THE PHARMACOLOGIC ACTION OF SOME ANALOGS OF 1-3,4-DIHY- DROXYPHENYL)-2-AMINO-1-BUTANOL (ETHYLNOREPINEPHRINE)

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1 THE PHARMACOLOGIC ACTION OF SOME ANALOGS OF 1-3,4-DIHY- DROXYPHENYL)-2-AMINO-1-BUTANOL (ETHYLNOREPINEPHRINE) A. M. LANDS, F. P. LTJDUENA, J. I. GRANT AND ESTELLE ANANENKO Pharmacology Section of the Sterling-Winthrop Research Institute, Rens8elaer, New York Received for publication January 21, 1950 The general pharmacologic action of 1-(3,4-dihydroxyphenyl)-2-amino-1-butanol (ethylnorepinephrine) has been described by Tainter and associates (1-7). This substance differs from the analogous ethanol derivative, arterenol, in that epinephrine-like excitatory effects are small or absent while, at the same time, inhibitory actions are prominent. Ethylnorepinephrine is an effective bronchodilator agent in experimental animals and in man (8). The cardiovascular actions of this drug are not great, being distinctly less than those of 1-(3,4-dihydroxyphenyl)-2-isopropylaminoethanol (N-isopropylarterenol, Isuprel ). Previous publications have established the effectiveness of N-isopropylartereno! (9-12) as a bronchodilator agent. This action is significantly greater than that of the analogous primary amine (arterenol) and the N-methyl derivative (epinephrine). Dr. A. Wayne Ruddy of the Chemistry Division of the Sterling- Winthrop Research Institute has recently synthesized several N-alkyl analogs of ethylnorepinephrine and the pharmacologic actions of these substances are described in this communication. Their structural formulae are shown in table 1. BRONCHODILATOR ACTION. Isolated Perfused Guinea Pig Lungs. Young adult guinea pigs ( gm.) were killed by a blow on the head, the chests were opened without damage to pulmonary tissue and the lungs immediately removed with the trachea intact. The trachea was cannulated and arranged for perfusion by the method of Soliman and von Oettingen, as modified by Tainter et al. (2). All drugs were dissolved in distilled water and injected into the perfusion system just above the tracheal cannula. Histamine acid phosphate was injected in sufficient dose ( mgm.) to cause a reduction of about 50 per cent in the flow through the lungs. The dose of bronchodilator drug that would prevent this reduction in flow, when injected simultaneously with the constricting dose of histamine, was estimated from the results obtained with graded doses. The activity of these drugs, expressed as percentage of the Isuprel potency, is shown in table 1. The N-cyclopentyl derivative (WIN 515) was found to be most effective and approximately equal to Isuprel in preventing histamine bronchoconstriction. The N-isopropyl derivative (WIN 3046) is slightly less and the N-cyclohexyl derivative (WIN 713) is distinctly less effective than WIN 515. The bronchodilator action of ethylnorepinephrine is approximately equal to that of WIN 713. Both WIN 3046 and WIN 515 are more effective than epinephrine (Suprarenin). It is interesting to note that comparable values were I Butanefrine, Suprarenin, Cobefrine, and Isuprel are the registered trade marks of Winthrop-Stearns Inc. Pentothal (thiopental sodium) is the registered trade mark of Abbott Laboratories. 45

2 46 LANDS, LUDUENA, GRANT AND ANANENKO obtained for both primary amines. Ethylnorepinephrine appears to be somewhat more effective than l-arterenol inasmuch as the former is the racemic mixture whereas the latter is the more active isomer. Protective Action in Guinea Pigs Exposed to Histamine. Protection against histamine aerosols was measured by the method described by Siegmund, Granger and Lands (10). Unanesthetized guinea pigs (weight gm.) were placed in an observation chamber and exposed to a histamine aerosol (0.2 per cent histamine diphosphate). The times required for the production of a) increased respiratory effort and b) asphyxial convulsions were determined. Following the control exposure, the guinea pigs were allowed to rest for TABLE 1 The bronchodilator potency of N-alkyl derivatives of 1-(S,4-dihydroxyphenyl)4-amino-1 - butanol against histamine as determined by various methods Compound Ethylnorepinephrine WIN 3046 WIN 515 W1N713 Epinephrine l-arterenol Isuprel HO-CH0HCHCHCH3 HY ACTIVITY (EXPRESSED IN TERMS OF NHR I ISUPRIL RATIOS) Structure H CH(CH,)2 :iii <> * Multiples of the effective dose of Isuprel Perfused guinea pig lung Histamine asthma in guinea pigs Barbitalized dog t Doses producing a 60 mm. Hg rise in blood pressure have little effect on the histamine bronchoconstriction. two hours. They were then injected intraperitoneally with the test drug and, after fifteen minutes, again exposed to histamine. The average delay in a and b was computed and these times have been combined into a single figure (protection, per cent) from which the activity in relation to that of Isuprel has been calculated (table 1) <8 t 1 The N-isopropyl derivative (WIN 3046) is most active and is about one-half as effective as Isuprel. By contrast with the results obtained by lung perfusion, the N-cyclopentyl derivative (WIN 515) is less effective than the N-isopropyl derivative (WIN 3046) but still has a high order of activity. WIN 3046 appears to be more resistant to destruction or inactivation in body fluids. Observations of this kind have been reported by West (13) who has shown that, after the injection of quinidine into the splenic artery, the ratio of equipressor doses of epinephrine by splenic artery and splenic vein injection is higher (7.5:1) than that for arterenol (4:1). The liver also was found to inactivate epinephrine more

