Acute effects of aspartic acid on ventilation of male and female rats

The effects of aspartic acid (aa) on ventilation were evaluated in awake male and female rats prior to and 15, 30, and 45 minutes after saline, 100 mg/kg or 580 mg/kg aa was injected subcutaneously. Subsequently, rats were exposed to hypoxic and hypercapnic gas challenges. In males, 100 mg/kg aa increased ventilation (VE) by increasing inspiratory flow rate (VT/TI), tidal volume (VT), and frequency of breathing (f) by 30 minutes, whereas in females VT was increased above saline levels only at 15 minutes. VE did not decrease over time. A dose of 580 mg/kg aa depressed ventilation in males for 2 hours by decreasing VT, VT/TI and f. In contrast, female rats exhibited a decreased ventilation only at 15 minutes which then began to return to saline levels by 45 minutes. Neither male nor female rats treated with either dose of aa showed a depressed response to hypoxia or hypercapnia. These data indicate that aa at two doses can affect the pattern of ventilation differently in male and female rats. One mechanism responsible for the differences noted between the two groups is the effect aspartic acid may have on testosterone production. An additional study comparing ventilatory responses of sham operated and castrated males to various doses of aa indicated that testosterone was not necessary to show the 'male' pattern of response.