In hypothyroid patients, altered microvascular structure and function may affect 
mood and cognitive function. We hypothesized that adult male hypothyroid rats 
will have significantly lower forebrain blood vessel densities (BVD) than 
euthyroid rats and that treatment with 3,5-diiothyroprionic acid (DITPA) (a 
thyroid hormone analog) or thyroxine (T(4)) will normalize BVDs. The euthyroid 
group received no thyroidectomy or treatment. The other three groups received 
thyroidectomies and pellets. The hypothyroid group received a placebo pellet, 
the DITPA group received an 80-mg DITPA-containing pellet, and the T(4) group 
received a 5.2-mg T(4) slow-release pellet for 6 wk. Body weights, cardiac 
function, and body temperatures were measured. A monoclonal antiplatelet 
endothelial cell adhesion antibody was used to visualize blood vessels. The 
euthyroid group averaged body weights of 548 +/- 54 g, while the hypothyroid 
group averaged a body weight of 332 +/- 19 g (P value < 0.001). Relative to the 
euthyroid group, the DITPA-treated group was significantly lighter (P value < 
0.05), while the T(4)-treated group was comparable in body weight to the 
euthyroid group. The same trends were seen with body temperature and cardiac 
function with the largest difference between the euthyroid and hypothyroid 
groups. BVD in the euthyroid group was 147 +/- 12 blood vessels/mm(2) and in 
hypothyroid group 69 +/- 5 blood vessels/mm(2) (P = 0.013) but similar among the 
euthyroid, DITPA, and T(4) groups. These results show that hypothyroidism 
decreased BVD in adult rat forebrain regions. Moreover, DITPA and T(4) were 
efficacious in preventing effects of hypothyroidism on cardiac function and BVD.