Late inflammatory and thrombotic changes in irradiated hearts of C57BL/6 wild-type and atherosclerosis-prone ApoE-deficient mice

BACKGROUND AND PURPOSE

Radiation-induced heart disease represents a late complication of thoracic radiotherapy. We investigated the inflammatory and thrombotic response after local heart irradiation in wild-type and atherosclerosis-prone mice.

MATERIAL AND METHODS

Atherosclerosis-prone ApoE(-/-) and C57BL/6 wild-type mice were sacrificed 20, 40, and 60 weeks after irradiation with 0.2, 2, 8, or 16 Gy. The expression of CD31, vascular cell adhesion molecule-1 (VCAM-1), thrombomodulin (TM), and CD45 were quantified by immunofluorescence staining of heart tissue sections.

RESULTS

Microvascular density decreased at 40 weeks after 16 Gy in C57BL/6 but not in ApoE(-/-) mice. CD31 expression declined in C57BL/6 mice at 40 weeks (8 Gy), but increased in ApoE(-/-) mice at 20 (2/8/16 Gy) and 60 weeks (16 Gy). Capillary area decreased in C57BL/6 at 40 weeks (8/16 Gy) but increased in ApoE(-/-) mice at 20 weeks (16 Gy). Endocardial VCAM-1 expression remained unchanged. TM-positive capillaries decreased at 40 weeks (8/16 Gy) in C57BL/6 and at 60 weeks (2/16 Gy) in ApoE(-/-) mice. Leukocyte infiltration transiently rose 40 weeks after 8 Gy (only ApoE(-/-)) and 16 Gy. After receiving a low irradiation dose of 0.2 Gy, no significant changes were observed in any of the mouse models.

CONCLUSION

This study demonstrated that local heart irradiation affects microvascular structure and induces inflammatory/thrombotic responses in mice in a dose- and time-dependent manner. Thereby, significant prothrombotic changes were found in both strains, although they were progressive in ApoE(-/-) mice only. Proinflammatory responses, like the increase of adhesion molecules and leukocyte infiltration, were more pronounced and occurred at lower doses in ApoE(-/-) vs. C57BL/6 mice. These findings indicate that metabolic risk factors, such as decreased ApoE lipoproteins, may lead to an enhanced proinflammatory and prothrombotic late response in locally irradiated hearts.

Late effects of local irradiation on the expression of inflammatory markers in the Arteria saphena of C57BL/6 wild-type and ApoE-knockout mice

Combined action of irradiation (IR), shear stress, and high blood pressure is well recognized to induce damage to vasculature, while data on pathological effects of IR in large peripheral vessels with low blood pressure are scarce. The purpose of the present study was hence to investigate time- and dose-dependent effects of local IR on inflammatory and prothrombotic processes in the Arteria (A.) saphena of C57BL/6 wild-type and apolipoprotein E (ApoE)-knockout mice. Single doses of 2, 5, 8, 10, or 16 Gy were locally delivered to the A. saphena of the left leg of the animals. The expression of CD31, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), E-selectin, monocyte chemoattractant protein-1 (MCP-1), and thrombomodulin (TM) was quantified by semiautomatic TissueFax fluorescence analysis in frozen arterial sections. Follow-up periods were 3, 6, 9, 12, or 18 months. Protein expression in the arterial wall displayed dose-dependent changes. Proinflammatory reactions were observed for CD31, E-selectin, ICAM, and VCAM already at doses of 2 Gy. Anti-inflammatory changes were detected for MCP-1 and TM. The effects were more pronounced in wild-type versus ApoE(-/-) mice. Changes remain mostly transient up to 16 Gy. Dose- and time-dependent changes in inflammatory and thrombotic mediators in the wall of the A. saphena were found after local IR but did not transform into histopathological consequences.

Association between the GH receptor/exon 3 genotype and the level of exon 3-positive GH-binding protein in human serum

OBJECTIVE

The human GH-binding protein (GHBP) is derived from the GH receptor (GHR) through proteolytic cleavage of its extracellular domain. Two isoforms of the GHBP exist, differing in the retention or exclusion of exon 3: E3(+)GHBP and E3(-)GHBP. Our study aimed to answer the questions whether the level of E3(+)GHBP in the serum correlates with the GHR exon 3 expression and whether or not the E3 genotype matches the mRNA expression pattern.

