CHOLINE AS A FACTOR IN THE ELABORATION OF ADRENALINE

Transcription

1 CHOLINE AS A FACTOR IN THE ELABORATION OF ADRENALINE R. L. STEHLE, K. I. MELVILLE AND FRANCES K. OLDHAM Department of Pharmacology, McGill University, Montreal Received for publication January 31, 1936 That the side chain of adrenaline is more or less closely related to choline seems to have escaped attention. This side chain differs from choline in being derived from the monomethyl derivative of ethanolamine, choline being the trimethyl compound. Q CH CH2 CR011 CR2 H--CH3 CH3-IT-CH, H C Adrenaline Choline Between adrenaline and acetyl choline, the sympathetic and parasympathetic hormones, there is thus sufficient chemical similarity to raise the question of the possible biological significance of the relationship. The amine radicals of adrenaline and acetyl choline are derived from two compounds out of four all of which at once assume biological interest. The hydroxide forms of these four amines are shown in column 1 of figure 1, and alongside each are shown the acetyl derivative and the catechol derivative respectively. Thus the amines, which are all indifferent substances physiologically (with the exception of choline, which itself has a weak parasympathomimetic action), by acetylation on the one hand or by the 473

2 H H H((OOCCH3 CR011 I CH2 I CH2 1 CH2 H H Ethanolamine hydroxide Arterenol hydroxide form form I V IX HCCOOCCH3 CR011 (H2 (H2 CR2 CH3-IT-0H CHJT- CH3-- Adrenaline II VI X hydroxide form HC HCOOCCH3 CR011 C113--0H CH3-IT-0H C113-IL CHH CH3H CH3H III VII XI H H H(0(00CCH3 CR011 CIL-IL CH3--0H CR,-1I-0H CH3 CH3 CH3 CH3 CR3 CHS Choline Acetyl choline IV VIII XII FIG

3 CHOLINE IN ELABORATION OF ADRENALINE 475 introduction of a catechol group on the other, are converted into parasympathomimetic and sympathomimetic substances respectively. The study of the variations in pharmacological activity in each of these series is the subject of the experimental part of this paper. It is of interest to note that, while acetyl choline is the most potent substance of its group, adrenaline is not the most potent among the four compounds of its series; compound IX, known as arterenol, is definitely more potent than adrenaline. The foregoing considerations raise an interesting question. Are wholly unrelated processes used in the elaboration of the two autonomic hormones in the organism? Since choline is such a ubiquitous substance, most investigators would probably regard acetyl choline as being derived from it by simple acetylation. But in the case of adrenaline the relation to choline has been overlooked, and investigators have thought of tyrosine or phenylalanine as possible precursors. If this is correct, the presence of the methyl group in adrenaline is a quirk of nature, tyrosine and phenylalanine being unmethylated; compound LX, as pointed out, is a more potent substance than adrenaline and is more closely related to tyrosine and phenylalanine than is adrenaline, yet nature would seem to have made the second rate substance when a better one was more readily available. That tyrosine or phenylalanine is the precursor of adrenaline has never received strong support. It would seem profitable therefore to direct attention away from the ring portion of the molecule and examine the possible implications of the side chain in the formation of adrenaline. If nature had used ethanolamine from which to derive both its autonomic hormones by acetylation or by the introduction of the catechol group, it would have had the best sympathetic hormone but a poor parasympathetic (see results below). If it had used choline, it would have had the best parasympathetic hormone but a poor sympathetic. If it had used compound II, it it would have had adrenaline and a weak parasympathetic hormone. Finally, if it had used compound III, neither hormone would have been very potent.

