Biomedical subjects

Ludwik K Malendowicz

Publications and source records attributed to Ludwik K Malendowicz.

At least 55 records · Page 3Linked to original sources

PubMed2004

Adrenomedullin (AM) and AM receptor type 2 expression is up-regulated in prostate carcinomas (PC), and AM stimulates in vitro growth of a PC-derived cell line by enhancing proliferation and decreasing apoptosis rates.

Adrenomedullin (AM) is a hypotensive peptide, that acts via the calcitonin receptor-like receptor (CRLR), whose interaction with the subtypes 2 and 3 of a family of receptor activity-modifying proteins (RAMP) gives rise to two distinct AM receptors, named AM1 and AM2 receptors. AM derives from the post-translational proteolytic cleavage of pro(p)AM, the last step of which involves the conversion of the inactive AM to active AM by the peptidyl-glycine alpha-amidating monooxigenase (PAM). Compelling evidence suggests that AM, in addition to exerting its well-known regulatory action on blood pressure and water and electrolyte balance, also possesses a growth promoting effect in several normal and neoplastic tissues, including human prostate. Conventional reverse transcription (RT)-polymerase chain reaction (PCR) demonstrated the expression of pAM, PAM, CRLR and RAMP(1-3) mRNAs in both prostate hyperplasias (PH) and carcinomas (PC), and semiquantitative PCR showed that pAM, PAM and RAMP3 mRNA expression was higher in PCs than PHs. Radioimmunoassay measured higher concentrations of immunoreactive AM in PCs than PHs. The expression of pAM, CRLR and RAMP1,2 mRNAs was also detected in the PC-derived cell lines PC-3 and DU-145, RAMP3 expression being restricted to the latter line. AM did not affect the growth rate (duplication time) of PC-3 cells, but it did significantly increase that of DU-145 cells. The growth promoting effect of AM was found to ensue from both the rise in the proliferation rate and the lowering in the apoptosis rate of DU-145 cells. These effects of AM were counteracted by the AM receptor antagonists CGRP(8-37) and AM(22-52), the former antagonist, which is more selective for AM2 than AM1 receptors, being more effective than the latter one. Both antagonists were per se able to induce a slow, but significant decrease in the basal growth rate of DU-145 cells by inhibiting proliferation and enhancing apoptosis, again CGRP(8-37) being more effective than AM(22-52). Taken together, our findings allow us to suggest that: i) endogenous AM system plays an important autocrine-paracrine growth promoting action in the human prostate, being possibly involved in the development of the malignant phenotype of epithelial cells; and ii) the tumor promoting effect of AM in the human prostate is mainly mediated by the AM2 receptor (CRLR/RAMP3) subtype.

Adrenomedullin↗

PubMed2003

Endogenous adrenomedullin system regulates the growth of rat adrenocortical cells cultured in vitro.

The expression of adrenomedullin (AM) system (AM and its receptors), as mRNA and protein, has been detected in the mammalian adrenal zona glomerulosa (ZG) cells. Evidence has been also provided that exogenous AM is able to enhance in vivo and in vitro the proliferative activity of ZG cells. However, the possibility that endogenous AM system may act as a physiological ZG growth regulator has not yet been demonstrated. Hence, we investigated whether the prolonged (48-72 h) suppression of AM gene transcription by a specific antisense oligonucleotide or the long-lasting (24-96 h) blockade of AM receptors by the selective antagonist AM(22-52) are able to affect the growth of rat ZG cells cultured in vitro. Freshly dispersed cells were incubated for 3 h with an AM antisense or a scrambled oligonucleotide, then they were cultured for 48 or 72 h, and proAM mRNA expression and AM content was checked by reverse transcription-polymerase chain reaction and radioimmune assay, respectively. Other ZG cells were cultured in the presence of AM and/or AM(22-52). Growth assay showed that AM (10(-8) M) decreased and AM(22-52) (10(-6) M) increased the duplication time of cultured cells. AM (10(-8) M) raised proliferation index and decreased apoptotic index of cultured cells, and AM(22-52) reversed these effects. AM(22-52) (from 10(-7) to 10(-6) M) and pAM gene suppression by the antisense oligonucleotide significantly lowered proliferation index and increased apoptotic index of cultured cells, both these effects being abrogated by AM (10(-8) M). It is concluded that endogenous AM system plays a relevant role in the autocrine-paracrine regulation of cultured rat ZG-cell growth.

