Excessive thyrotropin concentrations in the circulation of the spontaneously hypertensive rat

Thyroid funct-on in SHR was compared to that of inbred normotensive Wistar rats from Kyoto, and random bred Wistar rats from the United States. A marked increase in circulating thyrotropin concentration was found in SHR compared to controls. Serum thyroxine and T3 concentrations relative to controls, however, were variable and the concentrations in male and female SHR relative to Kyoto controls did not correspond with each other. No ready explanation for the circulating excess of thyrotropin, with mimimal increase in T4 and T3 concentrations, is available.