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ABSTRACT
The prolactin-producing cells of the bovine anterior pituitary were found to contain a vasoactive intestinal polypeptide (VIP) immunoreactive substance, thus suggesting a role for VIP in the regulation of prolactin release.
The pituitaries of the dw and lit strains of mutant mice, congenitally deficient in prolactin-producing cells, and hyt mice, which were found to have reduced numbers of prolactin-producing cells, showed a markedly reduced VIP immunoreactivity. Hypothalamic VIP immunoreactivity, however, was found to be unchanged in the three strains of mutant mice, indicating that the high concentration of VIP in the hypothalamus does not derive from the adenohypophysis through retrograde flow. The deficiency in the mutant mice seems to be due to the lack of prolactin target cells in the pituitary.
J. Endocr. (1988) 118, 179–185
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Of various PGs, PGE1 and PGE2 are shown to be the most potent stimulators of osteoclastogenesis in vitro. PGE receptors have been classified into four subtypes, EP1-EP4. Little is known about PGE receptors functioning in bone cells. In this study, using mouse marrow culture, we investigated which PGE receptors are important in osteoclast-like cell (OCL) formation induced by PGE. 11-deoxy-PGE1 (EP2, EP3 and EP4 agonist) stimulated OCL formation potently. Butaprost (EP2 agonist) stimulated it slightly, while sulprostone (EP1 and EP3 agonist) and ONO-AP-324-01 (EP3 agonist) did not. AH23848B (EP4 antagonist) inhibited PGE2-induced OCL formation in a dose-dependent manner. The expression of EP4 mRNA in mouse bone marrow was confirmed by RT-PCR. The results indicate an important role of EP4 in PGE2-induced OCL formation in marrow cultures and suggest therapeutic potential of EP4 antagonists in some clinical conditions with accelerated bone resorption.
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Gonadotropin-releasing hormone (GnRH) and its agonist analog (GnRHa) are well known to have luteolytic effects. We previously reported that prolactin (PRL) stimulated matrix metalloproteinase (MMP)-2 activity to degrade collagen type IV as a mechanism of structural luteolysis. The effects of GnRHa treatment on developed corpora lutea are unknown. In this study we assessed the effect of GnRH on MMP expression and induction of structural involution of developed corpora lutea of superovulated rats using GnRHa. Pregnant mare serum gonadotropin-human chorionic gonadotropin (hCG)-synchronized ovulation and luteinization were induced in immature female rats, followed by daily treatment with GnRHa from 5 days after hCG treatment. GnRHa-induced involution of corpora lutea was evident 3 days after the treatment, as shown by their markedly smaller size (60% of the control weight). Nine days after hCG injection, serum progesterone and 20alpha-dihydroprogesterone concentrations were as low as those associated with structural luteolysis. These findings revealed that GnRHa has the ability to induce structural luteolysis in superovulated rats in the same way that PRL does. To gain information on mechanisms of luteal involution induced by GnRHa, we performed gelatin zymography. This showed a significant increase in the active form of MMP-2 in the luteal extract of GnRHa-treated rats (more than twofold that of the control). Activation of pro-MMP-2 by membrane type-MMP (MT-MMP) is reported to be a rate-limiting step for catalytic function. Another function of MT-MMP is to degrade collagen types I and III. The plasma membrane fraction of corpora lutea of GnRHa-treated rats activated pro-MMP-2 of fetal calf serum, resulting in a marked shift of the 68-kDa band to the 62-kDa band in the zymogram. A Northern hybridization study also revealed simultaneous significant increases in expression of MMP-2 mRNA and MT1-MMP mRNA in corpora lutea of GnRHa-treated rats (more than threefold the control level). In summary, hormonal and histological features of corpora lutea of GnRHa-treated superovulated rats correspond to those of structural luteolysis. GnRHa stimulated the expression of MMP-2 and MT1-MMP in developed corpora lutea associated with involution. These findings support the conclusion that MMP-2, activated by MT1-MMP, and MT1-MMP itself, remodel the extracellular matrix during structural luteolysis induced by GnRHa.
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To explore the clinical significance of p53 in the pathogenesis of adrenal neoplasms, we investigated the incidence of p53 gene mutations in functioning human adrenal tumours using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique to screen p53 exons 4 to 9. We examined 29 adrenocortical adenomas (primary aldosteronism, n=17; Cushing's syndrome, n=12, all benign), and 33 phaeochromocytomas (benign solitary, n=18; benign multiple, n=5; malignant, n=10) in Japanese and Chinese patients. PCR-SSCP did not show any abnormal band-shifts in any of the adrenocortical adenoma and benign solitary phaeochromocytoma tissues. In contrast, six phaeochromocytoma tissues (two cases benign multiple, four cases malignant) showed PCR-SSCP band-shifts. Subsequent DNA sequencing analysis of the shifted bands revealed six cases with nine mutations or intronic sequence alterations: three cases contained sequence alterations within intronic regions, three cases with silent mutation (sequence alteration in codon without amino acid alteration), and three cases contained missense mutations (one case each in exons 5, 6 and 9). Immunohistochemical staining demonstrated that two of three cases with missense mutations and one case with an intronic sequence alteration over-expressed p53 protein in tumour cell nuclei. We observed no association between p53 gene mutation and p21/WAF1/Cip-1 expression. The relatively high incidence of p53 gene mutations or intronic sequence alteration in multiple and malignant phaeochromocytomas, but not in benign solitary cases, suggests that p53 mutation could play some role in the pathogenesis of multiple and/or malignant phaeochromocytomas.
