Functional Zonation of Adrenocortical Tissue in the Brush Possum (Trichosurus Vulpecula)

Abstract

The relationship of structure and function in the adrenal gland of the possum Trichosurus vulpecula, has been studied using in-vitro incubation techniques. It was shown that both 17\g=a\-hydroxycorticosteroids and 17-deoxycorticosteroids were produced from radioactive pregnenolone and progesterone, and that these transformations occurred both in the definitive cortex as well as in a special zone of hypertrophied tissue found only in the adult female.In support of earlier findings, it was also shown that the adrenal cortex of the possum has a remarkable capacity to produce C19 steroids (including androstenedione and testosterone) from the radioactive precursors. While most of the transformations occurred with equal efficiency in both types of tissue, the reduction of androstenedione to testosterone seemed to take place more readily in the special hypertrophied zone of the adult female.In studies in vivo, it was found that levels of testosterone in the peripheral blood of the adult female possum were extremely high compared with man. Variations in testosterone levels were not apparently correlated with the stage of the oestrous cycle. The possible pathways by which the adrenal products are synthesized, and their physiological implications are discussed.

Effect of ovariectomy on the social status of brushtail possums(Trichosurus vulpecula)in captivity

“…Alternatively, dominance behaviours could be maintained by adrenal steroids. Female possums have a "special zone" in their adrenal cortex (Bourne 1934;Vinson et al 1971) thought originally to produce testosterone (Vinson & Phillips 1969). Recent studies indicate, however, that female possums have very low levels of circulating testosterone (Allen & Bradshaw 1980;Curlewis et al 1985).…”

Hypertrophied adrenocortical tissue of the Australian brush-tailed possum (Trichosurus vulpecula): uniformity during reproduction

“…Vinson (1974) also reported that the formation of typical corticosteroids such as cortisol and corticosterone was much higher in the outer zones of the cortex than in the hypertrophied region. Weiss & Ford (1982), however, reported that 5ß-reduced pregnane derivatives were the major products when homogenates of the hypertrophied zone were incu¬ bated with radioactive progesterone, and Allen & Bradshaw (1980) reported plasma testosterone levels which were about 10% of those reported by Vinson et al (1971). It remains possible that one explanation for these different findings is that animals in different stages of the oestrous cycle were used but clearly the function of the hypertrophied region is still unclear.…”

“…At present, the precise function of the hypertrophied zone is a subject of some controversy. Vinson, Phillips, Chester Jones & Tsang (1971) suggested that it was a major site for synthesis of testosterone from androstenedione and that plasma testosterone levels in female T. vulpécula were un¬ usually high. Vinson (1974) also reported that the formation of typical corticosteroids such as cortisol and corticosterone was much higher in the outer zones of the cortex than in the hypertrophied region.…”

Identification of the major steroids in ovarian and adrenal venous plasma of the brush-tail possum (Trichosurus vulpecula) and changes in the peripheral plasma levels of oestradiol and progesterone during the reproductive cycle

“…Chester Jones et al (1964) have also described a substance in adrenal venous blood that was tentatively identified as testosterone and was present at levels up to 0-8 pmol/1. These authors, and subse¬ quently Vinson & Phillips (1969), Vinson, Phillips, Chester Jones & Tsang (1971), Vinson, Tyndale-Biscoe & Bancroft (1972) and Vinson (1974), attributed the ability of the adrenal gland to produce testosterone to the 'special zone' of the cortex. This zone, unique to the mature female possum, was first described by Bourne (1934).…”