4 476 R. L. STEHLE, K. I. MELVILLE AND F. K. OLDHAM Since, apparently, choline is the only one of the four amines which occurs in the body, it would seem as though any attempt to show a common genetic factor in the elaboration of the autonomic hormones must fall back upon choline. Supporting this view is the fact that the adrenal glands appear to be the tissue richest in choline. Hunt (1) long ago isolated choline from the adrenals. Lohmann (2) obtained more than 3 grams of the gold salt from 286 glands (cattle), by far the greater portion being in the cortex. Ciaccio (3) suggested that the function of the adrenal cortex was the elaboration of choline, and the function of the medulla the elaboration of adrenaline; apparently he regarded the elaboration processes as unrelated. Whether, if choline is used in the elaboration of adrenaline, demethylation takes place after or before the introduction of the catechol group is problematical. And in the demethylation process it is not clear why the body stops short of complete demethylation when, by removal of all the methyl groups, it would have provided a more potent sympathetic hormone. So far as the elaboration of acetyl choline is concerned, one must apparently regard this process as occurring wherever there are parasympathetic terminations. EXPERIMENTAL Of the twelve compounds which are the subject of the foregoing considerations, six have already been studied in other connections. In the adrenaline series the nonmethylated compound, arterenol, has been compared carefully with adrenaline by Schultz (4), who found it to be 1.5 times as potent. The dimethyl compound is mentioned by Biberfeld (5), who states that it is less active than adrenaline. The trimethyl compound does not appear to have been studied or even made. In the choline series the monomethyl compound was studied early, because it is the basis of the adrenaline side chain. Dakin 1 Two of the compounds used have not been prepared previously-vi and XII. The first was made by acetylation of the free base of II; the hydrochloride melts at 105#{176}C. The second was made by reflux.ing the base obtained from the hydrochloride of XI with methyl iodide; the iodide melts at 186#{176}C.

5 CHOLINE IN ELABORATION OF ADRENALINE 477 (6) states that 10 mgm. produced a slight (if any) rise in the blood pressure of a rabbit. The nonmethylated and dimethyl compounds have not been studied, though they are not new substances. In the acetyl choline series, acetyl choline is the only one studied. Of this group the dimethyl compound is new. To evaluate each series as a whole, the known substances were used as well as the new compounds. Bkod pressure action Figure 2 shows that 10 mgm. doses of the hydrochlorides of ethanolamine and methyl ethanolamine have very little vascular FIG. 2. CAT. AMYTAL ANESTHESIA A = 10 mgm. CH,CH,NH,HCl (I). B = 10 mgm..ch2ch,nhch,#{149}hc1 (II). C = 10 mgm..ch,ch2n(ch,)2.hc1 (III). D = 10 mgm..ch2ch,n(ch,),.cl (IV). action. The next homolog, dimethyl ethanolamine, has a slight depressor action, while choline has a relatively marked depressor action. Acetylation of these four compounds greatly augments the vascular effect. This has, of course, been known to hold for choline since the work of Hunt (6). In comparing these four compounds upon the blood pressure, the comparison was made on a molecular basis. Thus 6.23 mgm. of the nonmethylated compound contains 2000 times as many molecules as mgm.

6 478 R. L. STEHLE, K. I. MELVILLE AND F. K. OLDHAM of acetyl choline hydrobromide; 1.71 mgm. of the monomethyl substance contains 500 times as many molecules as mgm. of acetyl choline hydrobromide; and 0.26 mgm. of the dimethyl compound contains 52 times as many molecules as mgm. of acetyl choline hydrobromide. The hydrochlorides were employed in each case. Figure 3 shows therefore that the acetyl choline molecule is more than 50 times as active as the molecule of the dimethyl compound, more than 500 times as active as that of the monomethyl compound, and more than 2000 times as FIG. 3. CAT. AMYTAL ANESTHESIA A = 1.71 mgm. CH,COOCH,CH,NHCH,HCl (VI). B = mgm. acetyl choline hydrobromide (VIII). C = 6.23 mgm. CH,COOCH,CH2NH,HCl (V). D = Same as B. E = 0.26 mgm. CH,COOCH2CH,N(CH,).HCl (VII). active as that of the nonmethylated compound. Twenty-five milligram doses of all except acetyl choline, in which cases the dosage was 5 mgm., were tried in the spinal cat after atropinization. Acetyl choline raised the blood pressure in the usual fashion but the others were without action. The introduction of the catechol group into the four amines converted all into pressor substances in which the intensity of action decreased with increasing methylation (fig. 4). Even the choline derivative had some pressor action. In this case, the compound is a quaternary base, hence it was of interest to deter-

