AGE‐DEPENDENT EFFECTS OF PROGESTERONE ON VENTILATION AND APNEA IN RATS

Progesterone has been proposed as an alternative for apnea treatment in neonates but relevant data are rare. In rats aged 1, 4, 7, and 12 days we investigated the effects of progesterone (Prog, 4 mg/kg, i.p.) on baseline ventilation, hypoxic ventilatory response (HVR, 12% O2, 20 minutes), apnea frequency (for spontaneous and post‐sigh apneas), and arterial oxygen desaturation and bradycardia during apneas (Mouse‐Ox device). Control rats received a saline injection (2 ul/g i.p.). Prog had no effect on baseline ventilation, increased the peak HVR in 4 and 7 d‐old and the steady state HVR in 1, 4 and 7 d‐old, but had no effects in 12 d‐old rats. About 23% of all apneas were associated with desaturation and/or bradycardia independently of their types. Prog reduced the frequency of those apneas particularly in 1‐d‐old rats. These preliminary observations suggest that acute Prog injection stimulates HVR in rats less or equal to 7 d‐old and reduces apnea independently to its effect on HVR. Supported by Foundation of Stars.