We have previously demonstrated that trenbolone acetate (TBA) treatment of female lambs and rats reduces both plasma glucocorticoid concentrations and the adrenal response to ACTH. It has been suggested that this reduction in the catabolic glucocorticoids may aid the anabolic effects of this agent.

Four groups of 6 wether lambs were implanted with TBA (40 mg), TBA (35 mg) plus oestradiol (5 mg) or with a long-acting oestradiol implant (Compudose). Hourly blood samples were taken for 24 h periods just before and 10 days after treatment and Cortisol concentrations measured using a competitive protein binding assay.

If the classical analysis of variance procedure is followed ignoring the time correlation within individual animals then the residual sum of squares will be inflated and significant effects can be missed. The correlation can be modelled by extending the analysis of variance to include a Fourier Analysis. For each Fourier cycle considerd the variation can be explained in terms of an overall model, separate treatment models and separate individual models.