Characterization of myocardial hypertrophy in prehypertensive spontaneously hypertensive rats: interaction between adrenergic and nitrosative pathways.
OBJECTIVE
Left ventricular hypertrophy in human and experimental hypertension is not always associated with pressure overload but seems to precede an increase in blood pressure. In this study, performed in male 5-week-old prehypertensive spontaneously hypertensive rats (SHR; n = 65) and age-matched Wistar-Kyoto rats (n = 56), the relationship between myocardial structure and activation of the adrenergic and nitric oxide systems was evaluated.


RESULTS
Body weight, blood pressure and heart rate were similar in both groups. A higher left ventricle/body weight ratio was found in SHR, as a result of greater mononuclear (+47%) and binuclear (+43%) myocyte volumes, without changes in interstitial collagen. Both adrenergic and nitric oxide pathways were activated in SHR, as expressed by higher myocardial norepinephrine content, tyrosine hydroxylase activity, myocardial nitric oxide synthase 3 expression and protein nitration, indicating greater peroxynitrite (ONOO) generation from nitric oxide and superoxide. No difference was measured in nitric oxide synthase 1 expression, whereas nitric oxide synthase 2 was undetectable. A positive correlation between myocardial tyrosine hydroxylase activity and protein nitration was observed in SHR (r = 0.328; P < 0.01). Early treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl, from the third to the fifth week of age, reduced ONOO generation, protein nitration and sympathetic activation in SHR without changes in myocardial structure.


CONCLUSIONS
In prehypertensive SHR, left ventricular hypertrophy is associated with adrenergic and nitrosative imbalance. Early superoxide dismutase mimetic treatment in SHR effectively reduces higher myocardial ONOO generation, sympathetic activation, and heart rate without affecting the development of myocardial hypertrophy.
Cabassi
Aderville
A
Laboratory of Hypertension, Department of Internal Medicine, Nephrology and Health Sciences, University of Parma, Parma, Italy. cabassia@unipr.it
Dancelli
Simona
S
Pattoneri
Paolo
P
Tirabassi
Giovanni
G
Quartieri
Fabio
F
Moschini
Luigi
L
Cavazzini
Stefania
S
Maestri
Roberta
R
Lagrasta
Costanza
C
Graiani
Gallia
G
Corradi
Domenico
D
Parenti
Elisabetta
E
Tedeschi
Stefano
S
Cremaschi
Elena
E
Coghi
Pietro
P
Vinci
Simonetta
S
Fiaccadori
Enrico
E
Borghetti
Alberico
A
D000818:Animals; D006332:Cardiomegaly / Q000378:metabolism / Q000503:physiopathology*; D002395:Catecholamines / Q000378:metabolism; D006973:Hypertension / Q000378:metabolism / Q000503:physiopathology*; D007150:Immunohistochemistry; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D015538:Nitrosation; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D011941:Receptors, Adrenergic / Q000378:metabolism*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D002395:Catecholamines; D011941:Receptors, Adrenergic; D019001:Nitric Oxide Synthase; D014446:Tyrosine 3-Monooxygenase