Renal endothelin mechanism in altered thyroid states.
Endothelin (ET) mechanisms were studied in hyper- and hypo-thyroid states in rats. Hyperthyroidism was induced by daily administration of thyroxine (0.1 mg/kg, i.p.) for 8 weeks, while hypothyroidism was induced by daily administration of methimazole (10 mg/kg, i.p.) for 8 weeks. The concentration of endogenous ET-1 was determined in the kidneys using radioimmunoassay. Systemic hemodynamics and renal blood circulation was measured using a radioactive microsphere technique. A significant increase in systolic and diastolic blood pressure, heart rate and cardiac output was observed in hyperthyroid rats as compared to eu- and hypo-thyroid rats. Total peripheral resistance was found to be similar in eu-, hyper- and hypo-thyroid rats. The endogenous concentration of ET-1 in the kidneys was significantly lower in hyper- as compared to eu- and hypo-thyroid rats. The blood flow to the kidneys was significantly increased in hyper- as compared to eu- and hypo-thyroid rats. Infusion of ET-1 (100 ng/kg/min i.v. for 45 min) produced a significant decrease in blood flow to the kidneys of eu-, hyper- and hypo-thyroid rats. The decrease in blood flow was similar in eu-, hyper- and hypo-thyroid rats, indicating that the response of renal blood vessels to exogenous ET-1 is not altered during thyroid dysfunction. Since endogenous ET-1 is involved in the regulation of vascular tone, it may be concluded that in hyper-thyroid rats decrease in concentration of the renal ET-1 could be contributing to an increase in blood flow to the kidney.
Singh
G
G
Department of Pharmaceutics and Pharmacodynamics, University of Illinois at Chicago 60612.
Sharma
A C
AC
Thompson
E B
EB
Gulati
A
A
D000818:Animals; D016232:Endothelins / Q000032:analysis* / Q000494:pharmacology; D006439:Hemodynamics / Q000187:drug effects; D006980:Hyperthyroidism / Q000378:metabolism*; D007037:Hypothyroidism / Q000378:metabolism*; D007668:Kidney / Q000737:chemistry*; D008297:Male; D008713:Methimazole / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects; D013974:Thyroxine / Q000494:pharmacology
D016232:Endothelins; D008713:Methimazole; D013974:Thyroxine