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Endometrial prostaglandins (PGs) and the PGE2/PGF2alpha ratio play an important role in regulating the estrous cycle and establishment of pregnancy. The enzymes downstream of cyclooxygenase-2 may determine the PGE2/PGF2alpha ratio in the porcine uterus. Thus, we have cloned porcine PGF synthase (PGFS) and microsomal PGE synthase-1 (mPGES-1) and characterized their expression in porcine endometrium during the estrous cycle and early pregnancy. PGFS and mPGES-1 amino acid sequences possessed a high degree (>67% and >77%, respectively) of identity with the other mammalian homologs. There was little modulation of mPGES-1 throughout the estrous cycle; however, PGFS expression was highly up-regulated in endometrium around the time of luteolysis. During early pregnancy, PGFS at the protein level showed a time-dependent increase (low on d 10-13, intermediate on d 14-23, and high on d 24-25). In pregnancy, expression of mPGES-1 was intermediate on d 10-11 and low on d 14-17 and then increased after d 22, reaching the maximum on d 24-25. Immunohistochemistry showed localization of PGFS and mPGES-1 proteins mainly in luminal and glandular epithelium. Concluding, the spatiotemporal expression of PGFS throughout the estrous cycle indicates an involvement of PGFS in regulating luteolysis in the pig. The comparison of endometrial PGFS and mPGES-1 expression on d 10-13 of the estrous cycle and pregnancy suggest a supportive role of these enzymes in determining the increase of uterine PGE2/PGF2alpha ratio during maternal recognition of pregnancy. Moreover, high expression of both PG synthases after initiation of implantation may indicate their significant role in placentation.

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TSH secretion from the anterior pituitary is mainly regulated by TRH and thyroid hormones. We hypothesized that in addition the pituitary itself could modulate TSH production by sensing its own TSH release, enabling fine-tuning of TSH secretion. For such an ultra-short loop control, the pituitary should contain a TSH receptor (TSH-R). To find evidence for this we screened a human pituitary complementary DNA library with a digoxigenin-labeled TSH-R probe and found 2 positive clones of 32,000 plaques. One clone was sequenced and found to be completely identical to the thyroid TSH-R. T SH IS THE major regulator of thyroid hormone synthesis and secretion. The production of TSH in the anterior pituitary is modulated by thyroid hormones via a classical negative feedback mechanism and by TRH from the hypothalamus by a positive feedforward mechanism. In concert with other circulating factors, such as dopamine, somatostatin, and some steroids, TRH and thyroid hormones are seen as the main determinants to maintain normal TSH secretion.We hypothesized that, in addition, TSH secretion might be fine-regulated in a short loop feedback at the pituitary level through the TSH receptor (TSH-R). This hypothesis was developed on two grounds. Firstly, because we were intrigued by the well known clinical observation that many patients with Graves' hyperthyroidism continue to show suppressed plasma TSH levels despite adequate antithyroid treatment, resulting in clinical euthyroidism and normal (or even low) plasma T 4 and T 3 levels (1, 2). In our experience this is less often seen in patients with other forms of hyperthyroidism. We wondered whether TSH-R-stimulating antibodies might suppress TSH secretion by direct action on the pituitary. If so, the pituitary should contain a TSH-R. Several reports have now demonstrated that the TSH-R is present at extrathyroidal sites. In the intestine, for example, it appears to be involved in a local paracrine network of hormonal regulation of T cell homeostasis in response to locally produced TSH (3).Secondly, we hypothesized that it would be more efficient for the fine-tuning of TSH secretion (i.e. to keep TSH plasma levels within a certain range) if the pituitary was able to measure and regulate its own TSH production, in analogy to modern heating boilers, which regulate their heat production through built-in temperature sensors in addition to the room thermostat.A pituitary TSH-R might be involved in TSH secretion at the pituitary level in an autocrine fashion via a TSH-R on the thyrotroph itself. Alternatively, it might be mediated in a paracrine fashion through another cell type. A likely candidate for this is the folliculo-stellate (FS) cell (4), which is known to produce various cytokines and other regulatory factors, mostly notably IL-6 (5, 6).To test our hypothesis, we set out to study the presence and cellular localization of the TSH-R in the human anterior pituitary using several, independent methods aimed at finding both TSH-R messenger ribonucleic acid (mRNA) and protein. Ma...

