14C] GABA and [14C]GABA-pantoyl metabolism in mice

It is shown that more than 90% of the labelled substance D-[1-14C] calcium homopantotenate is rapidly removed from the organism with urea; 6-8% are products of its transformation, among them GABA is identified. An insignificant transformation of D-[1-14C] calcium homopantotenate up to 14CO2 is observed. After the preparation administration only unchanged D-[1-14C] calcium homopantotenate was found in the tissues, except of the liver where, as in urea, there is a nonidentified product with small Rf. [1-14C] GABA is rapidly transformed to 14CO2 and only its insignificant part is removed with urea, chiefly as products of transformation.     

The metabolism of [14C]nicotine in the cat

The metabolism of [2'-(14)C]nicotine given as an intravenous injection in small doses to anaesthetized and unanaesthetized cats has been studied. A method is described for the quantitative determination of [(14)C]nicotine and [(14)C]cotinine in tissues and body fluids. Nanogram amounts of these compounds have been detected. After a single dose of 40mug. of [(14)C]nicotine/kg., 55% of the injected radioactivity was excreted in the urine within 24hr., but only 1% of this radioactivity was unchanged nicotine. [(14)C]Nicotine is metabolized extremely rapidly, [(14)C]cotinine appearing in the blood within 2.5min. of intravenous injection. [(14)C]Nicotine accumulates rapidly in the brain and 15min. after injection 90% of the radioactivity still represents [(14)C]nicotine. Metabolites of [(14)C]nicotine have been identified in liver and urine extracts. [(14)C]Nicotine-1'-oxide has been detected in both liver and urine.     

The metabolism of [2-14C]indole in the rat

1. [2-¹⁴C]Indole has been synthesized from [¹⁴C]formate and o-toluidine via N[¹⁴C]-formyltoluidine. 2. When fed to rats, the ¹⁴C of [¹⁴C]indole (dose 70–80mg./kg. body wt.) is fairly rapidly excreted, and in 2 days an average of 81% appears in the urine, 11% in the faeces and 2·4% as carbon dioxide in the expired air. 3. Radioactivity is excreted in the urine as indoxyl sulphate (50% of the dose), indoxyl glucuronide (11%), oxindole (1·4%), isatin (5·8%), 5-hydroxyoxindole conjugates (3·1%), N-formylanthranilic acid (0·5%) and unchanged indole (0·07%). The faeces contain indoxyl sulphate (0·4% of the dose) and indole (0·2%), but the major metabolites have not been identified. 4. Fed to rats with biliary cannulae an average of 5·6% of a dose of [¹⁴C]indole (20–60mg./kg. body wt.) is excreted in the bile in 2 days. Radioactivity is present as indoxyl sulphate (0·8% dose) and 5-hydroxyoxindole conjugates (0·6%). 5. Rats further metabolize indoxyl into N-formylanthranilic acid and anthranilic acid, and oxindole into 5-hydroxyoxindole. 6. With rat-liver microsomes plus supernatant under aerobic conditions, indole gives indoxyl, oxindole, possibly isatin, N-formylanthranilic acid and anthranilic acid, but under anaerobic conditions gives only oxindole. Similarly, under aerobic conditions, oxindole gives 5-hydroxyoxindole, anthranilic acid and o-aminophenylacetic acid. 7. Indole is metabolized by two pathways, one via indoxyl to isatin, N-formylanthranilic acid and anthranilic acid, and the other via oxindole to 5-hydroxyoxindole and possibly to o-aminophenylacetic and anthranilic acid. 8. The following new compounds are described: 4-hydroxy-2-nitrophenylacetic acid, 3-, 4- and 5-benzyloxy-2-nitrophenylacetic acid, 5- and 7-hydroxyoxindole and 5-aminoacridine indoxyl sulphate.     

Oxidation of D-[U-(14)C] glucose and [1,12-(14)C] dodecanedioic acid by pancreatic islets from Goto-Kakizaki rats.

In pancreatic islets from hereditarily diabetic GK rats, [1,12 -(14)C] dodecanedioic acid (5.0 mM) was oxidized at a rate representing about 5 % of that of D-[U - (14)C] glucose (8.3 mM). Dioic acid and hexose failed to exert any significant reciprocal effects on their respective oxidation. The production of (14)CO(2) from [1,12 -(14)C] dodecanedioic acid was proportional to its concentration in the 0.2 - 5.0 mM range. These results were essentially comparable to those obtained in islets from control rats. They extend, therefore, to GK rats the knowledge that dodecanedioic acid acts as a nutrient in pancreatic islet cells.     

Bioconversion of alpha-[14C]zearalenol and beta-[14C]zearalenol into [14C]zearalenone by Fusarium roseum 'Gibbosum'.

Cultures of Fusarium roseium 'Gibbosum' on rice were treated with [14C]zearalenone, alpha[14C]zearalenol, or beta-[14C]zearalenol to determine whether a precursor-product relationship exists among these closely related fungal metabolites. Culture extracts were purified by silica gel column chromatography and fractionated by high-pressure liquid chromatography, and the level of radioactivity was determined. Within 7 days, the beta-[14C]zearalenol was converted to zearalenone, and no residual beta-[14C]zearalenol was detectable. Most of the alpha-[14C]zearalenol added was also converted into zearalenone with 14 days. In cultures treated with [14C]zearalenone, no radioactivity was noted in any other components.     

Relationship between synaptosomal uptake and release of [14C]gaba, [14C]diaminobutyric acid and [14C]beta-alanine.

[¹⁴C]GABA is taken up by rat brain synaptosomes via a high affinity, Na⁺-dependent process. Subsequent addition of depolarizing levels of potassium (56.2 MM) or veratridine (100 μM) stimulates the release of synaptosomal [¹⁴C]GABA by a process which is sensitive to the external concentration of divalent cations such as Ca²⁺, Mg²⁺, and Mn²⁺. However, the relatively smaller amount of [¹⁴C]GABA taken up by synaptosomes in the absence of Na⁺ is not released from synaptosomes by Ca²⁺ -dependent, K ⁺-stimulation. [¹⁴C]DABA, a competitive inhibitor of synaptosomal uptake of GABA (Iversen & Johnson , 1971) is also taken up by synaptosomal fractions via a Na ⁺ -dependent process; and is subsequently released by Ca²⁺ -dependent, K⁺-stimulation. On the other hand, [¹⁴C]β-alanine, a purported blocker of glial uptake systems for GABA (Schon & Kelly , 1974) is a poor competitor of GABA uptake into synaptosomes. Comparatively small amounts of [¹⁴C] β-alanine are taken up by synaptosomes and no significant amount is released by Ca²⁺ -dependent, K⁺-stimulation. These data suggest that entry of [¹⁴C]GABA into a releasable pool requires external Na⁺ ions and maximal evoked release of [¹⁴C]GABA from the synaptosomal pool requires external Ca²⁺ ions. The GABA analogue, DABA, is apparently successful in entering the same or similar synaptosomal pool. The GABA analogue, β-alanine, is not. None of the compounds or conditions studied were found to simultaneously affect both uptake and release processes. Compounds which stimulated release (veratridine) or inhibited release (magnesium) were found to have minimal effect on synaptosomal uptake. Likewise compounds (DABA) or conditions (Na⁺-free medium) which inhibited uptake, had little effect on release.