Histidinuria can be demonstrated at a very early stage of pregnancy. 1934, 1936, 1941b, 1943]. There is no histidine excretion in the urine

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1 612.63: : ON HISTIDINURIA. By R. KAPELLER-ADLER, Research Fellow of the University of Edinburgh. From the Department of Pharmacology, University of Edinburgh. (Received for publication, 15th March 1949.) L-HIsTIDINE normally occurs in the urine of pregnant women. Histidinuria can be demonstrated at a very early stage of pregnancy and persists throughout gestation [Voge, 1929; Kapeller-Adler, 1933, 1934, 1936, 1941b, 1943]. There is no histidine excretion in the urine of pregnant animals [Kapeller-Adler and Herrmann, 1934]. Results obtained in various investigations have revealed the existence of a relationship between the excretion of histidine and that of gonadotrophic hormones in human pregnancy, and have led to the theory that the increase of gonadotrophins in pregnancy may interfere with the normal enzymic breakdown of histidine by histidase [Kapeller-Adler and co-workers, 1935, 1936, 1937]. Page [1946] has put forward another explanation of pregnancy histidinuria, suggesting that this condition might be due to a decrease in the reabsorption of histidine in the renal tubules. This hypothesis is based on a study of the fate of L-histidine given intravenously or orally to pregnant and nonpregnant women. The experiments now to be described were designed to test the validity of Page's hypothesis on a larger number of subjects. The effects of injected and ingested L-histidine on the blood and urinary histidine levels were simultaneously followed in 62 different women, of whom some were normally pregnant, some toxeemic and some not pregnant. The results do not support Page's theory, but confirm previous findings regarding a reduced enzymic breakdown of histidine in pregnancy. METHODS. Colorimetric Estimation of Histidine in Blood.-No chemical method specific for histidine is sensitive enough for the determination of this amino acid in the blood. In recent years Barac [1937] and Schwarz and co-workers [1938, 1939] have advocated the use of Pauly's diazo reaction for the determination of histidine in blood filtrates. In the present work a colorimetric estimation of histidine based on Pauly's diazo reaction and proposed by Macpherson [1946] was used with minor modifications. 146

2 146 Kapeller-Adler Procedure: Dilute 5 ml. of citrated blood with 10 ml. of distilled H20 and add 10 ml. 4-4 per cent. (v/v) perchloric acid. Shake well and centrifuge. To 5 ml. of the clear supernatant add 1 ml. 1 per cent. sulphanilic acid in N HCI and 1 ml. 5 per cent. (w/v) NaNO2. Mix and stand 5 minutes, shaking the test-tube from time to time. Blow in from a rapid delivery pipette 3 ml. 20 per cent. (w/v) Na2CO3 (cryst.) and shake vigorously. Add 5 ml. 20 per cent. (v/v) ethanol and mix well. Read in the photoelectric colorimeter, using a green filter. Colorimetric Estimation of Histidine in the Urine. The previously described method [Kapeller-Adler, 1941b] is slightly modified. A large excess of the bromine reagent is added to the urine and after 10 minutes removed by phenol. The tiresome testing with potassium iodide starch paper for an excess of bromine is thus eliminated, and the test becomes more accurate in inexperienced hands. Procedure: Dilute 5 ml. of urine with 3 ml. of distilled H2O and add 2 ml. of bromine reagent (5 ml. of bromine and 500 ml. of glacial acetic acid are diluted with 1000 ml. of distilled H20 and the solution stored in a brown bottle). Shake well and stand for 10 minutes. Add 0*2 ml. of 10 per cent. (v/v) phenol solution, shake well, and add 0 5 ml. of a mixture of ammonia and ammonium carbonate. (Mix 400 ml. ammonia solution, sp. gr , with 200 ml. 10 per cent. (w/v) (NH4)2CO3.) Mix and place the tube into a beaker of boiling water for one minute. After cooling read in the photoelectric colorimeter, using a blue filter. Intravenous Injection.-In all cases the histidine content of the blood and of the night urine of the fasting patient was determined 24 hours before, immediately before, and 24 hours after the experiment. Twenty ml. of sterile 10 per cent. (w/v) L-histidine hydrochloride solution in saline, equivalent to 1 48 g. free histidine, was rapidly injected intravenously; the patient was given one glass of lemonade every hour during the experiment. Blood specimens were withdrawn at regular intervals (5, 15, 30, 60, 90 and 120 minutes after the injection), and histidine estimations carried out on the citrated whole blood. Specimens of urine were carefully collected by means of an indwelling catheter after 30, 60, 90, 120 and 150 minutes. Volume and specific gravity were recorded and the histidine outputs determined. Oral Administration.-Histidine was again estimated in the blood and in the night urine 24 hours before and 24 hours after the experiment as described above. Four g. of L-histidine hydrochloride, corresponding to 3 g. of L-histidine, were given to the fasting women, and the patients were again advised to drink one glass of lemonade every hour during the experiment. Blood specimens were taken after 1, 2, 3 and 4 hours, and voided specimens of urine carefully collected at intervals of 4, 8, 12 and 16 hours after histidine ingestion.

