Abstract:
Systolic blood pressures, basal metabolic rates, and circulating catecholamine levels were determined for hyperthyroid (TRX), hypothyroid (PTU), and euthyroid control (CON) rats. All three measurements were elevated in TXX animals, while PTU rats were determined to have decreased measurements when compared with CON and TRX rats.
Animals were sacrificed by either cervical dislocation or pentobarbital injection followed by
thoracic opening to test for sacrifice differences. Three aortic rings from each rat were
mounted in environmentally-controlled tissue baths and contracted with different concentrations (10 nM, 100 nM, and 1 mM) of phenylephrine (PE), an alpha-1 adrenoreceptor agonist. At steady state, methylene blue (MB) (10 mM), an endotheliumderived
nitric oxide (EDNO) inhibitor, was added and rings were allowed to contract further. At steady state, a high PI3 dose (10 mM) was added to produce maximum contraction. Irrespective of the sacrifice method, the basal release of EDNO as a percent of
the maximum force generated, was PTU>CON>TRX, while the mg of force unmasked by MB was not different. The trend in mg of force produced by PE was TRX>CON>PTU regardless of the initial PE concentration. As the concentration of the inital PE dose was increased, the percent of the total PE plus ME3 response that was due to MB alone decreased in CON rats. Sacrifice with pentobarbital followed by thoracic opening
eliminated the difference between TRX and CON expressed in animals sacrificed by cervical dislocation, while the relationship between CON and PTU was unchanged. Just as thyropathology differentially altered systolic blood pressure, basal metabolic rare, and circulating catecholamine levels, the basal release of EDNO in rat aorta was found to be dependent upon the thyroid state of the animal and the initial agonist-induced tone.