Adrenal Cortex↗

PubMed2003

Ghrelin and growth hormone secretagogue receptor are expressed in the rat adrenal cortex: Evidence that ghrelin stimulates the growth, but not the secretory activity of adrenal cells.

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), which has been originally isolated from rat stomach. Evidence has been previously provided that adrenal gland possesses abundant ghrelin-displaceable GHS-Rs, but nothing is known about the possible role of ghrelin in the regulation of adrenocortical function. Reverse transcription-polymerase chain reaction demonstrated the expression of ghrelin and GHS-R in the rat adrenal cortex, and high adrenal concentrations of immunoreactive ghrelin were detected by radioimmune assay (RIA). Autoradiography localized abundant [(125)I]ghrelin binding sites in the adrenal zona glomerulosa (ZG) and outer zona fasciculata (ZF). Ghrelin (from 10(-10) to 10(-8) M) did not affect either basal steroid hormone (pregnenolone, progesterone, 11-deoxycorticosterone, corticosterone, 18-hydroxycorticosterone and aldosterone) secretion from dispersed ZG and zona fasciculata/reticularis (ZF/R) cells (as evaluated by quantitative high pressure liquid chromatography), or basal and agonist-stimulated aldosterone and corticosterone production from cultured ZG and ZF/R cells, respectively (as measured by RIA). Ghrelin (10(-8) and 10(-6) M) raised basal, but not agonist-stimulated, proliferation rate of cultured ZG cells (percent of cells able to incorporate 5-bromo-2'-deoxyuridine), without affecting apoptotic deletion rate (percent of cells able to incorporate biotinylated nucleosides into apoptotic DNA fragments). The tyrosine kinase (TK) inhibitor tyrphostin-23 and the p42/p44 mitogen-activated protein kinase (MAPK) inhibitor PD-98059 abolished the proliferogenic effect of 10(-8) M ghrelin, while the protein kinase A and C inhibitors H-89 and calphostin-C were ineffective. Ghrelin (10(-8) M) stimulated TK and MAPK activity of dispersed ZG cells, and the effect was abolished by preincubation with tyrphostin-23 and PD-98059, respectively. Tyrphostin-23 annulled ghrelin-induced activation of MAPK activity. Taken together, the present findings indicate that (i) ghrelin and GHS-R are both expressed in the rat adrenal cortex, ghrelin binding sites being very abundant in the ZG; (ii) ghrelin does not affect the secretory activity of rat adrenocortical cells, but significantly enhances the proliferation rate of cultured ZG cells, without affecting apoptotic deletion rate; and (iii) the ZG proliferogenic action of ghrelin involves the TK-dependent activation of the p42/p44 MAPK cascade.

Adrenal Cortex↗

PubMed2003

Effects of leptin and leptin fragments on steroid secretion of freshly dispersed rat adrenocortical cells.

The biological actions of leptin on target tissues are mediated via several isoforms of receptors (Ob-Rs), which may differently interact with native leptin and its fragments. Based on the presence in the rat adrenals of at least two Ob-R isoforms and the conflicting findings on the effect of leptin on adrenocortical secretion, we investigated the effects of the native leptin and several leptin fragments (10(-8) and 10(-6)M) on aldosterone and corticosterone secretion from freshly dispersed rat zona glomerulosa (ZG) and zona fasciculata-reticularis (ZF/R) cells. Reverse transcription (RT)-polymerase chain reaction (PCR) showed the expression of Ob-Ra and Ob-Rb mRNAs in both ZG and ZF/R cells. Native murine leptin (1-147) enhanced aldosterone and corticosterone secretion from dispersed ZG and ZF/R cells, and similar effects were elicited by murine leptin fragment 116-130, and human leptin fragments 138-167, 150-167 and [Tyr] 26-39. Human leptin fragment 93-105 was ineffective, while fragment 22-56 decreased corticosterone output without affecting aldosterone secretion. Taken together, our findings indicate that in rat adrenocortical cells leptin and leptin fragments may differently interact with Ob-Rs or interact with different Ob-R isoforms. Moreover, they suggest that (1) the direct adrenocortical secretagogue effect of leptin mainly depends on the C-terminal sequence 116-166; and (2) the N-terminal sequence is not needed for leptin to activate Ob-Rs positively coupled to steroidogenesis, but is possibly responsible for a direct inhibitory effect on glucocorticoid secretion.

