A role for thyroid hormones in cold-induced elevation of blood pressure and cardiac hypertrophy.

The systolic blood pressures of two groups of rats that were exposed to cold (5 degrees C) for 4 weeks were elevated significantly above that of warm-acclimated controls maintained at 24 degrees C. At this time these groups were given the antithyroid drug aminotriazole in their food at 0.3 g/kg. At the same time, one group was given 15.8 micrograms thyroxine (T4)/kg body mass per day, while the second received 31.6. The doses were chosen as replacement (15.8 micrograms/kg) and twice replacement (31.8 micrograms/kg) for the rats. The results of the study revealed that both groups receiving aminotriazole and T4 had reductions in blood pressure within 1 week of initiation of treatment. Blood pressures reached control level after 5 weeks. Cardiac hypertrophy accompanying cold-induced hypertension was reduced with the lower dose of T4 and prevented with the higher dose. Serum concentrations of T4 and triiodothyronine (T3) in the two treated groups were reduced, while serum thyroid-stimulating hormone concentration and thyroid mass were increased above that of the warm-acclimated control group. This suggests that the rats were hypothyroid relative to the warm-acclimated control group. However, the treated rats grew at the same rate as nontreated, cold-exposed controls and had similar food and water intakes, a similar dipsogenic response to acute administration of isoproterenol, and similar colonic temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)