3 ANALOGS OF ETHYLNOREPINEPHRINE 47 rapidly than arterenol. Ethylnorepinephrine and the N-cyclohexyl derivative (WIN 713) were found to be weak bronchodilator drugs with Isuprel ratios approximating those obtained by lung perfusion. Bronchodilator Action in Anesthetized Dogs. Dogs were anesthetized with sodium thiopental (Pentothal) and sodium barbital and prepared for the determination of bronchodilator action by the pulley and lever method described by Jackson (14). Carotid blood pressure was determined by means of a mercury manometer and recorded kymographically. All drugs were dissolved in distilled water containing 0.1 per cent sodium acetone bisulfite and injected directly into the exposed femoral vein. Bronchoconstriction was induced by histamine acid phosphate in doses of 5-10 microgm./kgm. The dose of bronchodilator drug that would prevent approximately 75 per cent of the bronchoconstrictor action of histamine, when administered simultaneously with this latter drug, was determined. Results obtained are shown in table 1. By this test, WIN 3046 and WIN 515 are about one-ninth as active as Isuprel and somewhat more active than epinephrine. Both l-arterenol and ethylnorepinephrine are weak and it was not possible to obtain data from which an Isuprel ratio could be computed. The highest dose of epinephrine used (8 microgm./kgm.) produced only a 50 per cent decrease in the histamine constriction. The strong cardiovascular effects obtained precluded the use of higher doses. The above results are in essential agreement with those obtained by lung perfusion and by the histamine mist method as shown in tables 1 and 2. WIN 515 appears to be more active than WIN 3046 when administered by lung perfusion, less active when administered intraperitoneally in guinea pigs and equally active when administered intravenously in dogs (table 1). This difference may result from a more rapid rate of inactivation of WIN 515. The substitution of either an isopropyl or a cyclopentyl group on the amino nitrogen leads to a marked increase in bronchodilator action. The primary amine appears to be distinctly less effective by each of the test methods employed in this investigation. These results are in agreement with those recently reported by Siegmund, Beglin and Lands (15) for the corresponding ethanol analogs. CARDIOVASCULAR ACTION. Dogs, anesthetized as described above, were used for the determination of vasodepressor action. The test drugs were injected directly into the exposed femoral vein and the resultant changes in blood pressure recorded kymographically. The vasodepressor action of butanol derivatives is distinctly less than that of the corresponding ethanol derivatives (9, 11). The N-isopropyl analog, WIN 3046, has about 1/16 of the depressor action of the corresponding ethanol analog, Isuprel (table 2). The N-cyclopentyl derivative (WIN 515) is approximately equal in action to WIN The N-cyclohexyl derivative (WIN 713) and the primary amine, ethylnorepinephrine, are weak vasodepressor drugs. A comparison of the data in table 1 with those in table 2 suggests that both WIN 3046 and WIN 515 cause less vasodepression than does Isuprel when these drugs are administered in equal bronchodilator doses in anesthetized dogs. The pulse rate in barbitalized, atropinized dogs was determined before and after intravenous administration of the butanol derivatives. These compounds

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5 ANALOGS OF ETHYLNOREPINEPHRINE 49 produce cardiac acceleration but are much weaker than Isuprel, epinephrine and l-arterenol in this respect. Ethylnorepinephrine and WIN 713 are the weakest, their activity being about 1/220 and 1/1000 that of Isuprel, respectively. The extremely low activity of the last compound raises the question as to whether the minor increase in heart rate observed may not have been in large part due to reflexes mediated through the cardiac accelerators (stimulation) in response to the fall of pressure. In trying to determine the Isuprel ratio for these compounds, it was soon found that the ratio varied with different doses, that is, the dose/response curves of Isuprel and WIN 3046 have different