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ISABEL A. FORSYTH
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ZENA D. HOSKING
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SUMMARY

The 'local' method of pigeon crop assay, involving injection of prolactin into the skin overlying the crop, was found to be much more sensitive than the systemic method. It suffers, however, from two drawbacks: first, the problem of finding a suitable method to measure the response; and secondly, the considerable variation in response between birds, especially when pigeons of unknown origin and age must be used. The results of measuring the response by cutting out and weighing the stimulated area are described, together with the use of a balanced incomplete block design which, using 30 pigeons in a (2+2) dose assay, gave an index of precision (λ) of 0·2 or less.

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G. K. BENSON
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A. T. COWIE
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ZENA D. HOSKING
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The mammogenic potency of miroestrol, an oestrogenic substance isolated from the tuberous roots of the leguminous plant Pueraria mirifica, was estimated as 0·70 (with 5% fiducial limits of 0·40 and 1·18) relative to oestradiol in the ovariectomized rat, and as 2·2 (with 5% fiducial limits of 1·2 and 4·9) relative to oestrone in the mouse. The effects of miroestrol on the body weight and weights of the endocrine glands, with the exception of the thyroid in the rat, were qualitatively similar to those of oestradiol and oestrone. In the rat oestradiol (0·1 μg/day) inhibited the increase both in body weight and thyroid weight that occurred after ovariectomy, whereas miroestrol (0·1 μg/day) inhibited only the increase in body weight.

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P. E. HARTMANN
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A. T. COWIE
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ZENA D. HOSKING
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Five groups of five lactating rabbits each were used. Milk yield was recorded from the 8th day of lactation onwards and on the 10th day of lactation the rabbits received the following treatments: Group S, sham-operation with saline (1 ml/12 h); Group P, hypophysectomy with sheep prolactin (1 mg/12 h); Group H, hypophysectomy with human growth hormone (1 mg/12 h); Group B, hypophysectomy with bovine growth hormone (1 mg/12 h) and Group C, hypophysectomy with saline (1 ml/12 h). The injections of saline or hormones were continued for 5 days and at the end of this period a blood sample was taken, the animals were killed and their mammary glands removed for histological examination and assay of the following enzymes: 6-phosphogluconate dehydrogenase (EC 1.1.1.44), phosphofructokinase (EC 2.7.1.11), phosphoglucomutase (EC 2.7.5.1), UDP-glucose pyrophosphorylase (EC 2.7.7.9), acetyl-CoA carboxylase (EC 6.4.1.2), acetyl-CoA synthetase (EC 6.2.1.1) and ATP-citrate lyase (EC 4.1.3.8). On the 5th day after surgery the concentrations of blood l-lactate and pyruvate and plasma free fatty acids and protein were similar in all groups, whereas plasma glucose was higher in groups S, B and H than in groups P and C. Although the weights of pituitary target organs (adrenals, thyroid and ovaries) were similar in all groups, the weights (g/kg body weight) of mammary tissue varied markedly, group S being the heaviest and group C the lightest. Milk yields, 5 days after surgery, for groups P and H were about 50% that for S, whereas those for B and C were 15 and 4% respectively. Where possible the enzyme activity was expressed as a ratio of the rate of synthesis of the end product of the pathway in which the enzyme occurred. With the exception of acetyl-CoA carboxylase which may have had a rate-limiting role in the synthesis of milk fat, enzymic activity in vitro was in excess of that required in vivo for the synthesis of either milk fat or lactose. It appeared that the rate of milk synthesis depended upon the degree of maintenance of the secretory epithelial cells within the mammary gland rather than a block in the synthetic pathways within these cells.

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G. K. BENSON
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A. T. COWIE
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C. P. COX
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S. J. FOLLEY
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ZENA D. HOSKING
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SUMMARY

Hexoestrol (0·5 mg.) and progesterone (70 mg.) in oily solutions injected subcutaneously every day over a period of 150 days were more effective in inducing mammary growth and lactation in ovariectomized goats than crystalline suspensions of hexoestrol (intramuscular injection every 50 days) and progesterone (intramuscular injection every 30 days) given during the same period and at the same total dosage. Within treatments, the goats ovariectomized as adults, i.e. just before the hormone treatments were started, always had higher yields than goats ovariectomized in infancy.

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A. T. COWIE
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C. P. COX
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S. J. FOLLEY
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ZENA D. HOSKING
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J. S. TINDAL
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SUMMARY

Suspensions of oestradiol monobenzoate crystals (three intramuscular injections of 25 mg. at intervals of 50 days) in combination with suspensions of progesterone crystals (five injections of 2·1 g. at intervals of 30 days) were more effective in inducing mammary growth and lactation in ovariectomized goats than suspensions of hexoestrol and progesterone crystals administered at similar dose levels and intervals.

Daily injections of relaxin during the last 30 days of the above treatments reduced the milk yields apparently by inhibiting mammary growth.

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A. T. COWIE
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C. P. COX
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S. J. FOLLEY
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ZENA D. HOSKING
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M. NAITO
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J. S. TINDAL
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SUMMARY

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.

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