Beta-blockade antagonism of tyramine-induced rise in blood pressure

Summary The effect -adrenoceptor blockade on the pressor response to tyramine has been investigated in 6 healthy volunteers, each submitted to an i.v. tyramine pressor test before and after 7 days of propranolol 40 mg b.d. or indenolol 60 mg o.d. Tyramine was given as i.v. boluses of 1–6 mg, alternating with saline, in a randomized, single blind fashion.Prior to treatment tyramine caused a temporary, dose-dependent increase in systolic and diastolic blood pressure, whilst the heart rate remained unaffected. Both propranolol and indenolol reduced the pressor response to tyramine, as shown by a significant increase in ED₁₅, i.e. the dose of tyramine required to increase systolic blood pressure by 15%.     

The effect of angiotensin II on haemodynamic and plasma noradrenaline responses to tyramine infusion in man

Summary Six normal volunteers were studied on four separate occasions. On each occasion they received two concomitant infusions which were either placebo/placebo, placebo/tyramine, angiotensin II/placebo or angiotensin II/tyramine. Angiotensin II infusion was given at a constant rate of 2ng/kg/min whereas the tyramine infusion consisted of 10 min increments at 1.25, 2.5, 3.75, 5, 7.5 and 10 g·kg^–1·min^–1.Tyramine infusion caused a dose dependent increase in systolic blood pressure with increases in diastolic blood pressure and plasma noradrenaline only at the highest doses. These changes were not affected by concomitant angiotensin infusion.We have therefore found no evidence to support the enhancement of haemodynamic or plasma noradrenaline responses to tyramine infusion by low dose infusion of angiotensin II in man.     

Spontaneous atrial fibrillation initiated by tyramine in canine atria with increased sympathetic nerve sprouting

Sympathetic Activation and Atrial Fibrillation. Background: Chronic left ventricular myocardial infarction (LVMI) promotes atrial and pulmonary veins (PV) sympathetic nerve sprouting. Objectives: To test the hypothesis that sympathetic stimulation with tyramine initiates atrial fibrillation (AF) by early afterdepolarization (EAD)‐mediated triggered activity at the left atrial PV (LAPV) junction. Methods: LVMI was created in 6 dogs and 6 dogs served as controls. Six to 8 weeks later the activation pattern of the isolated LAPV was optically mapped using dual voltage and intracellular Ca⁺² (Ca_i²⁺)‐sensitive epifluorescent dyes before and after tyramine (5 μM) perfusion. Results: Tyramine initiated spontaneous AF in 5 of 6 atria but none in the control group (P < 0.01). The AF was initiated by late phase 3 EAD‐mediated triggered activity that arose from the LAPV junction causing functional conduction block in LA, reentry, and AF. The AF was subsequently maintained by mixed reentrant and focal mechanisms. The EADs arose during the late phase 3, when the Ca_i²⁺ level was 64 ± 12% of the peak systolic Ca_i²⁺ transient amplitude, a property caused by tyramine's simultaneous shortening of the action potential duration and lengthening of the Ca_i²⁺ transient duration in the LVMI group but not in the control. Tyrosine hydroxylase and growth associated protein 43 positive nerve sprouts were significantly increased in the sinus node, LAA, and the LSPV in the LVMI group compared to control (P < 0.01). Conclusions: Increased atrial sympathetic nerve sprouts after LVMI makes the LAPV junction susceptible to late phase 3 EAD‐mediated triggered and AF during sympathetic stimulation with tyramine.     

Synthesis and biological evaluation of N‐acylated tyramine sulfamates containing C–F bonds as steroid sulfatase inhibitors

Steroid sulfatase (STS) is responsible for the hydrolysis of biologically inactive sulfated steroids into their active un‐sulfated forms and promotes the growth of various hormone‐dependent cancers (e.g., breast cancer). Therefore, the STS enzyme is a promising therapeutic target for the treatment of steroid‐sensitive cancers. Herein, we report the synthesis and biological evaluation of sulfamate analogs as potential STS inhibitors based on N‐acylated tyramines that contain C–F bonds. The inhibitory effects of the analogs were tested using STS isolated from human placenta. Of the analogs tested, 4‐(2‐perfluoroundecanoylaminoethyl)‐phenyl sulfamate, 5r , demonstrated the greatest inhibitory effect, with an IC₅₀ value of 2.18 μm (IC₅₀ value of 2.13 μm for coumarin‐7‐O‐sulfamate was used as a reference). These findings were supported by the results our computational analyses performed using molecular docking techniques.     