3 On Histidinuria 147 RESULTS. The results of all the experiments are presented in figs. 1 to 8. Figs. 1 to 4 represent results obtained after the intravenous administration, and figs. 5 to 8 those found after ingestion of L-histidine hydrochloride. In each figure the blood histidine levels and the rate of histidine excretion (ordinate) are individually plotted against time (abscissa). On each curve is a number which identifies the patient, and also (in brackets) the number of weeks of gestation of the pregnant women. Intravenous Injection.-L-histidine intravenously injected to nonpregnant persons rapidly disappears from the blood-stream after an initial steep rise within the first 5 minutes after the injection (fig. 1). No histidine was found in the urine except for small traces in a few of the specimens. Page [1946] obtained similar results when investigating 9 non-pregnant women. As long ago as 1908 Engeland found that after subcutaneous injections of histidine to dogs only minute amounts were excreted in the urine. This finding was confirmed by Abderhalden and co-workers [1910], Kotake and Konishi [1922], and by Kijokawa [1933]. Guinea-pigs after subcutaneous injections of L-histidine hydrochloride did not excrete histidine, or only a small proportion of it [Kapeller-Adler and Kohut, 1934; Edlbacher and Heitz, 1942]. When in this work histidine was injected into 8 normal pregnant women (fig. 2) a completely different picture was obtained. As in non-pregnant persons, there was a steep rise in the blood histidine level within the first 5 minutes after the injection. But in contrast to the non-pregnant, all the pregnant women showed a very slow fall of the blood histidine within the first 2 hours after injection, although 24 hours after the injection it was found to have reached its initial value. Although the method used is not specific for histidine, it should be noted that the initial blood histidine values of pregnant persons were higher than those of non-pregnant ones. The blood histidine findings in this group of experiments are in contrast with the results of Page, who claims that injected histidine disappears at least as rapidly from the blood-stream of pregnant as from that of non-pregnant women. All the pregnant women in this investigation showed a distinct histidinuria before the experiment. There was in all cases an increase persisting for a few hours, in some a very considerable one, in the rate of histidine excretion after histidine injection. The rate of histidine excretion had, however, returned to its initial value 24 hours after the injections. The stage of pregnancy appeared to be irrelevant, similar results having been obtained between the 20th and 39th week of gestation. It should be recorded here that pregnant guinea-pigs do not, on injection of histidine, excrete this amino acid in the urine [Kapeller-Adler and Kohut, 1934; Eldbacher and Heitz, 1942]. Women suffering from mild pre-eclamptic toxeemia were subjected

4 148 Kapeller-Adler w z 5 (-I I C] 8 mn FIG. 1.-Non-pregnant ca.ses after 1*48 g. L-histidine i.v. FIG. 2.-Cases of normal pregnancy after 1-48 g. L-histidine i.v.

5 On Histidinuria 149 E1 z I- (I) I 0' O 0 -J co FIG. 3.-Cases of mild pre-eclamptic toxlemia after 1-48 g. L-histidine i.v. A-- 30 (29) ---A 30 (29) -x 23 (22) -a 25 24)... 7 c20) FIG. 4.-Cases of severe pre-eclamptic toxaemia after 1-48 g. L-histidine i.v.

