Chronic exogenous hyperinsulinaemia without sugar supplementation: acute salt-sensitive hypertension without changes in resting blood pressure.
OBJECTIVE
To study the effects of chronic insulin administration without sugar supplementation on blood pressure and response to acute saline loading in normal rats.


METHODS
Comparison of blood pressure, insulin and glucose levels in 24 insulin-treated and 12 control rats on regular rat chow (not supplemented with sugar).


METHODS
Sustained-release insulin implants (or sham implantation for the control rats) were administered subcutaneously. The sustained-release insulin implant size was gradually increased. Tail-cuff systolic blood pressure, insulin and glucose were measured twice a week for 8 weeks, after which intra-arterial blood pressure was recorded under resting conditions and 2 h after saline loading in seven insulin-treated and seven control rats.


RESULTS
Insulin-treated rats had a 1.2- to twofold increase in insulin without hypoglycaemia, a small but significant increase in glucose levels being found at weeks 6 and 8. When the rats were killed (week 8) triglyceride and fructosamine levels were increased in the insulin-treated rats in comparison with controls. Neither tail-cuff systolic blood pressure nor resting intra-arterial blood pressure differed between the two groups. However, acute saline loading resulted in significantly higher blood pressure in the insulin-treated rats, without altering renal Na+ excretion.


CONCLUSIONS
It is possible to produce mild hyperinsulinaemia without hypoglycaemia by gradually increasing subcutaneous sustained-release insulin administration without sugar supplementation. Such hyperinsulinaemia is associated with significantly higher glucose, fructosamine and triglyceride levels, and normal tail-cuff and resting intra-arterial blood pressure. Insulin may induce intolerance to acute volume loading that is not associated with Na+ retention.
Bursztyn
M
M
Department of Medicine, Hadassah University Hospital, Mount Scopus, Jerusalem, Israel.
Ben-Ishay
D
D
Mekler
J
J
Raz
I
I
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002241:Carbohydrates / Q000494:pharmacology; D004343:Drug Implants; D006973:Hypertension / Q000503:physiopathology; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012146:Rest; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
D002241:Carbohydrates; D004343:Drug Implants; D007328:Insulin; D012965:Sodium Chloride