Prevention of DOCA-induced hypertension in rats by chronic treatment with tryptophan

Hypertension developed within 5 weeks in uninephrectomized rats administered deoxycorticosterone acetate (DOCA, 30 mg/kg, s.c., weekly) and given isotonic saline to drink. Chronic dietary administration of tryptophan (50 g/kg food) reduced intake of saline solution and prevented the elevation of systolic blood pressure induced by treatment with DOCA alone. Treatment with tryptophan also protected against the reduction in urinary concentrating ability during a 24 h dehydration that is characteristic of DOCA-treated rats. Other tests were carried out to assess the responsiveness to the beta-adrenergic agonist, isoproterenol. The tests included measurement of drinking and heart rate following acute administration of isoproterenol. The characteristically depressed drinking response of DOCA-treated rats to acute administration of isoproterenol was returned to that of untreated controls by chronic treatment with tryptophan. However, the reduced chronotropic response of the heart of DOCA-treated rats to administration of isoproterenol was unaffected. The cardiac hypertrophy characteristic of DOCA-treatment was attenuated significantly by chronic treatment with tryptophan. These results suggest that tryptophan provides significant protection against the development of DOCA-induced hypertension, polydipsia, and cardiac hypertrophy in rats. The mechanism by which tryptophan protects is unknown and requires additional study.