Adrenal Cortex↗

PubMed2003

Tissue distribution of pneumadin immunoreactivity in the rat.

Pneumadin (PNM) is a decapeptide, originally isolated from mammalian lungs, which exerts a potent stimulating effect on arginine-vasopressin (AVP) release, thereby evoking an antidiuretic effect. We have established a specific radioimmunoassay (RIA) method for rat PNM determination, the sensitivity of which is sufficient for measuring tissue content of the peptide. Moreover, raised antibodies have been used for the immunocytochemical detection of PNM in several rat organs. As expected, high concentrations of PNM were detected by RIA in newborn and adult rat lungs and immunocytochemistry (ICC) localized PNM immunoreactivity (IR) in the bronchial and bronchiolar epithelium. Very high concentrations of PNM were measured by RIA in the prostate, and ICC showed that PNM-IR is contained in the epithelial cells. RIA and ICC demonstrated the presence of low amounts of PNM in the thymus. The highest content of radioimmunoassayable PNM was found in the kidneys and intestinal tract, but dilution test suggested the presence of some interfering substances in these tissues. Accordingly, ICC-detectable PNM-IR was absent in the kidneys and present only in the duodenal criptae and Brunner's glands of the intestinal tract. RIA did not measure sizeable PNM concentrations in the thyroid gland, but ICC showed PNM-IR in C-cells. RIA and ICC did not detected PNM in testes, seminal vesicles, ovaries, uterus, pancreas, liver, spleen, adrenal glands, and heart. Taken together, our findings suggest that PNM, in addition to its role as hypothalamo-pituitary AVP secretagogue, may be involved in the autocrine-paracrine functional regulation of other peripheral organs, like lungs and prostate and perhaps duodenum, thymus and thyroid gland.

Adrenal Glands↗

PubMed2003

Adrenomedullin stimulates proliferation and inhibits apoptosis of immature rat thymocytes cultured in vitro.

Adrenomedullin (AM) is a hypotensive peptide, which derives from the proteolytic cleavage of pro(p)AM, and acts through two subtypes of receptors, named L1-receptor (L1-R) and calcitonin receptor-like receptor (CRLR). CRLR functions as either a calcitonin gene-related peptide (CGRP) receptor or a selective AM receptor depending on which member of a family of receptor-activity-modifying proteins (RAMPs) is expressed: RAMP1 generates CGRP receptors, while RAMP2 and RAMP3 produce AM receptors. Reverse transcription (RT)-polymerase chain reaction (PCR) consistently allowed the detection of pAM and peptidyl-glycine alpha-amidating monooxygenase (the enzyme converting immature AM to the mature peptide) mRNAs in the thymus cortex of immature (10-day-old) rats. Accordingly, radioimmune assay (RIA) measured low but sizeable AM concentrations in this tissue. RT-PCR also demonstrated the presence of the specific mRNAs of L1-R, CRLR and RAMPs. AM (from 10(-9) to 10(-7)M) increased proliferation index and lowered apoptotic index of cultured immature rat thymocytes, and the effects were annulled by the AM receptor antagonist AM(22-52). In conclusion, our study demonstrated that (1) immature rat thymus cortex expresses AM and the AM receptors L1-R and CRLR/RAMP; and (2) AM, acting via AM(22-52)-sensitive receptors, exerts a potent growth promoting effect on immature rat thymus, by enhancing proliferation and lowering apoptotic death of thymocytes. Taken together, these findings could suggest that AM may play a role in the development of immunity.

Adrenomedullin↗

PubMed2003

Norbormide enhances late steps of steroid-hormone synthesis in rat and mouse adrenal cortex.