slopes. It was observed that gradually increasing doses of WIN 3046 did not produce a corresponding increase in heart rate. Experiments on six atropinized dogs, on which graded doses of Isuprel. and WIN 3046 were tested, showed that Isuprel was times more active than WIN 3046 when small doses were compared, and about 250 times when the larger doses were used, in producing cardio-acceleration. WIN 3046 and WIN 515 are about equally active. In two dogs in which a graduated series of doses of WIN 515 and WIN 3046 were injected, the observed decreases in the Isuprel ratios were comparable. The weak cardiac action of WIN 3046 and WIN 515 in relation to that of Isuprel, and especially the flatness of their dose/response curves, may have clinical importance. If man responds in a similar manner, the possibility of producing palpitation as a side effect would be less with these drugs than with Isuprel. In a few experiments on trained unanesthetized dogs, a determination was made of the effect of some of these drugs on blood pressure and heart rate. The drugs were injected intramuscularly and changes in blood pressure measured as previously described by Siegmund, Nash and Granger (16). In this method, a shaped cuff containing a child size sphygmomanometer bag is secured about the thigh of the dog and systolic pressure determined by palpation of the pedis dorsalis artery. This method is not difficult and with most dogs the pulse is quite distinct. The cuffs used in our laboratory give most satisfactory results when the dog weighs about 10 kgm. Representative results are shown in table 2. The effect of intramuscular injections of ethylnorepinephrine in the dosage used was quite variable causing a rise in blood pressure in two experiments and a fall in three - others. With doses of 42 microgm./kgm. the heart rate was increased by beats per minute. WIN 515 is much more potent than ethylnorepinephrine. Doses of 2.2 microgm./kgm. caused a small reduction in systolic pressure with a concomitant cardiac acceleration of 16 to 30 beats per minute. By comparison, with 2.2 microgm./kgm. of Isuprel the cardiac acceleration was greater (48 to 94 beats per minute). WIN 713 is relatively ineffective in that doses of 100 microgm. /kgm. causes negligible changes in blood pressure and only small increases in heart rate. Gay and Long (17) have reported that, in man, subcutaneous doses of mgm. of Isuprel cause tachycardia and palpitation in all instances tried. With doses 1/5 the above amounts, these side effects were observed in 41 per cent of all patients. Bresnick, Beakey, Levinson and Segal (18) have reported tachycardia, an increase of beats/mn., in man after intravenous injections

6 50 LANDS, LUDUENA, GRANT AND ANANENKO of 5 microgm. of Isuprel. An injection of 10 microgm. accelerated the pulse by 50 beats/mn. and caused alarming palpitations with some uneasiness. In experiments carried out in our laboratory with an adult male volunteer, wt. 80 kgm., the cardiovascular effects of WIN 515 were compared with those of the analogous ethanol derivative, WIN 5591 (1-(3,4-dihydroxyphenyl)-2-cyclopentylaminoethanol). Subcutaneousinjectionof 1.0 mgm. of WIN 515 caused changesin blood pressure from 132/88 to 148/72 ; an increase in pulse rate from 78 to 91 beats/mm. WIN 5591, in a subcutaneous dose of 0.5 mgm., caused changes in blood pressure from 132/87 to 140/70 ; an increase in pulse rate from 73 to 127 beats/mn. with distinct palpitation. Maximum effects were obtained in ten to twenty minutes following injections. With both drugs, there was flushing of the face and ears with an associated feeling of warmth. The reduction in diastolic pressure observed indicates a reduction in peripheral resistance, which is associated with cardiac stimulation and a resultant rise in systolic pressure. A dose of 0.5 mgm. of WIN 5591 caused a greater increase in pulse rate than did 1.0 mgm. of WIN 515. The weak stimulation of the heart produced by the ethylnorepinephrine derivatives, both in experimental animals and in man, is in agreement with the findings of Tainter et al. (1-8). These investigators have reported that, in man, intramuscular injections of 2.0 mgm. of ethylnorepinephrine caused an average increase in pulse rate of only 12 per cent of the initial rate associated with some reduction in diastolic pressure (8). ACTION ON THE INTESTINE AND UTERUS. Isolated segments of guinea pig ileum were arranged for the recording of motility as described by Miller, Becker and Tainter (19). The amount of drug required to induce relaxation was determined and the average amounts, expressed as the logarithm of the reciprocal of the ED50 (pd), are shown in table 2. The butanols are significantly less potent than the ethanols employed in this investigation. The two most active bronchodilator compounds, WIN 515 and WIN 3046, among the butanols, are less active than ethylnorepinephrine