Evidence is accumulating that pituitary hormone secretion is not only regulated by feedback from hormones produced in the target organs (long feedback) on the pituitary and the hypothalamus (feedforward), but also by a feedback of the hypophyseal hormones at the hypothalamic (short feedback) and the pituitary (ultra-short feedback) level. Inhibition of thyrotropin (TSH) and MSH secretion by pituitary preparations by adding exogenous TSH or MSH to the medium was already observed in the 1960s, as was the phenomenon that adrenocorticotropic hormone (ACTH) injected in the hypothalamus lowered plasma corticosterone levels. These early observations have now been corroborated by the demonstration of the receptors for various pituitary hormones in the hypothalamus and the adenohypophysis. The thyrotropin receptor (TSHR) is found on folliculo-stellate cells in the pituitary, which are known to influence the neighboring endocrine cells. This pituitary TSR-receptor is also recognized by TSHR receptor autoantibodies, which can downregulate TSH secretion independently from thyroid hormone levels, and are therefore thought to be responsible for the frequently observed suppressed TSH levels in patients with Graves' disease who are otherwise euthyroid.

Antithyroid treatment effectively restores euthyroidism in patients with Graves' hyperthyroidism. After a few months of treatment, patients are clinically euthyroid with normal levels of thyroid hormones, but in many patients TSH levels remain suppressed. We postulated that TSH receptor autoantibodies could directly suppress TSH secretion, independently from thyroid hormone levels, via binding to the pituitary TSH receptor. To test this hypothesis, we prospectively followed 45 patients with Graves' hyperthyroidism who were treated with antithyroid drugs. Three months after reaching euthyroidism, blood was drawn for the analysis of thyroid hormones, TSH, and TSH binding inhibitory Ig (TBII) levels. After 6.7 +/- 1.5 months since start of antithyroid treatment, 20 patients still had detectable TBII levels, and 25 had become TBII negative. The two groups had similar levels of free T(4) and T(3), but TBII-positive patients had lower TSH values than TBII-negative patients: median 0.09 (range < 0.01-4.30) mU/liter vs. 0.84 (0.01-4.20; P = 0.015). In addition, TSH levels correlated only with TBII titers (r = -0.424; P = 0.004), and not with free T(4) or T(3) values. Our findings suggest that TBII suppress TSH secretion independently of thyroid hormone levels, most likely by binding to the pituitary TSH receptor.

The protein tyrosine kinase (PTK) receptors and cytosolic signaling proteins as well as the protein tyrosine phosphatases (PTPs) have important roles in regulation of growth of the benign and malignant prostate gland. Here, we studied expression of the protein tyrosine phosphatase SHP-1 in prostate cancer cell lines and in human prostatic tissues. SHP-1 is expressed at a high level in LNCaP prostate cancer cells compared with PC3 cells. Silencing of SHP-1 expression with siRNA in LNCaP cells led to an increased rate of proliferation, whereas overexpression of SHP-1 by means of transient and stable transfection in PC3 cells led to a decrease in proliferation. Corresponding changes were observed in cyclin D1 expression. We further demonstrate that LNCaP and PC3 cells respond differently to IL-6 stimulation. SHP-1 overexpression in PC3 cells reversed IL-6 stimulation of proliferation, whereas in SHP-1-silenced LNCaP cells, IL-6 inhibition of proliferation was not affected. In addition, IL-6 treatment led to higher levels of phosphorylated STAT3 in SHP-1-silenced LNCaP cells than in control cells. Next, SHP-1 expression in human prostate cancer was analyzed by immunohistochemical staining of tissue microarrays comprising tumor specimens from 100 prostate cancer patients. We found an inverse correlation between the tumor level of SHP-1 expression and time to biochemical recurrence and clinical progression among prostate cancer patients. In conclusion, our results suggest that a decreased level of SHP-1 expression in prostate cancer cells is associated with a high proliferation rate and an increased risk of recurrence or clinical progression after radical prostatectomy for localized prostate cancer.