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myxoedema, defining hypothyroid conditions. Magnus-Levy (1895) was the first to demonstrate that respiratory metabolism was increased in hyperthyroidism and decreased in myxoedema. Indirect calorimetry allowed measurements of basal metabolic rate (BMR) and
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SUMMARY
The failure of adrenalectomized mice to respond to thyroxine by an increase in oxygen uptake was not reversed by intramuscular injections of thiamine. Thiamine-deficient mice were found to be incapable of responding to thyroxine by an increase in the metabolic rate.
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Laboratory of Endocrinology, Clinical Chemistry, Netherlands Institute for Neuroscience, Department of Physiology and Pharmacology, Departments of
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Laboratory of Endocrinology, Clinical Chemistry, Netherlands Institute for Neuroscience, Department of Physiology and Pharmacology, Departments of
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physiology. Within minutes after systemic administration, profound hypothermia, bradycardia, and decreased cardiac output occur. In addition, thyronamines rapidly induce metabolic alterations such as decreased metabolic rate and a dramatic shift to
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excised and insulin content was measured following extraction with 5mL/g of ice-cold acid ethanol (75% ethanol, 23.5% water, 1.5% concentrated HCl). Measurement of metabolic rate and locomotor activity Metabolic rate and locomotor activity were
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Thiouracil was administered to young guinea-pigs from a month before birth until either the time of birth or until they were 8 weeks old. The basal metabolic rate of these animals was depressed, their thyroids were hyperplastic and took up tracer doses of 131I more slowly than normal. Nevertheless the growth rate of such animals did not differ significantly from that of normal control guinea pigs.
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SUMMARY
When exposed to a low ambient temperature of 5 °C, adrenalectomized echidnas were able to increase their metabolic rate and to maintain their body temperature within the normal range for no more than 48 h — less than 12 h in five out of six animals. Thereafter, activity, metabolic rate, cardiac rate and body temperature declined and the animals became torpid.
When maintained with daily i.m. injections of 1–2 mg cortisol acetate/kg, adrenalectomized echidnas maintained activity and normal body temperature in the cold environment indefinitely. When cortisol injections were withheld and exposure to cold continued, normal body temperature was maintained for a further 10 days, after which it declined rapidly.
The onset of torpor was always preceded by a marked fall in plasma glucose concentration, as occurred in normal, but fasted, echidnas after prolonged exposure to cold. Both cortisol and corticosterone have glucocorticoid activity in echidnas, and torpor was prevented in adrenalectomized echidnas by preventing the fall in plasma glucose with either intermittent injections or constant rate infusions of glucose solutions.
The adrenal glands of normal echidnas exposed repeatedly to low environmental temperatures showed marked hypertrophy and increase in lipid content.
It is concluded that adrenocortical secretions are necessary for the metabolic response to cold stress in these prototherian mammals, and a major role of the corticosteroids is in maintenance of normal blood glucose concentrations, presumably by enhancing hepatic gluconeogenesis.
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There are many indications in clinical medicine that hypothyroidism is associated with inadequate reproductive function. Myxoedematous women, for example, often suffer from menstrual disturbances and seldom conceive and bear children [Rose, 1942]. A low metabolic rate is also often found in women attending fertility clinics [Nicodemus & Ritmiller, 1945], and many clinicians believe that thyroid extract is the most useful hormone in the treatment of infertility.
Experimental analysis of the apparent relationship between the thyroid and ovary has not, however, led to clear-cut conclusions. Thus, removal of the thyroid seems to have no effect upon the development of the reproductive system up to the time of maturity [Hammett, 1926], oestrous cycles beginning at ages within the normal range [Long & Evans, 1922; Lee, 1929]. According to Evans & Long [1921], too, the oestrous rhythm in the mature rat is unaltered by thyroidectomy. Later workers, however, report that both dioestrus and
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SUMMARY
Six groups each of 12 male albino rats were reared from day 21 of life at temperatures of 23, 34 or 37 °C. While the rats survived for unlimited periods at 23 and 34 °C, the animals reared at 37 °C succumbed within 5 days to heat stress. The latter group, when injected s.c. or i.p. with 50 mg dehydroepiandrosterone (DHA)/kg/day were no longer affected by the heat. During this treatment thyroid epithelial cell height doubled, colloid decreased by 20%, connective tissue did not change, the basic metabolic rate decreased by 10% and rectal temperatures of the treated rats increased with the ambient temperatures. Body weight increased only slightly, pituitary TSH decreased by 25%, serum TSH increased by over 50%, thyroxine and 125I uptake increased by 200%. The survival of the DHA-treated rats was apparently secured by blocking the hypothalamic thermoreceptors.
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A reduction in thyroid activity has been associated with various degrees of inanition and protein deprivation (Aschkenasy, Nataf, Piette & Sfez, 1962; Grossie & Turner, 1962, Yousef & Johnson, 1968). Furthermore, the sensitivity of the thyroid gland in response to TSH and as measured by an increase in basal metabolic rate is subnormal in rats fed a protein-free diet (Aschkenasy, 1961). On the other hand, the antigoitrogenic dose—response curves for l-tri-iodothyronine were not altered by protein depletion (Lerner & Leathem, 1963). More recently, Graig (1967) noted an increase in thyroidal lactic dehydrogenase activity as a possible specific response to thyroid-stimulating hormone (TSH). These data prompted an examination of the effect of protein deprivation on thyroidal lactic dehydrogenase (LDH) activity as influenced by thiouracil and thyroxine (T4).
Male Long—Evans rats, weighing 55–65 g., were initially fed a semi-purified protein-free diet for 10 days. During the next 10 days either