METHODS

Since exon 3 retention/deletion can be detected at the protein level using epitope-specific antibodies, we were able to quantify the two isoforms by means of specific immunoassays in a total of 37 individuals. Additionally, these persons were also genotyped for exon 3 by genomic PCR and tested for GHR exon 3 mRNA expression by RT-PCR.

RESULTS

We found a significant correlation between GHR exon 3 genotype and the ratio of E3(+)GHBP and E3(-)GHBP in the serum. Moreover, the genotype matched exactly the mRNA expression in fibroblasts and/or blood leukocytes in all samples investigated. The levels of E3(+)GHBP are more strongly correlated with body mass index, proinsulin and C-peptide than the levels of the E3(-) isoform.

CONCLUSIONS

Our results show that the GHR exon 3 genotype is in accord with the type of GHBP isoforms found in the serum. Our data thus support the idea that the presence of exon 3-retaining and -excluding GHR/GHBP isoforms results from a genomic deletion rather than from alternative splicing.

Leptin exists in tubuli seminiferi and in seminal plasma

Leptin is a 167-amino acid protein that stimulates gonadotrophin-releasing hormone secretion and exerts indirect effects on the gonads via neuropeptide Y, NPY. Recent research has suggested that leptin may also have an effect on testosterone secretion. To investigate the role of leptin in reproduction, leptin in testicular tissue and seminal plasma was examined in relation to leptin in serum, semen sample qualities and vasectomy. Seminal plasma and serum of 64 infertility patients, and 15 individuals after vasectomy, were assayed for leptin using a competitive 'in house' radioimmunoassay. The concentration of leptin in seminal plasma was significantly lower in the 'normal' semen sample group than in the 'pathological' group (Mean +/- SEM; 1.45 +/- 0.18 vs. 3.19 +/- 0.57 ng ml-1; P < 0.05), and showed a significantly negative correlation with percentage of motile spermatozoa (r = -0.46; P = 0.0005) and with the velocity straight line, VSL, (r = -0.30; P = 0.029). In contrast, leptin concentration in serum did not show any relationship with the spermiogram parameters. In testicular tissue, leptin was preferentially found within the tubuli seminiferi using anti-leptin polyclonal antibody, Ob A-20 Sc 842. The amount of leptin per ejaculate did not significantly change after vasectomy, and was not correlated to fructose, zinc or neutral alpha glucosidase in seminal plasma (P > 0.05). These results suggest that the amount of leptin in the genital tract, including the tubuli seminiferi, may influence the mechanisms involved in the motility development of spermatozoa.

Lineage restriction of the RARalpha gene expression in myeloid differentiation

To better understand the role of retinoids in myelopoiesis, expression of the retinoid receptor genes (retinoic acid receptors [RARs] and retinoid X receptors [RXRs]) were examined during differentiation of factor-dependent cell-Paterson (FDCP)-mixA4 murine progenitor cells. The major receptor expressed in undifferentiated A4 cells was RARalpha (primarily the RARalpha1 isoform). Following induction of myelomonocytic differentiation with granulocyte and granulocyte-macrophage colony-stimulating factors, a dramatic increase in RARalpha expression (particularly the RARalpha2 isoform) was seen. In contrast, expression of both RARalpha isoforms was rapidly extinguished upon induction of erythroid differentiation with erythropoeitin (EPO). A modest induction of RXRalpha expression was seen, particularly during differentiation in the myelomonocytic lineage. Low expression levels of RARgamma2 and RXRbeta remained unchanged, irrespective of differentiation pathway. Consistent with the gene expression patterns, RARalpha agonists and antagonists stimulated myelomonocytic and erythroid differentiation of FDCP-mixA4 cells, respectively. Taken together, these results suggest that erythropoiesis and granulopoiesis require diminished and enhanced RARalpha activities, respectively, which at physiological all-trans-retinoic acid (RA) concentrations may be accomplished by reciprocal effects of EPO and myelomonocytic growth factors on its expression. This hypothesis is corroborated by data showing that RA, which positively regulates RARalpha2 expression, can exert inhibitory effects on erythroid differentiation.

