Maintenance of receptors for luteinizing hormone by ovine placental lactogen in pseudopregnant rats

The relationship between serum prolactin concentration and pregnancy outcome in women with unexplained recurrent miscarriage

The role of prolactin in early pregnancy is controversial. The aim of this study was to evaluate the relationship between serum prolactin concentration and the risk of miscarriage in women with unexplained recurrent miscarriage (RM). A series of 174 women with unexplained RM, who had serum prolactin concentrations measured from January 2000 to September 2009 at the Recurrent Miscarriage Clinic in Royal Hallamshire Hospital in Sheffield, were included in this study. Among the 174 patients with unexplained RM, 40 patients did not conceive during the study period, 9 were lost to follow-up and 125 patients conceived again. Patients who did not conceive were significantly older than those who conceived (p < 0.05, OR: 1.08, 95% CI: 1.03-1.13). Among those who conceived again, the pregnancy outcome data were available for analysis in 109 patients. Those who miscarried were older (p < 0.05, OR: 1.1, 95% CI: 1.01-1.22) and had significantly lower serum prolactin concentrations (p < 0.05, adjusted OR: 0.99, 95% CI: 0.97-0.99) after adjustment has been made for age, than those who had a live birth. Lower basal serum prolactin concentrations were associated with an increased risk of miscarriage in a subsequent pregnancy in women with unexplained RM.

Native and recombinant bovine placental lactogens

The bovine placenta produces a wide variety of proteins that are structurally and functionally similar to the pituitary proteins from the GH/PRL gene family. Bovine placental lactogen (bPL) is a 200-amino acid long glycoprotein hormone that exhibits both lactogenic and somatogenic properties. The apparent molecular masses of purified native (n) bPL molecules (31-33 kDa) exceed 23 041 Da, which is the theoretical molecular mass of the protein core. At least six isoelectric variants (pI: 4.85-6.3) of bPL were described in cotyledonary extracts and three different bPL isoforms (pI: 4.85-5.25) were found in fetal sera. The bPL molecules that are detected in higher concentrations in peripheral circulation exhibit a more acidic pI than those present in placental homogenates. This may reflect an important glycosylation process occurring just prior to the bPL secretion. The bPL mRNA is transcribed in trophectoderm binucleate cells starting from Day 30 of pregnancy until the end of gestation. In mothers, bPL is involved in the regulation of ovarian function, mammogenesis, lactogenesis, and pregnancy stage-dependent adaptation of nutrient supplies to the fetus. Due to the higher fetal, compared to maternal concentrations of circulating hormone, it has been suggested that bPL primarily targets fetal tissues.

Mechanism of ruminant placental lactogen action: molecular and in vivo studies

Ruminant placental lactogens (PLs) are structurally related to prolactins (PRLs) and growth hormones (GHs) and are secreted by placentae. Ruminant PLs are unusual in their capacity to bind and activate PRL and GH receptors (Rs) from other species. The present minireview summarizes several works showing that unlike in heterologous species (rat, rabbit, human), in homologous (ruminant) species, PLs act by activating PRLRs or by heterodimerizing GHRs and PRLRs, and suggests that this may be the main mechanism of PL action in vivo. Mutations impairing the ability of ovine (o)PL or bovine (b)PL to form complexes with PRLRs (but not with GHRs) do not cause loss of biological activity, because the transient existence of the homodimeric complex is still sufficient to initiate the signal transduction; however, mutants do lose their ability to activate homologous PRLRs. To explain this difference, we proposed a novel term-minimal time of homodimer persistence-which assumes that to initiate the signal transduction, a "minimal time" of homodimer existence is required for transphosphorylation of associated JAK2s. In interactions between ruminant PLs and homologous PRLRs, this minimal time is met through the interaction with homologous PRLRs, which has a shorter half-life than with heterologous PRLRs. Thus oPL or bPL are active in cells possessing both homologous and heterologous PRLRs. Mutations of PLs decrease the affinity, shortening the "time of homodimer persistence." In heterologous interactions, the minimal time is still sufficient to initiate the biological activity, whereas in homologous interactions, which in any case are weaker, further destabilization of the complex shortens its persistence below the minimal time, causing loss of biological activity.