Carotid and vagal afferents and drug action on transcallosally evoked cortical potentials

The use of transcallosally evoked cortical potentials to study the action of intracarotidly injected drugs on cerebral synapses has necessitated the demonstration that vagal, baroreceptor, and chemoreceptor influences do not play essential roles in the drug effects observed-for example, the cerebral synaptic inhibitory action of serotonin.

The central vasomotor effects of 5-hydroxytryptamie

In the dog, injection of 5-hydroxytryptamine into the cerebral ventricles caused hypotension, inhibition of the pressor response to occlusion of the carotid artery and inhibition of the pressor or depressor response evoked by electrical stimulation of the central end of the cut vagus. Hypotension and inhibition of the vagal vasomotor response also occurred in dogs in which the carotid sinuses had been denervated and the vagi cut. The site of action was central. Local cerebral vascular changes could not have been responsible for the action. The central vasomotor effects of 5-hydroxytryptamine are mediated through the sympathetic outflow. Implications of these findings are discussed in relation to the effects of intravenous 5-hydroxytryptamine and the mechanism of action of reserpine.

A study of possible mediators of inflammatory reactions in the mouse foot

A number of compounds have been studied for their ability to antagonize the inflammatory reaction produced by injections of formaldehyde and 5-hydroxytryptamine in the mouse foot. An attempt has been made to elucidate the ways in which certain hydroxybenzoates, pyrazolones, sympathomimetic amines, flavone and flavanone glycosides, local anaesthetics, antihistamines and anti-5-hydroxytryptamine substances produce their anti-inflammatory effect.

The use of the guinea-pig ileum preparation for testing the activity of substances which imitate or antagonize the actions of 5-hydroxytryptamine and tryptamine

On the guinea-pig ileum, 5-hydroxytryptamine appeared to act in the same way as tryptamine on two types of receptor (morphine-sensitive and phenoxybenzamine(Dibenzyline)-sensitive). The actions of analogues of 5-hydroxytryptamine on the phenoxybenzamine-sensitive receptors resembled their actions on the rat uterus, and the actions on the morphine-sensitive receptors slightly resembled those on the rat fundus strip. The guinea-pig ileum preparation, however, did not appear to be more suitable than the rat uterus and rat fundus strip for testing the ability of compounds to imitate or antagonize 5-hydroxytryptamine.

Pharmacological properties of phenyldiguanide and other amidine derivatives in relation to those of 5-hydroxytryptamine

Cats in which the coronary and allied chemoreflexes could not be obtained with small intravenous doses of 5-hydroxytryptamine were insensitive also to phenyldiguanide. In cats which responded to phenyldiguanide with reflex falls of blood pressure and heart rate, abolished by vagotomy, the effects of graded doses (5 to 150 mug./kg.) of phenyldiguanide bore a striking resemblance to those produced initially by 5-hydroxytryptamine in somewhat smaller doses. Differences in the cardiovascular responses to the two drugs are attributed to additional (non-reflex) actions of 5-hydroxytryptamine. The reflex actions of both drugs were blocked reversibly also by 2-naphthylguanidine (500 mug.). Certain other drugs (bufotenine, procaine, S-decylisothiourea) antagonized the depressor action of phenyldiguanide as well as the reflex depressor action of 5-hydroxytryptamine. Like 5-hydroxytryptamine, phenyldiguanide and certain other amidine derivatives caused pain when applied to the base of blisters in human subjects. Unlike 5-hydroxytryptamine, phenyldiguanide did not constrict perfused rat blood vessels or increase the tone of the rat fundal strip preparation of Vane (1957). Phenyldiguanide did not affect the sensitivity of these smooth muscle preparations to 5-hydroxytryptamine, but other amidine derivatives proved to be moderately strong antagonists of the vasoconstrictor actions of 5-hydroxytryptamine and of adrenaline. Unlike 5-hydroxytryptamine, phenyldiguanide did not produce gastric haemorrhage in the mouse. Phenyldiguanide did not prolong chloral hydrate sleeping time in mice by the same mechanism as did 5-hydroxytryptamine. Phenyldiguanide was not highly toxic to mice (LD50 being 240 mg./kg.). It is concluded that phenyldiguanide and certain other amidine derivatives act on sensory receptors which respond to 5-hydroxytryptamine, but that they show little pharmacological resemblance to 5-hydroxytryptamine in other respects.

5-Hydroxytryptamine and transmission in sympathetic ganglia

Rat stellate ganglia were isolated and maintained in a moist chamber in which they were intermittently immersed in physiological saline containing low concentrations of the compound under investigation. 5-Hydroxytryptamine (serotonin) in concentrations as low as 1.3x10(-6) M reduced reversibly the threshold and increased the amplitude of responses to preganglionic stimulation. Certain antagonists of 5-hydroxytryptamine depressed reversibly the postsynaptic responses. Experiments in vivo supported this finding. It is suggested that 5-hydroxytryptamine facilitates transmission in the sympathetic ganglia of rats.