Expression of leptin (Ob) and leptin receptor (Ob-R) in human fibroblasts: regulation of leptin secretion by insulin

Leptin, a hormone of the cytokine family, is mainly synthesized by white adipocytes. As fibroblasts and adipocytes share a common stem cell origin, we hypothesized that connective tissue may be another candidate for leptin synthesis. We demonstrated leptin receptors, inclusive of all isoforms, on cultured fibroblasts (n = 13) by RT-PCR and immunohistochemistry. In contrast to its receptor, basal leptin mRNA expression and protein secretion were found in 8 of 13 cultures, reaching 1.4 ng/350,000 cells.24 h. Incubation with physiological insulin concentrations (1 nmol/liter) increased leptin secretion in fibroblast culture supernatants to 152% of basal levels. A maximal stimulation of the basal level up to 192% was found with 10 nmol/liter insulin after 24 h. Actinomycin D and cycloheximide abolished this effect, providing evidence that active RNA and protein synthesis are involved in insulin's action. Completing these in vitro results, we could show protein expression for leptin and leptin receptors in fibroblasts by immunostaining of human skin biopsies in situ. In conclusion, we provide evidence of leptin synthesis and secretion by human fibroblasts that are regulated by insulin. Leptin produced by fibroblasts may thus exert important local autocrine and paracrine actions and contribute to the total plasma pool. Hence it might in part account for variations in body mass index-dependent reference ranges of leptin as well as disruptions in the relationship between fat content and leptin.

Mutational analysis of the PRL receptor gene in human breast tumors with differential PRL receptor protein expression

PRL is a major growth and differentiating hormone in the human breast, with activation of the PRL-PRL receptor complex increasingly recognized as an important mechanism in the induction and progression of mammary tumors. Although constitutive activation of various hormone and growth factor receptors is newly recognized as a common cause of tumor development, the PRL receptor gene has not been analyzed for similar aberrations in breast and other tumors. Therefore, using bacterial artificial chromosomes containing the PRL receptor gene and intron-spanning PCR, we determined the exon-surrounding intron sequences providing primers for the first analysis of the entire coding region of the human PRL receptor gene. We examined the presence of PRL receptor in 41 breast tumors by immunohistochemistry and attempted a correlation of its expression to pathological grading of the disease. Then tumor cells were isolated by laser capture microdissection to examine DNA from 30 patients for PRL receptor mutations. The PRL receptor immunoreactive score did not correlate to the tumor size, histopathological grading, age, or family history of patients. PRL receptor immunoreactivity was predominantly found in steroid hormone receptor-positive tumors, but without overall correlation of immunoreactive score. In both PRL receptor-positive and PRL receptor- negative breast cancer cells, direct sequencing of the coding sequence of the PRL receptor gene did not detect any somatic or hereditary gene aberrations. In conclusion, PRL receptor mutations do not appear to be common in human breast cancer, suggesting that constitutive activation of the PRL receptor can be excluded as a major cause of mammary tumor genesis. The molecular structure of the PRL receptor seems to remain intact in tumor tissue, and systemic and local production of PRL may participate in tumor cell growth and proliferation through functional receptors.

