Abstract
We tested the hypothesis that neovascularization of embryonic hearts is independent of thyroid hormones. To dissociate the effects of hemodynamic load from the direct influence of thyroid hormones on coronary neovascularization, we grafted avascular, gestational day 12 rat hearts to the anterior eye chamber of adult rats receiving daily injections of thyroxine (T4; 0.25 mg/kg sc), propylthiouracil (PTU; 10 mg/kg ip), or saline (control). After 21 days, grafts were perfuse fixed and prepared for transmission electron microscopy. Neither T4 nor PTU treatment affected size or mass of the unloaded graft, or the volume densities of vessels, myocytes, or the extracellular matrix, which were determined by standard point-counting techniques. Thus neither exogenous administration of T4 nor the induction of hypothyroidism in host rats produced a significant effect on the growth or vascularity of the unloaded hearts. We conclude that vascular growth in embryonic rat hearts cultured in oculo is independent of thyroid hormones and that the angiogenic effect of thyroid hormones in loaded hearts is a consequence of increased work-related events.
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