6 150 Kapeller-Adler to the same treatment. Fig. 3 is representative of the results obtained. Four out of 7 of the cases investigated showed a higher initial blood histidine level ( mg. per cent.) than cases of normal pregnancy (about 2 mg. per cent.). As in normal pregnancy there was, on histidine injection, a very slow decline of the blood histidine, highly elevated within the first 5 minutes after the injection. The initial value, in some cases rather high, was attained 24 hours after the injection. As to the histidine excretion, only 2 cases (Nos. 21, 28) gave results comparable with those obtained in normal pregnancy. In the remaining cases the slight initial histidinuria was followed by a small increase in the rate of excretion after the injection. In 3 cases (Nos. 24, 26, 27) the urinary histidine had already returned to the initial small value 150 minutes after the injection. As can be seen from the corresponding blood histidine curve, the same 3 patients showed the highest blood histidine concentrations before and after the experiment. The results obtained in this group of women seem to indicate that in some cases of mild pre-eclamptic toxaemia there is a tendency for the retention of histidine in the body. This tendency appears to be even greater in women suffering from severe pre-eclamptic toxwamia (fig. 4). All patients of this group showed a rather high initial blood histidine value (3-4.8 mg. per cent.). Histidine injection was followed by a steep rise of the blood histidine within the first 5 mninutes, and after a slow decrease the normal high blood histidine level was reached 24 hours after the experiment. The results found in the urine were striking. In none of these cases was there more than a trace of histidinuria before, during, or after the experiment. These results clearly indicate that histidine both of endogenous and exogenous origin is not excreted, but seems to be retained in the bodies of women with severe pre-eclamptic toxeemia. This observation confirms previous findings [Kapeller-Adler, 1941 b, 1943], as a result of which it was concluded that a marked diminution, or total absence, of histidine excretion in pregnancy was a sign of toxaemia. Oral Administration.-On oral administration of 4 g. of L-histidine hydrochloride the blood histidine of non-pregnant persons rose to a peak within the first hour and fell rapidly within 3 to 4 hours after administration (fig. 5). In only 2 out of the 10 cases studied a very small amount of histidine was found in the urine. Cases of normal pregnancy showed a smaller rise of the blood histidine within the first hour, followed by a comparatively slow fall (fig. 6). At 4 hours after the oral dose of histidine the blood histidine was still high. There was a considerable, in some cases even a very steep, rise in the rate of histidine excretion within the first 8 hours after the beginning of the experiment, irrespective again of the month of pregnancy. Twenty-four hours after histidine ingestion the blood and urinary

7 On Histidinuria 151 histidine values returned to the normal. Similar results in pregnant and non-pregnant persons are quoted by Page [1946] after oral administration of histidine. A nmarked increase in histidinuria on oral application of L-histidine hydrochloride to pregnant women was previously reported [Kapeller-Adler and Schiller, 1935; Neuweiler and Grimm, 1940]. On ingestion of histidine, the elevated blood histidine levels persisted in most of the women with mild toxaemic pregnancy longer than in normal pregnancy (fig. 7). On the other hand, the urinary histidine output appeared to be in most of the cases smaller than under equal treatment in normal pregnancy. In all but 2 cases the rather low initial urinary histidine value was again attained after 24 hours. Finally, on oral administration- of histidine to women suffering from severe pre-eclamptic toxeemia (fig. 8), the blood histidine content, highly increased in the first hour of the experiment, remained high during the first 4 hours after the ingestion, and in one case was still rather high even 24 hours after the experiment (No. 19). In the urine of the same patient a verv small amount of histidine was recovered 8 hours after the experiment had begun. In all the other specimens of urine of this patient, as well as in all the urine specimens of the other two women, only a trace of histidine was found. DiscUSSION. Page's observation that on intravenous injection histidine disappears from the blood-stream of pregnant women at least as rapidly as from that of non-pregnant women has not been confirmed in this work. On intravenous as well as on oral application histidine leaves the bloodstream of pregnant women very slowly, large amounts of histidine being excreted in the urine at the same time. In non-pregnant women the injected as well as ingested histidine disappears rapidly from the blood and hardly any trace of it is found in the urine. Such results, along with those obtained in this work in cases of toxaemic pregnancy, are incompatible with Page's view that a lowered renal threshold is the only abnormality of histidine metabolism in pregnancy. They support the previously made suggestion [Kapeller-Adler and Haas, 1935; Kapeller-Adler and Herrmann, 1936; Kapeller-Adler and Boxer, 1937] that the activity of histidase is inhibited in human pregnancy. Changes in the histidine metabolism occurring in pregnancy toxaemia as compared with normal pregnancy are best shown in the moderate and severe cases (figs. 4 and 8), in which practically no histidine appeared in the urine in spite of the presence of high concentrations in the blood. This must have been due to renal failure. The milder toxasmic cases (figs. 3 and 7) mostly gave results intermediate between those obtained in moderate and severe cases and the normally pregnant women. This retention of histidine in the body of women suffering from toxaemic

8 1*52 Kapeller-Adler TIME (hour S) z 0 wll w ll xi) 60 5s / A \ FIG. 5.-Non-pregnant cases after 3 g. L-histidine per os. X-P I T I,\ a..v -a ME (hours) -31C39) ) * (34).* (37) -a^ 6 C28) -- 5 C24) K 4 C38) -a 7 (30) (36) FIG. 6.-Cases of normal pregnancy after 3 g. L-histidine per os.

