Role of the renin-angiotensin system in the development of thyroxine-induced hypertension.
OBJECTIVE
We evaluated the influence of chronic blockade of the renin-angiotensin system on hypertension induced by long-term thyroxin (T4) administration. To this end, we determined the effects of chronic treatment with captopril on blood pressure, cardiac hypertrophy and other renal and metabolic variables of hypertensive hyperthyroid rats.


METHODS
T4 was administered s.c. at 0.38 mumol/kg per day and captopril was given in the drinking water (1.38 mmol/l). Both treatments were maintained for 6 weeks. Control rats received tap water. After the treatment period, the rats were placed in metabolic cages. Later, blood pressure was measured in conscious rats by intra-arterial determination.


RESULTS
T4-treated rats showed an increased mean arterial pressure (MAP) whereas, in rats treated with T4 plus captopril, MAP was similar to that of the control group. Captopril did not affect the increased heart rate or ventricular weight/body weight ratio of hyperthyroid rats, but it improved the reduced creatinine clearance of these animals.


CONCLUSIONS
The elevation in blood pressure produced by long-term T4 administration was prevented by chronic blockade of the renin-angiotensin system. Captopril improved the renal function of hyperthyroid rats, but did not affect the relative cardiac hypertrophy of these animals.
García del Rio
C
C
Departamento de Fisiologia y Bioestadística, Facultade de Medicina de Granada, U. Experimental Virgen de las Nieves, Granada, Spain.
Moreno
M R
MR
Osuna
A
A
de Dios Luna
J
J
García-Estañ
J
J
Vargas
F
F
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001769:Blood / Q000187:drug effects / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D002216:Captopril / Q000494:pharmacology; D006339:Heart Rate; D006973:Hypertension / Q000139:chemically induced* / Q000473:pathology / Q000503:physiopathology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D012084:Renin-Angiotensin System / Q000502:physiology*; D013974:Thyroxine; D014556:Urine / Q000737:chemistry
D000959:Antihypertensive Agents; D002216:Captopril; D013974:Thyroxine