Streptozotocin: Its excretion and metabolism in the rat

Summary The excretion of radioisotope following the administration of three specifically¹⁴C-labelled forms of streptozotocin was investigated in the rat using ureter and bile duct cannulation techniques. The urine collected during the first hour following the administration of the drug contained the highest proportion of injected radioactivity (approximately 34% with (3-methyl-¹⁴C)-streptozotocin and approximately 40% each with (1-¹⁴C)- and (2-¹⁴C)-streptozotocin. Over the entire experimental period (6 hours), approximately 70% of the injected radioactivity of (1-¹⁴C)- and (2-¹⁴C)-streptozotocin appeared in the urine. With (3-methyl-¹⁴C)-streptozotocin, only 53% of the injected radioactivity appeared in the urine over the same period. In contrast to the high urinary excretion, less than 3 % of the injected radioactivity from all three radiolabelled streptozotocin samples appeared in the bile. The in vivo and in vitro metabolism of streptozotocin was also investigated. In addition to substantial amounts of unchanged drug, three radiolabelled metabolites (two major and one minor) were detected in the urine during the 6 hour collection period following the administration of (1-¹⁴C)- and (2-¹⁴C)-streptozotocin. In contrast, only unchanged (3-methyl-¹⁴C)-streptozotocin was detected in the urine collected over the same period following the administration of the methyl labelled drug. The two major metabolites were also produced when (1-¹⁴C)- and (2-¹⁴C)-streptozotocin were incubated with a rat liver supernatant fraction (100,000 X g). The liver was further demonstrated to be the major site of metabolism in isolated liver perfusion studies in which both (1-¹⁴C)- and (2-¹⁴C)-streptozotocin were quantitatively converted to the two major metabolites. The two major metabolites of (1-¹⁴C)-streptozotocin, whether produced in vivo or in vitro, were chromatographically homogeneous with the two major metabolites formed from (2-¹⁴C)-streptozotocin. Nicotinamide pretreatment had no apparent effect on the urinary excretion of streptozotocin and its metabolites.     

Kinetics of 14carbon dioxide excretion from 14C-urea by oral commensal flora

Background and Aim: Previous studies have shown that while performing the ¹⁴C‐urea breath test (¹⁴C‐UBT) for the detection of Helicobacter pylori (H. pylori), there is possibility of false‐positive results due to the other urease producing bacteria present in oropharynx, if breath samples are obtained within 30 min after administration of non‐capsulated ¹⁴C‐urea. Therefore, we have exclusively evaluated the kinetics of ¹⁴carbon dioxide (¹⁴CO₂) excretion by oral commensal flora to theoretically propose optimum breath collection timings for ¹⁴C‐UBT. Methods: Multiple breath samples up to 15 min were collected in 0.25 mmol benzethonium hydroxide from 25 healthy volunteers after they withheld 37 kBq (1 μCi) of ¹⁴C‐urea in their mouths for 15 s and then expectorated the tracer. The test was repeated on the same subjects without and with mouth cleansing protocols. Breath ¹⁴CO₂ content was measured by the Liquid Scintillation Counter (1409; Wallac, Turku, Finland) and results were expressed as ¹⁴CO₂ excretion per mmol breath CO₂ (% administered dose). Results: Peak breath radioactivity at 1 min in the former protocol was 3.53 times higher than the latter which declined subsequently with a half time of 1 min and 2.5 min, and reached baseline levels by 15 and 10 min, respectively. The peak radioactivity (100%) at 1 min declined by 94% and 97.8% in the former and later protocols, respectively, at 15 min. Although magnitude of the peak varied in different subjects, the shape of curve remained almost similar in all cases. Conclusions: Without mouth cleansing, oral micro flora excreted more ¹⁴CO₂ up to 15 min after administration of non‐capsulated ¹⁴C‐urea. Therefore, it is proposed that two breath samples may be obtained either at 15 and 20 min without or at 10 and 15 min with mouth cleansing protocols for reliable analysis of ¹⁴C‐UBT data for H. pylori detection.     