Expression and distribution of the prolactin receptor in normal rat liver and in experimental liver cirrhosis

Recent results have suggested a role for prolactin (PRL) as a regeneration factor in the liver. In order to investigate the involvement of prolactin in the pathogenesis of liver cirrhosis, we studied the expression of the prolactin receptor (PRLR) and PRL during the development of cirrhosis in an animal model. 30 male rats were exposed to CCl4 by inhalation. Phenobarbitone was added to the drinking water to accelerate the formation of toxic metabolites by enzyme induction. Two control groups of 30 animals each were treated with phenobarbitone only or received no treatment. 10 animals of each group were sacrificed 35, 55, and 70 days after initiation of treatment. Liver tissue was subjected to histological examination, which demonstrated fibrosis of different grades and cirrhosis in the CCl4-treated rats. Expression of PRLR mRNA was investigated by mRNA extraction, RT-PCR and computer-supported densitometric evaluation. Compared to control liver, PRLR mRNA was expressed at a higher level in fibrotic and cirrhotic liver specimens. In normal tissue, immunohistochemical staining showed a high concentration of PRLR around the central vein and in the epithelium of the bile ducts. This pattern of distribution was lost in fibrosis and cirrhosis. An accumulation of PRLR was demonstrated within the damaged cells. Neither PRL nor PRL mRNA was detectable in normal, fibrotic, or cirrhotic liver. We conclude that PRLR is distributed in normal rat liver in a typical pattern which is lost with increasing fibrosis. PRL is not produced by rat liver, indicating that PRL does not act through autocrine or paracrine mechanisms.

Soluble leptin receptor represents the main leptin binding activity in human blood

In human blood leptin circulates both free and bound to high molecular weight proteins. Hypothesising that these proteins may modulate ligand bioavailability and bioactivity of leptin, we investigated their molecular nature. Therefore, leptin binding activity was partially purified from human plasma using a leptin affinity column. Subjecting this preparation to size exclusion chromatography (SEC) we observed a coelution of leptin binding activity with levels of the soluble leptin receptor (sOB-R) determined by a newly developed ligand immunofunctional assay. In Western blot analysis the partially purified leptin binding activity exhibited sOB-R immunoreactivity in two bands of 110 and 140 kD. Following N-deglycosylation these bands were replaced by two bands with the molecular weight of 90 and 60 kD, suggesting two isoforms which are capable of leptin binding, as determined by cross-linking. Furthermore, different ratios of these isoforms were detectable in fractions of the leptin binding activity after separation by SEC. These findings indicate the formation of heterodimers and homodimers complexed with and without leptin. As the two sOB-R bands from Western blot analysis correspond to only two specific bands in cross-linking experiments with 125l-leptin, the role of both isoforms as leptin binding proteins appears to be exclusive. Therefore, our results indicate that sOB-R is the major leptin binding protein in the circulating human blood.

Leptin and the adrenal gland

BACKGROUND

Leptin is involved in the maintenance of energy balance acting on food intake, thermogenesis and energy expenditure. Via its receptor in the hypothalamus, leptin modulates the functioning of the hypothalamic-pituitary-adrenal axis and the systemic sympathetic/adrenomedullary system, which are closely linked to the regulation of energy balance and body weight. In regard of potential interactions of leptin and adrenal hormones this study intended to characterize the role of leptin in the human adrenal gland.

MATERIALS AND METHODS

A novel technique of laser capture microdissection was used to separate cortical and chromaffin cells for mRNA expression studies of leptin receptor isoforms and leptin mRNA in adrenal tissue and cell line NCI-H295. Immunostaining was used to localize leptin receptor in human adrenal slices. The influence of leptin on basal and ACTH-stimulated steroid hormone secretion and enzyme expression was assessed. The effect of leptin on proliferation and viability of adrenal cells in primary culture and of the NCI-H295 cell line was studied by the WST-1 assay and by 3H-thymidine test.

RESULTS

Our data demonstrate that leptin can regulate the human adrenal function directly, via its receptors on adrenocortical cells. Leptin decreased the corticotropin-stimulated release of steroid hormones in vitro without any effect on cell proliferation. Leptin did not significantly affect the expression of cytochrome P450 scc m RNA in humans, but decreased the ACTH stimulated expression of the cytochrome P450 17alpha mRNA [corrected].

CONCLUSIONS

The adipo-adrenal interaction mediated by leptin further underscores the close link of metabolism and stress regulation in humans.

A role for leptin in sexual maturation and puberty?

