Fate of methionine in the blood of mice were studied by a complex radiotracer technique. Absorption results of 3 radioactive methionines indicated that the uptake of methionine was very fast and about 92.8% of the dose was taken up from the blood stream into organs and tissues within 5 min. after bolus intravenous injection.
Since 5 min, after the injection, decrease of the radioactive concentration in the blood continued for 30 min., but it was slower compared to decrease within the first 5 min.. A major absorption of blood methionine into organs and tissues has been found to occur within a few minutes after i.v. injection of a tracer of radioactive methionines. Results of continuous counting and recording of ¹⁴CO expiratory rate indicated that there was the most intensive metabolic period occured 5 min.-20 min. after i.v. injection of 2 ¹⁴C-methionines. Therefore, a good time-dependent sequence between the absorption and consumption of blood methionine was found, though it was a little difficult by regular sampling techniques to find such a fine correlation. Both radiorespirometric plateau height and ¹⁴CO₂ expiratory rate (% of dose) of [1-¹⁴C] Met was 3 times higher than these of [methyl-¹⁴C] Met.
Excretion of a radioactive moiety of labeled methionines ito feces was miner and those of a radioactive moiety of labeled methionines into urine were attibuted by the specifically labeled position or radioactive atom, ³⁵S or ¹⁴C. The distribution of radioactivity in organs and tissues was estimated by a liquid scintillation counting. Also it was determined by a freeze-dried microautoradiography for diffusible components. Both results indicated that a majority of the administered methionine was utilyzed in muscle and skin, and about 50 % of dose were disposed at 8 hr. after the injection. Such an organ as pancreas was actively produced and excreted zymogen granules from the pancreas gland cells. It was suggested that a gentle reascending curve of the blood concentration during 30-90 min. after i.v. injection was attrjbuted to supply of serum proteins which were synthesized from radioactive methionines in the liver.

View full abstract

The absorption, distribution and excretion of bisoprolol were studied in rats after oral or intravenous administration of ¹⁴C-bisoprolol (1 mg/kg).
1. ¹⁴C-Bisoprolol was readily and almost completely absorbed from the gastrointestinal tract.
2. Following oral administration, serum levels of radioactivity reached a maximum at 1 hr, and declined relatively rapidly with a half-life of 1.2 hr.
3. Maximum levels of radioactivity in most tissues were reached within 1 hr after oral administration, and high levels of radioactivity were observed in the liver, kidney and lung. At 24 hr, slight radioactivity was found only in the excretory organs.
4. Excretion of radioactivity was 70-80 % and 15-25 % of the dose in urine and feces, respectively, within 72 hr in either route of drug administration. No sex difference was observed in excretion of radioactivity.
5. Biliary excretion of radioactivity was 22-26 % of the dose irrespective of dosage route, and partial reabsorption of biliary excreta occurred from the intestinal tract.
6. The extent of in vitro binding of ¹⁴C-bisoprolol to plasma proteins of various animal species was 18-23 % in rats, rabbits and dogs, while that in human was about 40 %. The binding of bisoprolol to human plasma proteins was not affected by other co-administered drugs. In the in vivo experiment, the percent binding of ¹⁴C-bisoprolol and/or its radioactive metabolites to the rat plasma protein was about 17 % after the intravenous dose and about 8 % after the oral dose.
7. Whole body autoradiograms obtained with pigmented rats demonstrated that specific binding of radioactivity to melanin containing tissues was noticed.

View full abstract

Accumulation characteristics of bisoprolol were studied in male rats after the consecutive oral administration (1 mg/kg/day) of ¹⁴C-bisoprolol for 14 days.
1. After single oral administration of ¹⁴C-bisoprolol to fasted and non-fasted rats, no significant differences were observed in the C_max, t_1/2 and AUC (0-24 hr) values of blood radioactivity levels between two groups.
2. During the consecutive oral administration, the blood radioactivity levels at 1 hr after each dosing reached the steady-state level following the second administered dose.
3. The daily excretion of radioactivity in urine and feces was almost constant throughout the period of consecutive administration. The cumulative excretion of radioactivity in the urine and feces accounted for 72.3 % and 29.3 % of the total dose, respectively, within 72 hr after the final administration. The excretion pattern was similar to that achieved in the single-dosing group.
4. At 1 hr after the consecutive oral administration (7 and 14 times), levels of radioactivity in the tissues tested were not significantly higher than those after single administration. At 24 hr after the final administration, radioactivity levels in most tissues decreased near the detection limit in either administration group.
5. Thus, there was not any accumulation of the drug and its metabolites in the organs and tissues of rats following the consecutive oral administration of this drug.