Effect of 5-hydroxytryptamine on the respiration of excised lamellibranch gill

5-Hydroxytryptamine, but not acetylcholine or catecholamines, stimulated the endogenous respiration of the excised gills of Modiolus demissus and mytilus edulis. Respiratory stimulation by 5-hydroxytryptophan is presumed to have occurred only after it had been decarboxylated to 5-hydroxytryptamine. 2-Bromolysergic acid diethylamide inhibited the effect of 5-hydroxytryptamine, while lysergic acid diethylamide mimicked it. The glycogen that was degraded during incubation of the gill cannot account for all of the oxygen that was consumed, indicating that some other substrate within the gill was also oxidized. That the metabolic actions of 5-hydroxytryptamine may be related to its cilio-acceleratory activity is discussed.

Pulmonary vascular effects of serotonin (5-OH-tryptamine) in dogs: its role in causing pulmonary edema

Rapid injection of serotonin (0.5–6.5 mg) was made into the pulmonary artery in 22 experiments in 12 open-chest anesthetized dogs. Serotonin caused pulmonary arteriolar and venous constriction in the majority of experiments, shown by an increase in the pressure gradients between the pulmonary artery and pulmonary artery wedge pressures, and between the latter and the left atrial pressure, respectively. Three groups of responses were obtained as far as the production of pulmonary edema is concerned. The first group (3 dogs) showed no pulmonary edema. The second ( group II—6 dogs) showed moderate to severe bilateral pulmonary edema without evidence of left heart failure. The third (3 dogs) also showed severe bilateral pulmonary edema but in the presence of left heart failure. In group II, the evidence suggests that an increase in capillary permeability is responsible, at least in part, for the pulmonary edema found. The similarity of results in group II to those obtained in the formation of bilateral pulmonary edema following unilateral starch embolization, suggests that serotonin could be the initiating factor in the neurohumoral mechanisms involved—or one of them.

Effects of 5-hydroxytryptamine on the dorsal muscle of the leech (Hirudo medicinalis)

5-Hydroxytryptamine has an inhibiting effect on the leech muscle. It reduces the contractions produced by acetylcholine or nicotine and accelerates the relaxation of the muscle when these substances are washed out. This acceleration of relaxation allows a more rapid assay of acetylcholine in this preparation.

A clinical and biochemical study of monoamine oxidase inhibition in depressed patients. II. 5-Hydroxytryptamine tolerance before and after Nialamide

In order to test whether a drug is an inhibitor of monoamine oxidase in the human subject, three main measures are available:

1. We can measure an increased excretion of the normal substrates of the enzyme, e.g. tryptamine (Sjoerdsma,et al., 1959b).

2. We can measure a decreased excretion of the metabolites resulting from the enzyme's action, e.g. 5-hydroxyindoleacetic acid (5-HIAA).

3. We can administer a loading dose of an enzyme substrate and observe how the subject deals with it before and after the drug, e.g. 5-hydroxytryptamine (Sjoerdsmaet al., 1958), and epinephrine (N-methyl-C14) (Resnicket al., 1958).

The responses of the Venus heart to catechol amines and high concentration of 5-hydroxytryptamine

The catechol amines excite the isolated heart of Venus mercenaria in a characteristic manner. This response was not obtained with phenethylamine, tyramine, ephedrine, or mescaline, nor with histamine, nor with the basic n-alkylamines. 5-Hydroxytryptamine had a distinctive effect at high concentrations (above 3x10(-6) M) different from that at lower doses. The response to high concentrations was dominated by an increase in muscle tone. Hearts exposed to high concentrations of 5-hydroxytryptamine and other tryptamine analogues for long periods became tachyphylactic to low doses of these substances. However, high doses of 5-hydroxytryptamine (about 2x10(-5) M) still excited the tachyphylactic heart, but the response was then like that to the catechol amines. When high bath temperatures rendered the heart insensitive to 5-hydroxytryptamine, high concentrations of this compound again had the catechol amine effect. The possibility of a physiological role for the catechol amines or high 5-hydroxytryptamine concentrations is discussed.

Pharmacological studies upon neurones of the lateral geniculate nucleus of the cat

Indoles related to 5-hydroxytryptamine, lysergic acid derivatives, phenethylamine derivatives and some other compounds have been applied electrophoretically to the neurones of the lateral geniculate nucleus of the cat anaesthetized with pentobarbitone sodium. Many of these compounds, particularly 4-, 5- and 7-hydroxytryptamine and ergometrine, depress the orthodromic excitation of the neurones by volleys in optic nerve fibres, but do not affect antidromic excitation by volleys in the optic radiation or chemical excitation by L-glutamic acid. It is concluded that the active depressants either block the access of the excitatory transmitter to subsynaptic receptors or prevent the release of the transmitter from optic nerve terminals. The structure-activity relationships of the depressant substances are discussed.