Leptin, the ob gene product, is involved in the regulation of body weight in rodents, primates and humans. It provides a molecular basis for the lipostatic theory of the regulation of energy balance. White adipose tissue and placenta are the main sites of leptin synthesis. There is also evidence of ob gene expression in brown fat. Leptin seems to play a key role in the control of body fat stores by coordinated regulation of feeding behaviour, metabolic rate, autonomic nervous system regulation and body energy balance. Apart from the function of leptin in the central nervous system on the regulation of energy balance, it may well be one of the hormonal factors that signal to the brain the body's readiness for sexual maturation and reproduction. During late pregnancy and at birth when maternal fat stores have been developed, leptin levels are high. During these developmental stages leptin could be a messenger molecule signalling the adequacy of the fat stores for reproduction and maintenance of pregnancy. At later stages of gestation leptin could signal the expansion of fat stores in order to prepare the expectant mother for the energy requirements of full-term gestation, labour and lactation. Leptin serum concentrations change during pubertal development in rodents, primates and humans. In girls, leptin serum concentrations increase dramatically as pubertal development proceeds. The pubertal rise in leptin levels parallels the increase in body fat mass. In contrast, leptin levels increase shortly before and during the early stages of puberty in boys and decline thereafter. Testosterone has been found to suppress leptin synthesis by adipocytes both in vivo and in vitro. The decline of leptin levels in late puberty in boys accompanies increased androgen production during that time and most likely reflects suppression of leptin by testosterone and a decrease in fat mass and relative increase in muscle mass during late puberty in males. This overview focuses on those topics of leptin research which are of particular interest in reproductive and adolescent medicine.

Immunohistochemical and ultrastructural localization of leptin and leptin receptor in human white adipose tissue and differentiating human adipose cells in primary culture

Leptin is mainly produced in white adipose tissue and acts both at distant sites and locally at the tissue from which it originates. The cellular and subcellular localization of leptin and its receptor (Ob-receptor [Ob-R]) and their relationship to various stages of fat cell maturation have not been characterized as yet. Therefore, we analyzed leptin and Ob-R by using reverse transcriptase-polymerase chain reaction, immunohistochemistry, and ultrastructural immunogold labeling in human white adipose tissue and in human adipocyte cell cultures at early and late stages of differentiation. Both leptin and its receptor were present in mature unilocular fat cells. The thin cytoplasmic rim of the adipocytes exhibited the strongest expression of both leptin and Ob-R. At early stages of differentiating human adipocytes, leptin was mainly expressed in multilocular preadipocytes, whereas the Ob-R was found predominantly on fibroblast-like cells. Other cellular components of human white adipose tissue were characterized by anti-CD31 for endothelial cells, anti-CD68 for macrophages, and antibodies specifically labeling B-cells and T-cells. In addition to fat cells, endothelial cells were immunopositive for the full-length leptin receptor. On the ultrastructural level, leptin was mainly found attached to cellular membranes and in small alveolate vesicle-like structures in the cytoplasm of adipocytes. Leptin was also present on the cell membranes of endothelial cells and macrophages. We conclude that the expression of the Ob-R in human white adipose tissue is not restricted to adipocytes but is present in resident endothelial and immune cells. Ultrastructural localization studies revealed an association of leptin with cell membranes and small vesicles. The cellular and subcellular distribution of leptin and its receptor suggests an important autocrine and paracrine role for leptin in human adipose tissue.

Leptin and its receptor in normal human gastric mucosa and in Helicobacter pylori-associated gastritis

BACKGROUND

Leptin, a newly discovered weight-reducing hormone, is mainly produced in fat cells. Recently, this hormone has been reported to be produced in rat gastric mucosa cells. In the present study we analyzed the localization and expression of leptin and its receptors in normal human gastric mucosa and in patients with Helicobacter pylori-associated gastritis.

METHODS

Plasma leptin levels and gastric mucosa leptin content were determined in 39 patients with dyspepsia. Cellular localization of leptin and of the signaling receptor (Ob-RL) were assessed by immunohistochemistry. Reverse transcriptase polymerase chain reaction (RT-PCR) for leptin receptor isoforms was performed on gastric epithelial cells isolated by laser-capture-microdissection.

