Abstract
Summary
Thyroid activity of both male and female spontaneous hypertensive (SH) rats was studied by measurements of uptake and rate of release of 131I, urinary excretion of 131I, and thyroxine secretion rate (TSR). In addition, thyroid glands were removed at death and weighed. Radioactivity of the thyroid gland of male rats measured at intervals after administration of 131I revealed a significantly reduced maximal uptake at 21.5 hr after injection and a reduced rate of release. The mean biological half-life of 131I for the control group was 37.8 ± 3.1 (SE) hr compared to 54.8 ± 7.2 hr for hypertensives (P < 0.05). Similar results were observed for females in that biological half-life of 131I was 32.2 ± 1.2 hr compared with 84.1 ± 4.1 hr for hypertensives (P < 0.01). Urinary excretion of 131I by hypertensive rats at 24, 48, and 72 hr after injection of 131I did not differ from control in either experiment. Thyroid weight at autopsy was increased significantly above that of normotensive controls. TSR was measured indirectly in a third group of male spontaneously hypertensive and normotensive rats. TSR of control rats was estimated to be 0.97 μg T4/100 g body wt/day and 1.35 μg T4/100 g body wt/day for SH rats. The results are consistent with the suggestion that the method for measurement of TSR in hypertensive rats gives an artifactu-ally high value because TSH secretion is elevated.
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