Norbormide (N) is a vasoconstrictor agent, which acts selectively on the peripheral arteries of the rat, through the activation of the phospholipase C (PLC) cascade and the stimulation of Ca(2+) entrance in the vascular myocytes. Several endogenous vasoconstrictor agent (e.g. angiotensin-II (ANG-II) and endothelin-1 (ET-1)), that stimulate PLC pathway, are also able to enhance aldosterone secretion by the adrenal gland. Hence, we examined the effects of norbormide ((0.5, 1.0 or 5) x 10(-5)M) on corticosteroid-hormone secretion from adrenal slices of rats and mice. Quantitative HPLC assay showed that under basal conditions rat and mouse adrenal quarters secreted progesterone (PROG), 11-deoxycorticosterone (DOC), 18-hydroxy-DOC (18OH-DOC), corticosterone (CORT), 18-hydroxy-corticosterone (18OH-CORT) and aldosterone (ALDO), as well as large amounts of pregnenolone (PREG) when its metabolism was blocked by 10(-5)M cyanoketone. Norbormide concentration-dependently raised the secretion of all post-DOC steroids assayed, decreased progesterone and DOC production, and did not affect pregnenolone release. In conclusion, norbormide is able to enhance late steps of steroid synthesis, i.e. those leading to the transformation of DOC to corticosterone and aldosterone, without affecting early steps. This is an interesting finding because the other main endogenous adrenal secretagogues are known to stimulate both early and late steps of steroid synthesis. The mechanism underlying the selective activating action of norbormide on 11beta- and 18-hydroxylation remains to be investigated.

18-Hydroxycorticosterone↗

PubMed2003

Role of the endogenous adrenomedullin system in regulating the secretion and growth of rat adrenal cortex.

The expression of components of the adrenomedullin (AM) system (AM and its receptors) has been detected in mammalian adrenal zona glomerulosa (ZG) cells, and evidence has been provided that AM is able to inhibit agonist-stimulated aldosterone secretion from and to enhance the proliferative activity of ZG cells. However, there has been no evidence that the endogenous AM system acts as a physiological regulator of ZG function. Hence, we investigated whether the suppression of AM gene transcription by a specific antisense oligodeoxynucleotide (ODN) is able to alter the secretion and growth of rat ZG cells cultured in vitro. ZG cell cultures were examined 0, 2, 4, 6 and 8 days after treatment with scrambled sense (S)-ODN (control cultures) and AM antisense (A)-ODN. Control cultures, as well as freshly dispersed ZG cells and ODN-untreated cultures, expressed AM as mRNA and protein. A-ODN treatment suppressed AM expression within 4 days and the suppression lasted until day 6. Confluent control cultures displayed basal and angiotensin-II (Ang-II), K(+)- and adrenocorticotropic hormone (ACTH)-stimulated aldosterone secretions similar to those of ODN-untreated cultures. A-ODN treatment magnified the aldosterone response to Ang-II and K+ at days 4 and 6 (but not at day 8), without affecting the basal or ACTH-stimulated secretion. As compared to ODN-untreated and control cultures, non-confluent A-ODN-treated ones showed a 40% elongation in the duplication time, a significant decrease in the proliferation index, and a marked rise in apoptotic index from day 4 to day 8. In conclusion, our study validates the use of A-ODN to block the endogenous AM system, showing that suppression of AM-synthesis requires at least 2 days to become appreciable and persists for at least 6 days. Moreover, it provides the first evidence that endogenous AM plays a physiological role in cultured rat ZG cells, by exerting a buffering action on their acute secretory response to Ang-II and K+ and by maintaining normal basal proliferative and apoptotic activities.

Adrenocorticotropic Hormone↗

PubMed2003

Effects of adrenomedullin and its fragment 22-52 on basal and ACTH-stimulated secretion of cultured rat adrenocortical cells.