Studies on inflammation. 1. The effect of histamine and serotonin on vascular permeability: an electron microscopic study

The mechanism, whereby histamine and serotonin increase the permeability of blood vessels, was studied in the rat by means of the electron microscope. The drugs were injected subcutaneously into the scrotum, whence they diffused into the underlying (striated) cremaster muscle. An intravenous injection of colloidal HgS was also given, in order to facilitate the identification of leaks by means of visible tracer particles. After intervals varying from 1 minute to 57 days the animals were killed; the cremaster was fixed, embedded in methacrylate, and examined with the electron microscope. One to 12 minutes after the injection, the blood vessels of the smallest caliber (3 to 5 micra as measured on electron micrographs) appeared intact. Numerous endothelial openings were present in blood vessels with a diameter of 7 to 8 micra or more. These gaps were 0.1 to 0.8 micra in width; portions of intercellular junctions were often present in one or both of the margins. The underlying basement membrane was morphologically intact. An accumulation of tracer particles and chylomicra against the basement membrane indicated that the latter behaved as a filter, allowing fluid to escape but retaining and concentrating suspended particulate matter of the size used. Uptake of tracer particles by endothelial vesicles was minimal. Phagocytosis by endothelial cells became more prominent at 3 hours, but as a secondary occurrence; the pericytes were actively phagocytic at all stages. At the 3-hour stage no leaks were found. The changes induced by histamine and serotonin were indistinguishable, except that the latter was more potent on a mole-to-mole basis. In control animals only small accumulations of tracer particles were found in the wall of a number of blood vessels. With regard to the pathogenesis of the endothelial leaks, the electron microscopic findings suggested that the endothelial cells become partially disconnected along the intercellular junctions. Supporting evidence was provided at the level of the light microscope, by demonstrating—in the same preparation—the leaks with appropriate tracer particles¹, and the intercellular junctions by the silver nitrate method. The lipid nature of the chylomicron deposits observed in electron micrographs was also confirmed at the level of the light microscope, using cremasters fixed in formalin and stained in toto with sudan red.

Studies on inflammation. II. The site of action of histamine and serotonin along the vascular tree: a topographic study

While it is an established fact that histamine and serotonin increase the permeability of blood vessels, the exact portion of the vascular tree which is so affected has not been conclusively demonstrated. The present study was undertaken to clarify this point. Our experiments were based on a method to which we refer as "vascular labeling," and which permits one to identify leaking vessels by means of visible accumulations of foreign particles within their walls. The mechanism of the labeling, elucidated by previous electron microscopic studies, is the following. Histamine and serotonin cause the endothelial cells of certain vessels to separate, and thus to create discrete intercellular gaps. Plasma escapes through these gaps, and filters through the basement membrane. If the plasma has been previously loaded (by intravenous injection) with colloidal particles of a black material such as carbon or mercuric sulfide, these particles—too large to pass through the basement membrane—will be retained and accumulate in visible amounts within the wall of the leaking vessel. This method is used to maximal advantage if the tissue is cleared and examined by transillumination in toto, so that leaking vessels can be accurately identified in their relationship to the vascular tree. As a test tissue we used the rat cremaster, a laminar striated muscle which can be easily excised with its vascular supply virtually intact. The rats were prepared with an intravenous injection of carbon or HgS, and a subcutaneous injection into the scrotum of histamine, serotonin, or NaCl (as a control). The injected drug diffused into the underlying cremaster and the vessels became labeled. One hour later, when the carbon had been cleared from the blood stream, the animal was killed. The cremaster was excised, stretched, fixed in formalin, cleared in glycerin, and examined by transillumination under a light microscope. The lesions induced by histamine and serotonin were identical. The leaking vessels, as indicated by the carbon deposits, always belonged to the venous side of the circulation. The heaviest deposits were found in venules 20 to 30 micra in diameter. The deposits decreased towards larger venules up to a maximum diameter of 75 to 80 micra, and towards the finer vessels until the caliber reached approximately 7 micra. Essentially spared by the deposits were the finest vessels, 4 to 7 micra in diameter, and constituting an extensive network oriented along the muscular fibers. By killing animals at varying intervals after the injections, it was found that the carbon particles were slowly removed from the vascular walls by the action of phagocytic cells. After 10 months there was still enough carbon locally to be recognized by the naked eye.

Interrelation between progesterone, 5-hydroxytryptamine and HP1325 in the decidual response in ovariectomized mice

Experiments were carried out to study quantitatively in ovariectomized mice the relationship between the dosage of progesterone and the formation of decidual tissue, and to determine whether this relationship would be modified by simultaneous administration of either 5-hydroxytryptamine or an amine oxidase inhibitor HP 1325. As neither of these drugs produced any change in the decidual response at two different levels of progesterone, their toxic effects are probably due to interference with the endocrine activity of the ovary.