7 CHOLINE IX ELABORATION OF ADRENALINE 479 mine the effect after atropine in the spinal cat. No evidence of ganglionic stimulation was observed: that is, the pressor effect of 5 mgm. was no greater after atropine than before atropine. A 3 C.\, SHill. H - - = == J FIG. 4. (..T. AMYTAL ANESTHESIA A = 0.01 mgm. arterenol (racemic) (IX). B = 0 01 mgm. adrenaline (racemic) (X). ( = 0.1 mgm. HO. (H.( H2N(CH3),.HI (XI). I) = 1.0 mgm. HOCHCH2N(CH3):rI (XII). B = Same as (. F = Same as D but 5.0 mgm. #{163}4 ci ions upon the intestine The acetyl derivatives only were studied for their actions upon the intestine. Figure 5 shows that acetyl choline is more than 40 times as potent as the acetate of dimethyl ethanolamine, somewhat less than 1000 times as active as the acetate of monomethyl ethanolamine, and about 20,000 times as active as the acetate of ethanolamine. Actions upon the heart In this case also the acetyl derivatives only were studied. Figure 6 shows that acetyl choline is more than 50 times as active

8 FIG. 5. RABBIT ILEUM IN TYR0IE S SOLUTION A. a = 1:5000 CH3CO.OCH2CH2NH2HCI (V). h = 1:100,000,000 acetyl choline hydrobromide (VIII). B. a = 1:20,000,000 acetyl choline hydrobromide (VIII). b = 1:20,000 CH3CO.OCH2CH2NH(H3H(l (VI). c = Same as a. d = Salne as c. C. a = 1:20,000,000 acetyl choline hydrobromide (VIII). h = 1:500,000 CH3CO.OCH2CH2N((H3)2 H(l (VII). c = Same as a. I I ut I fr] T1 Ii I! I I ii I I FIG. 6. ISOLATED FROG HEART (RANA PIPIENS). A = 1:100,000 CH3CO OCH2CH2N(CH3)2 HC1 (VII). B = 1:5,000,000 acetyl choline hydrobromide (VIII). C = Same as A. D = 1:10,000 CH3CO.OCH2CH2NHCH3HC1 (VI). E = 1:10,000,000 acetyl choline hydrobromide (VIII). F = 1:250 CH3CO. OCH( H2NH2 HCI (V). 480 STRAUB METHOD

9 CHOLINE IN ELABORATION OF ADRENALINE 481 as the acetate of dimethyl ethanolamine, more than 500 times as potent as the acetate of monomethyl ethanolamine, and about 40,000 times as active as the acetate of ethanolamine. SUMMARY The chemical relationship between choline and the side chain of adrenaline is pointed out. This relationship, together with the fact that the adrenal gland is especially rich in choline, indicates that choline may be important for the elaboration of both the autonomic hormones. The effects upon the blood pressure of the acetyl and catechol derivatives of choline and of the bases derived from choline by progressive demethylation are given. The acetyl derivatives of the same bases were also compared upon the isolated frog heart and upon the intestine of the rabbit. REFERENCES (1) HuNT, R.: Am. J. Physiol. 3, xviii (1903). (2) LMANN, A.: Centralb. F. Physiol. 21, 139 (1907-8). (3) CIAccIo, C.: Arch. f. exper. Path. u. Pharmakol. 78, 347 (1915). (4) SCHULTZ, W. H.: Bull. 55, U. S. Hygienic Laboratory (1909). (5) BIBEEFELD, J.: Med. Kim. 2, 1177 (1906). (6) DAKIN, H. D.: Proc. Roy. Soc. London, Ser. B 76, 498 (1905). (7) HUNT, R.: Bull. 73, U. S. Hygienic Laboratory, (1911).