inhibitor activity with IC50 values of 0.45-6.0 microM. Modification of the 1-acetic acid moiety by esterification, substitution of an alpha-methyl group, or insertion of an additional methylene unit results in reduced inhibitory potency. Structure-activity data also suggests that both the benzene and 2-oxopyridine rings of 9a-e contribute substantially toward activity and that inhibitory potency is influenced by aromatic ring substituents.

Synthesis and rat lens aldose reductase inhibitory activity of some benzopyran-2-ones.

A number of 4,7-disubstituted benzopyran-2-ones were synthesized and evaluated for crude rat lens aldose reductase inhibitory activity. Substituents on position 4 included CH3, CO2H, CH2CO2H, CH = CHCO2H, and CH2CH2CO2H. The aromatic substituents included OH, OCH3, OCOCH3, CH2CH3, and Cl. Also included in the study were 3-oxo-3H-naphtho[2,1-b]pyran-1-acetic, 2-oxo-2H-naphtho[1,2-b]pyran-4-acetic, and 1-naphthylacetic acids. The benzopyran and naphthopyran derivatives were prepared by the classical von Pechmann reaction. General structure-activity relationships reveal that optimal enzyme inhibitory activity is displayed by those compounds possessing the acetic acid moiety. For example, the most potent derivative, 3-oxo-3H-naphtho[2,1-b]pyran-1-acetic acid with an IC50 of 0.020 microM, is as potent as sorbinil (IC50 = 0.017 microM) in the crude rat lens aldose reductase assay.