HPLC analysis of salinomycin in human plasma using pre-column oxidation and automated heart cut column switching.

Salinomycin is a polyether antibiotic used to promote growth in cattle and poultry. Workers may be exposed to salinomycin through handling of animal feeds that contain the drug and it is necessary to monitor plasma samples from these workers for salinomycin to ensure safety. A method for analysis of salinomycin in plasma samples was therefore developed. Salinomycin and the internal standard narasin are extracted into iso-octane then subjected to silica gel solid-phase extraction in which the sample is washed with methylene chloride-methanol (98.5:15) then eluted with a 90:10 proportion of the same mixture. Both salinomycin and narasin are oxidized with pyridinium dichromate to form a chromophore absorbing at 225 nm. The concentrated product was injected onto a C18 pre-column and heart cut from 1.85 to 3.65 min onto a C18 analytical column. The method was shown to be selective for salinomycin and narasin in six blank plasma samples. The method was linear over a range of 15-300 ng ml-1 with a detection limit of approximately 5 ng ml-1. The mean absolute recovery was found to be 93.4 and 97.9% for salinomycin and narasin, respectively. The method was accurate to within 5% at all concentrations studied. Within-run and between-run precision were both less than 8% RSD at all concentrations studied and the method was suitable for the purpose of monitoring plasma from exposed agricultural workers.

Covalent binding of two pyrrolizidine alkaloids, senecionine and seneciphylline, to hepatic macromolecules and their distribution, excretion, and transfer into milk of lactating mice.

Two macrocyclic 14C-pyrrolizidine alkaloids (PA's), senecionine an seneciphylline, were studied regarding the distribution, excretion, transfer into milk, and covalent binding to hepatic macromolecules in BALB/c mice. After injection, radioactivity was rapidly excreted in the urine and feces (84% or greater) within 16 hr. The liver contained over 1.5% of the dose at 16 hr. A small amount, 0.04%, of the dose was transferred into the milk in 16 hr; the majority of radioactivity was found in the skim-milk fraction, suggesting that the PA's were transferred to the milk as water-soluble metabolites. Both PA's covalently bound to liver macromolecules (DNA, RNA, and protein). The binding to calf thymus DNA and microsomal macromolecules was measured in vitro. The binding was diminished in the absence of O2 or a NADPH-generating system or by boiling the microsomes. No inhibition of the binding by KCN was observed.

Palmitate and octanoate metabolism in bovine mammary tissue.

Effect of glucose on palmitate and octanoate metabolism was studied in bovine mammary tissue slices. Glucose stimulated palmitate esterification principally to form partial glycerides while decreasing palmitate oxidation. Glucose stimulated octanoate but not palmitate incorporation into triacylglycerols, suggesting that availability of intracellular medium-chain fatty acids may limit the final acylation reaction in triacylglycerol synthesis.