We have performed 7 experiments in rats on the effects of systemic treatment with fludrocortisone (9a-FF) given in a variety of doses over a variety of times, in the AM and in the PM. These experiments were designed to determine the best treatment protocol to use in the head-down rat model studies which were performed at NASA-Ames Research Center during the final year. The results of the experiments in non-stressed rats have been, on the whole, disappointing in that we have so far been unable to obtain direct evidence that the 9a-FF acts as a mineralocorticoid. In the ultimate experiments using control and suspended rats, we showed mineralocorticoid and glucocorticoid effects of 9aFF. However, suspension served in our rats as a chronic stressor when they were examined 5 d after the onset of treatment.
