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K. BROWN-GRANT

Summary.

The presence of a silk thread in the lumen of the upper half of one horn of the uterus of the rat renders that horn sterile. The raised uterus-plasma concentration for radio-iodide that normally occurs on Day 3 of pregnancy is abolished by such a thread placed unilaterally; the control horn shows a normal response. The increase in the uterus-plasma ratio for 131I produced by the administration of progesterone to ovariectomized rats is significantly reduced, but not abolished, in a uterine horn carrying a thread. The inhibition by oestrogen of this response to progesterone is enhanced by the presence of a thread. Changes in the radio-iodide concentration ratio may provide a convenient model system for studies on the mechanism of action of an IUCD in the rat.

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K. BROWN-GRANT

Summary.

Administration of 1% potassium perchlorate solution by mouth from Day 2 to Day 8 has no effect on the course of gestation in pregnant rats or on the decidual response to trauma in pseudopregnant rats.

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K. BROWN-GRANT

Summary.

The incidence of the Bruce effect (block of pregnancy in newly-mated female mice exposed to the smell of male mice of another strain) is significantly lowered in mice anaesthetized with `Avertin' (tri-bromethanol and amylene hydrate) 10 to 12 days before mating. Pentobarbitone anaesthesia may have a similar effect. `Avertin', but not pentobarbitone anaesthesia, also prevents the appearance of the Whitten effect. The use of `Avertin' in the investigation of neuro-endocrine effects involving the olfactory system is not advisable.

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K. BROWN-GRANT and M. R. SHERWOOD

During a limited period (Day 3 to Day 5) of early pregnancy the epithelial cells of the endometrium of the rat develop the ability to accumulate inorganic iodide from the blood and to maintain a very high intracellular concentration of this ion (Brown-Grant, 1965; Brown-Grant & Rogers, 1967). These changes occur just before the normal time of blastocyst implantation but their physiological significance in normal pregnancy is not known. If endometrial accumulation of iodide is prevented by the oral administration of perchlorate to the mother, pregnancy still proceeds normally (Brown-Grant, 1966a). When implantation is delayed by ovariectomy early in pregnancy followed by the administration of progesterone alone or by concurrent lactation, the changes in endometrial iodide concentration still occur but are not immediately followed by implantation (Brown-Grant, 1966b). The

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G. J. R. HOVELL, R. CULLEN and K. BROWN-GRANT

The infusion of solutions of iodine into the uterus through the cervical canal has been practised as a therapeutic measure in certain cases of infertility in farm animals. Little is known about the possible mode of action of such treatment, though Ekman, Holmberg, Settergren & Thorell (1965) have shown that iodide is rapidly absorbed from the uterine lumen in the cow and have suggested that systemic as well as local effects might be involved. On the other hand, iodide has been shown to be present in the cervical mucus in women at a concentration above that in plasma (see Brown-Grant, 1961, for references) and in the rat, a very high concentration of iodide relative to plasma has been demonstrated in the oviduct and

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K. BROWN-GRANT, G. FINK, FENELLA GREIG and M. A. F. MURRAY

Summary.

Male rats given 250 μg oestradiol benzoate by subcutaneous injection on Day 4 of postnatal life showed a marked delay in the onset of the pubertal increase in the weight of the testes and seminal vesicles and in spermatogenesis but not a complete failure of sexual development. The increase in plasma testosterone concentration at puberty was also delayed in oestrogen-treated males but the eventual increase in seminal vesicle weight was closely related in time to the delayed increase in plasma testosterone concentration. Both plasma LH and FSH concentrations were reduced for about 10 days after oestrogen administration as compared to control values. After 22 days of age, plasma LH concentration did not differ significantly from the control values. The plasma FSH concentration of the oestrogen-treated males showed a delayed rise to values equal to or higher than those of controls of the same age. The delayed rise in plasma FSH concentration in the oestrogen treated males preceded the delayed rise in plasma testosterone in these animals. The decrease in plasma FSH concentration from the high prepubertal values to the lower values in adults occurred at different ages in the control and in oestrogen-treated rats but in both groups the decrease occurred as plasma testosterone levels were increasing and the first wave of spermatogenesis was reaching completion. The increase in plasma FSH concentration after castration was reduced in oestrogen-treated males during the period throughout which FSH levels in the intact animals were subnormal but the levels in oestrogen-treated males castrated after the delayed rise in FSH had occurred did not differ from control values. It is suggested that the delayed sexual maturation of male rats treated with high doses of oestrogen in the neonatal period is related principally to abnormalities in the secretion of FSH.

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K. BROWN-GRANT, J. M. DAVIDSON, M. R. SHERWOOD and C. M. TAPPER

In the course of a study on the effects of mating on plasma lh concentrations in the rat, a serendipitous finding was that plasma samples collected from male rats shortly after copulation often showed obvious evidence of haemolysis. These observations prompted a more detailed investigation.

Adult Wistar rats were maintained under reversed lighting (lights on from 21.00 to 11.00 hours). Mating tests were carried out under observation in subdued lighting between 14.00 and 18.00 hours. Females were made highly receptive by the subcutaneous injection of 100 μg of oestradiol benzoate in oil 48 hr before tests were begun. Under these conditions, a normal ejaculatory series in the male rat consists of some ten to fifteen mounts with brief penile intromissions, separated by short intercopulatory intervals, over a period of