Adrenomedullin (ADM) and its receptors are expressed in the adrenal cortex, where ADM is currently known to inhibit agonist-stimulated aldosterone secretion from zona glomerulosa (ZG), without affecting either basal aldosterone release or the secretory activity of zona fasciculata-reticularis (ZF/R) cells. These functional findings have been obtained using freshly dispersed adrenocortical cells, but evidence has been provided that ADM is able to enhance basal aldosterone secretion from rat capsule-ZG preparations. Hence, we investigated the effect of ADM and ADM22-52, a putative antagonist of ADM receptors, on the secretory activity of rat adrenal cell cultured in vitro for 72 h. Cultures were exposed for 3 or 24 h to 10(-7) M ADM and/or ADM22-52, in the absence or the presence of 10(-8) M ACTH, and the concentration of aldosterone and corticosterone in the culture medium was measured by radioimmune assay. ADM and/or ADM22-52 raised basal aldosterone secretion at 3 h, but not 24 h exposure, and did not affect ACTH-stimulated aldosterone production. Corticosterone secretion was not changed at 3 h. In contrast, at 24 h exposure ADM22-52 alone or with ADM decreased basal corticosterone secretion; ADM evoked a small rise in ACTH-stimulated corticosterone production, and the effect was annulled by ADM22-52. These puzzling findings are interpreted in light of the fact that i) our cultures were actually a mixture of ZG, ZF/R and medullary chromaffin cells; ii) ADM stimulates adrenomedullary cells to release catecholamines, which are able to enhance aldosterone secretion from ZG cells; and iii) the prolonged exposure to ADM may modify, under in vitro culture conditions, ZF/R cells, switching their phenotype from an ADM-unresponsive to an ADM-responsive one. Our study casts doubts on the selectivity of ADM22-52 as ADM receptor antagonist, and stresses that great caution must be used in comparing adrenal-secretion findings obtained with different in vitro techniques.

Adrenal Cortex↗

PubMed2003

Human skin keratinocytes and fibroblasts express adrenomedullin and its receptors, and adrenomedullin enhances their growth in vitro by stimulating proliferation and inhibiting apoptosis.

Adrenomedullin (ADM) is a hypotensive peptide, which originates from the proteolytic cleavage of pro(p)ADM and acts via two subtypes of receptors, named L1-R (L1-R) and calcitonin-receptor-like receptor (CRLR). L1-R is selective for ADM depending on the expression of the subtype 1 or the subtypes 2 and 3 of a family of chaperones, called receptor-activity-modifying proteins (RAMPs). Compelling evidence indicates that ADM, in addition to regulating blood pressure and water and electrolyte balance, also exerts a major growth promoting action in several normal and neoplastic cells. Reverse transcription (RT)-polymerase chain reaction (PCR) allowed the detection of pADM, L1-R and CRLR mRNAs in cultured human skin keratinocytes and fibroblasts. RAMP1 and RAMP2 (but not RAMP3) mRNAs were present, but their level of expression was rather weak, thereby suggesting that L1-R is the main subtype of ADM receptor in both keratinocytes and fibroblasts. ADM concentration-dependently raised the proliferation rate and lowered the apoptotic rate of both keratinocytes and fibroblasts cultured in vitro, maximal effective concentration being 10(-8) M. The effects of 10(-8) M ADM was annulled by the putative ADM-receptor antagonist ADM22-52 (10(-6) M). ADM22-52 also lowered basal proliferative activity of keratinocytes and fibroblasts, without affecting their apoptotic deletion rate. Taken together, these findings allow us to conclude that i) human skin keratinocytes and fibroblasts express ADM and its receptors; and ii) endogenous ADM system promotes the growth of keratinocytes and fibroblasts cultured in vitro, by enhancing their proliferative activity and lowering their apoptotic deletion.

Adrenomedullin↗

PubMed2003

Effects of prolonged exendin-4 administration on entero-insular axis of normal and streptozotocin-induced diabetic rats.

The effects of the glucagon-like peptide 1 (GLP-1) receptor agonist exendin-4 (EX4) and antagonist EX4(9-39) EX4-A on entero-insular axis have been investigated in normoglycemic and streptozotocin (STZ)-induced diabetic rats. Rats were administered daily subcutaneous injections of 1 nmol/kg EX4 and/or EX4-A for 7 days, and were decapitated 3 h after the last injection. In STZ-untreated rats, EX4 reduced body-weight (BW) gain and raised glycemia, and the effects were prevented by EX4-A; conversely, EX4 did not alter plasma concentrations of insulin, glucagon and leptin. STZ-treated rats displayed body and hematochemical alterations typical of experimental diabetes: decrease in BW and insulin blood level, coupled with normal glucagon plasma concentration and marked hyperglycemia. In diabetic rats, both EX4 and EX4-A decreased BW gain, thereby suggesting a mechanism at least in part independent of GLP-1 receptors. EX4 did not alter glucagon blood level, but decreased glycemia and raised insulin and leptin plasma levels. These effects were annulled by EX4-A, which indicates that they occur through the activation of GLP-1 receptors. Collectively, our findings add support to the view that EX4 can be considered an important therapeutical tool to improve glucose metabolism in diabetes.

