THE METABOLISM OF RESERPINE. I. STUDIES IN THE MOUSE WITH C-14 LABELED RESERPINE

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1 THE METABOLISM OF RESERPINE. I. STUDIES IN THE MOUSE WITH C-14 LABELED RESERPINE PAUL NUMEROF, MAXWELL GORDON ANI) JACQUES M. KELLY Squibb Institute for Medical Research, New Brunswick, New Jersey Received for ptiblication July 18, 1955 Extracts of Ranwolfia serpenlina Benth have been used clinically in India for a long time (Chakravarti, 1953). It was the isolation from H. serpenlina of reserpine (Muller et al., 1952), however, and the demonstration of its sedative (Mub- 1cr et al., 1952) and mild hypotensive properties (Bein, 1953) which has stimulated the recent extensive investigations of this alkaloid. In the investigation of the pharmacological properties of reserpine, studies from this Institute were reported (Rubin and Burke, 1954) in which a biological response in mice indicated an effective oral dose to be sixteen times the intravenous dose. These results suggested poor oral absorption of reserpine, due, possibly, to extensive inactivation in the gastrointestinal tract. Since there was essentially no definitive information available on reserpine absorption, blood levels, degradation and excretion, reserpine containing radioactive carbon was prepared and its fate studied in the mouse. METHODS. Synthetic. Synthesis of 8,4,5-trirnethoxybenzoic acid-carboxyl-c-14. The carboxyl labeled 3,4,5-trimethoxybenzoic acid was prepared by carbonation of 3,4,5-tnmethoxyphenyl lithium. A solution of 120 mgm. (0.485 millimoles) of 3,4,5-trimethoxy bromobenzene (Kohn and Steiner, 1947; Kohn and Grun, 1925) in 5 ml. of anhydrous ether, was placed in the reaction vessel of a carbonation apparatus (Van Bruggen et at., 1950). Dry nitrogen was slowly passed into the system to prevent the entry of any water. The solution was chilled to 600C. with a dry ice-isopropyl alcohol mixture and a solution of butyl lithium in pentane, 0.39 millimoles, was added under a constant flow of dry nitrogen. Amu immediate precipitate occurred, even at -60#{176}C. The cooling bath was removed and, while the flask was allowed to warm to room temperature,2 the reaction vessel was connected to the carbon dioxide generator. After evacuation of the system to about 0.1 mm., the contents of the reaction vessel were frozen in liquid nitrogen. Radioactive carbon dioxide was libcrated from the generator by the addition of concentrated sulfuric acid to 30 mgm. of barium carbonate C-14 with an isotope enrichment of 29.6 per cent C-14. The radioactive carbon dioxide was frozen out on the contents of the reaction vessel amid carbonation was effected at -60#{176}C. in the imsual manmier. After carbonation was complete, the reaction mixture was acidified with 5 per cent hydrochloric acid and then extracted with ether. The ether solution was then extracted with 5 per cent sodium bicarbonate solution. After acidification of the sodium bicarbonate solution, the labeled 3,4,5-trimethoxyhenzoic acid was re- 1 Presented before the Division of Biological Chemistry, 126th Meeting, American Chemical Society, New York, N. Y.. September 12-17, We are indebted to Dr. W. H. Langham, of the Los Alamos Sciemititic Litboratory, for helpful discussion Oil the butyl lithiimm-aryl bromide exchange. Good yields of 3,4,5-tnmethoxybenzoic acid were obtained regularly only under the conditions indicated. If the exchange reaction mixture wa.s kept at room temperature for five minutes, or at -60#{176}Cfor longer periods before carbonation was attempted, only small amounts of 3,4,5-trimethoxybenzoic acid were obtained. 427

2 428 NUMEROF, GORDON AND KELLY Br2 HO--Br 2.CH32S04 -Br Br I. Butyl Lithium * I. SOd2 * COOH 2. CO2 2. Methyl Reserpate Methyl Reserpate: R H Reserpine: R = II C- Fio. 1. The preparation of 3,4,5-trimethoxybenzoyl-(carboxyl-C-14) methyl reserpate (reserpine). extracted into ether; the ether solution was washed with water and then the solvent was removed by evaporation. The residue was recrystallized from water to give 38 mgm. (90 per cent) of 3,4,5-trimethoxybenzoic acid carboxyl-c-14. Esterification of methyl re8erpate. Thirty milligrams of 3,4,5-trimethoxybenzoic acid (0.142 millimoles, 3 millicuries) were converted to the acyl halide by treatment at room temperature for one hour with 2 ml. of freshly distilled thionyl chloride. The solution was then heated to boiling and the excess thionyl chloride was distilled off at about twenty millimeters. After keeping the residual solids at a pressure of 0.2 mm. for five minutes, there was no detectable odor of free thionyl chloride. A solution of methyl reserpate, mgm., millimoles, in 2 ml. of anhydrous pyridine was added, and the solution was allowed to stand overnight at room temperature. Three milliliters of water were added, and after fifteen minutes at room temperature, 5 ml. of 3 per cent sodium bicarbonate was added. The solution was extracted with four 10 ml. portions of chloroform, the chloroform extract dried over anhydrous sodium sulfate, and then evaporated to dryness. The residue (47 mgm.) was dissolved in 10 ml. of benzene and chromatographed over acid-washed alumina (ph = 4.5) (Neuss et at., 1954). The major fractions from the column were combined, evaporated to dryness and recrystallized from methanol to give 6.8 mgm. of labeled reserpine with a specific activity of 5 X 10 disintegrations/minute/milligram. Both the melting point and the infrared spectrum of the radioactive reserpine were identical with those of an authentic sample. The sequence of organic chemical operations involved in this synthesis are shown in figure 1. Animal Experiments. Each mouse (about 20 grams imi weight) was kept in an individual The authors wish to express their appreciation to Dr. Frank Weisenborn, of the Division of Organic Chemistry, for making samples of methyl reserpate available.

METABOLISM OF RESERPINE IX THE MOUSE 429 TABLE 1 Urinary excretion of oral trimethoxybenzoic ac-id Time % of Dose in Urine % of Dose in Feces ITS. 4 8 24 94 86 93 0.02 1.0 0.

3 METABOLISM OF RESERPINE IX THE MOUSE 429 TABLE 1 Urinary excretion of oral trimethoxybenzoic ac-id Time % of Dose in Urine % of Dose in Feces ITS one-liter beaker equipped with a wire screen to serve as a urine-feces separator. Reserpine, either orally or intravenously,4 was given in equi-effective ptotic doses with 96 micrograms/ mouse for the oral dose and 6 micrograms/mouse for the intravenous dose. At the end of each test period the animals were sacrificed. The liver, heart, spleen, brain, kidney, stomach, small intestine and large intestine were kept separate; the residual carcass was then homogenized in a Waring blendor. The organs were dried, powdered and then extracted with hot chloroform followed by hot acetone, ethanol and acetic acid. These first three extracts were combined, concentrated and examined for reserpine and trimethoxybenzoic acid by paper chromatography. Descending chromatograms on Whatman * 1 paper were used employing the upper phase of the system : 80 parts of n-butanol, 5 parts of benzene and 15 parts of buffer (Fewster and Hall, 1951). All portions of the solvent system are in volumeto-volume ratios; the buffer consists of 1.5 N ammonia-1.5 N ammonium carbonate. The Rf values for reserpine and trimethoxybenzoic acid in this system are approximately 0.9 and 0.3, respectively. All chromatograms were cut into one-inch squares and the radioactivity determined in a flow counter. In addition, identification of trimethoxybenzoic acid and reserpine was carried out by addition of non-labeled material as carrier with isolation and crystallization to constant specific activity. RESULTS. Labeled trimethoxybenzoic acid, when given orally at the same molar level as in an oral dose of reserpine, resulted in the urinary excretion of essentially all the radioactivity as unchanged material within four hours. The data from these experiments are shown in table 1. After an oral dose of reserpine, per cent of the administered radioactivity appeared in the urine after four hours. Essentially all of this radioactivity was trimethoxybenzoic acid; in only a few cases was any intact reserpine found. Furthermore, the relative amounts of trimethoxybenzoic acid and reserpine in the urine remained unchanged even after 24 hours as shown in table 2. The entire gastrointestinal tract, from stomach to feces, was pooled in the first experiment on reserpine distribution. As shown in table 2, the entire tract contained almost half of the administered radioactivity. In subsequent experiments, the tract was sectioned and the radioactivity associated with each section was determined. The percentage of activity associated with any one section of the tract at four hours varied in the two animals studied; however, the total amount of activity in the tract of these two animals was quite similar. After 8 and 24 hours most of the activity associated with the gastrointestinal tract was contained in fecal matter; only small amounts of activity remained in the stomach, small intestine and large intestine. Radioactivity in the tissues, such as liver, spleen, kidney, blood and brain, 4The authors wish to express their appreciation to Miss M. H. Waugh and Mr. J. Mangano for their assistance in the care and preparation of the animals.

