In adult female hamsters hypothyroidism stimulates D1 receptor-mediated breathing without altering D1 receptor expression

Hypothyroidism affects cardiopulmonary regulation and function of dopaminergic receptors. Here we evaluated effects of 5 months of hypothyroidism on dopamine D1 receptor modulation of breathing in female hamsters using a D1 receptor antagonist SCH 23390. Euthyroid hamsters (EH) served as controls. Results indicated that hypothyroid female hamsters (HH) exhibited decreased body weights and minute ventilation (V_E) following hypoxia due to decreased frequency of breathing (F). Moreover, SCH 23390 administration in HH increased V_E by increasing tidal volume during exposure to air, hypoxia and following hypoxia. Relative to vehicle, SCH 23390 treatment decreased body temperature and hypoxic V_E responsiveness in both groups. In EH, SCH 23390 decreased F in air, hypoxia and post hypoxia, and V_E during hypoxia trended to decrease (P=0.053). Finally, expression of D1 receptor protein was not different between the two groups in any region evaluated. Thus, hypothyroidism in older female hamsters affected D1 receptor modulation of ventilation differently relative to euthyroid animals, but not expression of D1 receptors.