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H J Paust

Publications and source records attributed to H J Paust.

12 recordsLinked to original sources
PubMed2002

The expression of the RLF/INSL3 gene is reduced in Leydig cells of the aging rat testis.

The relaxin-like factor (RLF), which is the product of the INSL3 gene, is highly expressed in the fetal and adult-type Leydig cells of all species so far examined. In adult testes it is upregulated at puberty but appears subsequently to be expressed in a constitutive manner, independently of acute changes in the hypothalamic-pituitary-gonadal (HPG) axis. Functional hypogonadism with decreased testosterone is prevalent in the aging male. In order to test whether this is a property of the HPG axis, or of the Leydig cells themselves, RLF/INSL3 was used as an independent marker to assess rat Leydig cell differentiation status. Hybridization analysis showed that in the testes of old (2 years) rats, RLF/INSL3 mRNA expression was dramatically reduced, compared to young (3 months) animals. This was also evident at the protein level using immunohistochemistry. The results suggest that increasing functional hypogonadism in older male mammals is likely caused by a dedifferentiation of the Leydig cells themselves.

Aging↗
PubMed2000

Presence of a 5-HT7 receptor positively coupled to adenylate cyclase activation in human granulosa-lutein cells.

Although serotonin (5-HT) has been shown to stimulate progesterone production by human granulosa-lutein cells (hGLC), the receptor type and associated signaling pathway remain uncharacterized. We report here that 5-HT receptors in these cells are positively coupled to adenylate cyclase activity. Formation of cAMP was stimulated by 5-HT and its agonists in a dose- and time-dependent manner. Mianserin, amoxapine, and loxapine were equipotent in antagonizing 5-HT-induced cAMP formation. For both cAMP formation in cells and adenylate cyclase assay using membrane fractions, the rank order of potency for agonists of 5-HT were: 5-carboxy-aminotryptamine >5-HT> or =5-methoxytryptamine, consistent with a typical pharmacological profile of human 5-ht7 (h5-ht7) receptor. Sequence data of amplified complementary DNA fragments reverse transcribed from hGLC RNA revealed complete identity with published sequence of h5-ht7 receptor complementary DNA. Northern analysis showed the presence of 2.8-kb h5-ht7 transcripts in hGLC. The three variants h5-ht7A, h5-ht7B, and h5-ht7D were also detected in hGLC. Preincubation of hGLC with 5-HT (10(-8)-10(-6) M) resulted in a marked reduction in the cAMP response when the cells were subsequently stimulated with gonadotropin, and this heterologous desensitization could be reversed by 5-ht7 receptor antagonist clozapine. These data demonstrate that h5-ht7 receptor is present and stimulate cAMP formation in hGLC. In addition, the h5-ht7 receptor seems to be implicated in the heterologous down-regulation hCG-stimulated cAMP response in hGLC, with a possible ramification for luteal insufficiency.

Adenylyl Cyclases↗
PubMed1999

Endothelin and endothelin receptors A and B in the human testis.

Human testicular capillaries interconnect Leydig cells and seminiferous tubules. Microcirculation and blood flow are therefore essential for the maintenance of spermatogenesis. The expression and the localisation of ET (endothelin) and its receptors in testicular tissue, in seminiferous tubules and in human testicular capillaries were studied. ET-1 mRNA was detected in whole testicular tissue and in seminiferous tubules whereas isolated testicular capillaries were negative. Big ET-1 (Big endothelin 1) and ET peptides were localised in Leydig and Sertoli cells whereas interstitial and intramural capillaries (within the lamina propria) remained unstained. ET was also found in mature spermatids. ET-A (endothelin receptor A) mRNA was detected in seminiferous tubules and whole testicular tissue whereas testicular blood vessels were negative. ET-A immunostaining was displayed in Leydig and Sertoli cells and in spermatids. ET-B (endothelin receptor B) mRNA was detected in whole testicular tissue, seminiferous tubules and in testicular capillaries. ET-B peptide was prominent in Leydig cells, peritubular cells, endothelial cells and pericytes of interstitial and intramural capillaries as well as in vascular endothelial and smooth muscle cells. From these results we conclude that ET produced in Leydig and Sertoli cells can act in a paracrine manner via ET-B on the human testicular microvasculature and the peritubular cells. The presence of both ET-A and ET-B in Leydig cells and of ET-A in Sertoli cells leads to the assumption that ET could influence these cells as an autocrine factor.