9 On Histidinuria 153 FIG. 7.-Cases of mild pre-eclamptic toxemia after 3 g. L-histidine per os. i o... o. 19(27) E z 0 I- 7 Z 6 - in) 4 04 I Oi2 00 -J -:/5(30),5.-'>>,26(31) l0* T IME(hours). /, '\\ I - - -X 25(30)...O 19(27) -* 26(31) T2 26E FIG. 8.-Cases of severe pre-eclamptic toxaemia after 3 g. L-histidine per os.

10 154 Kapeller-Adler pregnancy gains importance with regard to the potential conversion of this neutral amino acid to its potent derivative, histamine [Kapeller- Adler, 1941a, 1941c, 1943]. Finally, Page has observed that in contrast with L-histidine, D-histidine on injection is largely excreted in the urine of both pregnant and non-pregnant women alike, high blood curves having been obtained in both groups. This is presumably due to the fact that, as Edlbacher [1926] has demonstrated, histidase metabolizes only L-histidine, leaving D-histidine intact. SUMMARY. 1. L-histidine was given intravenously and orally to pregnant and non-pregnant women, and was estimated in the blood by a modified diazo reaction and by its reaction with bromine in the urine. 2. On intravenous as well as on oral application, L-histidine disappeared only very slowly from the blood-stream of pregnant women as compared with non-pregnant women, large amounts of it being simultaneously excreted in the urine. This observation does not confirm the results of Page, who found that on intravenous injection L-histidine leaves the blood-stream of pregnant women at least as quickly as that of non-pregnant persons. It seems, moreover, to support the previously suggested theory of a reduced activity of histidase in human pregnancy. 3. In severe toxaemia of pregnancy no histidine could be detected in the urine even after the injection or ingestion of histidine although the blood levels remained high. This indicates a retention of L-histidine by the kidney. 4. The results obtained in mild pregnancy toxaemia were intermediate between those found in severe toxaemia and in normal pregnancy. ACKNOWLEDGMENTS. I wish to thank Professor J. H. Gaddum, F.R.S., for valuable criticism and kind interest in this work. I am very much indebted to Professor R. J. Kellar for permission to use the clinical material. I am especially thankful to Professor Morris, Dr. Noble, and the nursing staff of the Department of Obstetrics of the Western General Hospital, Edinburgh, for valuable assistance in obtaining the clinical material. My thanks are also due to the Medical Research Council for a whole-time grant held when this work was carried out.

11 On Histidinuria 155 REFERENCES. ABDERHALDEN, E., EINBECK, H., and SCHMIDT, J. (1910). Hoppe-Seyl. Z. 68, 395. BARAC, G. (1937). C.R. Soc. Biol. Pari8, 124, 266. EDLBACHER, S. (1926). Hoppe-Seyl. Z. 157, 106. EDLBACHER, S., and HEITZ, F. (1942). Ibid. 276, 117. ENGELAND, R. (1908). Ibid. 57, 49. KAPELLER-ADLER, R. (1933). Biochem. Z. 264, 131. KAPELLER-ADLER, R. (1934). Klin. Wschr. 13, 21. KAPELLER-ADLER, R., and KOHUT, H. (1934). Biochem. Z. 272, 341. KAPELLER-ADLER, R., and HERRMANN, H. (1934). Klin. Wschr. 13, KAPELLER-ADLER, R., and HAAS, F. (1935). Biochem. Z. 280, 232. KAPELLER-ADLER, R., and SCHILLER, W. (1935). Klin. Wschr. 14, KAPELLER-ADLER, R., and HERRMANN, H. (1936). Ibid. 15, KAPELLER-ADLER, R. (1936). Ibid. 15, KAPELLER-ADLER, R., and BOXER, G. (1937). Biochem. Z. 293, 207. KAPELLER-ADLER, R. (1941 a). Biochem. J. 35, 213. KAPELLER-ADLER, R. (1941 b). J. Ob8tet. Gyna3c. 48, 141. KAPELLER-ADLER, R. (1941c). Ibid. 48, 155. KAPELLER-ADLER, R., and ADLER, E. (1943). Ibid. 50, 177. KIJOKAWA, M. (1933). Hoppe-Seyl. Z. 214, 38. KOTAKE, Y., and KONISHI, H. (1922). Ibid. 122, 230. MACPHERSON, H. T. (1946). Biochem. J. 40, 470. NEUWEILER, H., and GRIMM, W. (1940). Klin. Wschr. 19, 155. PAGE, E. W. (1946). Amer. J. Obstet. Gyncec. 51, 553. SCHWARZ, A., RIEGERT, A., and BRICKA, M. (1938). C.R. Soc. Biol. Paris, 129, SCHWARZ, A., RIEGERT, A., and BRICKA, M. (1939). Ibid. 131, 519. VOGE, C. (1929). Brit. med. J., 1, 829.