Some hormonal influences on glucose and ketone body metabolism in normal human subjects

Control of glucose and ketone body metabolism is integrated by a variety of hormones. Insulin is the major anabolic hormone, and its actions are antagonized by rapidly acting catabolic hormones, such as glucagon and the catecholamines, and by others such as cortisol, growth hormone and the thyroid hormones, which generally have more delayed effects. In the normal human subject, the effects of catabolic hormones to raise blood glucose are limited by a compensatory increase in insulin secretion, and these effects are enhanced in insulin deficiency. Hyperketonaemic actions of the catabolic hormones may result from increased supply of non-esterified fatty acids from lipolysis, although glucagon has a major direct action to increase ketogenesis at the liver. As expected, these actions are also restricted in normal humans by the compensatory rise in insulin secretion. Hyperketonaemia does, however, occur with adrenaline (epinephrine) and noradrenaline (norepinephrine), even in the presence of mildly elevated insulin concentrations. These catecholamines may assume particular importance in mobilization of lipid fuels in milder forms of stress, when insulin secretion is normal or mildly increased. In severe stress, when there is catecholamine-induced suppression in insulin secretion, lipolytic and hyperketonaemic effects of all the catabolic hormones may be manifest. Starvation in humans also results in diminished insulin secretion and increased catabolic hormone secretion. The relative importance of individual hormones in lipid mobilization during starvation is uncertain, although glucagon, growth hormone, noradrenaline and, possibly, dopamine may all play a part.

Thyroid hormone stimulation of extracellular signal-regulated kinase and cell proliferation in human osteoblast-like cells is initiated at integrin alphaVbeta3

The aim of the present study was to examine whether triiodo-l-thyronine (T(3)) or l-thyroxine (T(4)) rapidly activated the mitogen-activated protein kinase (MAPK) intracellular signalling cascade in osteoblast-like cells and investigate whether this activation was initiated at the integrin alpha(V)beta(3) cell surface receptor. Using PCR and western blotting, the expression of integrin alpha(V)beta(3) mRNA and protein was demonstrated in the human osteoblast-like cell lines MG-63 and SaOS-2. The treatment of MG-63 cells with T(3) (10 nM) or T(4) (100 nM) for 10 min stimulated extracellular signal-regulated kinase activity (ERK, a component of the MAPK pathway) as determined by fluorescent immunocytochemistry and an immunocomplex activity assay (T(3) by 10.7-fold, P<0.01 and T(4) by 10.4-fold, P<0.01 compared with control). T(3) (10 nM) and T(4) (100 nM) also significantly stimulated thymidine incorporation into MG-63 cells by 2.3+/-0.7-fold (P<0.01) and 2.1+/-0.1-fold (P<0.05) respectively. To establish whether transient ERK activation via the integrin alpha(V)beta(3) cell surface receptor mediated these effects, MG-63 cells were pretreated for 30 min with the specific MAPK kinase inhibitor, U0126 (1 microM), or an anti-integrin alpha(V)beta(3)-blocking antibody. Both pretreatments significantly inhibited T(3)- and T(4)-stimulated ERK activation and abolished T(3)-stimulated thymidine incorporation (P<0.01). T(4)-stimulated incorporation was significantly inhibited from 2.1- to 1.3-fold above control (P<0.05). Thus, our results suggest that T(3) and T(4) rapidly stimulate ERK activation in MG-63 cells via integrin alpha(V)beta(3) and that one functional effect of this ERK activation is increased DNA synthesis.

