CHRONIC EXOGENOUS HYPERINSULINEMIA WITHOUT SUGAR SUPPLEMENTATION - ACUTE SALT-SENSITIVE HYPERTENSION WITHOUT CHANGES IN RESTING BLOOD-PRESSURE

Objective: To study the effects of chronic insulin administration with out sugar supplementation on blood pressure and response to acute sali ne loading in normal rats. Design: Comparison of blood pressure, insul in and glucose levels in 24 insulin-treated and 12 control rats on reg ular rat chow (not supplemented with sugar). Methods: Sustained-releas e insulin implants (or sham implantation for the control rats) were ad ministered subcutaneously. The sustained-release insulin implant size was gradually increased. Tail-cuff systolic blood pressure, insulin an d glucose were measured twice a week for 8 weeks, after which intra-ar terial blood pressure was recorded under resting conditions And 2 h af ter saline loading in seven insulin-treated and seven control rats. Re sults: Insulin-treated rats had a 1.2- to twofold increase in insulin without hypoglycaemia, a small but significant increase in glucose lev els being found at weeks 6 and 8. When the rats were killed (week 8) t riglyceride and fructosamine levels were increased in the insulin-trea ted rats in comparison with controls. Neither tail-cuff systolic blood pressure nor resting intra-arterial blood pressure differed between t he two groups. However, acute saline loading resulted in significantly higher blood pressure in the insulin-treated rats, without altering r enal Na+ excretion. Conclusions: It is possible to produce mild hyperi nsulinaemia without hypoglycaemia by gradually increasing subcutaneous sustained-release insulin administration without sugar supplementatio n. Such hyperinsulinaemia is associated with significantly higher gluc ose, fructosamine and triglyceride levels, and normal tail-cuff and re sting intra-arterial blood pressure. Insulin may induce intolerance to acute volume loading that is not associated with Na+ retention.