but somewhat more active than WIN 713. Action on the small intestine in situ was determined as described below. Dogs were anesthetized by sodium thiopental and sodium barbital. A small incision was made in the abdominal wall along the mid-line, an L-rod inserted and the lower limb of this attached to the wall of the ileum. At a distance of about 3 cm. from the point of attachment, a thread was sutured to the serosa and passed over a pulley to a light muscle lever. The L-rod with the attached intestinal segment was clamped securely to a ring stand and the abdominal incision closed around a glass ring, leaving the thread to the small intestine free to move without mechanical interference. Changes in tonus and motility were recorded kymographically. All drugs were dissolved in distilled water and injected into an exposed femoral vein. WIN 3046 and WIN 515 are potent epinephrine-like inhibitory agents. Doses of 5-10 microgm./kgm. cause distinct reductions in tonus and motility of the intestine (table 2). In this action they are about 1/10-1/20 as effective as Isuprel. WIN 713 and ethylnorepinephrine are much less effective, doses of microgm./kgm. being required to produce a definite reduction in tonus and motility. The action of WIN 713 is rather prolonged but the greater duration of action may result from the larger dose and a resultant greater time required for its elimination from the circulation.

7 ANALOGS OF ETHYLNOREPINEPHRINE 51 The isolated guinea pig uterus was arranged for the recording of motility as described for the isolated intestinal segment. Pituitrin (to make a muscle bath concentration of pd 7.6) was used to induce contracture. This contracture was greatly reduced by both WIN 515 and WIN 3046 at a concentration of about 1 : 500 million (jd 8.7) in 50 per cent of the strips. Ethylnorepinephrine and WIN 713 are much less effective (table 2). The uteri of anesthetized dogs were arranged in situ for the recording of motility, as described for the intestine, in situ. Intravenous doses of 5-10 microgm. /kgm. of WIN 515 and WIN 3046 caused a prompt reduction of spontaneous motility in most experiments (table 2). In an occasional animal, the uterus appeared to be resistant to the spasmolytic action of all of the drugs used in this investigation. WIN 713 and ethylnorepinephrine are distinctly less effective than WIN 515 and WIN 3046 in bringing about uterine relaxation. A few experiments were carried out on the non-gravid rabbit uterus in situ. In these, the animal was anesthetized and arranged for the recording of uterine motility as previously described for the dog. WIN 3046, in an intravenous dose of microgm./kgm., caused a reduction in the amplitude of spontaneous contraction, lasting for five to ten minutes. Comparable effects were obtained with Isuprel in intravenous doses of 1-2 microgm./kgm. Intramuscular injections of microgm./kgrn. of WIN 3046 caused reductions in motility lasting for seven to thirty minutes. By comparison, epinephrine and l-arterenol in intravenous doses of 1-2 microgm./kgm. caused a marked increase in motility of the non-gravid uterus. STIMULATING ACTION ON THE CENTRAL NERVOUS SYSTEM. The stimulating action of these sympathomimetic amines on the central nervous system of albino rats has been determined by the method described by Schulte, Tainter and Dille (20). The drugs were dissolved in distilled water and injected subcutaneously into adult albino rats. In this method, the movements of each experimental animal activates a work adder whose revolutions are recorded by means of an electrical counter. None of the butanol derivatives described in this communication cause significant stimulation of the central nervous system. In fact, the data may indicate a mild depression of motor activity. This is in agreement with the observations of Waterman (21) who found a reduction in spontaneous activity of albino rats after the administration of Isuprel. Both epinephrine and arterenol have been reported to be more stimulating than ethylnorepinephrine (7). Results obtained in our experiments did not indicate any important differences from the control values. The butanol derivatives are distinctly less toxic than epinephrine and l-arte- ACUTE INTRAVENOUS TOXICITY. Albino mice of the Webster strain weighing 20 ± 2 gm. were used for the determination of intravenous toxicity. The volume administered was maintained at 0.35 ± 0.15 cc. and was injected into a tail vein at the rate of 1.0 cc. per minute. Groups of ten or more animals were medicated at each dose level with dosages arranged at equal logarithmic intervals. Following injection, each group of mice was placed in a wire screen cage measuring 10 x 7 x 7 inches in which water and food were available at all times. The LD6, ± its standard error were calculated by the method of Miller and Tainter (22) and expresses the total mortality at the end of 24 hours.