Vanadate prevents glucocorticoid-induced apoptosis of osteoblasts in vitro and osteocytes in vivo

Skeletal mass is maintained by a balance between formation and resorption, cell proliferation and apoptosis. In vitro, glucocorticoids (GCs) decrease extracellular signal-regulated kinases (ERK) activation by mitogens, thus inhibiting osteoblast proliferation. Both ERK activity and proliferation are restored by co-treatment with the protein tyrosine phosphatase inhibitor, vanadate. Since ERK signalling may also be anti-apoptotic, we explored the effects of vanadate on GC-induced apoptosis in vitro and in vivo. Apoptosis in MBA-15.4 pre-osteoblasts increased from 6 h and remained up to eightfold higher through 6 days of 10(- 6) M dexamethasone (Dex) treatment. Co-incubation with 10(- 7) M vanadate markedly reduced apoptosis at all time points. Vanadate also prevented GC-induced poly-ADP-ribose polymerase cleavage. We assessed the transcriptional profiles of seven anti-apoptotic proteins (Bcl-2, Bcl-X(L), inhibitors of apoptosis protein-1 (IAP-1), IAP-2, X-linked IAP (XIAP), Fas-associated death-domain-like IL-1beta-converting enzyme-inhibitory protein (FLIP(Long)) and FLIP(Short)) in osteoblasts subjected to various stimuli using real-time quantitative PCR. Although these anti-apoptotic genes responded to different mitogenic conditions, Dex failed to repress their expression, and in fact significantly up-regulated Bcl-X(L), IAP-2 and XIAP. Dex may therefore induce apoptosis by up-regulating pro-apoptotic gene expression. We have previously demonstrated that rats treated with GC develop low formation osteoporosis (bone histomorphometry and DEXA) and skeletal fragility (breaking strength) that were largely prevented by co-treatment with vanadate. We report here that vertebrae from rats treated with 3.5 mg/kg per day methylprednisolone for 9 weeks showed increased incidence of terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick end-labelling-positive apoptotic osteocytes, which was reduced by vanadate co-treatment. We conclude that vanadate prevents GC-induced apoptosis of pre-osteoblasts in vitro and osteocytes in vivo, and this may contribute to its bone-sparing effects in vivo.

Exogenous expression of glucagon-like peptide 1 receptor and human insulin in AtT-20 corticotrophs confers cAMP-mediated gene transcription and insulin secretion

The insulinotrophic effects of glucagon-like peptide 1 (GLP-1) are mediated by its seven-transmembrane receptor (GLP-1R) in pancreatic beta-cells. We have transiently transfected the GLP-1R and a proopiomelanocortin (POMC) promoter-driven human preproinsulin gene vector (pIRES) into the AtT-20 pituitary corticotrophic cell line, to investigate the possibility of creating a regulated, insulin-expressing cell line. Receptor expression was confirmed by RT-PCR and functionality was demonstrated by measuring changes in cAMP levels in response to GLP-1. Rapid (5 min) stimulation of cAMP production was observed with 100 nM GLP-1, 24 h after transfection of 2 microg GLP-1R DNA. AtT-20 cells co-transfected with GLP-1R and human glycoprotein hormone alpha-subunit or rat POMC promoters revealed GLP-1-stimulated cAMP activation of transcription. Co-transfection of the pIRES vector with the GLP-1R resulted in GLP-1-stimulated activation of POMC promoter-driven preproinsulin gene transcription but insulin secretion was not detected. However, using an adenoviral expression system to infect AtT-20 cells with GLP-1R and the preproinsulin gene (including 120 bp of its own promoter) resulted in a 6.4 +/- 0.6-fold increase in cAMP and a 4.9 +/- 0.8-fold increase in insulin secretion in response to 100 nM GLP-1. These results demonstrate, for the first time, functional GLP-1R-mediated preproinsulin gene transcription and secretion in a transplantable cell line.

FSH secretion predominates in vivo and in vitro in patients with non-functioning pituitary adenomas

OBJECTIVE

Non-functioning pituitary adenomas (NFPAs) are characterised by the lack of symptoms of hormone hypersecretory syndromes but in vitro studies have demonstrated that tumour cells may stain for gonadotrophins and/or their alpha- or beta-subunits. In this study, we aimed to examine the pattern of secretion of LH and FSH from a series of pituitary adenomas cultured in vitro and where data were available to relate the results to pre-operative serum gonadotrophin levels.