Animals↗

PubMed2003

Effects of preproglucagon-derived peptides and exendins on steroid-hormone secretion from dispersed adrenocortical cells of normal and streptozotocin-induced diabetic rats.

Many lines of evidence have shown that preproglucagon-derived peptides affect steroid secretion from dispersed adrenocortical cells, and that streptozotocin (STZ)-induced experimental diabetes alters adrenocortical-cell function. Hence, we compared the effects of glucagon, glucagon-like peptide (GLP)-1 and GLP-2 on basal and ACTH-stimulated secretion of dispersed adrenocortical cells from normal and STZ-induced diabetic rats. We also examined the effects of exendins (EX) 3 and 4, because EX4 is known to be a potent and long-lasting agonist of GLP-1 receptors. STZ-induced diabetes moderately enhances basal and ACTH-stimulated secretion from dispersed zona glomerulosa (ZG) cells, without significantly affecting corticosterone production from dispersed zona fasciculata-reticularis (ZF/R) cells. In normoglycemic rats, glucagon increased basal aldosterone and corticosterone secretion from ZG and ZF/R cells, GLP-2 raised both basal and ACTH-stimulated aldosterone secretion and ACTH-stimulated corticosterone output, and EX4 increased basal corticosterone secretion. In contrast, glucagon, GLP-2 and EX4 did not elicit secretory responses from adrenocortical cells of diabetic rats. GLP-1 and EX3 did not alter secretion of dispersed adrenocortical cells of either normal or STZ-treated rats. Taken together, our findings indicate that preproglucagon-derived peptides enhance steroid secretion from adrenocortical cells of normal, but not STZ-induced diabetic rats. It is suggested that the prolonged exposure to low concentrations of insulin causes unresponsiveness of adrenocortical cells to glucagon, GLP-2 and EX4, which may contribute to the hyporeninemic hypoaldosteronism and alterations in glucocorticoid metabolism occurring in experimental diabetes.

Adrenal Cortex↗

PubMed2003

Ghrelin, an endogenous ligand for the growth hormone-secretagogue receptor, is expressed in the human adrenal cortex.

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), which was originally isolated from rat stomach. Ghrelin and GHS-R are also expressed in several peripheral tissues, including adrenal glands, and this prompted us to study ghrelin expression and ghrelin-binding site localization in the human adrenal cortex, and the possible effect of this peptide on corticosteroid-hormone secretion. Reverse transcription-polymerase chain reaction (RT-PCR) and radioimmune assay (RIA) showed sizeable expression of ghrelin mRNA and protein in six human adrenal cortexes. Autoradiography evidenced abundant [125I]ghrelin binding sites in the adrenal zona glomerulosa and outer zona fasciculata. However, ghrelin (10(-6) M) did not significantly affect either basal or agonist (ACTH and angiotensin-II)-stimulated early and late steps of steroid-hormone synthesis from adrenocortical slices (as measured by quantitative high pressure liquid chromatography). Since zona glomerulosa is the cambium layer involved in the growth maintenance of adrenal cortex, the present coupled RT-PCR, RIA and autoradiographic findings could suggest the involvement of ghrelin in the autocrine-paracrine regulation of human adrenal growth.

18-Hydroxycorticosterone↗

PubMed2003

Exendin-4, a GLP-1 receptor agonist, stimulates pituitary-adrenocortical axis in the rat: Investigations into the mechanism(s) underlying Ex4 effect.