8 52 LANDS, LUDUENA, GRANT AND ANANENKO renol but are approximately equal to Isuprel (table 3). The primary amine, ethylnorepinephrine, is least and the N-isopropyl derivative, WIN 3046, most toxic. There does not appear to be any correlation between the nature of the N-alkyl substituent and toxicity. It is important that the systemic toxicity of these new compounds is extremely low in proportion to their high bronchodilator activity. DISCUSSION. The butanol compounds described in this publication have an epinephrine-like inhibitory action. In this, they most nearly resemble Isuprel and other N-alkylarterenol derivatives previously described (9-12). The rat uterus has been frequently used as an indicator of epinephrine-like inhibitory action inasmuch as it is relaxed by most sympathomimetic amines without evidence of excitation. Gaddum et al. (23) have reported that relaxation of this organ is obtained in the order Isuprel > epinephrine> 1-(3,4-dihydroxyphenyl) -2-amino-1-propanol (Cobefrine) > ethylnorepinephrine > l-arterenol. Hista- TABLE 3 The acute intravenous toxicity of N-alkyl derivatives of 1-(S,4-dihydroxyphenyl)--amino-1- butanol in albino mice COMPOUND ANIMALS USED LDio ± S.E. mgm./hgm. Ethylnorepinephrine ± 1.04 (8) W1N ±2 W1N ±7 WIN ±4 Epinephrine ± 0.2 (26) l-arterenol ± 1.0 (26) Isuprel ± 7 (27) mine-constricted guinea pig bronchioles are relaxed in the order Isuprel > WIN 3046> WIN 5570 > ethylnorepinephrine> arterenol > Cobefrine (table 4). Ahiquist (24) has reported for the intestine (isolated and in situ) an inhibitory action of epinephrine > arterenol > Cobefrine > Isuprel. After Dibenamine blockade, he observed depressor action in the order Isuprel > epinephrine > Cobefrine> arterenol. Gaddum et al. (23) found that the rat colon is relaxed by l-arterenol = ethylnorepinephrine > epinephrine = Isuprel> Cobefrine. Inhibitory potency appears to vary widely with different organs. Isuprel is most effective on the rat uterus, guinea pig bronchioles and dog vascular bed and least effective on the intestine. Cobefrine is more effective than ethylnorepinephrine on the rat uterus but less effective on the colon and perfused guinea pig lung. These data make generalization difficult. However, it would appear that N-alkyl substitution increases and lengthening of the side-chain from ethanol to propanol or butanol decreases inhibitory potency. The cat nictitating membrane responds to epinephrine and epinephrine-like substances by contraction and has been frequently used as an indicator of sympathetic excitatory action. Ahlquist (24) has reported that this organ is stimu-

9 ANALOGS OF ETHYLNOREPINEPHRINE 53 lated in the order epinephrine > arterenol > Cobefrine > Isuprel. Gaddum et at. (23) have similarly reported that epinephrine = l-arterenol > ethylnorepinephrine > Cobefrine > Isuprel. Vasoconstriction in the femoral vascular bed following intra-arterial injection is in the order arterenol > d,l-epinephrine > Cobefrine > Isuprel (dilator) (24) and for the perfused rabbit ear, epinephrine > t-arterenol > ethylnorepinephrine > Cobefrine (23). These data suggest that both lengthening of the side-chain and substitution of an N-alkyl group larger than methyl are unfavorable for excitatory action. Excitatory action on the heart does not correlate well with either of the above described actions. Cobefrine (25) has been reported to be distinctly TABLE 4 Summary of the effect of modifying the side-chain and the N-alkyl substituent on sympathomimetic activity HO -CHOHCH-R I EFFECTIVE DOSE PERPUSED EEART RATE RATIO Structure PIG LUNG Histamine Blood pressure (DOG) mist (dog) Compound (guinea pig) R R microgm./ effectf Dose micro. rsicrogm. ei 