STREPTOZOTOCIN DIABETES MODIFIES ARTERIAL-PRESSURE AND BAROREFLEX SENSITIVITY IN RATS

Although an increased prevalence of hypertension is associated with in sulin-dependent diabetes, little is known about the effect of streptoz otocin (STZ) diabetes on arterial pressure (AP) regulation in rats. Ch anges in AP induced by STZ, as well as associated factors in blood pre ssure-regulation such as baroreflex sensitivity, plasma renin activity (PRA) plasma glucose and insulin levels and endothelium participation , were studied in male Wistar rats weighing 287 +/- 10 g. The same sev en 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 inhib ition of nitric oxide synthesis with NG-nitro-L arginine methyl ester (L-NAME, 10 mg/kg iv bolus plus infusion at 20 mg kg(-1) h(-1)) on AP was evaluated in another set of rats (6 normal and 5 submitted to STZ treatment). STZ induced hyperglycemia (306 +/- 19 mg/dl), a reduction in mean arterial pressure (MAP, from 116 +/- 5 to 101 +/- 4 mmHg) and no changes in HR (320 +/- 10 vs 298 +/- 14 bpm). The tachycardic respo nse to arterial pressure decreases was impaired (-2.29 +/- 0.5 vs -4.5 +/- 0.7 bpm/mmHg, in control) while the bradycardic response to arter ial pressure increases was unchanged. Pressure responsiveness to pheny lephrine was impaired after STZ (3.78 +/- 0.4 vs 6.73 +/- 0.8 mmHg mu U-1 ml(-1), in control). Plasma insulin (6.7 +/- 0.6 vs 5.3 +/- 1.2 mu U/ml) and PRA (6.8 +/- 0.8 vs 7.9 +/- 1.6 ng ANG I ml(-1) h(-1)) were similar before and after STZ. L-NAME induced similar increases in nor mal (+44.67 +/- 0.41 mmHg) and STZ-diabetic rats (+46.50 +/- 15 mmHg). These data show that 5-day STZ diabetes decreases AP and induces impa irment of baroreflex sensitivity, These changes do not seem to be rela ted to plasma insulin levels, PRA or nitric oxide synthesis.