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B. T. Donovan

Summary. Information concerning the weight at the onset of a period of oestrus, the timing of oestrus, the age at first oestrus and the lighting conditions was collected from the records of 1364 ferrets and reviewed for evidence indicating that the animals became sexually mature around a particular, critical, weight. None was found, but the results suggest that there is a minimum weight, around 420 g, below which oestrus does not occur.

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F. R. BLATCHLEY and B. T. DONOVAN

The changes in luteal function during pregnancy and pseudopregnancy in the ferret have previously been assessed by the study of the morphology of the ovaries and uterine tract (Hammond & Marshall, 1930; Donovan, 1967) but, with the development of competitive protein-binding techniques, the measurement of progesterone in small quantities of blood has become possible. We have used this procedure to assess progestin secretion by ovarian tissue in anoestrous, oestrous and pseudopregnant ferrets, and also after hypophysectomy.

Blood samples (2 ml), withdrawn by cardiac puncture under Nembutal anaesthesia, were centrifuged as soon as possible after collection and the plasma was stored at −20° C until assay. Plasma progestin concentrations were measured in 0·1-ml aliquots in triplicate as described previously (Blatchley, Donovan, Horton & Poyser, 1972), the limit of sensitivity being 0·8

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K. P. BLAND and B. T. DONOVAN

Summary.

Removal of the conceptuses (decidua+embryos) from the uterus of the guinea-pig between the 9th and 15th days after mating allowed the recurrence of oestrus at, or only slightly after, the time it would have occurred had not fertile mating taken place. The transfer of a single 6-day blastocyst to the uterus of unmated cycling animals resulted in pregnancy in three of six animals in which the cycles of the host and donor were synchronized. Normal development was never observed after transfer of 9- to 11-day implanted conceptuses (without associated decidua) to the uterus. Blastocysts and 9- to 10-day implanted conceptuses transferred to the spleen developed in eight of thirteen animals. The ectopic placental tissue did not prevent the normal recurrence of oestrus. Grafts developing from a single 11- to 12-day implanted conceptus in the spleen maintained the corpora lutea and delayed oestrus until after the 20th day in thirteen of twenty-four animals. The guinea-pig placenta appears to produce a systemically-active substance capable of neutralizing the luteolytic abilities of the uterus. This anti-luteolytic hormone probably acts only between Days 12 to 25 after mating.

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K. P. BLAND and B. T. DONOVAN

Summary.

Successful primary abdominal implantation and development has been induced in the guinea-pig by transection of the oviducts 1 to 3 days after mating although attempts made to induce tubal implantation by ligature of the utero-tubal junction failed.

Development also took place in four out of eighteen pre-implantation eggs (aged 4 to 5 days post coitum) transplanted into the kidney or abdominal muscle. In six cases, where post-implantation conceptuses (aged 9½ and 12 days post coitum) were transplanted into the spleen, testes or anterior chamber of the eye, growth and differentiation was observed on each occasion.

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Francesca R. Blatchley and B. T. Donovan

Department of Physiology, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, U.K.

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B. T. DONOVAN and A. N. LOCKHART

Summary.

The effect of differing lighting schedules upon the timing of the influx of leucocytes into the vaginal smear of the guinea-pig, and hence of ovulation, was examined. The timing of this event was altered following advancement of the light—dark sequence by 12 hr, and implies that the timing of ovulation in this species is influenced by light.

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Barbara Gledhill, H. M. Fraser and B. T. Donovan

Summary. Administration of ovine antiserum containing antibodies against synthetic LH-RH to spayed female ferrets caused an immediate fall in plasma LH concentration and by 2 h after injection circulating levels had declined by 70–80%. A further decline of 50% was observed on Day 2, but by Day 4 a return to normal levels had begun and control values were regained on Day 6. In contrast, the fall in plasma FSH concentration was delayed, with a significant reduction being first observed on Day 2 and minimal values occurring on Day 4. Control values were regained by Day 7.

The results accord with the concept that a single hypothalamic releasing factor controls the tonic secretion of both pituitary hormones. However, the slow change in FSH secretion implies that the mechanism for FSH release may be more autonomous than that for LH.