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ABSTRACT
The concentrations of oestradiol and oestrone in peripheral plasma of male and female ferrets 5 days before and 7, 15 and 30 days after birth were measured. Both steroids were present in high concentrations prenatally. Much lower levels were found in samples collected on day 7 and later, when the concentrations were similar to those of adult gonadectomized animals. No significant sex difference was seen for the concentration of either steroid at any age studied. These results, and those previously reported showing the absence of a circulating binding protein and the presence of oestradiol receptors in the hypothalamus in the perinatal period in this species, suggest that brains of both males and females are exposed to significant amounts of oestrogen during development. These findings lend support to the possibility that prenatal exposure to oestrogen plays a role in organizing the potential for female behaviour in male and female ferrets.
J. Endocr. (1984) 100, 161–166
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Department of Endocrinology, Growth and Reproduction, Erasmus University, Faculty of Medicine, Rotterdam, The Netherlands
(Received 1 March 1978)
In several avian species the ability of exogenous oestrogen to induce nest-building and in some instances courtship behaviour after ovariectomy is significantly enhanced by exposing the birds to long environmental photoperiods (Steel & Hinde, 1972; Liley, 1976). The same lighting stimulus will also induce ovarian activity in intact birds and a related phenomenon has also been reported in the sheep (Raeside & McDonald, 1959; Fletcher & Lindsay, 1971). In the studies on sheep, it was reported that ovariectomized ewes primed with progesterone displayed sexual behaviour in response to treatment with oestradiol benzoate more readily during the normal breeding season, when days were short, than at other times of the year. This communication reports a failure to obtain comparable results in another seasonally breeding mammal, the ferret (Mustela furo).
Female ferrets were purchased
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SUMMARY
Sexually immature male ferrets received electrolytic lesions in the rostral mediobasal hypothalamus, and another group of males received sham operations. Testicular size, as estimated by weekly palpation, increased rapidly after the placement of lesions. Four weeks after the operation the right testis and epididymis were found to weigh significantly more in lesioned than in sham-operated animals, whereas body weight was the same in the two groups. The right testis of lesioned ferrets had a significantly higher Leydig cell index as well as significantly larger luminal and outer diameters of the seminiferous tubules. In addition, histological examination and classification of the seminiferous tubules showed that spermatogenesis was advanced in lesioned ferrets, with pachytene spermatocytes being the most advanced germ-cell type present in a significantly higher percentage of tubules, and spermatogonia being the most advanced germ-cell type present in a significantly lower percentage of tubules. Finally, at this time the concentration of testosterone per testis was significantly higher in lesioned than in sham-operated ferrets. When the remaining testis was biopsied 20 weeks after the operation it was found that spermatogenesis was still more advanced and the concentration of testosterone in blood was significantly higher in lesioned ferrets. By the time autopsy was performed 38 weeks after the operation, all parameters of testicular function in the sham-operated male ferrets had caught up with those of lesioned animals.
In a second experiment it was found that hypothalamic lesions accelerated testicular growth without interfering with the subsequent occurrence of an annual regression and recrudescence of the testes.
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Gonadectomized rats bearing s.c. Silastic capsules containing crystalline oestradiol-17β diluted with cholesterol, or oestradiol-17β dissolved in sesame oil were tested for the presence of a diurnal rhythm in the display of lordotic behaviour. In experiment 1, female rats received four consecutive tests at intervals of 8 h in a lighting regimen of 12 h light: 12 h darkness beginning 4, 14 and 28 days after implantation of 5 mm capsules of oestradiol. After a single test on day 4, male rats were tested on days 14–15 only, at the same times as the female rats. Female animals were tested while vaginal–cervical stimulation was prevented by vaginal masking beginning 35 days after implantation of oestradiol. In experiment 2, lordotic responsiveness of female rats was assessed beginning 4 days after implantation of oestradiol once on each of 3 consecutive days, with each test occurring at a different time of day. Finally, in experiment 3, female rats were tested as in experiment 1 beginning 4 days after implantation of lower threshold amounts of oestradiol in oil-filled capsules. In no experiment were changes in lordotic behaviour observed as a function of the time of day. These findings failed to support recent reports of a sexually dimorphic rhythm in lordotic responsiveness to oestradiol in the rat.
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ABSTRACT
Administration of the synthetic steroid, 17β-hydroxy-17α-methyl-estra-4,9,11-triene-3-one (methyltrienolone, R1881), which is an androgen receptor agonist not metabolized in vivo, at doses of 400, 800 or 2400 μg/kg s.c. in propylene glycol stimulated mounting and ejaculation only slightly in sexually experienced castrated rats. A similar low level of mating was observed in a group of castrated rats given testosterone at doses of 400 followed by 800 μg/kg. However, when treated with a higher dose of testosterone (2400 μg/kg) these castrated rats displayed significantly higher levels of mounting and ejaculation than rats treated with any of the doses of R1881. Also, when this higher dosage of testosterone was substituted for each dose of R1881, significant increments in mounting and ejaculation occurred in all groups. These findings show that R1881 is only marginally effective in restoring sexual behaviour in castrated rats, suggesting that the activation of neural androgen receptors cannot by itself account for the activational effect of testosterone on mating behaviour in gonadally intact male rats.
J. Endocr. (1987) 113,15–20
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Daily administration of oestradiol benzoate, beginning 10 days after mating, stimulates lordosis behaviour in deciduomata-bearing pseudopregnant rats, but not in pregnant rats. The inhibition of this behaviour during pregnancy was not prevented by reducing the number of conceptuses to two, by removing the fetuses while leaving the placentas in utero, or by removing the ovaries and administering progesterone to prevent abortion. Removal of the uterus or fetuses and placentas on day 12, however, led to high levels of lordosis behaviour. Thus, it is likely that the placenta produces a factor which inhibits the behavioural responsiveness to oestrogen.
Plasma levels of progesterone, androsterone and dihydrotestosterone were higher during the second half of pregnancy than in the second half of pseudopregnancy prolonged by uterine decidualization. The possible involvement of these steroids in the inhibition of lordosis behaviour was investigated by increasing their levels in deciduomata-bearing pseudopregnant rats and determining the effect on oestrogen-induced lordosis behaviour. Little suppression of this behaviour was seen when the pseudopregnant rats were treated with progesterone or androsterone whereas treatment with dihydrotestosterone resulted in a significant inhibition of lordosis behaviour. However, the dose of dihydrotestosterone required to do so resulted in high, non-physiological plasma levels of this steroid. No inhibition of lordosis behaviour was observed when dihydrotestosterone levels were approximately threefold those normally present in pregnant rats. It is concluded that none of these three steroids is primarily responsible for the suppression of lordosis behaviour during pregnancy.
