Stereology of the myocardium in hypertensive rats. Differences in relation to the time of inhibition of nitric oxide synthesis

Structural changes in the myocardium following inhibition of nitric oxide synthesis were studied quantitatively within two different periods. Four groups of 10 rats were studied: control and L-NAME (NG-nitro-methyl-ester-L-arginine) groups for 25 and for 40 days. L-NAME was administered at 50 mg/kg per day in the drinking water. On the 26th and 41st days, the hearts were examined. Volume densities of myocytes (Vv[m]), cardiac interstitium (Vv[int], numerical density of myocytes (Nv[m]) and mean cross-sectional area of the myocytes (A[m]) were determined. Comparing the L-NAME animals with their respective controls showed the arterial pressure (AP) and the heart weight (HW) to be increased in the L-NAME animals. At 25 days, and more obviously at 40 days, the myocytes were hypertrophied with increase of myofibrils (A[m], greater in L-NAME rats). There were some areas with ischaemic lesions, inflammatory infiltrates and perivascular and interstitial fibrosis. The intramyocardial arteries had a thick tunica media and tunica intima. At 25 days the myocardium showed no stereological difference between L-NAME and controls, but by 40 days there was decreased Vv[m] and Nv[m] and increased Vv[int] in the exposed group. Inhibition of NO synthesis provoked a time progressive myocardial change, quantified by stereology.

[Morphology and stereology of the myocardium in hypertensive rats. Correlation with the time of nitric oxide synthesis inhibition]

PURPOSE

To study structural changes of the myocardium in relation to the time of nitric oxide synthesis inhibition.

METHODS

Four groups of 10 rats each were studied: 2 control groups and 2 groups with administration of L-Name (50 mg/kg/day), one during 25 days and the other during 40 days. The animals were then sacrificed and the hearts were prepared for study in light microscopy, where sections strained by picro-sirius were studied with and without polarized light for analysis of the cardiac interstitium collagen. Volume densities of myocytes (Vv[m]) and interstitium (Vv[int]), the numerical density of myocytes (Nv[m]) and the mean cross-sectional area of myocytes were (A[m]) also determined.

RESULTS

The L-Name animals were compared with the respective controls. In the L-Name rats, the tail arterial pressure increased 74.5 and 90.2% in the 25 days group and in the 40 days group, respectively. The heart weight increased 50% in the 25 days group and 28.6% in the 40 days group. The myocardium of the L-Name animals presented myocyte hypertrophy with increased A(m), perivascular and interstitial fibrosis, thickness of the tunica intima and tunica media of the intramyocardial arteries. In the 40 days group the L-Name animals had decreased Vv(m) and Nv(m) and increased Vv(int).

CONCLUSIONS

Inhibition of nitric oxide synthesis provokes myocardial changes that progress with the time of L-Name administration. The stereology is useful to determine and to evaluate the myocardial changes in this model of arterial hypertension.