1.0 l-arterenol H H (27)* d,l-arterenol 174 >100 (10) (26) Cobefrine CH, H 1140 (2) + epi (26) (30, 31) Ethylnor- C2H5 H , (5) epinephrine Isuprel - ijj Isuprel H CH(CH,), WIN 5570 CH3 CH(CH,) WIN 3046 C,H5 CH(CH,) * References cited. t +, pressor; -, depressor. more stimulating than either arterenol or ethylnorepinephrine (5) when the dog heart-lung preparation is used. Ahlquist (24) has reported that the increase in rate and amplitude of contraction in dogs, following intravenous injection, is marked for Isuprel and less for Cobefrine and arterenol. Marsh et at. (12) perfused rabbit and cat hearts and found that the stimulating effect of Isuprel > d,l-epinephrine = d,l-arterenol. Intravenous injection in the anesthetized dog (table 4) caused an increased rate of contraction with Isuprel > WIN 5570 > WIN No clear correlation between molecular structure and myocardial stimulation is apparent in these data. There is probably therapeutic importance in the observation that the butanol derivatives, WIN 515 and WIN 3046, cause comparatively little myocardial stimulation but still are effective bronchodilator agents. A comparison in anesthetized dogs of bronchodilator (table 1) with cardiac stimulating action indicates that effective bronchodilator doses

10 54 LANDS, LUDUENA, GRANT AND ANANENKO of the N-cyclopentyl (WIN 515) and N-isopropyl (WIN 3046) derivatives have much less stimulating action on the heart than Isuprel. It is interesting to note that the substitution of a cyclopentyl group on the nitrogen increases activity as much as isopropyl substitution. This is in agreement with the findings of Siegmund et at. (15), who have reported N-cyclopentylarterenol to be somewhat more effective than Isuprel in relaxing histamine-constricted bronchi in guinea pig lung perfusion. Butanefrine and the N-cyclohexyl derivative (WIN 713) are distinctly less potent than WIN 515 and WIN The hyperglycemic action of epinepb.rine appears to be more closely related to sympathetic excitatory than to sympathetic inhibitory action. McChesney, McAuliff and Blumberg (26), using rabbits as the test animal, found the hyperglycemic action of WIN 3046, WIN 515, Isuprel and ethylnorepinephrine to be negligible. l-arterenol was reported to have 12 per cent of the hyperglycemic action of epinephrine. No excitatory action on the central nervous system of rats was observed in these experiments with the butanol derivatives whereas the ethanol derivatives, epinephrine and l-arterenol, may cause stimulation (27). Acute intravenous toxicity in mice was low for the butanol derivatives when compared with that of epinephrine and l-arterenol (28). The toxicity of Isuprel is comparable to that of WIN 515 and WIN 3046 (29). These data suggest that sympathetic excitatory action on smooth muscle, mobilization of blood sugar, stimulation of the central nervous system and acute toxicity are related. Sympathetic inhibitory action is largely confined to smooth muscle inasmuch as no appreciable effects were observed on blood sugar and the central nervous system and acute toxicity is comparatively low. Myocardial stimulation does not appear to be correlated to either of the above functions. Greatest stimulation is obtained with the depressor drug, Isuprel, and with the excitatory drug, Cobefrine, and least with ethylnorepinephrine and the N-cyclohexyl derivative (WIN 713). SUMMARY 1. The pharmacologic actions of N-isopropyl (WIN 3046), N-cyclopentyl (WIN 515) and N-cyclohexyl (WIN 713) analogs of 1-(3, 4-dihydroxyphenyl)- 2-amino-1-butanol (ethylnorepinephrine, Butanefrine) on bronchial tonus, blood pressure, heart rate, intestinal and uterine tonus and activity of the central nervous system, as well as systemic toxicity, have been investigated in comparison with those of 1-(3, 4-dihydroxyphenyl)-2-isopropylaminoethanol (Isuprel), epinephrine and l-arterenol. 