Blotting, Southern↗
PubMed1997

New aspects of Leydig cell function.

Previous studies indicated that the Leydig cells of the human testes show similarities to neuroendocrine cells. In this context, the local synthesis of two neuroactive signaling molecules, namely nitric oxide (NO) and C-type natriuretic peptide (CNP), both acting via the second messenger, cyclic guanosine monophosphate (cGMP), might be of physiological relevance. By immunoblotting, immunohistochemical analyses and affinity crosslinking experiments, respectively, the presence of soluble guanylate cyclase (sGC), the NO receptor, and of guanylate cyclase B (GC-B), representing the CNP receptor, was demonstrated in Leydig cells, seminiferous tubules and blood vessels of the human testis. Moreover, cGMP and its binding protein cGMP-dependent protein kinase type I (GK I) were found in these structures. The functional activity of the two receptors was proved by generation of cGMP in response to treatments with the NO donor, sodium nitroprusside (SNP), and with CNP, respectively. As indicated by immunohistochemical analyses and by treatments of cells with either SNP or CNP, human Leydig tumour cells and MA10 cells, representing a mouse Leydig tumour cell line, were found to be distinguished by a reduced expression of the receptors for NO and CNP. Furthermore, expression levels of the components of the two cGMP-generating systems were found to be widely unchanged in Leydig cells during different ontogenetic stages. Though cGMP has been shown to influence testosterone release, the constant developmental expression patterns of NO and CNP apparently independent of differences in androgen production, the down-regulation of their receptors in tumorous cells, and the presence of GK I, may point to additional autocrine functions of these factors and of cGMP in Leydig cells. Moreover, possible paracrine actions of NO and CNP may include relaxation of seminiferous tubules and blood vessels in order to modulate sperm transport and testicular blood flow, respectively. These findings suggest that Leydig cell-derived factors may exert activities different from or in addition to those involved in the regulation of testosterone production.

Adult↗
PubMed1997

Synthesis of C-type natriuretic peptide (CNP) by immortalized LHRH cells.

Former studies have indicated an influence of natriuretic peptides on LHRH secretion. In this report we demonstrate local synthesis of CNP in immortalized LHRH neurons (GT1-7 cells). Using reverse transcription-polymerase chain reaction and RNase protection assays a transcript for the CNP precursor was identified in these cells. Immunocytochemical data revealed the presence of the peptide CNP in GT1 cells, using a specific polyclonal antiserum against CNP. Electron microscopic immunohistochemical investigations also showed the strongest CNP-immunoreactivity in some small vesicles, providing initial evidence for the potential secretion of this peptide by immortalized LHRH neurons. Subsequent experiments demonstrated also that CNP elevates LHRH production in static cultures of GT1 cells. These data show for the first time the co-production of the functionally relevant natriuretic peptide, CNP, by immortalized LHRH neurons. Together with the recent demonstration of CNP receptor expression by these cells, we suggest that CNP may represent a novel autocrine regulator of LHRH neuronal activity. It remains to be elucidated, however, to what extent CNP expression in immortalized LHRH neurons reflects a co-localization in situ of CNP and LHRH peptides.

Animals↗
PubMed1997

Localization of endothelin-1 and endothelin-receptors A and B in human epididymis.

Expression of mRNA of endothelin-1 (ET-1) and its receptors, endothelin receptor A (ET-A) and endothelin receptor B (ET-B), in human epididymis was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Immunohistochemistry was performed on longitudinal sections through whole normal human epididymides. ET-1 mRNA was detected in caput, corpus and cauda epididymidis. Immunohistochemically, ET-1 was localized mainly in ciliated cells of efferent ducts and in some principal cells of epididymal duct. Larger arteries, but not epididymal microvasculature, contained ET-1 immunoreactivity. ET-A and ET-B mRNAs were detected in caput, corpus and cauda epididymidis. In efferent ducts, ET-A immunoreactivity was localized in ciliated cells. In the proximal region of the epididymal duct, ET-A immunostaining was localized mainly in basal cells whereas the distal region was devoid of ET-A immunoreactivity. Throughout the epididymis, blood vessels stained positive for ET-B. Furthermore, ET-B immunoreactivity was found in ciliated cells of efferent ducts and in basal cells of the distal epididymal duct. The fact that ciliated cells of efferent ducts contain ET-1 and both types of receptors indicates that ET-1 acts as an autocrine factor in these cells. ET-1 produced by efferent ducts and epididymal duct may control epididymal blood flow in a paracrine manner via ET-B receptors in epididymal blood vessels.