Exendin-4 (Ex4) is a potent and long-lasting agonist of glucagon-like peptide-1 (GLP-1), which has been previously found to stimulate pituitary-adrenal axis in the rat. Aim of the present study was to gain insight into the mechanism(s) involved in the Ex4-induced rise in the rat plasma concentrations of ACTH, aldosterone and corticosterone. Preliminary time- and dose-response studies showed that the maximum stimulating effect of Ex4 occurred within 1 or 2 h and at dose ranging from 0.5 to 2.0 nmol/100 g body weight. The GLP-1 receptor (GLP-1R) antagonist Ex(9-39) did not significantly affect ACTH, aldosterone and cortico-sterone responses to Ex4. Neither the administration of CRH and arginine vasopressin (AVP)-receptor antagonists nor adrenal demedullation prevented pituitary-adrenal axis responses to Ex4. The prolonged (4 or 6 days) suppression of the pituitary ACTH release by dexamethasone impaired corticosterone, but not aldosterone response to Ex4. The following conclusions are drawn: i) Ex4 stimulates rat pituitary-adrenal axis through receptors other than the classic GLP-1R; ii) neither CRH and AVP nor medullary catecholamines are involved in the Ex4-induced stimulation of ACTH release; iii) ACTH stimulation accounts for the rise in corticosterone plasma concentration; and iv) the aldosterone secretagogue effect of Ex4 occurs via a mechanism independent of the stimulation of either ACTH or medullary catecholamines.

Adrenal Cortex↗

PubMed2003

Prolonged exendin-4 administration stimulates pituitary-adrenocortical axis of normal and streptozotocin-induced diabetic rats.

Evidence is available that exendin-4 (EX4), a glucagon-like peptide-1 receptor (GLP-1R) agonist acutely stimulates hypothalamo-pituitary-adrenal (HPA) axis in the rat. EX4 is a potent insulinotropic agent, which is currently under clinical trial for treatment of type 2 diabetes. Since diabetes is known to affect adrenal function, we investigated the effects of the prolonged administration of EX4 and/or the GLP-1R antagonist EX4(9-39) (EX4-A) (daily subcutaneous injections of 1 nmol/kg EX4 and/or EX4-A, for 7 days) on the HPA axis of normoglycemic and streptozotocin (STZ)-induced diabetic rats. In STZ-untreated rats, chronic EX4 treatment did not change the blood level of ACTH. In contrast, it evoked a marked rise in the plasma concentrations of aldosterone and corticosterone, these effects being reversed by EX4-A. In STZ-induced diabetic rats, prolonged EX4 administration increased the plasma levels of ACTH, aldosterone and corticosterone. EX4-A did not prevent the first two effects of EX4, and annulled the latter one. These findings allow us to draw the following conclusions: i) EX4 prolonged exposure desensitizes hypothalamo-hypophyseal GLP-1R in normal rats, and exerts an ACTH-independent GLP-1R-mediated aldosterone and corticosterone secretagogue effect; and ii) experimental diabetes induces the expression of EX4 receptors other than the classic GLP-1R, whose activation mediate the ACTH and aldosterone, but not corticosterone, secretagogue effects. Our study provides evidence that metabolic dysregulations occurring in STZ-induced diabetic rats are able to profoundly affect the response of the HPA axis to GLP-1.

Adrenocorticotropic Hormone↗

PubMed2003

Effects of prolonged cholecystokinin administration on rat pituitary-adrenocortical axis: role of the CCK receptor subtypes 1 and 2.

Many lines of evidence indicate that cholecystokinin (CCK) and its receptors, named CCK1-R and CCK2-R, are expressed in the hypothalamo-pituitary-adrenal (HPA) axis, the function of which they acutely stimulate. However, the role of endogenous CCK system in the regulation of HPA axis is still unknown. To address this issue we investigated the effect of the prolonged (6-day) administration of CCK, CCK-R antagonists (CCK-RAs) and pentagastrin (PG), a CCK2-R agonist, on adult rat HPA axis. Semiquantitative reverse transcription-polymerase chain reaction showed that CCK treatment lowered the expression of CCK1-R and CCK2-R mRNAs in the pituitary, but not adrenal gland. ACTH plasma concentration was not affected by any treatment. Neither CCK nor PG administration induced significant changes in the blood levels of aldosterone and corticosterone. CCK1-RA, although being per se ineffective, in the presence of CCK raised plasma levels of aldosterone and corticosterone; conversely, CCK2-RA, either alone or in the presence of agonists, lowered the blood concentrations of the two hormones. CCK, but not PG, treatment decreased relative adrenal weight, and morphometry showed that CCK-induced adrenal atrophy was coupled to decreases in the volume of adrenocortical zones, which in turn mainly depended on the lowering in the volume and number of adrenocortical cells. PG administration raised and CCK2-RA per se decreased the volume and number of adrenocortical cells. Taken together, these findings allow us to draw the following main conclusions: i) the prolonged exposure to elevated CCK concentrations down-regulates CCK-R expression in the pituitary gland, which accounts for the lack of effect of CCK on ACTH secretion; ii) adrenal CCK1-Rs and CCK2-Rs inhibit and stimulate, respectively, corticosteroid secretion; and iii) endogenous CCK system plays a minor role in the physiological regulation of rat HPA axis, its main effect being the CCK2-R-mediated maintenance of adrenocortical-cell number.