2. These ethylnorepinephrine derivatives lower blood pressure of barbitalized dogs, WIN 713 being distinctly less active than either WIN 3046 or WIN 515. The latter derivatives are about equally active but distinctly less active than Isuprel. 3. The ethylnorepinephrine derivatives increase the heart rate of barbitalized dogs but are considerably less effective than Isuprel. WIN 3046 and WIN 515 are equally active and more potent than ethylnorepinephrine or WIN WIN 3046 and WIN 515 are much more effective bronchodilator agents

11 ANALOGS OF ETHYLNOREPINEPHRINE 55 than WIN 713 or ethylnorepinephrine. Their potency approaches that of Isuprel. In the anesthetized dog, Isuprel is approximately ten times more bronchodilator but times more effective in increasing the heart rate. These ratios suggest that cardiac stimulation, as an undesirable side effect, would be less likely to occur with therapeutic doses of WIN 3046 and WIN 515 than with Isuprel. 5. WIN 3046, WIN 515 and WIN 713 exert a weak inhibitory action on the isolated guinea pig intestine. Isuprel is more than 1000 times more potent; epinephrine and t-arterenol are intermediate in potency. WIN 3046 and WIN 515 are distinctly more potent than WIN 713 or ethylnorepinephrine on the intestine in situ in barbitalized dogs. Epinephrine and l-arterenol are slightly more effective than Isuprel and many times more effective than ethylnorepinephrine and its analogs on the intestine in situ. 6. WIN 3046, WIN 515, epinephrine and Isuprel are strong inhibitors, of comparable potency, on the isolated guinea pig uterus stimulated with pituitrin. Ethylnorepinephrine, WIN 713 and l-arterenol are much weaker inhibitory agents. 7. WIN 3046, WIN 515, WIN 713 and ethylnorepinephrine do not increase the spontaneous activity of rats, as determined by the jiggle-cage method. 8. The ethylnorepinephrine derivatives have an acute intravenous toxicity (mouse) comparable to that of Isuprel and are much less toxic than epinephrine or l-arterenol. 9. Evidence is presented which suggests that the structural requirements for myocardial stimulation differ from those favorable for sympathetic excitatory or inhibitory action. ACKNOWLEDGEMENT. The authors are indebted to Dr. 0. H. Siegmund for the determination of bronchodilator action in guinea pigs by the histamine mist method; to Dr. J. 0. Hoppe for the determination of acute intravenous toxicity; to Mrs. Nettie Beglin and Mrs. Janina Draude for technical assistance throughout this investigation. REFERENCES 1. TAINTER, M. L.: Arch. internat. de pharmacodyn. et de therap., 46: 192, TAINTER, M. L., PEDDEN, J. R., AND JAMES, M.: THIS JOURNAL, 51: 371, PEDDEN, J. R., TAINTER, M. L., AND CAMERON, W. M.: THIS JOURNAL, 55: 242, CAMERON, W. M., AND TAINTER, M. L.: THIS JOURNAL, 57: 152, CAMERON, \V. M., CRIsiuoN, J. M., WHITSELL, L. J., AND TAINTER, M. L.: THIS JOUR- NAL, 62: 318, CAMERON, W. M., WHITSELL, L. J., CiusMoN, J. M., AND TAINTER, M. L.: THIS JOUR. NAL, 63: 340, SCHULTE, J. W., REIF, E. C., BACHER, J. A., LAWRENCE, \V. S., AND TAINTER, M. L.: THIS JOURNAL, 71: 62, TAINTER, M. L., CAMERON, W. M., WHITSELL, L. J., AND HARTMAN, M. M.: Tuis Joua- NAL, 81: 269, LANDS, A. M., NASH, V. L., MCCARTHY, H. M., GRANGER, H. R., AND DERTINGER, B. L.: THIS JOURNAL, , SIEGMUND, 0. H., GRANGER, H. R., AND LANDS, A. M.: THIS JOURNAL, 90: 254, LANDS, A. M., NASH, V. L., DERTINGER, B. L., GRANGER, H. R., AND MCCARTHY, H. M.: THIs JOURNAL, 92: 369, 1948.

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