4 430 NUMEROF, GORDON AND KELLY TABLE 2 Di8tribution of radioactivity, in per cent of administered dose, after oral reserpine Time Tissues Urine Stomach Ine Inte Feces Rec#{176}.rery Ii s lost (1:0) % (l:4) 9 (1:10) 3 (4:1) 52 (4:1) 1.4 (10:1) (1:5) 0.1 (0:1) (1:1) (1:3) * The data in this column represent the sum of the radioactivity present in the liver, heart, spleen, brain, kidney and carcass. In almost every case the radioactivity in the organs was only a few per cent, with 2-5 per cent in the residual carcass. t This figure is the amount of radioactivity found in the brain of this animal. The numbers in parentheses indicate t.he ratio of trimethoxvbenzoic acid to reserpine for that particular fraction. was generally quite low. However, in the first 24 hour experiment, a concentration of 10 per cent of the starting dose, all as TMB, was found in the brain. These results could not be duplicated in the five additional animals that were run, and the nature of the peculiar results obtained with this animal are obscure..\fter four hours blood radioactivity concentrations were of the order of 1-2 per cent, with the plasma activity present entirely as trimethoxybenzoic acid. The radioactivity of the erythrocytes, which constituted about 70 per cent of the total blood activity, was so firmly bound that identification could not be made. Erythrocyte radioactivity, even after hemolysis, could not be ext.racted into organic solvents under neutral, alkaline or acid conditions. The results of the intravenous experiments, as shown in table 3, indicate that the patterns after oral and intravenous reserpine are, in general, quite similar. Urinary excretion of radioactivity, essentially all as trimethoxybenzoic acid, accounts for per cent of the administered radioactivity. After four hours the radioactivity in the gastrointestinal tract is distributed * Figures in parentheses refer to the ratio of trimethoxybenzoic acid to reserpine. t Urine recovery was incomplete. TABLE 3 Distribution of radioactivity, in per cent of administered dose, after intravenous reserpine : Tissue Urine Stomach Feces Recrery (1:5)* 17 (l:5) (1:3) 22 (1:5) l2t t (1:3) 18 (1:4) (1:5)

5 METABOLISM OF RESERPINE IN THE MOUSE 431 almost equally between the large intestine and feces ; only traces of activity appear in the stomach. At 8 and 24 hours the stomach still contains only traces of radioactivity. The distribution in the remainder of the tract is somewhat more variable, although the maj or portion of the radioactivity is associated with the feces. As in the oral experiments, tissue concentration of radioactivity in liver, spleen, kidney, blood and brain was low. DIscussIoN. The facile elimination in the urine of orally administered tnmethoxybenzoic acid suggested that the appearance of this material could be used as a criterion for the rapidity of reserpine breakdown. The most striking result of the intravenous experiments was the finding of the fecal excretion of a considerable percentage of intact reserpine. Although the percentage of intact reserpine in the feces is higher after intravenous administration than after oral, the actual amount by weight is less. Using the highest percentage figures for fecal reserpine content, there are present about 2.2 micrograms from the intravenous experiments and about 7.2 micrograms from the oral experiments. The significance of these findings, in terms of the degradation of reserpine in the intestines, will be evaluated in subsequent studies. Of considerable interest were the results on the tissue distribution of reserpine. I n view of the marked alteration in behavior produced by reserpine, it was striking t.o observe such a diffuse distribution with minimal retention in tissue. No organ showed a preponderance of retention of radioactivity. Of particular interest was the finding of only traces of reserpine in the brains of all but one of the animals studied. The reasons for the retention of such a large percentage of the dose in the brain of this one animal are still obscure. SUMMARY Heserpine, labeled vith carbon-14 in the carboxyl group of the trimethoxybenzoyl moiety, has been prepared and its metabolism studied in the mouse. The drug was given at equi-effective ptotic doses of 96 micrograms/mouse orally and 6 micrograms/mouse intravenously. Reserpine, whether given orally or intravenously, is rapidly metabolized; per cent of the dose appears in the urine as tnimethoxybenzoic acid within four hours. Fecal excretion of unchanged reserpine is about 8 per cent after an oral dose of 96 micrograms and about 35 per cent after an intravenous dose of 6 micrograms. The authors wish to express their appreciation to Dr. J. C. Burke and Dr. B. Rubin for helpful discussion during the course of this work. BEIx, H. J.: Experientia, 8: 338, REFERENCES CHAKRAVARTI, M. D.: Brit. Med. J., 1390, FEWSTER, M. E., AND HALL, B. A.: Nature, 168: 78, ItOHN,M.,AND STEINER, L.:J.Org. Chem., 12:30, Komix, M., AND Gnux, S.: Monatsh., 46: 86, MULLER, J. M., SCHLITTLER, E., AND BEIN, H. J.: Experientia, 8: 338, NEITSS, N., BoAz, H. E., AND FORBES, J. W.: J. Am. Chem. Soc., 76: 2463, RUBIN, B., AND BURKE, J. C.: Fed. Proc., 13: 400, VAN BRUGGEN, J. T., CLAYCOMB, C. K., AND HUTCHENS, T. T.: Nucleonics, 1: 45, 1950.

III. TOXICOKINETICS. Studies relevant to the toxicokinetics of inorganic chloramines are severely

III. TOXICOKINETICS. Studies relevant to the toxicokinetics of inorganic chloramines are severely III. TOXICOKINETICS Introduction Studies relevant to the toxicokinetics of inorganic chloramines are severely limited. However, studies done with various chlorinated amino compounds (including organic