OBJECTIVE: To study the quantitative changes in intramyocardial blood vessels in rats in whom nitric oxide synthesis was inhibited. METHODS: Four groups of 10 rats were studied: control (C25 and C40) and L-NAME (L25 and L40). The animals L25 and L40 received L-NAME in the dosage of 50mg/kg/day for 25 and 40 days, respectively. On days 26 and 41 the animals in groups 25 and 40 were sacrificed. Analysis of the myocardium was performed using light microscopy and stereology. RESULTS: Arterial blood pressure and heart weight increased 74.5 and 57.8% after 25 days and 90.2 and 34.6% after 40 days, respectively. Comparing the L-NAME rats with the respective controls revealed that vessel volume density decreased 31.3% after 40 days, and the vessel length-density decreased 53.5% after 25 days and 25.7% after 40 days. The mean cross-sectional area of the vessels showed an important reduction of 154.6% after 25 days. The intramyocardial vessels decreased significantly in length- density in the L-NAME animals. The mean cross-sectional area of the vessels, which normally increases during heart growth between 25 and 40 days, showed a precocious increase by the 25th day in the L-NAME rats. This suggests an increase of the size of the heart, including blood vessels. CONCLUSION: The inhibition of the NO synthesis provokes rarefaction in the intramyocardial vessels that progresses with the time of administration of L-NAME.

OBJETIVO: Estudar mudanças estruturais do miocárdio decorrentes do tempo de inibição da síntese do óxido nítrico. MÉTODOS: Estudaram-se 4 grupos de 10 ratos: controle e L-Name (50mg/kg/dia) com 25 e 40 dias de experimentação. Os animais foram sacrificados e os corações processados tecnicamente para estudo em microscopia de luz, onde cortes corados pelo picro-sirius foram estudados com e sem luz polarizada para análise do colágeno do interstício cardíaco. Determinaram-se densidades de volume de miócitos (Vv[m]) e interstício cardíaco (Vv[int]), densidade numérica de miócitos (Nv[m]) e área transversal dos miócitos (A[m]). RESULTADOS: Compararam-se os animais L-Name com os respectivos controles. Nos L-Name a pressão da cauda aumentou 74,5 e 90,2% aos 25 e 40 dias, respectivamente. O peso cardíaco aumentou 50% e 28% aos 25 e 40 dias, respectivamente. O miocárdio dos animais L-Name apresentou hipertrofia de miócitos com aumento da A(m), fibrose perivascular e intersticial, espessamento das túnicas íntima e média das artérias intramiocárdicas. Aos 40 dias diminuíram Vv(m) e Nv(m) e aumentou Vv(int). CONCLUSÃO: Inibição da síntese do óxido nítrico provoca modificações miocárdicas que progridem com o tempo de administração de L-Name. A estereologia é uma metodologia útil para determinar e avaliar as modificações miocárdicas decorrentes deste modelo experimental de hipertensão arterial.

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 (50mg/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 stained 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). CONCLUSION: 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.