Ovariectomy at 3 or 10 weeks of age does not affect the ventilatory response to hypoxia in adult rats

Although an ovariectomy is the routine approach used to study the role of ovarian hormones on respiratory control, the results have often been contradictory. We tested the hypothesis that the ventilatory response to hypoxia is modified by the age at which the ovariectomy is performed. Female rats were ovariectomized either atan early (3 weeks old, i.e., prepubertal) or late (10 weeks old, i.e., adult) stage, and ventilation was then assessed at 12 weeks of age using wholebody plethysmography. The control group included sham-operated rats that had undergone the same surgical procedure but were not ovariectomized. Independent of the age at which surgery was performed, ovariectomy significantly decreased circulating progesterone and 17-b-estradiol levels without reducing them below their detection threshold. Despite that decrease, there was no difference in baseline minute ventilation or in the ventilatory response to hypoxia (FiO2 = 12%, 20 min; expressed as the percentage of increase from baseline) between ovariectomized and sham-operated rats. These results suggest that ovariectomy at either a young or at an adult age is insufficient to completely suppress circulating hormones and disrupt the regulation of ventilation.