Fecal and urinary excretion of six iodothyronines in the rat

Fecal and urinary excretion rates of six iodothyronines were assessed in the rat maintained under normal steady state physiological conditions, to gain a more comprehensive understanding of the mechanisms of control of normal thyroid hormone economy and metabolism. Groups of young adult male rats were injected with trace doses of T4, T3, rT3, 3,3'-diiodothyronine (T2), 3',5'-T2, or 3'-monoiodothyronine, each labeled with 125I, and feces and urine were collected separately for up to 10 days. Pooled fecal pellets were homogenized in saline, extracted in ethanol, evaporated under vacuum, and reconstituted in NaOH. Fecal extracts and urine were chromatographed on Sephadex G25 columns under conditions providing quantitative separations of components of interest. A new technique was also developed, based on a model of the in vitro extraction and measurement process, to correct chromatographic results for possible variable recoveries and possible artifactious degradation of radioactively labeled components. No iodothyronines or their conjugates were excreted in urine; all radioactivity was in the form of iodide. In feces, about 30% of the [125I]T3 injected was excreted as T3; and 24% of the [125I]T4 injected was excreted as T4, plus 4% as T3. Together, these results imply that about 24% of endogenous T4 production is excreted as T4 and 76% is irreversibly metabolized; and for T3, about 30% of endogenous T3 production is excreted as T3 and 70% is degraded. For the nonhormonal iodothyronines, about 6% of injected monoiodothyronine, 3% of injected 3',5'-T2, 2% of injected 3,3'-T2, and less than 1% of injected rT3 were excreted in feces as such, indicating that these substances are nearly completely deiodinated in vivo. Very little (1-7%) iodide was excreted as such in feces, which also were devoid of measurable conjugates. An open question is whether the substantial wastage of thyroid hormones in feces represents poor hormone economy in the usually accepted sense or a functional property of overall thyroid hormone regulation.     

Factors affecting the absorption and excretion of lead in the rat

A reliable method for studying lead absorption and excretion in rats is described. Lead absorption occurs primarily in theduodenum where lead enters the epithelial mucosal cells. There is a relative mucosal block for lead with increasing intraluminal doses. Certain substances which bind lead and increase its solubility enhance its absorption. Iron, zinc, and calcium decrease the absorption of lead without affecting its solubility, probably by competing for shared absorptive receptors in the intestinal mucosa. The total body burden of lead does not affect lead absorption. Thus, lead does not have a feedback mechanism which limits absorption. Lead absorption is increased during rapid periods of growth and in iron-deficient animals. It is diminished with starvation and in iron-overloaded animals. The excretion and kinetics of tracer doses of radiolead were quantified. Erythrocytes seem to serve an important role in transport. Excretion occurs in urine and stool. Bile is an important route of excretion in the gut. Although most of a tracer dose is rapidly excreted, the excretory process is limited permitting lead accumulation primarily in bone.     

Appraisal of the 14C-glycocholate acid test with special reference to the measurement of faecal 14C excretion

The ¹⁴C-glycocholate test, including the measurement of marker corrected faecal ¹⁴C, has been assessed in the following groups of subjects: normal controls (18), patients with diarrhoea not attributable to altered bile acid metabolism (21), patients with diverticula of the small intestine (12), patients with previous resection of ileum and often proximal colon (34), and established ileostomists (10). Patients with diverticular disease had increased breath ¹⁴CO₂ excretion, but normal faecal excretion of ¹⁴C, and this test was more frequently abnormal than the Schilling test. Ileostomists excreted increased amounts of faecal ¹⁴C, even when the ileum was intact and apparently normal. The pattern after resection was complex. Breath ¹⁴C output was normal if the ileal resection was less than 25 cm in length, although some of these patients had increased faecal ¹⁴C excretion if, in addition, at least 15 cm of proximal colon had been resected or by-passed. Longer ileal resections were associated with increased breath and/or faecal ¹⁴C excretion, depending in part on the length of colon resected or by-passed and the 24 hour faecal volume. Fewer than half these patients had both increased breath and faecal excretion of isotope and faecal ¹⁴C alone was occasionally normal with an ileal resection of 50 cm of more. The ¹⁴C-glycocholate test was more frequently abnormal than the Schilling test in this group. The use of faecal marker correction had only a minor impact on the results. These data suggest that, in patients with ileal resection, faecal ¹⁴C, like faecal weight, is determined by the extent of colonic resection as well as by the amount of ileum resected.     

Hepatobiliary excretion of bacterial formyl-methionyl peptides in rat

The bacterial chemotactic peptide formyl-met-leu-phe and its radioiodinated analog formyl-met-leu-[¹²⁵I]tyr are rapidly excreted by the liver into bile following portal or systemic venous infusions in rats or after absorption from the gut lumen. To determine the molecular structural requirements for hepatobiliary excretion of formyl-methionyl peptides, structure-activity studies using portal venous infusions of 24 structural analogs of formyl-met-leu-tyr were performed in rats with biliary cannulae. Hepatic extraction of peptides was studiedin vivo using external gamma counting after portal infusion. Efficient hepatobiliary excretion was not restricted to bioactive formyl peptides, but showed a broad specificity for different amino-acylated (formyl, acetyl, propionyl, carbobenzoxy) di- and tripeptides and no requirement for methionine in position one or for a free carboxy terminus. However, nonacylated peptides and an acyl-amino acid showed little excretion. Hepatic extraction of peptide was also related toN-acylation. Hepatic extraction and excretion ofN-acyl peptides were also related to hydrophobicity. Thus, the presence of anN-acyl group is the key determinant of biliary excretion of inflammatory bacterial f-met peptides in the rat.This work was supported by a grant from the Medical Research Council of New Zealand. Dr. R.P. Anderson holds a New Zealand Medical Research Council Training Fellowship.     

