The Journal of endocrinology
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Replacement of the 3'-halogen of the tri-iodothyronine (T3) molecule by a propyl-group produces a thyromimetic analogue, 3'-isopropyl-3,5-di-iodo-L-thyronine (T2iPr), with high biological potency. A serum thyroid-stimulating hormone (TSH) suppression test with one single intraperitoneal injection of 3 or 30 nM-T3 or T2iPr or with 30 or 300 nM-thyroxine (T4) per kg body weight was performed on 56 adult male Lewis rats which were maintained for 3 weeks on an iodine-deficient diet containing 0.2% 6n-propyl-2-thiouracil (PTU). Blood was withdrawn from each rat by cardiac puncture 24 h before and 3, 7, 24 and 48 h after application of the iodothyronines. ⋯ Pituitary concentrations of growth hormone, TSH, prolactin and FSH were significantly reduced by the treatment with PTU. There was also a slight, but insignificant reduction of pituitary concentrations of LH. Treatment with T3, T4 or T2iPr stimulated the reaccumulation of growth hormone, TSH, prolactin, LH and FSH in the pituitary gland.
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Hypothalamic corticotrophin releasing factor (CRF) activity was determined in five dogs with spontaneous hyperadrenocorticism and in three control animals (one untreated, one treated with high doses of ACTH for 2 months and one treated with high doses of cortisone for 2 months). Hypothalamic CRF activity was low or undetectable in four dogs with Cushing's syndrome due to an adrenocortical tumour. The results are compatible with a pituitary origin for pituitary-dependent hyperadrenocorticism in the dog but are not conclusive; direct information about the rates of hypothalamic CRF secretion is required.
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Ovariectomized rats were given a single dose of synthetic oestrogen or progestogen, or both combined. On selected days after treatment one rat from each treatment group was killed and myometrical contractility in response to spasmogens was measured isometrically in isolated tissue baths. Contractility persisted at a low level after ovariectomy without steroid replacement (controls) for the 60 days of the experiment. ⋯ Progestogen treatment did not influence contractility to a significant degree when compared with saline, except that the contractions were sometimes of higher frequency and more irregular in size. There was a less powerful potentiating action on contractility with combined oestrogen and progestogen treatment than with oestrogen alone. It reached a maximum in 4 days and declined more rapidly than with oestrogen-treated preparation but was still vigorous for up to 30 days.