RESULTS

Leptin content of the corpus gastric mucosa in H. pylori-positive patients was significantly increased (4.6+/-1.2. n = 15) as compared with the H. pylori-negative group (27.5+/-0.5 pg/mg, n = 24, P = 0.006). The presence of leptin immunoreactivity was shown in the lower half of corpus epithelial glands. By RT-PCR no leptin mRNA was detectable in human gastric tissue. In contrast, expression of both Ob-R(L) and the leptin receptor isoforms could be detected in gastric epithelial cells. Leptin receptor protein was detected throughout the mucosa.

CONCLUSIONS

Leptin itself is stored and secreted but not produced in human gastric mucosa. The functional receptor and all isoforms are present in human gastric mucosa. H. pylori-associated gastritis leads to significant increases in local leptin concentration in the gastric corpus.

Detection of Ob-receptor in human adrenal neoplasms and effect of leptin on adrenal cell proliferation

Leptin, a hormone mainly secreted from adipose tissue, communicates a metabolic signal to the adrenal gland. Ob-Receptor (Ob-R) expression was reported in rat, mice and human adrenal glands. This study intended to investigate possible differences in the Ob-R expression and distribution of Ob-R protein in human adrenal tumors as compared to normal adrenal tissue. Proliferative effects of leptin were analyzed in the human adrenocortical carcinoma cell line (NCI-H295). The full length Ob-R mRNA and the isoforms B219.1 and B219.3 could be demonstrated by RT-PCR in all adrenal tumors (n=8), the tumor cell line (NCI-H295) and normal tissue. In contrast the Ob-R isoform B219.2 was absent in the carcinoma cell line and in most of the adrenal tumors (n=5), whereas it was present in normal adrenals. The Ob-R protein could be demonstrated in benign and malignant adrenocortical tumors. Pheochromocytomas showed only a weak immunostaining with the human Ob-R antibody. Human leptin did not affect the proliferation or variability of adrenal tumor cells as demonstrated by [3H]-thymidine assay and WST-1 test. In conclusion, although functional leptin receptors are expressed in human adrenal tumors, leptin does not regulate tumor cell proliferation.

Expression of Ob receptor in normal human adrenals: differential regulation of adrenocortical and adrenomedullary function by leptin

The major effects of leptin, an adipostatic hormone produced in fat tissue, are exerted through the hypothalamic-pituitary-adrenal axis and the systemic sympathetic/adrenomedullary system at the level of the central nervous system. Here, we examined the direct effects of leptin on the adrenal gland, a peripheral end organ of both the hypothalamic-pituitary-adrenal axis and the sympathetic/adrenomedullary system. As cortical and chromaffin tissues are intermingled in the human adrenal, we employed the novel technique of laser capture microdissection to analyze these systems separately. Functional full-length leptin receptor messenger ribonucleic acid and all human isoforms Ob219.1-3 were demonstrated by RT-PCR in both cortical and medullary tissue. Immunohistochemical staining of leptin receptor protein, however, demonstrated a strong signal only in the adrenal cortex, whereas there was weak positive staining in the medulla. Corticotropin (ACTH)-induced adrenal aldosterone, cortisol, and dehydroepiandrosterone secretion was inhibited by leptin in a concentration-dependent manner, whereas this hormone had no significant effect on catecholamine release by primary cultures of human adrenal chromaffin cells. Leptin itself was not expressed in human adrenal tissue, excluding a local paracrine or autocrine function of this peptide. In conclusion, this is the first report identifying functional leptin receptor in human adrenal tissue and showing a differential action of leptin on human adrenocortical and chromaffin hormone production. This peripheral action of leptin on the adrenal gland provides an additional important link between the human stress response and body weight regulation.