Endothelin-1↗
PubMed1996

Expression of C-type natriuretic peptide in the bovine pineal gland.

Recent studies have pointed to membrane-bound guanylyl cyclases (GCs) type A and type B in the rat pineal gland, which augment levels of cyclic GMP (cGMP) in response to atrial natriuretic peptide (ANP), brain-type natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). The present report demonstrates for the first time the expression of CNP in the bovine pineal gland. The CNP prohormone transcript (unlike pre-pro-ANP) was found by reverse transcriptase (RT)-PCR in bovine pineal extracts. CNP immunoreactivity (ir) was revealed in a subpopulation of pinealocytes in situ and in nearly all pinealocytes in culture. Electron microscopic immunohistochemical investigations showed the presence of CNP-ir in cytoplasmic vesicles, providing evidence for the potential secretion of this peptide by pineal cells. Furthermore, the CNP receptor (GC-B) and GC-A (receptor for ANP and BNP) were identified by RT-PCR. Although melatonin secretion was unaffected, natriuretic peptides were able to elevate markedly cGMP production in cultured bovine pinealocytes with a rank order of potency of CNP > BNP = ANP. These findings describe a tissue CNP system in the bovine pineal gland and suggest that CNP may be a local auto- or paracrine modulator of pineal function.

Animals↗
PubMed1996

Natriuretic peptides in the human testis: evidence for a potential role of C-type natriuretic peptide in Leydig cells.

Functional studies indicate that natriuretic peptides have direct effects on Leydig cells of the testis. In this report, we demonstrate local synthesis of one member of the natriuretic peptide family, C-type natriuretic peptide (CNP), in Leydig cells of human testes. Using RT-PCR assays, messenger RNA (mRNA) for the CNP precursor was detected in human testis and found to be prominently expressed in Leydig cells. Immunohistochemical analyses revealed CNP to be almost exclusively associated with Leydig cells. Distinct differences in the staining intensity-including cells without detectable staining-suggest a heterogeneity of CNP expression within the Leydig cells. Moreover, the presence of transcripts for the CNP receptor, a particulate guanylate cyclase, termed GC-B, was demonstrated by RT-PCR in human testis and in isolated Leydig cells. The expression of this receptor in human testis membranes could be confirmed by affinity labeling with 125I-labeled CNP. These findings demonstrate, for the first time, the production of a natriuretic peptide in human Leydig cells. The occurrence of CNP and its receptor in the human testis points to a local role of the peptide, presumably acting in an auto- or paracrine manner to modulate organ-specific functions.

Adult↗
PubMed1991

Cloning of a cDNA encoding a novel putative G-protein-coupled receptor expressed in specific rat brain regions.

A cDNA clone encoding a novel putative G-protein-coupled receptor was isolated from a rat brain cDNA library using a PCR-amplified cDNA fragment as a hybridization probe. The 3,615-bp-long nucleotide sequence predicts a single open reading frame of 1,173 bp coding for 391 amino acids, giving a calculated molecular weight of 42.75 kD. The amino acid sequence shares features common to many other receptors, including the seven membrane-spanning hydrophobic regions and putative asparagine-linked glycosylation and phosphorylation sites. Northern blot analysis reveals that a corresponding approximately 3.7-kb mRNA is expressed in specific brain regions such as hypothalamus, cortex, hippocampus, and thalamus but not in other organs analyzed. Although the ligand for this receptor has not yet been identified, it shares some similarities with the vascular type-1 angiotensin II receptor, the vasoactive intestinal peptide (VIP) receptor, and the chemotactic receptors for human C5a anaphylatoxin and the formyl peptide fMet-Leu-Phe.

Acetyl-CoA C-Acyltransferase↗