314 J. Physiol. (1958) I44, 3I4-336 THE ACTION OF SYMPATHOMIMETIC AMINES IN ANIMALS TREATED WITH RESERPINE BY J. H. BURN AND M. J. RAND From the Department of Pharmacology, University of Oxford (Received 3 June 1958) The impression left in the minds of those who have read the account of the sympathomimetic amines written by Barger & Dale in 1910 has been that these substances in the main were found to differ only quantitatively in activity. From time to time, however, there have been observations which furnished a hint of qualitative differences. Perhaps the first of these was the discovery by Tainter & Chang (1927) that under the influence of cocaine the action of tyramine was abolished, although, as Frohlich & Loewi had shown in 1910, the action of adrenaline was potentiated. In 1931 Burn & Tainter ob- served that tyramine and ephedrine had no action on the denervated pupil, though to adrenaline it was supersensitive. In 1932, Burn recorded that denervation of the cat's foreleg by removal of the stellate ganglion led to a loss of the vasoconstrictor action of tyramine and of ephedrine, though not of that of adrenaline. Burn also found that in the perfused dog's hind leg tyramine and ephedrine had, compared with adrenaline, only a fraction of the constrictor action they would be expected to have, judging from the pressor effect in the spinal cat. He observed, however, that the constrictor action could be restored if adrenaline was added to the blood perfusing the hind leg, and that this restoration could not be effected by adding pituitary (posterior lobe) extract instead. Fleckenstein & Burn (1953) found that after denervation of the nictitating membrane it became more sensitive only to those amines which were catechol derivatives; that to the derivatives of phenylethanolamine it was less sensitive and to the derivatives of phenylethylamine it was nearly insensitive. Flecken- stein & Bass (1953) and Fleckenstein & St6ckle (1955) showed that the nor- mally innervated nictitating membrane after full doses of cocaine behaved in exactly the same way. These various observations have remained incoordinated and unexplained. Recently, however, Carlsson, Rosengren, Bertler & Nilsson (1957) found that, in cats treated with reserpine, the intravenous injection of tyramine had no SYMPATHOMIMETIC AMINES 315 pressor effect. In explanation they said that 'tyramine belongs to a group of sympathomimetic amines which are fully active only in the presence of an intact adrenergic system'. We have recently observed (Burn & Rand, 1957, 1958b) that when rabbits and dogs were treated with reserpine, the noradrena- line-like substance demonstrated by Schmiterl6w (1948) to be present in the wall of the aorta disappeared. We also observed that the constrictor action of nicotine in the perfused rabbit's ear disappeared, and were led to the con- clusion that nicotine exerted this constrictor action by releasing a noradrena- line-like substance from the vessel wall or perhaps from chromaffin cells in its neighbourhood. It therefore seemed to us possible that the failure of tyramine to exert its pressor action in the cat after treatment with reserpine was due to the fact that tyramine normally acted by releasing a noradrenaline-like substance from the vessel walls. We now describe experiments to test the action of a series of sympathomimetic amines from this point of view. METHODS Observations of four kinds have been made. The effect of sympathomimetic amines has been examined (1) on the blood pressure, the spleen and the nictitating membrane of the spinal cat; (2) on the arterial resistance and venous outflow of the perfused dog hind leg; (3) on the outflow of the perfused rabbit ear; and (4) on spiral strips of rabbit aorta set up in an isolated organ bath. Spinal cats were prepared under ether anaesthesia, dividing the cord at the 2nd cervical verte- bra and destroying the brain. Records of the spleen volume and of the contractions of the nicti- tating membrane were made as described by Burn (1952). For the hind leg perfusion one dog was bled under ether anaesthesia from the carotid artery into a jar containing heparin, and its lungs were prepared for perfusion by one of a pair of Dale-Schuster (1928) pumps. Perfusion was begun through the lungs, which were ventilated by oxygen with 5 % CO2. A second dog was then anaes- thetized. After dividing the rectum and the inferior mesenteric artery between ligatures, the right external iliac artery was tied, and a cannula was inserted pointing towards the aorta. The body wall was divided in sections between ligatures along the course ofthe left external iliac artery. Poupart's ligament was cut. Branches of the left external iliac from