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CHRONIC SALT LOADING AND CARDIOVASCULAR‐ASSOCIATED CHANGES IN EXPERIMENTAL DIABETES IN RATS

1 High‐sodium intake may increase blood pressure and diabetes is a salt‐sensitive condition. In the present study, we evaluated cardiovascular changes and their neurohumoral mechanisms in streptozotocin (STZ)‐diabetic rats that underwent chronic salt loading. 2 We studied male Wistar rats (150–280 g) 14 days after the injection of either STZ (50 mg/kg, i.v.; D; n = 18) or citrate buffer (C; n = 16). After the induction of diabetes, animals were maintained for 14 days with free access to standard rat chow and tap water (C and D groups) or 1% NaCl solution (C‐S and D‐S groups). We conducted two experiments. Experiment 1 consisted of basal arterial pressure (AP) measurement (30 min) followed by the evaluation of AP responsiveness to phenylephrine and sodium nitroprusside. One day later, with the rats anaesthetized, a blood sample was collected to test for glycaemia, plasma angiotensin‐converting enzyme (ACE) activity and renin. Kidneys were removed for the determination of tissue ACE activity. Experiment 2 comprised 24 h urine collection followed by 3 days of cardiovascular records, which consisted of a 30 min basal AP measurement, followed by injection of blockers of the vasopressin system, the renin–angiotensin system (RAS) and the sympathetic system. Basal haemodynamic data, baroreflex evaluation and AP responses to blockade of the vasopressin system with vasopressin V1 receptor antagonist (aAVP; 10 mg/kg, i.v.), the RAS by losartan (10 mg/kg, i.v.) and the sympathetic system by hexamethonium (20 mg/kg, i.v.) were determined. 3 Glycaemia was similar between C and C‐S (P = 0.612) and between D and D‐S (P = 0.552), but higher in diabetic compared with non‐diabetic rats (P < 0.0001). The D‐S rats had an increment of 24% in mean AP compared with D (120 ± 4 vs 97 ± 2 mmHg, respectively; P = 0.0001), which was not seen in C‐S compared with C rats. A positive association was noted between urinary sodium and mean AP (r = 0.37; P = 0.04). Plasma renin was undetectable in D‐S rats. The response to acute drug blockade of vasopressin and the RAS was similar among groups, but hexamethonium elicited a more pronounced decrease in AP in D‐S compared with D rats (P = 0.001). 4 The main neurohumoral mechanisms of salt‐induced cardiovascular changes in STZ‐diabetes are increased sodium and vascular sensitivity to adrenergic stimuli, which act in combination to produce a final result of higher AP levels, a finding not observed in control rats. Baroreflex derangements induced by diabetes were not affected by salt overload.