Age and hypothyroidism affect dopamine modulation of breathing and D2 receptor levels

During and following hypoxic exposure young male hypothyroid hamsters treated with the dopamine D2 receptor agonist bromocriptine increased breathing, while ventilation was depressed in bromocriptine-treated euthyroid hamsters. Moreover, D2 receptor expression was increased in carotid bodies and striatum, but not in the nucleus tractus solitaries (NTS) of hypothyroid relative to euthyroid hamsters. Here ventilation was determined in older male hypothyroid and euthyroid hamsters given vehicle or bromocriptine, and exposed to baseline air, hypoxia, and then air. Bromocriptine without hypoxia served as a time control. Relative to vehicle, bromocriptine depressed ventilation in both groups exposed to air or to hypoxia, but hypothyroid bromocriptine-treated hamsters increased ventilatory responsiveness to hypoxia, while euthyroid hamsters decreased ventilatory responsiveness to hypoxia and exhibited post-hypoxic depression. Hypothyroidism had no effect on D2 receptor expression in carotid bodies or striatum, but increased it in the NTS. Thus, in hamsters bromocriptine modulates breathing and expression of D2 receptor depending on the length of hypothyroidism.

► In euthyroid hamsters D2 agonist treatment depressed ventilation in air, during and after hypoxia. ► Hypothyroidism increased hypoxic ventilatory responsiveness following D2 receptor stimulation. ► Hypothyroidism prevented D2 receptor mediated post-hypoxic depression. ► Hypothyroidism increased D2 receptor levels in the NTS not in striatum or carotid bodies.