the aorta to about 1 cm below Poupart's ligament were tied, as were also the corresponding veins. The continuation of the aorta below the origin of the external iliac arteries was tied. When the dissection was complete, perfusion was begun by the second pump through the left hind leg at the moment of tying the aorta to arrest the natural circulation. In some experiments the left lumbar sympathetic chain was prepared for stimulation; in these the dog was first eviscerated and the left kidney removed. After the arrest of the natural circula- tion, the dog was cut in half, the perfusing cannula was tied into the aorta and the blood collected from the vena cava. By this method the ganglia of the sympathetic chain were perfused. In these experiments there was an interval of 7 min between the arrest of the natural circulation and the start of the perfusion. In all perfusions mass ligatures were tied so as to enclose the whole circumference of the body wall above the area perfused. An outflow record was obtained by using Stephenson's recorder (1949). When stimulating the sympathetic chain shielded electrodes, each a silver plate 3 mm wide, were used; stimuli were square-wave pulses of 2-5 mA strength, 1 msec duration and 20-25/sec frequency. The perfusion of the rabbit ear was arranged as previously described (Burn, 1952) using Stephen- son's outflow recorder (1948). 316 J. H. BURN AND M. J. RAND Reserpine was dissolved in 20% ascorbic acid solution making the solution up to 10 mg/ml. as required. Injections were made intraperitoneally. Dogs were given 0-5 mg/kg on two successive days, the dog being killed on the third day. Cats were given 2-5-5-0 mg/kg on two successive days, and rabbits were given 3 mg/kg on two successive days. Fig. 1. Upper record is that of the nictitating membrane; lower record that of blood pressure in the spinal preparation. (a) Normal cat; injection of 10 i&g noradrenaline produced a small rise of blood pressure; 4 mg tyramine hydrochloride produced a large rise of blood pressure and large contraction of the nictitating membrane. (b) Cat treated with reserpine. Note that the effects were reversed; 4 mg tyramine had a very slight effect on the blood pressure and none on the nictitating membrane; 10 iLg noradrenaline had a large effect on the blood pressure. (c) Same as (b); after the intravenous infusion of 0-12 mg noradrenaline, the effect of 4 mg tyramine on the blood pressure was much greater than in (b). RESULTS Action of tyramine Fig. 1 shows records taken from experiments in two spinal cats, the one a normal cat, and the second a cat treated with reserpine. In Fig. 1la the injection of 10 pg noradrenaline into the normal cat caused a small rise of blood pressure, whereas the injection of 4 mg tyramine hydrochloride caused a large rise of blood pressure and a large contraction of the nictitating mem- brane. In Fig. 1lb the same injections were made into a cat treated with reserpine. The effect of 4 mg tyramine hydrochloride was very small and there was no contraction of the nictitating membrane, while the effect of 10 pg noradrenaline was very much larger than in the normal cat. A solution of SYMPATHOMIMETIC AMINES 317 noradrenaline was then prepared in a burette and the burette was connected to the femoral vein. An infusion of noradrenaline at a uniform rate was begun and maintained until 012 mg noradrenaline had entered the cat. The infusion caused a large rise of blood pressure, but although the rate of infusion was kept constant, the blood pressure fell as the infusion continued, though the extent of this fall varied in different experiments. At the end of the infu- sion the point at which the blood pressure returned to its former level was noted, and an injection of 4 mg tyramine was made again, as shown in Fig. 1 c. Fig. 2. Upper record is that of the spleen volume; lower record that of blood pressure, in the spinal preparation. (a) Normal cat. (b) Cat, treated with reserpine, in which 2 tg adrenaline had a greater effect on the spleen volume than 10 jg in (a), and in which 1 mg tyramine had no action, though it contracted the spleen in (a). An infusion ofnoradrenaline was then made, after which (c) 1 mg tyramine again caused contraction. The rise of blood pressure was much greater than in Fig. 1 b and there was also a small contraction of the nictitating membrane which was absent in Fig. 1 b. The events shown in Fig. 1 were observed in many experiments. When the pressor action of tyramine had been restored, as in Fig. 1 c, then repeated injections of tyramine had a declining effect, but a further infusion of nor- adrenaline would restore it a second time. In other experiments the spleen volume was recorded, as shown in Fig.