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To determine whether the adrenal gland of the bandicoot is actively producing steroid hormones at birth, the cellular structure was examined by electron microscopy, and the concentration of cortisol in the gland was determined by radioimmunoassay. Two distinct cell populations were seen in the adrenal gland. One group of cells possessed dark staining granules, normally observed in catecholamine-secreting cells, and the second group contained large amounts of smooth endoplasmic reticulum and mitochondria with tubulo-vesicular cristae. Both features are characteristic of steroid-secreting cells. A concentration of 0.094 ng of cortisol per adrenal was determined by pooling glands from nine individual newborn bandicoots. This evidence of cortisol secretion from the bandicoot adrenal at birth indicates that, as in many eutherians, the marsupial adrenal may play an important role in determining the length of gestation.

The effectiveness of trilostane and azastene as inhibitors of adrenal steroidogenesis was compared by in-vitro and in-vivo methods. A radioimmunoassay was developed for the measurement of cortisol in ovine plasma, incubation medium and tissue extract using a specific antiserum raised against cortisol 21-acetate,3-carboxymethyloxime:bovine serum albumin. Trilostane (20 mumol/l) decreased cortisol synthesis and release both in unstimulated and in ACTH-stimulated adrenal tissues in vitro. The same concentration of azastene had a lesser effect on unstimulated adrenals and was completely ineffective in blocking the stimulatory action of ACTH. In vivo, trilostane suppressed adrenal steroidogenesis in pregnant and cyclic ewes but the suppression in pregnant ewes was over a longer period, and after lower doses. It is concluded that trilostane had an inhibitory effect on ovine adrenal steroidogenesis both in vitro and in vivo.

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