EXAGGERATED PRESSER AND CHRONOTROPIC RESPONSE TO CHRONIC HYPERINSULINEMIA IN SH VERSUS WKY RATS

Insulin resistance and the sympathetic nervous system have been sugges ted to be important factors in the blood pressure response to hyperins ulinemia. This study was designed to investigate whether the response to chronic hyperinsulinemia in 14-week-old SH rats (n = 6), which are reported to be insulin resistant and to have a hyperresponsive sympath etic nervous system, would differ from that in WKY rats (n = 5). Mean arterial pressure (MAP) and heart rate (HR) were monitored 19 h/day by computer. After a 4-day control period, insulin (1.5 mU/kg/min) and g lucose (19.3 [WKY] or 13.5 [SH] mg/kg/min) were infused intravenously for 7 days. Plasma insulin increased from 43 +/- 7 and 68 +/- 7 mU/mL to 75 +/- 4 and 91 +/- 11 mU/mL in WKY and SH rats, respectively, with no decrease in plasma glucose in either group. MAP during control ave raged 99 +/- 2 and 130 +/- 4 in WKY and SH rats, respectively, and inc reased 2 +/- 2 mm Hg above control in WKY rats and 18 +/- 4 mm Hg in S H rats on day 1 of insulin. However, after day 2 the change from contr ol was no longer significantly different between the groups and averag ed 11 +/- 2 and 15 +/- 6 mm Hg above control on day 7 in the WKY and S H rats, respectively. The change in heart rate from control was 5 +/- 5 and 21 +/- 9 beats per minute in the WKY and SH rats on day 1 of ins ulin, and this difference also diminished with time. These results dem onstrate that SH rats have a transiently exaggerated presser and chron otropic response to hyperinsulinemia relative to WKY rats.