Adrenal Cortex↗

PubMed2003

Pneumadin in the ventral prostate and seminal vesicles of estradiol-treated rats: RIA and immunocytochemical studies.

Pneumadin (PNM) is a decapeptide (the rat peptide: Tyr-Gly-Glu-Pro-Lys-Leu-Asp-Ala-Gly-Val-NH2) isolated from mammalian lungs. Human and rat PNM differ only by substitution of one amino acid--Tyr/Ala. PNM evokes an antidiuretic effect via a potent stimulation of arginine-vasopressin (AVP) release. By means of recently established, highly specific RIA method, high concentration of PNM had been found in the rat ventral prostate. Castration resulted in a profound drop in PNM concentration, an effect prevented by testosterone replacement. The present studies were aimed at investigating the effect of prolonged estradiol administration on PNM concentration, content and localization in the prostate and seminal vesicles of the rat. Depo estradiol (estradiolum valerianicum) administration to adult male rats resulted in a notable atrophy of ventral prostate and seminal vesicles. During the entire experiment (till day 30 after administration), PNM concentration in ventral prostate was similar to that seen in intact animals, while peptide content per gland was markedly lowered. PNM immunostaining was observed in prostate epithelium of estradiol-treated rats and its localization resembled that observed in intact animals. Nearly 40 times lower PNM concentration than in ventral prostate was found in seminal vesicles. In contrast to prostate, on days 20 and 30 of estradiol treatment PNM concentration in seminal vesicles was higher than in intact rats. However, due to profound seminal vesicle atrophy, PNM content per entire gland was notably lowered in estradiol-injected rats. By immunocytochemistry, PNM-immunoreactive substances were not found in seminal vesicles of either intact or estradiol-administered rats. High PNM concentration in the rat prostate suggests its important role in the function of the gland.

Animals↗

PubMed2002

Orexins and adipoinsular axis function in the rat.

Orexin A and B are recently identified as peptides that are derived from the same precursor and their expression is highly specifically localized in neurons located in the lateral hypothalamic area, a region implicated in the feeding behaviour. These peptides appear to be a part of a complex circuit that integrates the aspects of energy metabolism, cardiovascular function, hormone homeostasis and sleep/wake behaviours. The functional linking of orexins with leptin and insulin suggests the possibility of its involvement in the regulation of the adipoinsular axis, and the present investigation was designed to examine the potential role of orexins in this axis regulation. In all the tested doses (8, 16 and 40 nmol/kg body weight (b.w.)), subcutaneous (s.c.) injections of orexin A caused the significant increase in insulin and leptin blood levels. These elevations were observed 60 and 120 min after peptide administration. On the other hand, after the orexin B administration, elevated insulin and leptin blood concentrations were found only at 60 min of the experiment, and in that time point, the increases were comparable to that evoked by orexin A. In comparison with the control animals, the administration of orexins for 7 days resulted in a significant gain in body weight. Prolonged administration of either orexin A or orexin B significantly elevated insulin and leptin blood concentrations. Under these conditions, the orexin A effect on the leptin secretion was more marked than on the insulin secretion, and this difference is reflected by the lowered insulin/leptin molar ratio. These results suggest that orexins play an important role in the adipoinsular axis function and may be a significant regulator of both insulin and leptin secretion. In this regard, we suggest the updated functional model of Kieffer and Habener [Am. J. Physiol.: Endocrinol. Metab. 27 (2000) E1] that proposed the adipoinsular axis. Our model is extended by the probable humoral links between orexins and leptin and orexins and insulin and points on the dependence of the effects evoked by orexins, leptin and insulin on the blood glucose levels.

Adipocytes↗