EFFECT OF ROUTE OF ADMINISTRATION ON THE CARCINOGENIC ACTION OF DIETHYLNITROSAMINE (N-NITROSODIETHYLAMINE)

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RAT MAMMARY GLAND METABOLISM RELATIVE TO EPITHELIAL AND CONNECTIVE TISSUE CONTENT

The respiration rate of rat mammary gland slices increased directly with the epithelial proliferation induced by pregnancy and lactation. In the absence of glucose the respiration was depressed, particularly in slices with the largest epithelial content. Dinitrophenol (5 x 10–5 m) provided a metabolic distinction between the epithelium of pregnant and lactating mammary glands; it stimulated the respiration of the former and depressed the respiration of the latter. The rate of anaerobic glycolysis (q1acN2) for mammary epithelium was adduced to be 4–5 µl/hr mg dry nonfat tissue and the rate remained in that range during lactation and pregnancy; the rate of aerobic glycolysis increased during pregnancy and decreased during lactation. Alkaline phosphatase activity did not vary directly with the mammary epithelium content and it was suggested that the rate of epithelial cell proliferation (mitoses) and hormonal factors might also be of importance in determining the total activity observed. The increase in glucose 6-phosphate dehydrogenase and 6-phosphogluconic acid dehydrogenase activity during pregnancy and at the onset of lactation was not directly related to the increase in mammary epithelium.

THE EFFECT OF 1-ALPHA-METHYLALLYLTHIOCARBAMOYL-2-METHYLTHIOCARBAMOYL HYDRAZINE (ICI 33828) ON LACTATION IN THE RAT

The administration of 1-α-methylallylthiocarbamoyl-2-methylthiocarbamoyl hydrazine (ICI 33828) to lactating rats in doses ranging from 5 to 40 mg. daily resulted in a marked inhibition of litter growth. When oxytocin (1 i.u. twice daily) was administered in addition to ICI 33828 (5 mg. or 20 mg. daily) the depression in litter growth rate was largely overcome. Histological studies indicated that the mammary glands of the treated mothers were secreting, but that the pups were unable to obtain the available milk without exogenous oxytocin. It is suggested that ICI 33828 acts on the hypothalamus by blocking the release of oxytocin and possibly enhancing the release of prolactin.

THE EFFECTS OF THE DURATION OF TREATMENTS WITH OESTROGEN AND PROGESTERONE ON THE HORMONAL INDUCTION OF MAMMARY GROWTH AND LACTATION IN THE GOAT

The effects of the duration of hormonal treatments for inducing mammary growth and lactation were studied in ovariectomized goatlings. The injection periods were 35, 70 or 140 days for each of three hormone treatments. Treatment H: hexoestrol (0·5 mg./day); treatment HP: hexoestrol (0·5 mg./day) and progesterone (70 mg./day) and treatment HHP: treatment H for the first 40% of the period followed by treatment HP for the rest of the period. One half-udder was removed from each goat at the end of the injection period for histological examination, i.e. just before milking was started, and the other half after the peak of lactation had been attained.

In general the longer the injection period the sooner were peak milk yields obtained, the interval from the beginning of the injection period to the peak yield ranging from 32 to 41 weeks. With treatment H the best yields were obtained from goats treated for only 35 days, the best yields with treatment HP were from goats treated for 140 and 70 days. On the basis of the total milk yield for the first 24 weeks of lactation, the treatment giving the highest yields was HP for 140 days; then, in descending order of efficacy, came HP for 70 days, H for 140 days, H for 35 days, HHP for 140 days, HHP for 70 days, H for 70 days, HHP for 35 days and HP for 35 days.

With the exception of treatment H for 140 days, in which lactogenesis was induced during the injection period, the half-udders removed at the peak of lactation were significantly heavier than their contralateral halves removed before milking was started. Considerable growth of glandular tissue had occurred during lactation, i.e. after the hormonal treatments had ended. It is presumed that this growth is the result of the milking stimulus acting by way of the anterior pituitary; since the goats were ovariectomized ovarian hormones cannot have been involved.

INDUCTION OF MILK SECRETION IN THE RABBIT BY REMOVAL OF THE TELENCEPHALON

Extirpation of the telencephalon resulted in mammary growth and milk secretion in intact and in ovariectomized estrogen-primed rabbits. These effects were apparent within I week after the operation. More restricted lesions in the neocortex and olfactory bulbs did not induce these changes. From these results it is suggested that removal of the telencephalon causes release of prolactin and possibly ACTH from the adenohypophysis.