SUMMARY.-An assay is described for measuring the concentration of specific, high-affinity oestradiol receptors in the cell supernatant fraction of breast tumour biopsies. The (Gorski et al, 1968;Jensen et al., 1968).The presence of oestrogen receptors has been demonstrated in hormonedependent tumours in experimental animals. notably in some dimethylbenzanthracene-induced mammary tumours in the rat and in oestrogen-induced kidney tumours in the hamster (King, Smith and Steggles, 1970;Mobbs, 1966; Sander and Attran-iadal, 1968

A quantitative method was used to determine the concentration of high-affinity oestradiol-receptor sites in rat uterine supernatant preparations under various physiological conditions. Cyclic changes in concentration were observed during the oestrous cycle, with a maximum occurring in late dioestrus. The changes followed a similar pattern in endometrium and myometrium, although concentrations were higher in the former. In pseudopregnancy the concentration was initially low, rising to a maximum on the tenth day. In early pregnancy a high concentration of receptor was found to be associated with the developing placenta, but this declined in later stages of pregnancy. After ovariectomy or combined ovariectomy and adrenalectomy the receptor concentration remained at a constant low value that could be increased by treatment with oestradiol. The receptor concentration was considerably higher in immature than in adult uteri.

The present work was initiated by the observation of Reifenstein, Homburger & Dobriner (1950) that 3a: 1 1l-dihydroxy-5p-androstan-17-one (1 l,B-hydroxyaetiocholanolone), a minor component of the urinary 17-oxo steroids, was significantly associated with neoplastic growth. The re-examination of this problem has led to the development of a micro method for the quantitative separation and determination of the individual compounds which comprise the 17-oxo steroid fraction of urine. Callow, Callow & Emmens (1938) first applied the Zimmermann (1936) reaction with m-dinitrobenzene and ethanolic potassium hydroxide for the determination and isolation of androgen metabolites from urine. Extension and development of this work led to the isolation and characterization of a large number of urinary steroids, many of which were 17-oxo steroids (Dobriner, Lieberman & Rhoads, 1948a; Lieberman, Dobriner, Hill, Fieser & Rhoads, 1948; Lieberman, Fukushima & Dobriner, 1950). In contrast to the large-scale work of the American investigators, Dingemanse, Huis in't Veld & De Laat (1946) described a method for the analysis of the 17-oxo steroid fraction which could be applied to a urine sample smaller than a 24 hr. sample. The fraction was adsorbed on alumina and the individual compounds were eluted from the alumina with benzene containing increasing concentration of ethanol; the ethanol concentration was increased stepwise. This method in its original form and in the many modifications to which it gave rise (Robinson & Goulden, 1949; Zygmuntowicz, Wood, Christo & Talbot, 1951; Pond, 1951) has been of great value in the study of 17-oxo steroid metabolism. The essentials of a reliable method for the analysis of the urinary 17-oxo steroid fraction are quantitative extraction, complete separation of compounds, unequivocal identification and precise determination. The existing methods do not fulfil these requirements and, in particular, are unsuited to the determination of the 11-hydroxy-17-oxo steroids. Three main improvements have been introduced. The 17-oxo steroids are excreted almost exclusively in the conjugated form as glucuronides

The exploitation of predator signals by potential prey is well researched, but relatively little is known about how predators exploit chemical cues (either deliberate signals or waste by-products) produced by their prey. In Finland, the urine of some small rodents ( Microtus spp. and Clethrionomys spp.) is reflective in the ultraviolet range of wavelengths, and diurnal raptors with ultraviolet vision use these urine marks to track their rodent prey. This study examines the potential for such a phenomenon in Australian systems by studying the ultraviolet properties of urine from 13 native and introduced mammal species that are variously preyed upon by raptors. Urine from all 13 species displayed various levels of ultraviolet absorbance in their urine and fluorescence in the ultraviolet range. However, no signs of ultraviolet hyper-reflectance were detected, suggesting that the urine of European voles have unique ultraviolet properties. Ultraviolet-sensitive predators in Australia may be able to distinguish between species based on variation in the ultraviolet absorbance of their urine, but ultraviolet properties did not differ between prey and non-prey species, nor marsupial and placental groups. Moreover, because many natural surfaces are ultraviolet absorbing, it is unlikely that raptors could rely upon the ultraviolet properties of urine to target key prey species.