Terry L. Johnson

Absorption, distribution, metabolism, and excretion of [1-14C]-perfluorohexanoate ([14C]-PFHx) in rats and mice

The absorption, tissue distribution, elimination, and metabolism of [1-¹⁴C]-PFHx in rats and mice dosed orally at 2 or 100 mg/kg was evaluated following a single dose or after 14 consecutive doses. Absorption was rapid in rats as evidenced by a short time to maximum concentration (C(max)) of 30 min in male rats and 15 min in female rats at both the 2 and 100mg/kg dose level. The plasma elimination half-life was somewhat longer in males (1.5-1.7 h) than in females (0.5-0.7 h). Absorption in the mouse was also rapid with the maximum plasma concentration occurring between 15 and 30 min after dosing. The maximum concentration was not appreciably different between male and female mice (8 μg equiv./g at 2 mg/kg; ~350 μg equiv./g at 100 mg/kg). The primary route of elimination was via the urine. PFHx was not metabolized in rat or mouse hepatocytes, nor were any metabolites observed after oral dosing in either rodent species. Essentially 100% of the dose was eliminated in urine within 24 h demonstrating that PFHx is readily absorbed and bioavailability approaches 100%, even at a dose as high as 100 mg/kg. The route and extent of elimination was unchanged after 14 days of daily dosing. Tissues were collected at three time points (rat: 0.5, 2, and 24 h; mice: 0.25, 1, and 24 h) after dosing to investigate the tissue clearance kinetics of PFHx following a single dose at 2 or 100 mg/kg. In all tissues except skin, PFHx was not quantifiable 24 h after dosing in both sexes of the two species.

Effects of organotins on rat platelets

Incubation of rat platelets with organotins inhibited their capacity to take up 5-hydroxytryptamine-14C (5-HT-14C) and stimulated the release of preloaded 5-HT-14C as well as endogenous 5-HT. Similar but less pronounced effects also were observed when platelets from rats treated intraperitoneally with organotins were examined. The relationships of organotin structure to 5-HT uptake inhibition and 5-HT release were similar, with the most active compounds being the trisubstituted derivatives bis(tri-n-butyltin) oxide, tri-n-butyltin chloride, tricyclohexyltin hydroxide, tri-n-propyltin chloride, and triphenyltin hydroxide. Scanning electron micrographs revealed increased platelet aggregation and shape change in organotin treated samples as compared to vehicle treated controls. It was suggested that the action of organotins on rat platelets was due, at least in part, to their known ability to interfere with ATPase mediated systems.

Biogenic amine uptake by nerve cords from the American cockroach and the influence of amidines on amine uptake and release

Uptake of 5-hydroxytryptamine (5-HT) by isolated whole nerve cords of the American cockroach, Periplaneta americana (L.), involved a dual component system, with one component consisting of rapid active uptake and the other of passive diffusion. Using high performance liquid chromatography with electrochemical detection, it was shown that nerve cords contained 5-HT levels of about 350 ng/g and an equivalent amount of 5-hydroxyindoleacetic acid (5-HIAA), a 5-HT metabolite not previously reported in cockroach nerve cords. Amidines had no discernable effect on uptake of 5-HT or octopamine by nerve cords or on endogenous levels of 5-HT and 5-HIAA in cords.

Influence of formamidines on biogenic amine levels in rat brain and plasma.

Biogenic amine levels in samples of whole brain and plasma following treatment of rats with chlordimeform (CDF), its two N-demethyl metabolites (DMC and DDC), p-chloroamphetamine (PCA), and harmaline were separated by high performance liquid chromatography equipped with fluorescence or electrochemical detection systems. At 1 hr following s.c. injection, CDF (200 mg/kg) caused a reduction in levels of norepinephrine (NE), 5-hydroxytryptamine (5-HT), and tyramine (TRM), an increase in dopamine (DA), and no change in levels of beta-phenethylamine (PEA) in samples of whole rat brain, whereas DMC (100 mg/kg) and DDC (25 mg/kg) effected reductions of brain levels of NE, 5-HT, TRM, and PEA with no change in DA. The effect of DMC (100 mg/kg) on NE and DA levels in brain was followed periodically for 24 hr. Following a significant decrease at 1 hr, NE levels increased to a maximum at 12 hr and remained higher than controls throughout the remainder of the 24 hr test period. DA levels increased during the initial 12 hr and remained significantly higher than controls for the remaining 12 hr. The influence of s.c. vs i.p. administration of DMC (100 mg/kg) on brain amine levels was examined. Intraperitoneal treatment generally resulted in lower amine levels in DMC and vehicle treated animals. Differences in treatment effects were similar for all amines except for 5-HT in which s.c. injection produced a slight reduction, while i.p. injection resulted in a two-fold increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of rat platelet 5-hydroxytryptamine uptake by chlordimeform

Chlordimeform, a formamidine insecticide and acaricide, and two of its toxic N-demethyl metabolites inhibited rat blood platelet 5-hydroxytryptamine (5-HT) uptake. A direct relationship existed between formamidine uptake inhibitory potency and N-demethylation. Didemethylchlordimeform, the most potent formamidine inhibitor of 5-HT uptake examined, had a pI50 of 4.2. However, it was appreciably less active than the classical inhibitor imipramine, which yielded 86.4% inhibition of 5-HT uptake at a concentration of 1.10(-5) M.