Vitamin B 12 excretion by the rat small intestine

Two phases of intestinal excretion are demonstrated after a parenteral dose of ⁵⁸Co vitamin B₁₂. The first phase was maximal immediately after injection, and was related to plasma radioactivity. The second phase was delayed 36 to 48 hours and was related to labelled cells reaching the tips of the villi. The loss of vitamin B₁₂ through increased exudation and rapid cell exfoliation together with failure of reabsorption may play a part in the deficiency state seen in the coeliac syndrome.     

Effects of anesthetic agents on bile pigment excretion in the rat

Anesthesia-induced alterations in bilirubin conjugation were studied. Rats were fitted with bile duct and jugular vein catheters while anesthetized with diethyl ether, ketamine or pentobarbital. As anesthesia abated, bile was collected for the next 5 hr and analyzed for flow rate, total bilirubin excretion and bilirubin glucuronide composition. The high-performance liquid chromatography method used allowed direct analysis of bile without derivatization or extraction. Ether anesthesia was associated with a reversible suppression of diglucuronide formation and total bilirubin excretion, with reciprocal monoglucuronide changes. Bile flow and pigment excretion were variable with ketamine. Pentobarbital provided the most uniform excretion data, although the ratio of C-8:C-12 monoglucuronide varied with all drugs. These data are consistent with recently reported drug-induced alterations in hepatic uridine diphosphoglucuronic acid concentration and support the hypothesis that alterations in this substrate concentration are capable of influencing rates of hepatic glucuronide formation.     

Influence of oxytocin on sodium excretion in the anaesthetized Brattleboro rat

The contribution of oxytocin to the maintenance of renal Na+ excretion in the Brattleboro rat has been examined in animals infused with hypotonic saline. Brattleboro rats exhibited hypernatraemia and hyperosmolality associated with greatly increased plasma concentrations of oxytocin by comparison with Long-Evans control rats. Neurohypophysectomy to remove the secretion of the remaining posterior pituitary peptide, oxytocin, led to greatly diminished rates of Na+ excretion in the Brattleboro rat. Oxytocin replacement to achieve plasma levels equivalent to those in intact Brattleboro rats produced a substantial and sustained natriuresis in the neurohypophysectomized animal. Oxytocin secretion evoked in response to saline infusion would thus appear to be effective in promoting renal Na+ excretion in the absence of vasopressin in the Brattleboro rat.     

Estrogenic effects on urinary 6-sulphatoxymelatonin excretion in the female rat

ABSTRACT: The pattern of melatonin production during the estrous cycle of the rat was measured by monitoring urinary 6-sulphatoxymelatonin (aMT.6S) excretion. Adult rats were maintained under a 14L: 10D photoperiod and urine was collected at hourly intervals over a 5-day period using an automated collection system; the concentration of aMT.6S was assayed by RIA and hourly outputs were calculated. Each nightly collection of urine was assigned to an estrous cycle stage as determined by the vaginal smear of the preceding morning. Total aMT.6S excretions (mean ± SEM) during estrous, metestrous, diestrous, and proestrous stages were 493 ± 49, 539 ± 44, 562 ± 40, and 646 ±51 pmol/night, respectively (n = 7). The excretion of aMT.6S was significantly higher on the night of proestrus compared to each of the other stages ( P < 0.05). To determine whether estrogen was responsible for the increased aMT.6S excretion during proestrus, rats were studied before and after ovariectomy and following implantation with estradiol implants. Total overnight aMT.6S excretion was reduced by 31 % in ovariectomized animals relative to the intact state ( P < 0.05) and restored to the intact levels by administration of estradiol ( P < 0.05). It was concluded that estradiol can modulate melatonin production in adult rats, and that the changing pattern of aMT.6S excretion throughout the estrous cycle may provide a basis for a functional relationship between pineal activity and reproduction in this species.     

Distribution of 4-14C-mofebutazone in the rat

To further elucidate the distribution and differentiation of mofebutazone in comparison to phenylbutazone, 6 rats received 200 mg/kg 4-14C-mofebutazone corresponding to approx. 27 microCi/animal. 2 animals were sacrificed each time after 45 min, 6 h and 24 h. The 4-14C-plasma level was determined at the corresponding test periods and the radioactivity eliminated within 24 h in the urine was also determined. In addition autoradiograms of the whole animal were prepared for each animal. According to this study 4-14C-mofebutazone is distributed mainly in the metabolisation and elimination organs, a moderate activity was to be found under the skin and muscle tissue, but none, however, in the central nervous system and the bone marrow. Nearly 81% of the substance was eliminated after 24 h and with exception the colon the corresponding autoradiograms were practically free of activity. Because of the short half-life time and the rapid elimination mofebutazone does not lead to any accumulation.