METHODS

The in vitro secretion of LH and FSH was measured from 46 cultured NFPAs and compared with pre-operative serum gonadotrophin levels in 38 patients. Peritumorous 'normal' pituitary cell cultures from 20 additional pituitary tumour patients were used for comparison with the NFPA group.

RESULTS

A median pre-operative LH:FSH ratio of 0.33:1 was found in 38 patients with NFPAs. Preferential secretion of FSH was also documented from media of 46 NFPAs cultured in vitro with a median LH:FSH ratio of 0.32:1. A significant correlation (r = 0.43, P < 0.01) was observed between serum and media levels of FSH but not LH. Peritumorous 'normal' pituitary cells released LH and FSH in a reversed ratio (median LH:FSH ratio = 3.6:1, P < 0.01 compared with NFPAs).

CONCLUSIONS

This study has evaluated pre-operative serum gonadotrophin levels and in vitro release of hormones in cultures of surgically removed tissue from patients with NFPAs. The data suggest preferential secretion of FSH occurs both in vitro and in vivo. By demonstrating that NFPAs cultured in vitro reflect the in vivo situation of preferential secretion of FSH, it may be possible in future to perform functional studies using this system to elucidate the cellular and molecular mechanisms involved in the development of an imbalance in gonadotroph cells preferentially overproducing FSH in NFPAs.

Absence of pituitary adenylate cyclase-activating polypeptide-stimulated transcription of the human glycoprotein alpha-subunit gene in LbetaT2 gonadotrophs reveals disrupted cAMP-mediated gene transcription

Hormone regulation of anterior pituitary expression of the common glycoprotein hormone alpha-subunit (alphaGSU) is mediated by multiple response elements residing in the first -435 bp of the human promoter. In rat pituitary cells and mouse alphaT3-1 precursor gonadotrophs, the human alphaGSU promoter is strongly responsive to activators of the adenylyl cyclase/cAMP pathway, such as the hypothalamic releasing hormone, pituitary adenylate cyclase-activating polypeptide (PACAP) and forskolin (an adenylyl cyclase activator). However, the role of PACAP and cAMP in regulating alphaGSU transcription in the more differentiated LbetaT2 gonadotroph is unclear. Here, we investigate the regulation of the human alphaGSU promoter by PACAP and forskolin in LbetaT2 and alphaT3-1 gonadotrophs. PACAP failed to stimulate alphaGSU promoter activity or cAMP production in LbetaT2 cells, in marked contrast to alphaT3-1 cells. LbetaT2 gonadotrophs expressed extremely low levels of any PACAP type 1 receptors (PAC(1)-R) isoform by RT-PCR and lacked PAC(1)-R by radioligand binding. Forskolin stimulated the alphaGSU promoter in LbetaT2 cells, but by less than 30% of the response seen in alphaT3-1 gonadotrophs. This blunted cAMP transcriptional effect was not due to different levels of cAMP generation, or altered expression of the cAMP target proteins CREB, Akt, CBP or ICER. However, only LbetaT2 cells showed detectable expression of the protein kinase A type IIalpha regulatory subunit. Binding of activating transcription factor-2 and phosphorylated CREB to the consensus CRE was observed in both LbetaT2 and alphaT3-1 gonadotrophs, yet forskolin failed to stimulate either CRE- or CREB-mediated transcription in LbetaT2 cells. Collectively, these data demonstrate the lack of functional PACAP receptors in LbetaT2 gonadotrophs, and a pronounced attenuation in the responsiveness of this differentiated gonadotroph cell line to cAMP stimulus.

The effect of growth hormone replacement therapy on adrenal androgen secretion in adult onset hypopituitarism

OBJECTIVE

Growth hormone replacement therapy in GH-deficient children is associated with enhanced adrenal androgen production, raising the possibility that GH might stimulate adrenocortical hormone secretion. This has not been extensively investigated in adults to date. GH is a potent modulator of the activity of the 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) enzyme and by altering cortisol metabolism can affect the function of the hypothalamo-pituitary-adrenal (HPA) axis and therefore potentially of adrenal androgen secretion. This study examined the effects of GH replacement in GH-deficient adults on adrenal androgen secretion.