Influence of organotins on rat platelet aggregation mechanisms

The effects of ten organotins on rat platelet aggregation mechanisms were examined. Bis(tri-n-butyltin)oxide was the most potent inhibitor of both ADP- and collagen-induced aggregation, and it was the only organotin that directly induced aggregation. It also increased the latent period for induction of aggregation by collagen. Triphenyltin hydroxide was a weak inhibitor of both ADP- and collagen-induced aggregation. However, in contrast to bis(tri-n-butyltin)oxide, it decreased the latent period for collagen-induced aggregation. A similar effect also was observed with diphenyltin dichloride, phenyltin trichloride, and cyhexatin. Tri-n-butyltin chloride and tetra-n-butyltin demonstrated specificity in their action since aggregation induced by ADP but not collagen was inhibited. Tri-n-propyltin chloride, trimethyltin chloride, and fenbutatin oxide were without discernible effect on rat platelet aggregation.

Formamidine-mediated inhibition of rat platelet aggregation.

The formamidine pesticide chlordimeform (CDF) was a strong inhibitor of aggregation of rat platelets induced by collagen and arachidonic acid and was a weak inhibitor of that induced by ADP. With the exception of 4-chloro-o-formotoluidide which was an inhibitor of arachidonic acid-induced aggregation only, the CDF metabolites were without discernible effect on aggregation induced by these agents. Amitraz, another formamidine pesticide, inhibited arachidonic acid-induced aggregation but was without effect on that induced by collagen or ADP. Inhibition of collagen- and/or arachidonic acid-induced aggregation by formamidines was concentration-dependent. Although platelets underwent shape change, primary aggregation was markedly inhibited, and secondary aggregation was abolished in some cases. CDF, its two N-desmethyl metabolites, and octopamine, but not amitraz, caused significantly elevated levels of cyclic AMP in platelet rich plasma as compared to controls; however, this effect did not fully account for the action of formamidines on aggregation.

Effect of formamidines on 5-hydroxytryptamine uptake and biogenic amine levels in rat platelets

Uptake of radioactive 5-hydroxytryptamine (5-HT) by platelets from rats treated intraperitoneally with the insecticide/acaricide chlordimeform (CDF) at 25 mg/kg was not significantly influenced at 1 h; however, uptake of this amine by platelets from rats treated with its N- monodemethyl metabolite (DMC) at the same dosage was significantly inhibited (37%). Two reversed phase high performance liquid chromatographic systems with electrochemical detection were developed with a capacity to separate 11 biogenic amines and related compounds. Only 5-HT, norepinephrine (NE), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were consistently detected in platelets and plasma samples. At 1 h and/or 24 h postinjection, CDF effected significant decreases in platelet levels of 5-HT, NE, and DA and plasma levels of 5-HT, whereas platelet and plasma levels of DOPAC were significantly increased. DMC effected significant decreases in both platelet and plasma levels of 5-HT. These in vivo studies confirmed previous in vitro experiments which demonstrated that formamidines inhibited uptake of 5-HT by platelets and released endogenous stores of amines from platelets.

Excretion balance, metabolic fate, and tissue residues ofN-phenyl-N′-1,2,5-thiadiazol-3-ylurea (photothidiazuron) in rats

Photothidiazuron-14C, a major photoconversion product of thidiazuron defoliant on cotton leaves, was rapidly absorbed and eliminated following oral administration to rats. By 96 hr posttreatment, 90.7% of the administered dose was accounted for in the urine (75.5%) and feces (15.2%). Between 5.0 and 10% of the radioactive material in the urine partitioned into ethyl acetate. In addition to photothidiazuron and several unknowns, the following metabolites were present: 4-hydroxyphenylphotothidiazuron, phenylurea, and 4-hydroxyphenylurea. There was also some evidence for the presence of 4-hydroxyacetanilide. The major portion of the radioactivity (>90%) remained in the urine after extraction with ethyl acetate. Cleavage data withbeta-glucuronidase and aryl sulfatase indicated that at least 12.1% and 6.3%, respectively, of the urinary radioactive materials were conjugated with glucuronic and sulfuric acids. Compounds included 4-hydroxyphenylurea, 4-hydroxyphenylphotothidiazuron, and several unknowns. Fractionation of the feces indicated that about 10% of the radioactive material was organosoluble, about 20% was water soluble and about 70% was unextractable from the fecal residue. Tissue levels of radioactivity were low and in the ppb range.