Differential expression of prolactin receptor (PRLR) in normal and tumorous adrenal tissues: separation of cellular endocrine compartments by laser capture microdissection (LCM)

PRL stimulates adrenal steroidogenesis. In this study, we compared the PRLR expression in normal and tumorous adrenal tissues and investigated a potential proliferative effect of PRL in adrenal cells. mRNA expression of long and intermediate forms of PRLR was detected in both normal adrenal cortex as well as benign and malignant adrenal tumors and in the human adrenocortical carcinoma cell line NCI-H295. Molecular analysis of cells procured by LCM clearly demonstrated that PRLR mRNA is expressed in the adrenal cortex but not in the medulla. Immunostaining revealed PRLR protein in all three zones of the normal adrenal cortex. Furthermore, adrenal carcinomas and adenomas stained positive for the PRLR, while in phaeochromocytomas as in the normal adrenal medulla, no specific staining was observed. By WST-1 test, we could show that PRL (10(-7) M) decreased proliferation and viability of adrenal cells in primary cell culture suggesting that PRL is not a mitogenic factor of adrenocortical cells.

Basal steroidogenic activity of adrenocortical cells is increased 10-fold by coculture with chromaffin cells

Historically, catecholamine-producing chromaffin cells and steroid-producing adrenocortical cells have been regarded as two independent endocrine systems that are united under a common capsule to form the adrenal gland. There is increasing evidence for bidirectional interactions, with regulatory influences of adrenocortical secretory products on adrenomedullary functions and vice versa. However, the direct involvement of chromaffin cells on the regulation and maintenance of cortical function has not yet been demonstrated. Therefore, we analyzed glucocorticoid secretion and P450 messenger RNA (mRNA) expression in bovine adrenocortical cells in cocultures with chromaffin cells compared with those in pure cortical cell cultures. Cortisol release from cortical cells in coculture with chromaffin cells was 10 times as high (mean +/- SEM, 1035 +/- 119%) as that from the same number of isolated cortical cells (100 +/- 11%). By a [3H]thymidine incorporation assay, it was demonstrated that this effect was not due to a higher proliferation rate. Northern analysis revealed an increasing expression of P450(17alpha) mRNA in the coculture from days 1-5, whereas in isolated cortical cells, P450(17alpha) mRNA decreased, leading to a 6-fold difference on day 5. Inhibitors of protein (cycloheximide) or RNA (actinomycin D) synthesis completely annulled the observed increase in cortisol release, indicating that de novo protein synthesis is required for this activation of adrenocortical steroidogenesis. Addition of the cyclooxygenase inhibitor indomethacin reduced the stimulatory effect, suggesting that this stimulation is in part mediated by PGs. Locally produced ACTH, catecholamines, and interleukin-1 accounted for 43% of the effect. Secretory products of chromaffin cells that act in concert are believed to be responsible for the stimulation of steroidogenesis in the coculture. The coculture system is an in vitro model that corresponds to the in vivo situation in the intact adrenal gland, where both endocrine cell systems are in close contact. Our data demonstrate the requirement of intraadrenal cellular communication for the full strength of the adrenocortical hormonal response.

Functional aspects of the effect of prolactin (PRL) on adrenal steroidogenesis and distribution of the PRL receptor in the human adrenal gland

Hyperprolactinemia is one of the most common disorders in endocrinology. A role for PRL on the human adrenal gland has been postulated in various clinical studies. We have demonstrated for the first time the expression of the PRL receptor in the human adrenal gland and in human adrenal primary cell cultures using PCR and immunohistochemical methods. Using immunostaining, we could detect the PRL receptor in all three zones of the adrenal cortex. Only weak staining was observed in the adrenal medulla. The influence of PRL on the secretion of cortisol, aldosterone, and androgens in human primary cell cultures was investigated. After stimulation with PRL (10(-7) mol/L), we measured increased concentrations of cortisol (155 +/- 9.8%; P < 0.005%), aldosterone (122 +/- 3.7%; P < 0.005), and dehydroepiandrosterone (121 +/- 8.6%; P < 0.05) in the cell supernatant. PRL did not affect the expression of messenger ribonucleic acid of cytochrome P45017 alpha in human adrenal cell cultures. In conclusion, we found the PRL receptor in the human adrenal gland. We postulate that PRL has a direct effect on adrenal steroidogenesis, thereby regulating adrenal function, which may be of particular relevance in clinical disorders with hyperprolactinemia.