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- Author: F. S. vom Saal x
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Summary. Four experiments were conducted with CF-1 house mice (Mus domesticus) to examine the relationship between a female's prior intrauterine position (2M = between 2 male fetuses, 1M = next to one male fetus, 0M = not next to a male fetus) and the timing of puberty and length of subsequent oestrous cycles under a variety of housing conditions. The results of Exp. 1 confirmed that the presence of males was required for females to enter puberty and exhibit regular oestrous cycles, regardless of prior intrauterine position. When housed individually after weaning either with a male in the cage or separated by a wire mesh partition, 0M-females ovulated and mated at a younger age and had shorter post-pubertal oestrous cycles than did 2M-females (1M-females were intermediate between 0M- and 2M-females). Other females were also housed after weaning with a male or separated by a wire mesh partition from a male in a variety of social environments (4 0M-females and 1 2M-female, 4 2M-females and 1 0M-female, 5 1M-females, 3 0M-females and 3 2M-females). The objective of these different housing conditions was to determine whether prior intrauterine position influenced the transmission of and/or sensitivity to cues that delay puberty and prolong subsequent oestrous cycles. Relative to 2M-females, 0M-females both produced more potent cues and were more sensitive to the cues (again, 1M-females were intermediate between 0M- and 2M-females). Specifically, in the presence of other females, puberty was delayed and post-pubertal oestrous cycles were prolonged to the greatest extent in 0M-females. Prior intrauterine position is therefore a source of individual variation in the production of and sensitivity to cues that modulate the timing of puberty and the length of subsequent oestrous cycles in female mice. The findings suggest that prenatally-androgenized 2M-females may have a reproductive advantage over other females at high population densities.
Keywords: pheromones; puberty; oestrous cycle; intrauterine position; sexual differentiation; mouse
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Summary. Female mice that had developed in utero between 2 male (2M females) or 2 female (0M females) fetuses were housed individually at 32 days of age in the presence of a male. The 0M females had a significantly shorter cycle. When the females were housed in groups of 5 in the presence of a male, cycle length in OM females was significantly longer than that of 2M females for the first cycle recorded, but this relationship reversed completely by the third and fourth cycles. These results are compatible with a hypothesis that former intrauterine proximity to male fetuses affects the intrinsic timing of the oestrous cycle and the capacity to emit oestrus-suppressing cues and/or the sensitivity to such cues.
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Summary. In litter-bearing mammals, the course of development of male and female fetuses is affected by the presence of other fetuses of the same or opposite sex located nearby within the uterus. The transport of testosterone between rat fetuses was examined by implanting a Silastic capsule containing [3H]testosterone into the amniotic sac of a fetus at either the ovarian or cervical end of a uterine horn on days 19 and 20 of pregnancy. The amount of testosterone that was recovered from the amniotic fluid of other fetuses 12 h later was determined. The amniotic fluid surrounding the adjacent fetus on the cervical side of the implanted fetus contained three times as much [3H]testosterone as did the adjacent fetus on the ovarian side, regardless of where in the uterus the implant was made. The movement of dye injected into the uterine lumen was towards the cervix. Intraluminal fluid movement may thus mediate the greater transport of [3H]testosterone towards the cervix than towards the ovary.
Our findings support the hypothesis that transport of testosterone between fetuses occurs across the fetal membranes via diffusion, such that any fetus (male or female) located between male fetuses receives the greatest supplement of testosterone.
Keywords: intrauterine position; intrauterine transport; sexual differentiation; rat
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The effect of changes in maternal corticosterone concentrations, induced by maternal stress, maternal adrenalectomy or both, on concentration of corticosterone in serum and in adrenals of mouse (Mus domesticus) fetuses was examined. Higher baseline serum corticosterone concentrations were found in female fetuses than in male fetuses; however, there was no sex difference in the content of corticosterone in adrenals collected from these fetuses. Sex differences were observed in the fetal response to changes in maternal concentrations of serum corticosterone resulting from stress (bright light and heat) or adrenalectomy, and both factors eliminated the sex difference in corticosterone in fetal serum. When females were injected i.v. with [3H]corticosterone on day 17 of pregnancy, significantly more 3H was recovered from the serum of female than of male fetuses 15 min after the injection, while more 3H was recovered from placentae of male fetuses. This finding suggests that the difference in serum corticosterone in male and female mouse fetuses is due to greater transport of corticosterone from maternal blood across the placenta of female than of male fetuses.
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The effects of location within the left or right uterine horn, position within each uterine horn, and fetal sex on fetal bodymass, blood flow to individual uterine segments associated with fetuses, and blood flow to the maternal portion of the placenta were investigated in rats. Sprague–Dawley rats were anaesthetized on day 5, 10, 15, 20, 21 or 22 of pregnancy, and radioactive microspheres with diameters of 15 mm were injected via a left ventricular cannula to measure blood flow to tissues. Tissues were weighed wet, and the rate of blood flow, corrected for wet mass (ml min−1 g−1 tissue), was calculated. Microspheres were not detected in fetuses, suggesting that they did not pass from maternal into fetal blood. Uterine blood flow was greater at the cervical and ovarian ends than in the middle of the uterus; on day 15 the rate of blood flow at the cervical and ovarian ends of each uterine horn was over twice that in the middle. The blood flow to the right uterine horn was greater than to the left horn. Blood flow to placentae increased dramatically between day 15 and day 20. There were marked differences in architecture between the uterine artery feeding the ovarian end of the right and left uterine horn, and blood flow to placentae located at the ovarian end of the right uterine horn was greater than to placentae in the same location in the left uterine horn. The blood flow to placentae and fetal bodymass were greater for female than for male fetuses on day 20, but on day 22 the reverse was observed. There was no effect of the number of fetuses in the same uterine horn on blood flow to the uterus or placentae, or on fetal or placental mass.
