Substrate Specificities of Phenylalanine and Tyrosine Hydroxylase: Role of Aspartate 425 of Tyrosine Hydroxylase

Our previous studies have shown that naloxone-induced morphine withdrawal increases the hypothalamic-pituitary-adrenocortical (HPA) axis activity, which is dependent on a hyperactivity of noradrenergic pathways [nucleus tractus solitarius (NTS) A2] innervating the hypothalamic paraventricular nucleus (PVN). Short-term regulation of catecholamine biosynthesis occurs through phosphorylation of tyrosine hydroxylase (TH), which enhances enzymatic activity. In the present study, the effect of morphine withdrawal on site-specific TH phosphorylation in the PVN and NTS-A2 was determined by quantitative blot immunolabeling and immunohistochemistry using phosphorylation state-specific antibodies. We show that naloxone-induced morphine withdrawal phosphorylates TH at Serine (Ser)-31 but not Ser40 in PVN and NTS-A2, which is associated with both an increase in total TH immunoreactivity in NTS-A2 and an enhanced TH activity in the PVN. In addition, we demonstrated that TH neurons phosphorylated at Ser31 coexpress c-Fos in NTS-A2. We then tested whether pharmacological inhibition of ERK activation by ERK kinase contributes to morphine withdrawal-induced phosphorylation of TH at Ser31. We show that the ability of morphine withdrawal to stimulate phosphorylation at this seryl residue is reduced by SL327, an inhibitor of ERK1/2 activation. These results suggest that morphine withdrawal increases noradrenaline turnover in the PVN, at least in part, via ERK1/2-dependent phosphorylation of TH at Ser31.

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INVOLVEMENT OF CATECHOLAMINES IN THE MYOCARDIUM OF RATS SUBMITTED TO EXPERIMENTAL MODEL OF PORTAL HYPERTENSION

ABCD Arquivos Brasileiros de Cirurgia Digestiva (São Paulo) ◽

10.1590/0102-672020180001e1383 ◽

2018 ◽

Vol 31 (3) ◽

Cited By ~ 1

Author(s):

Antonella VINHOLI ◽

Marília Da Cruz FAGUNDES ◽

Danieli Cristina PIGOZZO ◽

Fernando Bermudez KUBRUSLY ◽

Luiz Fernando KUBRUSLY ◽

...

Keyword(s):

Portal Hypertension ◽

Tyrosine Hydroxylase ◽

Portal Vein ◽

Mesenteric Artery ◽

Wistar Rats ◽

Statistical Significance ◽

Immunohistochemical Analysis ◽

Immunohistochemical Expression ◽

Marked Area

ABSTRACT Background: The role of autonomic nervous system in the development and maintenance of portal hypertension is not fully elucidated. It is known that the gene expression of norepinephrine in the superior mesenteric artery varies with time, and it may contribute for splanchnic vasodilation and its consequent hemodynamic repercussions. It is still not known exactly how the adrenergic expression behaves at the heart level in the initial stages of this process. Aim: To evaluate the immunohistochemical expression of the enzyme tyrosine hydroxylase (tyrosine 3-monooxygenase), involved in the synthesis of norepinephrine, in the myocardium of rats submitted to partial ligation of the portal vein. Methods: Twenty-four Wistar rats were divided into two groups: Sham Operated and Portal Hypertension. The partial ligation was performed in the Portal Hypertension group, and after 1/6/24 h and 3/5/14 days the animals were euthanized. Immunohistochemical analysis was performed to quantify the expression of the stained enzyme using the ImageJ program. Results: The Portal Hypertension group expressed percentages between 4.6-6% of the marked area, while the Sham Operated group varied between 4-5%. Although there was no statistical significance, the percentage stained in the Portal Hypertension group followed an increasing pattern in the first 6 h and a decreasing pattern after 24 h, which was not observed in the Sham Operated group. Conclusion: The expression of noradrenaline in rat myocardium during the first two weeks after partial ligation of the portal vein, with tyrosine hydroxylase as marker, did not show differences between groups over time.

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