The production of mammary carcinomas in rats by 9,10-dimethyl-1,2-benzanthracene and its relationship to the oestrous cycle

Sprague-Dawley rats aged 50 days were given single oral doses of the carcinogen, DMBA.Rats receiving the carcinogen at the same stage of the oestrous cycle were grouped together and mammary tumour production was compared between these groups.When the carcinogen was given during di-oestrus the mean number of tumours per animal was significantly greater than when it was given at other stages in the oestrous cycle. There was considerable variation in total tumour yield from one batch of animals to another.

The detection by immunofluorescence of casein in rat mammary glands

Rabbits were immunised against casein and whey proteins from rat milk. The immune globulins were conjugated to fluorescein isothiocyanate and the labelled antibodies were used to stain histological sections. Casein was located in unfixed and fixed cryostat sections of lactating rat mammary glands but better preparations were obtained using fixed paraffin embedded material. Casein was consistently present in sections of lactating mammary glands and was found on the gastric mucosa of suckling baby rats; it was not, however, found in any other organ in the body. The localisation of whey proteins was unsatisfactory in cryostat sections and the antigenicity of these proteins was completely destroyed by histological fixation and paraffin embedding.

Preparation of fat cell-"free" rat mammary gland

The uptake and clearance of chemical carcinogens by mammary tissue are for the most part obscured by the large amount of fat surrounding the mammary parenchymal tissue. This is due primarily to the lipophilic nature of the carcinogenic polycyclic hydrocarbons. Therefore, it became necessary to develop a procedure whereby mammary gland adipose tissue cells may be separated from mammary parenchymal tissue without removal of intracellular lipid or the disruption of the tissue beyond histologic recognition. The procedure developed involves the incubation of the tissue with the enzyme collagenase in a tissue culture medium for 1-1½ hr. This is followed by several sodium chloride washes which effectively remove any adhering intact fat cells. Lipid content of the collagenasetreated preparation was decreased from approximately 60% to 2% when compared with the untreated control gland. The procedure described effectively separates intact fat cells from mammary parenchymal tissue but maintains a histologic state in which mammary ducts and alveoli may be readily identified.

The distribution of [1,2-3H]testosterone in the tissues of female rats

(1) The incorporation of [1,2-3H]testosterone in vivo into various tissues of virgin, pregnant, post-partum and tumour-bearing female rats was studied.

(2) In virgin female rats the clearance of radioactivity from mesenteric fat, mammary gland, uterus, spleen, lung and blood was similar. This similarity in the rates of clearance of radioactivity for all the tissues examined was also found for the tissues of pregnant, post-partum, and tumour-bearing rats.

(3) After the administration of [1,2-3H]testosterone different amounts of radioactivity were found in each of the tissues examined. In virgin rats the levels of incorporation were fat > uterus ≥ mammary gland > lung > blood ≥ spleen. This pattern was also obtained in post-partum and tumour-bearing animals; the tumours in the latter behaved in a similar way to normal mammary glands. In the pregnant rat, the foetus incorporated the least amount of radioactivity.

The apparent immunofluorescence of tissue mast cells

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