View full abstract

Foeto-placental transfer and excretion of bisoprolol into milk were studied in pregnant rats and lactating rats after the oral or intravenous administration of ¹⁴C-bisoprolol (1 mg/kg)
1. When ¹⁴C-bisoprolol was orally or intravenously administered to pregnant rats on 19 ?? 20 th day of gestation, very little radioactivity was transferred to fetuses through the placenta in either route of the drug administration.
2. The maximum level of radioactivity in the fetus was reached 1 hr after oral dosing and was about 2/5 of plasma levels.
3. Amount of radioactivity transferred into a fetus was about 0.25 % of the oral dose.
4. When ¹⁴C-bisoprolol was orally or intravenously administered to lactating rats on 11 ?? 13th day after parturition, very little radioactivity was transferred to sucklings via milk.
5. The concentrations of radioactivity in the milk were slightly higher than those in plasma, however, the time course of radioactivity in the milk was similar to that in plasma.
6. Amount of radioactivity transferred into a suckling via milk was about 0.2 % of the oral dose.

View full abstract

Absorption, distribution and excretion of [¹⁴C] zonisamide were studied in rats after 14 consecutive daily oral administration at the dose of 20 mg/kg.
1. Plasma levels at 24 hr after each administration tended to elevate slightly on 10 th day and became 1.2 fold of those after single administration. Maximum levels after the last administration, of about 17.4μg eq./ml were reached at 3 hr and decreased with half life of about 7.0 hr, and were virtually similar to that after single administration.
2. After repeated administration, the levels in plasma and most tissues were 1.2-1.5 times as high as those after single administration. At the time of the maximal plasma levels, most tissue levels were within the range of 2 fold of plasma levels except for levels in preputial gland, erythrocytes and liver. The distribution was similar to that after single administration. Autoradiographic findings on the distribution were essentially consistent with radiometric results.
3. During repeated administration, urinary excretion of radioactivity were virtually constant at about 80% of dose after second administration, and fecal excretion, about 10% after 7th administration. Within 120 hr after the last administration, urinary and fecal excretion amounted to about 83% and 13%, respectively. The excretion was similar to that after single administration.

View full abstract

Visualizing the localization of given xenobiotics in the body becomes possible by means of application of macroautoradiography, though there are still many problems, which we have to solve near future, and also there are a few limited evaluation points. In the most important of the problems is whether or not autoradiographic results are quantitatively reliable in a conventional manner. Many reports have been published in this field as described in this article briefly since 1961. However, all of them were limited in a mechanical improvement how to read the shading of blackening on the recorded photo film compared with a density control.
In this article, the remains of the problems are pointed out and discussed in detail. First, essential factors are determined for quantitative macroautoradiography.
(1) To use radioisotopes with soft β emitters for the tracer of given xenobiotics in major cases. (2) To keep a given thickness of the thin sections through a contact period with the photosensitive material., (3) To elucidate whether or not there is a good and simple correlation between the radioactivity concentration (dpm/μm³ × μm in thickness) of a soft β emitters and relative intensity developed at a localized photosensitive material, and finally, (4) To express a resulting image more finely, comparatively, quickly, and easily with computer assistance.
Results are given the most important factor for quantitative macroautoradiography to keep a given thickness of the thin section without any dryness. Dryness caused impossible correction of selfabsorption of soft emitters in the substances. The conventional X-ray films have too many and complex factors to calculate and simplify correctly the radioactivity concentration from the resulted autoradiographic image. And the majority of the factors might be in secret for covering the production pattents. Consequently, the conventional X-ray film is available for highly resolving, more impressible, and more microanalytic autoradiography of soft β emitters but not quantitative macroautoradiography.
For this, we recommend “Imaging Plate”. Flexible plastic plate coated with fine photosimulable phospher crystals (BaFBr: Eu²⁺), which was developed by Miyahara et al, Fuji Photo Fim Co. Results indicated good correlation between the relative intensity of PSL (Intensity × exposure time) and the radioactivity concentration (dpm/μm³ × μm in given thickness) of each tissue, assumed by correcting the selfabsorption of ¹⁴C in the thin sections.

View full abstract

Several in vitro experimental techniques have been developed to investigate the transport mechanism of drugs across the blood-brain and blood-cerebrospinal fluid barrier. In this article, I summarize the previous transport studies carried out with the isolated and cultured cerebral microvessels, focusing on the transport vector of ligands across the blood-brain barrier. I also describe the transport properties of organic anions snd cations in the isolated choroid plexus, in relation to the role of this tissue in eliminating ligands from the cerebrospinal fluid. The methodology, advantage and limitation of each experimental technique are briefly discussed.

View full abstract

The determination of antidepressants in blood is necessary to obtain the best therapy of patients who are being treated with some of tricyclic or tetracyclic antidepressants. Various methods using high performance liquid chromatography (HPLC) are reported for an analysis of these compounds. The methods involve the manual sample preparation (liquid-liquid, solid-phase extraction columns), semiautomated sample preparation and automated sample preparation. Normal-or reversed-phase columns with functionalities such as C-18, CN, C-1, C-8, and phenyl are used for the separation of antidepressants. This mini-review includes also the determination of selected metabolites.

View full abstract