Antihypertension and anti-cardiovascular remodeling by phenylalanine in spontaneously hypertensive rats: effectiveness and mechanisms.
OBJECTIVE
To investigate mechanisms of anti-hypertension and anti-cardiovascular remodeling by phenylalanine (phe) in spontaneously hypertensive rats (SHRs).


METHODS
The comparison of blood pressure (BP) increment with the ages and cardiovascular changes of SHRs was made between the 3% phe-intervented group (SHR-phe) and the control SHRs group. Detection of the structural changes with the VIDAS digital vedio-frequency processing technique and light and electron microscopy were made. The cell growth and proliferation of cultured smooth muscle cells (CSMCs) of the thoracic aortas or myocardial fibroblasts were evaluated by measuring the 3H-thymidine counts per minute (cpm) incorporated into the new synthesized desoxyribonucleic acid (DNA) and determining the cell number with the crystal violet stain technique. The Ca2+ influx was measured in counts/min of 45CaCl2 after incubating it with 5 different concentrations of phenylalanine and the intracellular [Ca2+]i by Fura-II/Am indicator. The total messenger ribonucleic acid (mRNA) of the myocardium was extracted and Northern blot analysis was performed with the probe collagen alpha 2 (I) cDNA. The tyrosine hydroxylase (TH) activity was measured by high-performance liquid chromatography (HPLC) with electrochemical detector after having reacted with its substrate tyrosine and other reagents. The catecholamine contents in brain homogenat were detected by HPLC method. The comparison of pharmacokinetics of phenylalanine among SHR-phe, SHRs and control Wistar Kyoto (WKY) rats was made after intravenous injection of 3H-L-phe (1 ml/kg) by PK-GRAPH Program for kinetic calculation. The 3H-L-phe uptake by CSMCs after incubating for definite intervals was also detected and compared.


RESULTS
Phenylalanine could prevent the increase of BP with ages and the heart weight (heart/body weight index). The aortic media thickness and the collagen content in the myocardium were decreased significantly in SHR-phe. Whereas the dearranged cardiovascular structure was much improved. The mechanisms might be direct and specific inhibition of the DNA synthesis and proliferation of cardiovascular cells which may be related to the inhibition of collagen alpha 2(I) cDNA, c-fos and c-myc expression. Other mechanisms may include decrease of intracellular [Ca2+]i and an inhibition of central sympathetic activity due to the results of higher TH activity in the caudate nucleus and higher adrenaline content in the posterior hypothalamus. Besides, partial recovery of phenylalanine metabolic aberrants existed in SHRs seems to be another possibility for its effectiveness.


CONCLUSIONS
Phenylalanine intervention could exert a definite anti-hypertension and anti-cardiovascular remodeling effects on SHRs like seen in human essential hypertension. Its mechanisms might be related to direct inhibition of growth in the cardiovascular cells, decrease of central sympathetic activity, the reverse of the exhibited phenylalanine metabolic aberrants in SHRs, and a decrement of intracellular [Ca2+]i.
Zhao
G
G
Ruijin Hospital, Shanghai Second Medical University, Shanghai Institute of Hypertension, Shanghai 200025, China.
Li
Z
Z
Gu
T
T
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001013:Aorta, Thoracic / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D001808:Blood Vessels / Q000187:drug effects / Q000473:pathology; D001835:Body Weight / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002319:Cardiovascular System / Q000187:drug effects* / Q000503:physiopathology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006973:Hypertension / Q000503:physiopathology*; D008854:Microscopy, Electron; D008928:Mitochondria / Q000187:drug effects / Q000648:ultrastructure; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009206:Myocardium / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D009929:Organ Size / Q000187:drug effects; D010649:Phenylalanine / Q000494:pharmacology*; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY
D000959:Antihypertensive Agents; D012333:RNA, Messenger; D010649:Phenylalanine; D003094:Collagen; D004247:DNA; D002118:Calcium