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Summary. The production of ovine chorionic somatomammotrophin (OCS) was demonstrated in the trophoblast from Days 16–17 of pregnancy. Concentrations in the placenta rose slowly until about Day 100 when there was a rapid increase to reach 70 ± 5 μg prolactin equivalent/g fresh placental tissue and 15 ± 2 mg/placenta on Day 120. After Day 140, the concentrations decreased. It is suggested that OCS may be luteotrophic and have an effect on fetal growth.
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Summary. In the sow, a dramatic increase of LH specific binding was observed during the second half of pregnancy. This was due to an increase in receptor number (41 fmol and 95 fmol/mg protein at Days 50 and 105 respectively). The apparent association constant was unchanged. The pattern of prolactin receptor content showed two peaks at Day 60 and Day 105. Prolactin receptors increased earlier during pregnancy than did LH receptors, suggesting a possible role of prolactin in the induction of LH receptors.
In the ewe, the receptor content of LH and prolactin did not change very much during pregnancy. The corpus luteum showed normal luteal function until parturition although it was not necessary for maintenance of pregnancy in the ewes.
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The ontogeny of testicular LH and FSH receptors was studied in New Zealand rabbits from 20 to 180 days postpartum. The concentrations of free receptors (per mg total proteins) were very low at day 20. They increased steeply at day 30 for the LH receptor and at day 50 for the FSH receptor. Three RNA bands (1.2, 2.5 and 3 kb) were repeatedly detected on northern blots for the LH receptor and two bands (1.2 and 2.2 kb) were detected for the FSH receptor. The 1.2 kb band (which cannot give rise to full-length, membrane-anchored receptor) was present throughout the 20–180 day period for each receptor. However, the higher molecular mass bands were nearly undetectable at day 20. The 2.5 and 3 kb bands of the LH receptor increased twofold between day 20 and day 120, while the 2.2 kb band of the FSH receptor increased fivefold between day 20 and day 75. Thus the very low concentrations, or even absence, of the larger transcripts of both LH and FSH receptors were correlated with the inability to detect their cognate protein until 20 days of age. Subsequently, coordinated increases in high molecular mass transcripts and protein were observed for both receptors. Total LH receptor content increased in parallel to the previously reported increase in plasma testosterone between day 65 and day 100. FSH receptor density began to increase steeply at day 50, just at the onset of spermatogenesis. Thus, postnatal testicular development in the rabbit seems to entail the transcription of high molecular mass, translatable transcripts of the gonadotrophin receptors.
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The aim of the present study was to correlate the number of prolactin and LH receptors in the ovary with the changes in sexual behaviour that occur within a few days following parturition in rabbits. Multiparous New Zealand white rabbits at days 0, 3 and 10 of lactation were tested for their receptivity upon presentation to a male. Rabbits were classed as either receptive or nonreceptive at each stage of lactation; half of the animals in each class were treated with bromocryptine to examine the effects of prolactin deprivation. Ovarian receptors for LH and prolactin, as well as the concentration of their corresponding mRNA, were measured at each stage of lactation in every group. Results indicate that receptive behaviour is correlated with significantly more follicles on the rabbit ovary (diameter > 1 mm; P < 0.05) and an increase in the concentration of LH receptor mRNA (P < 0.001) and prolactin receptors (P < 0.05). In addition, on day 4 of lactation, there were significantly fewer follicles in nonreceptive rabbits (P < 0.05). LH receptor content remained constant on days 1 and 4 of lactation but increased on day 11 (P < 0.05). Bromocryptine treatment had no effect on the number of follicles or on the amount of LH receptor mRNA in does, but it significantly increased LH receptors (P < 0.01), and the concentration of prolactin receptor mRNA (P < 0.001), particularly on day 11 of lactation (P < 0.05), and prolactin receptor content (P < 0.001). Receptive rabbit ovaries therefore display more follicles that can respond to an LH surge via newly transcribed LH receptors than do nonreceptive. Bromocryptine treatment seems to relieve some repressive activity exerted by prolactin on the number of LH receptors in the rabbit ovary.
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Our objective was to determine the effect of ovine interferon-τ (IFN-τ) on prolactin receptor (PRL-R) gene expression in the ovine endometrium. IFN-τ is an embryonic cytokine which, via its paracrine anti-luteolytic activity, plays a critical role in maternal recognition of pregnancy in ruminants. Using ribonuclease protection assay procedures, we compared endometrial PRL-R mRNA levels in ewes that were intrauterine injected with either 2 mg bovine serum albumin or 2 mg recombinant ovine IFN-τ on day 10 of the oestrous cycle (day 0 = day of oestrus). IFN treatment significantly increased the abundance of both the long and short forms of PRL-R mRNA in the ovine uterus, but had no effect on the long:short form ratio. In situ hybridization experiments revealed that the increase in abundance of PRL-R mRNA in the uterus was localized to the glandular compartment of the endometrium. In pregnant ewes, a similar increase in PRL-R mRNA abundance was found to occur in ovine endometrium on days 14–15 post conception. Collectively, these data provided strong evidence that IFN-τ modulates the level of lactogenic hormone receptor mRNA in the ovine uterus. Whether the effect of IFN-τ on PRL-R expression is mediated directly or influenced, at least in part, by progesterone remains to be elucidated.
