Streptozotocin diabetes modifies arterial pressure and baroreflex sensitivity in rats

RESUMO

Although an increased prevalence of hypertension is associated with insulin-dependent diabetes, little is known about the effect of streptozotocin (STZ) diabetes on arterial pressure (AP) regulation in rats. Changes in AP induced by STZ, as well as associated factors in blood pressure regulation such as baroreflex sensitivity, plasma ren activity (PRA), plasma glucose and insulin levels and endothelium participation, were studied in male Wistar rats weighing 287 + or - 10 g. The same seven conscious rats were used for all measurements before and after STZ diabetes. AP pulses were stored on a videotape recorder and processed by a data acquisition system. Baroreflex sensitivity was evaluated by measuring heart rate (HR) changes induced by AP variations produced by phenylephrine and sodium nitroprusside injection. The effect of inhibition of nitric oxide synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg iv bolus plus infusion at 20 mg kg-1h-1) on AP was evaluated in another set of rats (6 normal and 5 submitted to STZ treatment). STZ induced hyperglycemia (306 + or - 19 mg/dl), a reduction in mean arterial pressure (MAP, from 116 + or - 5 to 101 + or - 4 mmHg) and no changes in HR (320 + or - 10 vs 298 + or - 14 bpm). The tachycardic response to arterial pressure decreases was impaired (-2.29 + - 0.5 vs -4.5 + or - 0.7 bpm/mmHg, in control) while the bradycardic response to arterial pressure increases was unchanged. Pressure responsiveness to phenylephrine was impaired after STZ (3.78 + or - 0.4 vs 6.73 + or - 0.8 mmHg µU-1 ml-1, in control). Plasma insulin (6.7 + or - 0.6 vs 5.3 + - 1.2 µU/ml) and PRA (6.8 + or - 0.8 vs 7.9 + or - 1.6 ng ANGI ml-1h-1) were similar before and after STZ. L-NAME induced similar increases in normal (+44.67 + or - 0.41 mmHg) and STZ-diatetic rats (+46.50 + or - 15 mmHg). These data show that 5-day STZ diabetes decreases AP and induces impairment of baroreflex sensitivity. These changes do not seem to be related to plasma insulin levels, PRA or nitric oxid synthesis: