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PubMed2004

Characterization of mice doubly transgenic for parathyroid hormone-related protein and murine placental lactogen: a novel role for placental lactogen in pancreatic beta-cell survival.

Transgenic overexpression of either parathyroid hormone-related peptide (PTHrP) or mouse placental lactogen type 1 (mPL1) in pancreatic beta-cells, using the rat insulin II promoter (RIP), results in islet hyperplasia either through prolonged beta-cell survival or through increased beta-cell proliferation and hypertrophy, respectively. For determining whether the two proteins might exert complementary, additive, or synergistic effects on islet mass and function when simultaneously overexpressed in beta-cells in vivo, RIP-PTHrP and RIP-mPL1 mice were crossed to generate mice doubly transgenic for PTHrP and mPL1. These double-transgenic mice displayed marked islet hyperplasia (threefold), hypoglycemia, increased beta-cell proliferation (threefold), and resistance to the diabetogenic and cytotoxic effects of streptozotocin compared with their normal siblings. Although the phenotype of the double-transgenic mice was neither additive nor synergistic relative to their single-transgenic counterparts, it was indeed complementary, yielding the maximal salutary phenotypic features of both individual transgenes. Finally, mPL1, for the first time, was shown to exert a protective effect on the survival of beta-cells, placing it among the few proteins that can improve function and proliferation and prolong the survival of beta-cells. Placental lactogen 1 is an attractive target for future therapeutic strategies in diabetes.

Animals↗
PubMed1992

Placental corticotropin-releasing hormone and pituitary-adrenal function during pregnancy.

The placenta secretes large amounts of the hypothalamic releasing hormone, corticotropin-releasing hormone (CRH), into both the maternal and fetal circulation during pregnancy. We characterized the relationship between maternal plasma CRH and products of the pituitary and adrenal in order to investigate the physiologic role of placental CRH in modulating maternal pituitary-adrenal function. Plasma was obtained from 8 women at biweekly intervals between 21 and 40 weeks of full-term pregnancy for CRH, adrenocorticotropin (ACTH), alpha-melanocyte-stimulating hormone (alpha MSH), cortisol, and dehydroepiandrosterone sulfate (DHEAS) measurements by radioimmunoassay. Eighteen women were also studied once at 22-34 weeks of pregnancy with plasma CRH and 24-hour urinary free cortisol measurement. Eight nonpregnant women served as control subjects. Plasma CRH was undetectable in the nonpregnant subjects and rose over the time period studied in the pregnant women. Concentrations of afternoon ACTH and cortisol also rose during pregnancy while DHEAS levels declined in the pregnant women. The alpha-MSH levels were beneath the level of detection (< 20 pg/ml) in both the pregnant and nonpregnant subjects. The overall mean afternoon ACTH concentration was higher in the pregnant than in the nonpregnant women (11.4 +/- 1.8 vs. 5.9 +/- 1.8 pg/ml; p < 0.05), although the ACTH levels in both groups remained within the normal range. The mean plasma cortisol concentrations were higher in the pregnant women, while the mean DHEAS levels were lower in the pregnant women when compared to the nonpregnant subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1991

An essential role of domain D in the hormone-binding activity of human beta 1 thyroid hormone nuclear receptor.

By analogy with steroid receptors, human placental thyroid hormone nuclear receptor (hTR beta 1) could be divided into four functional domains: A/B (Met1-Leu101), C (Cys102-Ala170), D (Thr171-Lys237), and E (Arg238-Asp456). The E domain was thought to bind thyroid hormone. To evaluate whether domain E alone is sufficient to bind T3 or requires the presence of other domains for functional T3-binding activity, a series of deletion mutants was constructed. The mutants were expressed in Escherichia coli, and the expressed proteins were purified. Analysis of the T3-binding affinity and analog specificity of the purified truncated hTR beta 1 indicated that domain E alone did not have T3-binding activity. Extension of the amino-terminal sequence of domain E to include part of domain D yielded a mutant (Lys201-Asp456) with a Ka for T3 of 0.5 +/- 0.2 x 10(9) M-1. Further extension to include the entire domain D (Met169-Asp456) yielded a mutant with T3-binding activity with a Ka of 0.8 +/- 0.1 x 10(9) M-1. Further extension of the amino-terminal sequence to include domain C increased the affinity for T3 by nearly 2-fold (Ka = 1.5 +/- 0.4 x 10(9) M-1). The Ka for the wild-type hTR beta 1 is 1.5 +/- 0.2 x 10(9) M-1. Furthermore, mutant (Met169-Asp456) binds to 3',5',3-triiodo-L-thyropropionic acid, D-T3, L-T4, and L-T3 with 307%, 37%, 7%, and 0.1%, respectively, of the activity of L-T3. This order of analog affinity is similar to that of the wild-type hTR beta 1.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1990

Mechanism of action of interleukin-1 beta in increasing corticotropin-releasing factor and adrenocorticotropin hormone release from cultured human placental cells.

The present study evaluated the possible effect and mechanism of action of interleukin-1 beta in regulating the release of corticotropin-releasing factor and adrenocorticotropin hormone from human cultured placental cells. With the use of a primary monolayer culture of human placental cells at term, the addition of interleukin-1 beta increased the release of immunoreactive corticotropin-releasing factor with a dose- and time-dependent effect. The intracellular concentration of both cyclic adenosine monophosphate and cyclic guanosine monophosphate increased in the presence of interleukin-1 beta. The addition of indomethacin, a prostaglandin synthesis inhibitor, partially reversed the effect of interleukin-1 beta. The same doses of interleukin-1 beta stimulated the release of adrenocorticotropin hormone and this effect was partially reversed by the addition of a synthetic corticotropin-releasing factor antagonist or by indomethacin. This study showed that interleukin-1 beta increases the release of corticotropin-releasing factor and adrenocorticotropin hormone from cultured placental cells. This effect is associated with increased intracellular cyclic nucleotide concentrations and is in part reversed by a prostaglandin synthesis inhibitor.

Adrenocorticotropic Hormone↗
PubMed1993

Effect of homologous placental lactogens, prolactins, and growth hormones on islet B-cell division and insulin secretion in rat, mouse, and human islets: implication for placental lactogen regulation of islet function during pregnancy.

Up-regulation of maternal islet function is essential to accommodate the increased demand for insulin during pregnancy. Previously, we suggested that lactogenic activity regulates islet function during pregnancy. However, this hypothesis was based on the effect of homologous PRLs on islets, since the homologous placental lactogens (or islets) were unavailable. In this study we examine the direct effects of homologous placental lactogens (PL), PRL, and GH on insulin secretion and B-cell division in rat, mouse, and human islets in vitro. Neonatal rat islets were cultured for 8 days in the presence of 0-1000 ng/ml rat PL-I (rPL-I), rPRL, or rGH. Media were changed daily, and the insulin concentration was determined. rPL-I and rPRL (500 ng/ml) treatment resulted in a 2-fold increase in insulin secretion. rGH (1000 ng/ml) elicited a 30% increase in insulin secretion. Similarly, cell replication, as indicated by BrdU incorporation into B-cells, was increased 4-fold in the presence of rPL-I and rPRL. The ED50 for insulin secretion and 5'-bromo-2'-deoxyuridine (BrdU) incorporation was 70 ng/ml for rPL-I and 150 ng/ml for rPRL. Similarly, in adult rat islets, insulin secretion was increased 1.6-fold, and B-cell replication increased 3-fold in the presence of the lactogenic hormones. Neonatal mouse islets were cultured for 8 days in the presence of 500 ng/ml mouse (m) PL-I, mPL-II, mPRL, or mGH. mPL-I, mPL-II, and mPRL treatment resulted in a 2-fold increase in insulin secretion. mGH elicited a 30% increase in insulin secretion. BrdU incorporation into B-cells was increased 3-fold in the presence of mPL-I and mPRL and 2-fold in the presence of mPL-II. Adult human islets were cultured for 8 days in the presence of 1 microgram/ml human (h) PL, hPRL, or hGH. For human islets isolated from six pancreata obtained from females, hPL (138 +/- 10%), hPRL (133 +/- 9%), and hGH (117 +/- 3%) significantly increased insulin secretion compared to that from control islets. This study compares the direct effects among homologous PLs, PRLs, and GHs on insulin secretion and B-cell division in rat, mouse, and human islets. The results indicate that placental lactogen directly regulates islet function in several species and is probably the principal hormone responsible for the increased islet function observed during normal pregnancy.

Adult↗