1. Stroke-prone spontaneously hypertensive rats (SHRsp) have been used widely to test agents putatively capable of vascular protection. These animals present an accelerated time course of hypertension and a reduced life-span. When fed a high-sodium diet from the eighth week of life, a further acceleration in blood pressure increase is obtained, and rats start to die after 5 weeks of diet as a consequence of cerebral haemorrhage. In this model, angiotensin-converting enzyme (ACE) inhibitors were repeatedly proved to prevent vascular lesions and death. Notably, this effect was independent of any hypotensive effect. On the contrary, diuretics were shown not to be equally effective. A combination of ACE inhibitors and diuretics, although known to have synergistic effects in the therapy of hypertension, has never previously been tested.
2. Our aim was to study the effects of long-term treatment with the ACE inhibitor delapril (12 mg day−1 kg−1), the thiazide-like diuretic indapamide (1 mg day−1 kg−1), and their combination (12 and 1 mg day−1 kg−1 respectively), on the survival of SHRsp rats fed a high-sodium diet from the eighth week of life onwards. The effects of the treatments on blood pressure, body weight, food and fluid intake, diuresis, proteinuria and the appearance of lesion signs and death were assessed weekly. When control rats reached 50% mortality, they were killed, together with some drug-treated rats, to compare lesions in brain and kidney. The other drug-treated rats continued treatments until 50% mortality was reached in two treatment groups.
3. All drug treatments were able to delay death significantly when compared with control rats, which reached 50% mortality after 6 weeks of salt loading. This event was preceded by a highly significant increase in proteinuria, diuresis and fluid intake that took place 3 weeks after the increase in blood pressure over the initial range. In delapril- or indapamide-treated SHRsp these changes were never seen, even when animals started to die. In the combination-treated group, a significant increase (P < 0.01) in fluid intake and diuresis, but not proteinuria, was observed from the third week of treatment onwards.
4. Treatment with delapril or indapamide did not block the progressive increase in blood pressure as observed in control animals. However, the increase in blood pressure was markedly retarded with respect to control rats. At variance with this, in combination-treated animals blood pressure levels were maintained until the end of the experiment within the 99% confidence interval initially observed in control animals.
5. Infarctual and haemorrhagic cerebral lesions were observed in 38% of control rats; no lesions were noted in brains of age-matched rats receiving a drug treatment. Kidneys from control animals presented major degenerative lesions of glomeruli and arteries, characterized by fibrinoid necrosis. This condition was absent in drug-treated animals, which presented minor signs of ischaemic lesion. Heart hypertrophy, when heart weight was expressed as a percentage of body weight, was similar in saline-, delapril- or indapamide-treated rats. At variance with this, in combination-treated animals the heart weight to body weight ratio was significantly (P < 0.01) lower than in the other groups.
6. In conclusion, the diuretic indapamide showed similar protective effects as the ACE inhibitor delapril on acute vascular lesions and survival of SHRsp. Moreover, their combination synergized in preventing heart hypertrophy consequent to long-term hypertension. This result is probably related to the enhanced diuresis and the better control of blood pressure levels selectively found in combination-treated animals.