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For many years it was thought that bilateral adrenalectomy in the rat was fatal only in a fraction of cases, but during the last 15 to 20 years it has been shown that the rat is no exception to the rule that the removal of the adrenal glands is followed by symptoms of adrenal insufficiency and death [Britton, 1930; Firor & Grollman, 1933; Swingle & Remington, 1944]. The percentage of animals which survive bilateral adrenalectomy and the length of the survival period of those which die show considerable variations. Gillman & Golberg [1942] have listed the data of some fifteen different investigators on the duration of the life span of rats and the percentage of indefinite survivals following adrenalectomy. While most of the average life spans range approximately from 5 to 9 days, the highest average listed is 17·8 days. The causes for such variations have been partly elucidated. The
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In order to study the rate of growth of organs under endocrine control and to determine the time of onset or cessation of growth-promoting endocrine influences, it is usually necessary to relate the rate of growth of the organ in question to that of the body as a whole.
Relative growth analysis, as developed by Huxley [1924], can easily be applied to teat growth as has been done by Bottomley & Folley [1938] for the guinea-pig and Folley, Scott Watson & Bottomley [1941] for the goat, since teat length is an easily measured quantity. In the case of the mammary gland, however, the only suitable quantitative criterion is the mammary-gland area and this can be used only with animals such as the mouse, rat or monkey in which the mammae consist of relatively flat sheets of tissue.
The first attempt to correlate mammary growth with the growth rate of some
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SUMMARY
The daily milk yields and the concentrations of fat, protein and lactose in the milk were studied throughout lactation in New Zealand White (NZW) and Dutch rabbits. The highest daily milk yields, 270 g. in the NZW and 140 g. in the Dutch rabbits, occurred at the end of the third week of lactation; on a body weight basis the yields were similar being 61·0 and 62·3 g. milk/kg. body weight for the NZW and Dutch rabbits respectively. Over a 6-week period the total milk yields were 6940 g. for the NZW and 3820 g. for the Dutch rabbits.
In both breeds considerable changes occurred in the composition of the milk after the third week of lactation. During the first 3 weeks the concentrations of fat, protein and lactose were approximately 15–17, 11 and 1·8–2·0 g./100 ml. milk respectively, but during the fourth to the sixth week the values for fat and protein increased to 25–30 and 18–20 g./100 ml. respectively, while lactose declined to 0·5 g./100 ml. or less.
Sheep prolactin (25 i.u. injected s.c. twice daily for 2 days) in late lactation was galactopoietic, augmenting both the daily milk yield and the concentration of lactose in the milk.
From days 9 to 31 of lactation the NZW litters gained 0·45 g. body weight/g. of milk consumed, the Dutch litters gained 0·38 g./g. of milk. This difference in weight increment was highly significant (P < 0·001) and was apparently due not to a higher calorie content of the milk of the NZW does but to a greater efficiency of milk utilization by the NZW litters.
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SUMMARY
Attempts to maintain lactation in rats, hypophysectomized on the 4th day of lactation, with extracts of ox and rat pituitary and various purified anterior-pituitary hormones (prolactin, growth hormone (GH), adrenocorticotrophin (ACTH)), singly and in various combinations, are described.
Slight replacement effects were seen with pituitary extracts and with prolactin alone (25 i.u. twice daily). Higher milk yields (about 25% of normal) were obtained with a larger dose of prolactin (50 i.u. twice daily). ACTH and/or GH in combination with the lower dose of prolactin (25 i.u. twice daily) enhanced the replacement value of prolactin, but no such synergistic action was seen when they were combined with the higher dose (50 i.u. twice daily). Neither ACTH nor GH, when administered alone, had any replacement value, although a slight replacement was obtained when they were administered together. Intermedin alone failed to maintain lactation. In no case was complete maintenance of lactation achieved, although yields of almost half the normal were obtained in two rats receiving prolactin (25 i.u. twice daily) and ACTH (4 i.u. once daily). No evidence of gross changes in the calorie content of the milk during replacement therapy was obtained.
The difficulties of assessing the degree of maintenance of milk secretion and the possible significance of fragments of anterior-pituitary tissue remaining after hypophysectomy are discussed.
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SUMMARY
Mammary gland slices (incubated in vitro) from hypophysectomized rats used less glucose and produced more lactic acid than similar slices from normal animals. The accumulation of lactic acid was observed in the presence of glucose or glucose plus acetate as added substrates, but not in acetate alone or in the absence of added substrates. Hypophysectomy led to a substantial decrease in the respiratory quotient of the mammary gland slices. Neither ovariectomy, adrenalectomy, thyroidectomy, parathyroidectomy nor sham hypophysectomy caused the appearance of the above metabolic changes in mammary gland slices.
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SUMMARY
Ablation of the posterior lobe of the pituitary in the lactating rat abolished the milk-ejection reflex so that the pups could only be reared if injections of oxytocin were given to the mothers twice daily. When, however, these posterior lobectomized rats became pregnant a second time, parturition was normal and the milk-ejection reflex was sufficiently restored for the rats to rear their litters without oxytocin being administered. The animals, however, continued to exhibit diabetes insipidus. Measurements of residual neurohypophysial tissue showed that hypertrophy of the neural stalk had occurred after posterior lobectomy.
These findings are discussed in relation to recent studies on the site of formation and the liberation of posterior-pituitary hormone(s) after hypophysectomy.
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SUMMARY
The rates of absorption of a number of steroid compounds and synthetic oestrogens from subcutaneously implanted tablets in mice, rats and cows are presented and compared with those observed by other workers.
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The effects of adrenalectomy have been studied mainly in the rat, dog and cat, and to a lesser extent in the guinea-pig and rabbit. Scant attention, however, has been given to the study of the effects of adrenalectomy in the smaller ruminants. In 1901, Moore & Purinton investigated the survival period after adrenalectomy in two adult female goats and two kids. The kids were unilaterally adrenalectomized a few hours after birth, and the second adrenal removed 34–35 days later. Both died 49–66 hr. after completion of adrenalectomy. One of the adult goats died 8 days after removal of the second adrenal, the other remained normal and was killed 22 days after the operation. No gross adrenal tissue was found at autopsy. In sheep, the effects of adrenalectomy have been studied by Strand, Anderson & Allcroft [1934]. Five animals were successfully adrenalectomized and survived 34–60 hr. after removal of the second
