D1 Dopamine Receptor Modulation of Breathing in Young Hypothyroid Female Hamsters

Abstract

Previously we noted in 8 month old female hamsters hypothyroid (H) for 5 months that administration of the dopamine D1 receptor antagonist SCH 23390 (SCH) in saline increased ventilation (VE) while animals were exposed to air, hypoxia and air following hypoxia (PH) relative to saline. These ventilatory responses to SCH were dissimilar to those observed in euthyroid age‐matched females (E). The increased VE's were due to increased tidal volumes (VT), but not frequency of breathing (F). In the present study effects of SCH on VE were studied in 15 four month old female hamsters rendered H for two months by administration of propylthiouracil in drinking water. Fifteen age and gender matched female E hamsters served as controls. Ventilation was measured in conscious hamsters using plethysmography. Relative to saline, 0.025 mg/kg SCH decreased VE during exposure of the H hamsters to air, PH and hypercapnia by decreasing F (due to increases of inspiratory & expiratory times), without affecting VT. Similar decreases in VE occurred in E hamsters exposed to air and hypercapnia. Hypoxic responsiveness, lower in H saline‐treated hypothyroid hamsters, was increased by SCH to levels comparable to those in E hamsters. No effects of SCH were noted on hypercapnic responsiveness. Thus, age and the length of hypothyroidism affect D1 receptor modulation of ventilation in female hamsters.Funding: COBRE Pilot Grant