Chronic exogenous hyperinsulinaemia accelerates the development of hypertension in spontaneously hypertensive rats

1. An association between hyperinsulinaemia, insulin resistance and hypertension was previously described in spontaneously hypertensive rats (SHR). We therefore tested whether chronic exogenous hyperinsulinaemia, which did not affect blood pressure of normotensive rats, may aggravate hypertension in young SHR. 2. Insulin was administered for 4 weeks by a graded increase of a sustained release insulin implant, without carbohydrate supplementation. 3. Initial bodyweight of seven SHR and five sham-implanted control SHR, aged 6-8 weeks, was not different between the groups or by week 4. 4. Glucose levels decreased in the treated rats [2-way ANOVA F(1:10) = 18.7. P < 0.005] and were 7.3 +/- 0.1 mmol/L in the controls and 4.4 +/- 0.7 mmol/L in the treated SHR, respectively. Insulin levels were comparable at baseline and increased to 1002 +/- 978 pmol/L in treated rats at week 4 while remaining 270 +/- 78 pmol/L in the controls [F(1:10) = 6.1, P < 0.05]. The systolic blood pressure (tail-cuff) was significantly increased in insulin treated SHR in weeks 1-3[F(1:10) = 5.1, P < 0.05] though it was comparable at baseline and week 4. 5. In the presence of a hypertensive predisposition, chronic exogenous hyperinsulinaemia accelerates the time course of the development of hypertension without affecting its severity.