,8-IMINAZOLYLETHYLAMINE is the amine which is produced when carbon dioxide is split off from histidine. It was first prepared synthetically by Windaus and Vogt'. Recently Ackermann2 obtained a large yield of the base by submitting histidine to the action of putrefactive organisms. It has been shown that several of the amines thus related to amino-acids possess marked physiological activity. The activity of j8-iminazolylethylamine was discovered in the course of the investigation of ergot and its extracts by G. Barger and one of us3, who attributed this structure to a base which they obtained, and which in minute doses produced tonic contraction of the uterus. The synthetic substance, and the base produced by splitting off carbon dioxide from histidine by bacterial action or by chemical means, were found to have an identical action. Meanwhile Kutscher4 had simultaneously and independently described the isolation from ergot of a base having this action and presumably identical with that obtained by Barger and Dale. By its chemical properties this first ergot base of Kutscher was not distinguishable from 8-iminazolylethylamine; but certain apparent differences in the physiological action of the two bases, observed by Ackermann and Kutscber-5, led them to the conclusion that the ergot base, though closely related to 8-iminazolylethylamine, is not identical with it. The alleged difference in action, on the existence and cause of which our experiments throw light, was as follows: the

The physiological action of β-iminazolylethylamine

Anaphylaxis

Modification of the cardiac rhythm by histamine has been appreciated almost since the compound's isolation from ergot by Barger and Dale in 1910. The major arrhythmogenic actions of histamine are an Hi-receptor-mediated slowing of atriovenrricular (AV) conduction and H2-receptor-mediated increases in sinus rate and ventricular automaticity. These actions were elucidated by observing the salutary effects of histamine antagonists on the arrhythmias of anaphylaxis, and by administering exogenous histamine to various cardiac preparations in the presence and absence of histamine antagonists. The ability to record transmembrane action potenrial(s) (TAP) from single cells has permitted the study of electrophysiological mechanisms underlying histamine-induced arrhythmias.

Histamine and cardiac arrhythmias.

Carbenoxolone sodium has been shown to accelerate the rate of healing of both gastric and duodenal ulcers, but its overall value in duodenal ulcer is probably less because of the high rate of natural remission of duodenal ulcers. Further studies are required to decide whether it should be used prophylactically to delay ulcer recurrence. Carbenoxolone may act by affecting both the proliferative activity of gastric epithelium and the differentiation of the epithelial cells to produce mucus (as well as favourably altering the physicochemical properties of mucus and by reducing peptic activity), factors which may be relevant ot the prevention of acute gastric ulcers. Some studies suggest that carbenoxolone adds to the effect of hospitalisation and bed rest on ulcer healing. Whether bed rest confers additional benefit to the drug's ulcer healing effect in outpatients is also uncertain. There is no evidence that accelerated healing by carbenoxolone is associated with improved overall prognosis. Carbenoxolone is of greatest benefit in accelerating the healing of gastric ulcers in patients for whom hospitalisation is not possible or desirable, but it should only be used in the ambulatory patient when careful and regular observation of serum electrolytes (particularly potassium), blood pressure and weight is possible and when it is known that the patient will attend regular follow-up. Patient must be educated in the proper use of the drug. If severe mineralocorticoid-like toxic effects such as sodium and water retention and hypokalaemia appear, as they do in a variable proportion of patients but most frequently in those receiving excessive doses, carbenoxolone should be stopped and the complication treated; they respond to thiazide diuretics and potassium supplements, and probably to amiloride given in conjunction with a low dose of a thiazide diuretic. Treatment with carbenoxolone can continue with concurrent diuretic therapy in patients with less severe side-effects. Optimum therapeutic effect in gastric ulcer with the least side-effects is achieved with a dosage of 100mg carbenoxolone tablets 3 times daily for the first week followed by 50mg 3 times daily thereafter, best taken before meals. A lower dosage is desirable in the elderly and in those with liver, cardiac or renal disease. Barium meal or preferably endoscopic examinations should be performed regularly and therapy continued until the ulcer is healed. Dosage for duodenal ulcer is 50mg 4 times daily, in special positioned-release capsules. These are best taken about 20 minutes before meals.

Carbenoxolone: A Review of its Pharmacological Properties and Therapeutic Efficacy in Peptic Ulcer Disease

Histamine receptors in the cardiovascular system

Pharmacological characterization of cardiac histamine receptors: sensitivity to H1-and H2-receptor agonists and antagonists.

Histamine is released into the systemic circulation during anaphylaxis, by drugs and by surgical procedures. Studies in animal models have conclusively demonstrated that released cardiac histamine is a major mediator of arrhythmias that occur during anaphylaxis and following the administration of histamine-releasing drugs. Several lines of evidence suggest a similar arrhythmogenic role for cardiac histamine in humans: (1) The human heart is rich in histamine; (2) cardiac histamine can be readily released from human heartin vitro by therapeutic concentrations of drugs; (3) histamine has potent arrhythmogenic effects on the human heartin vitro.

Dysrhythmias caused by histamine release in guinea pig and human hearts.

This review addresses the putative role of intracellular calcium ions in the regulation of sodium transport by renal tubules. Cytoplasmic calcium-ion activities in proximal tubules of Necturus are less than 10−7 M and can be increased by lowering the electrochemical potential gradient for sodium ions across the peritubular cell membrane, or by addition of quinidine or ionomycin to peritubular fluid. Whereas lowering of the peritubular Na concentration increases cytosolic [Ca++] and [H+], ionomycin, a calcium ionophore, raises intracellular [Ca++] without decreasing pHi. The intracellular calcium-ion level is maintained by transport processes in the plasma membrane and membranes of intracellular organelles, as well as by calcium-binding proteins. Calcium ions inhibit net transport of sodium by reducing the rate of sodium entry across the luminal cell membrane. In the collecting tubule this inhibition is caused, at least in part, by an indirect reduction in the activity of the amiloride-sensitive sodium channel.

Chi-Ho Lee

Papers

Pharmacological characterization of cardiac histamine receptors: sensitivity to H1-and H2-receptor agonists and antagonists.

Dysrhythmias caused by histamine release in guinea pig and human hearts.

Intracellular calcium ions as regulators of renal tubular sodium transport.