Enzymatic synthesis of isotopomers of tyramine labeled with deuterium and tritium

The combined chemical and enzymatic methods of synthesis of five isotopomers of L ‐tyrosine, L ‐Tyr, and their derivatives, i.e. corresponding isotopomers of tyramine (TA), labeled with deuterium and tritium have been reported. Two‐step synthesis consists with introduction of deuterium or tritium label into intermediate L ‐Tyr using isotope exchange followed by enzymatic decarboxylation using enzyme tyrosine decarboxylase (EC 4.1.1.25). This way five isotopomers of L ‐tyrosine, i.e. [2‐²H]‐L‐, [2‐³H]‐L‐,[2‐²H/³H]‐L‐, [3′,5′‐²H₂]‐L‐,[3′,5′‐³H₂]‐L ‐Tyr, and six isotopomers of tyramine i.e. [1S‐²H]‐, [1S‐³H]‐, [1S‐²H/³H]‐, [3′,5′‐²H₂]‐, [3′,5′‐²H₂]‐, [2′,6′‐²H₂]‐TA were obtained. Copyright © 2007 John Wiley & Sons, Ltd.     

Limited potentiation of blood pressure response to oral tyramine by brain-selective monoamine oxidase A-B inhibitor,TV-3326 in conscious rabbits

TV-3326 is a novel cholinesterase inhibitor that produces irreversible brain-selective inhibition of monoamine oxidase (MAO)-A and B and has antidepressant-like activity in rats after chronic oral administration. This study determined whether TV-3326 would cause less potentiation than other irreversible MAO-inhibitors of the blood pressure (BP) response to oral tyramine in conscious rabbits. Dose-response curves were established for the increase in BP induced by tyramine (5-200 mg/kg) administered orally via a naso-pharyngeal tube. From these, the dose that increased BP by 30 mmHg (ED(30)) was computed for each rabbit before and after oral administration of clorgyline, 1 mg/kg for one week, tranylcypromine 10 mg/kg, once, moclobemide, 20 mg/kg 3 times and TV-3326, 26 mg/kg for 2 weeks. Clorgyline, tranylcypromine and TV-3326 inhibited brain MAO-A by 90%; the former two inhibited intestinal MAO-A by 85-97% but TV-3326 had no effect. Tranylcypromine and clorgyline produced 6 and 20-fold increases in the pressor response to tyramine while TV-3326, like moclobemide, only potentiated it 2-fold. If TV-3326 is found to produce as little potentiation of the tyramine response in human subjects, it may be a potentially useful therapeutic agent for the treatment of Alzheimer's disease with depression.     

A quantitative approach to the initial clinical trial of tricyclic antidepressants: A comparison of Leo 640 and nortriptyline

Summary This report describes a phase I clinical trial of a new tricyclic imipramine analogue (Leo 640) with a hydrogen atom in one of the N-methylgroups substituted by a p-chlorobensoyl. To get an objective assessment of the effects of Leo 640 we utilized the fact that tricyclic antidepressants inhibit the uptake of tyramine (thereby blocking its indirect sympathomimetic effects) and noradrenaline into peripheral adrenergic nerves. Dose-response (systolic pressor effects) curves for tyramine (TA) were established before and during treatment with Leo 640. Adrenergic nerves from the rat iris were incubated in the patient's plasma drawn immediately before the TA tests. The inhibitory effect of the endogenous plasma level of Leo 640 (and/or its metabolites) on the uptake of³H-noradrenaline (³H-NA) in these nerves was then determined. — Leo 640 was given orally in successively increasing doses (up to 1.1–5.6 mg/kg/day) to fifteen patients with various forms of depression. The duration of treatment was usually 3–4 weeks. Leo 640 caused a blockade of TA- pressor responses. Plasma of all treated patients inhibited the uptake of³H-NA in the rat iris. The results in the two tests were reasonably well correlated (p<0.01). — The results in the TA- and rat-iris tests were compared with those obtained with nortriptyline (NT) in the same dose-range in nine other patients. In comparison with NT, Leo 640 had a more pronounced inhibitory effect on TA-responsesin vivo than of³H-NA uptake in adrenergic nervesin vitro. A possible explanation might be that Leo 640 has an -receptor blocking effect. — For both Leo 640 and NT, poor correlations were found between the doses (mg/kg) used and the objective effects, when different patients were compared, probably due to marked interindividual differences in pharmacokinetics. — It is concluded that the dose-range of Leo 640 should be similar to that of NT in terms of the effects onperipheral adrenergic neurons.A preliminary account of this paper has appeared (Siwerset al. 1969).     

An investigation of components of variance and tachyphylaxis in a placebo-controlled intravenous tyramine study

AIMS: To explore inter- and intra-volunteer variability for the dose of intravenous tyramine eliciting a 20 mmHg increase in systolic blood pressure from baseline (TYR20) and to evaluate potential tachyphylaxis. METHODS: Twelve healthy volunteers received blinded placebo-controlled ascending and descending sequences of intravenous tyramine injections on two separate occasions. The TYR20 was derived by linear interpolation, using three interventions to deal with missing data. RESULTS: Analysis of covariance (ancova) demonstrated no significant difference in TYR20 between sequences, regardless of the missing data methodology applied. Inter-volunteer variability was 2.4-3.4 times larger than within-volunteer variability. No evidence of tachyphylaxis was seen using either the sign test or generalized additive models. CONCLUSIONS: Since inter-volunteer variability was greater than intra-volunteer variability, a crossover study design would be a more efficient study design, and the descending sequence of injections could be omitted since tachyphylaxis was not demonstrated.