Prevention of DOCA-induced hypertension in rats by chronic treatment with tryptophan

AHR canonical pathway: in vivo findings to support novel antihypertensive strategies

Essential hypertension (HTN) is a disease where genetic and environmental factors interact to produce a high prevalent set of almost indistinguishable phenotypes. The weak definition of what is under the umbrella of HTN is a consequence of the lack of knowledge on the players involved in environment-gene interaction and their impact on blood pressure (BP) and mechanisms. The disclosure of these mechanisms that sense and (mal)adapt to toxic-environmental stimuli might at least determine some phenotypes of essential HTN and will have important therapeutic implications. In the present manuscript, we looked closer to the environmental sensor aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor involved in cardiovascular physiology, but better known by its involvement in biotransformation of xenobiotics through its canonical pathway. This review aims to disclose the contribution of the AHR-canonical pathway to HTN. For better mirror the complexity of the mechanisms involved in BP regulation, we privileged evidence from in vivo studies. Here we ascertained the level of available evidence and a comprehensive characterization of the AHR-related phenotype of HTN. We reviewed clinical and rodent studies on AHR-HTN genetic association and on AHR ligands and their impact on BP. We concluded that AHR is a druggable mechanistic linker of environmental exposure to HTN. We conclude that is worth to investigate the canonical pathway of AHR and the expression/polymorphisms of its related genes and/or other biomarkers (e.g. tryptophan-related ligands), in order to identify patients that may benefit from an AHR-centered antihypertensive treatment.

Deoxycorticosterone acetate (DOCA)-induced sodium appetite in group-housed mice

Research investigating sodium hunger in mice has failed to produce evidence that mineralocorticoids are involved in sodium appetite. In our own laboratory, doses of deoxycorticosterone acetate (DOCA) ranging from 1 mg/kg to 20 mg/kg have failed to induce a sodium appetite. In rats, glucocorticoids have been effective in potentiating mineralocorticoid-induced sodium appetite. Recent research has suggested that the mouse, like the rat, does possess mineralocorticoid sensitivity for sodium hunger but, unlike the rat, has a strong dependency on an accompanying glucocorticoid action. The present experiment was conducted to study the effects of DOCA on sodium appetite in mice under housing conditions that attempted to eliminate the reduction of corticosterone associated with social isolation. Therefore, male GHSC mice were group-housed and were tested within two counterbalanced treatment conditions. One condition consisted of an injection of 10 mg/kg DOCA on 2 consecutive days, and the other condition consisted of an injection of the vehicle on 2 consecutive days. Group-housed male GHSC mice showed a significantly larger amount of NaCl consumption after injections of DOCA than after injections of the vehicle.

Effect of dietary tryptophan on the development of hypertension in the Dahl salt-sensitive rat

Dahl salt-sensitive rats are inbred on the basis of their tendency to develop hypertension when placed on a high salt diet. The present study investigated the effects of chronic dietary tryptophan (trp) at 50 g/kg food on the development of hypertension in these animals under conditions of both normal and elevated dietary salt. Dietary trp attenuated the development of hypertension in inbred Dahl salt-sensitive (DS/JR) rats and had no effect upon the patterns of development of systolic blood pressures in the normotensive controls, the inbred Dahl salt-resistant (DR/JR) rat and the outbred parental Sprague Dawley (SD) rat. Cardiac hypertrophy, which is associated with Dahl salt-induced hypertension, was blocked by the high trp diet. Further work will be necessary to elucidate the mechanisms by which dietary trp protected against the development of hypertension and cardiac hypertrophy in DS/JR rats.

Effect of chronic dietary treatment with 1-tryptophan on spontaneous salt appetite of rats

Chronic dietary treatment with 1-tryptophan (2.5 and 5.0% in food) reduced the exaggerated spontaneous NaCl intake induced by deoxycorticosterone acetate (DOCA) in rats. In the absence of DOCA, chronic (4-week) dietary treatment with 1-tryptophan (5.0% in food) failed to affect significantly spontaneous NaCl intake. In addition, treatment with tryptophan in the absence of DOCA failed to affect significantly systolic blood pressure, plasma renin activity, plasma aldosterone concentration, and the weights of the heart, kidneys, adrenals, and thyroid gland. It also failed to affect the specific binding of [125I]-Ang II to neuronal membranes isolated from the diencephalon of the rats. However, the contents of both serotonin and 5-hydroxyindoleacetic acid in the lower brain stem were increased significantly by chronic treatment with tryptophan. These results suggest that the effect of chronic treatment with tryptophan to reduce the salt appetite of DOCA-treated rats is a specific effect of this amino acid under these conditions and may be related to the ability of tryptophan to prevent the upregulation of specific Ang II receptors induced by DOCA.