DESIGN

Prospective study of the effect of GH replacement therapy on adrenal androgen production in patients with adult onset hypopituitarism over a 12-month period.

PATIENTS AND METHODS

Thirty adult GH-deficient patients were classified into two groups according to their cortisol responses to an insulin-induced hypoglycaemia or a glucagon stimulation test: 13 patients were adrenocorticotropic hormone (ACTH)-sufficient (nine females, age 45.1 +/- 3 years), whereas 17 patients were ACTH-deficient (11 females, age 45.5 +/- 3 years). Serum samples were collected before patients were initiated on GH replacement therapy using a dose titration regimen, and after 6 and 12 months on GH therapy for measurement of serum IGF-I, dehydroepiand-rosterone sulphate (DHEAS), Delta4-Androstenedione (A4), testosterone, cortisol, sex hormone binding globulin (SHBG) and cortisol binding globulin (CBG).

RESULTS

Six months after the initiation of GH replacement therapy, serum IGF-I levels were within the normal age-related reference range in both groups of patients and this was maintained at 12 months [in all patients 0 vs. 6 months: median (interquartile range): 92.5 ng/ml (73-116 ng/ml) vs. 191 ng/ml (159-224 ng/ml), P < 0.01]. In both ACTH-sufficient and -deficient groups of GH-deficient patients, pretreatment serum DHEAS levels were lower than the normal age-related reference range (P < 0.01); the ACTH-deficient patients had significantly lower DHEAS levels than the ACTH-sufficient patients [median (interquartile range): 0.5 micro mol/l (0.4-1.2 micro mol/l) vs. 1.5 micro mol/l (0.6-2.7 micro mol/l), P < 0.05]. Following GH replacement therapy, median levels of serum DHEAS levels rose from 1.5 micro mol/l (0.6-2.7 micro mol/l) to 1.9 micro mol/l (1.9-3.9 micro mol/l) in ACTH-sufficient patients, increasing in 11 of the 13 patients (P < 0.02). In this group, the median percentage increase from baseline was 32% at 6 months (P < 0.05). In contrast, baseline serum DHEAS levels [0.5 micro mol/l (0.4-1.2 micro mol/l)] declined in or from the measurable range in 47% of ACTH-deficient patients [median -16%; range -36-0] and only in one patient a + 0.2 micro mol/l increase was observed. GH dose requirements tended to be lower in ACTH-sufficient patients [1.2 U/day (0.8-1.4 U/day) vs. 1.6 U/day (1.0-2.0 U/day); P = 0.062]. There were no significant changes in serum testosterone, A4, SHBG and/or CBG levels, compared to the pretreatment levels, in either group of patients over the 12 months of GH replacement.

CONCLUSIONS

This study shows that median serum DHEAS levels are significantly lower in GH-deficient patients, even those with intact ACTH reserve, than in aged-matched controls. GH replacement therapy is associated with a significant increase in mean serum DHEAS only in ACTH-sufficient patients. These findings are consistent with either (i) GH stimulation of adrenal androgen production in the permissive presence of ACTH or (ii) an inhibitory effect of GH on 11beta-HSD type 1 activity leading to enhanced cortisol clearance, subsequent activation of the HPA axis and ACTH-mediated androgen secretion.

The relationship between pituitary tumour transforming gene (PTTG) expression and in vitro hormone and vascular endothelial growth factor (VEGF) secretion from human pituitary adenomas

OBJECTIVE

Pituitary tumour transforming gene (PTTG) is a recently identified protooncogene, ubiquitously expressed in pituitary tumours at levels higher than those detected in normal pituitary. Although the precise function of PTTG protein is unknown, in vitro experiments have shown that it induces angiogenesis. In this study, we have examined the potential relationship between the level of PTTG expression and tumour phenotype, tumour size, in vitro pituitary hormone secretion and release of vascular endothelial growth factor (VEGF), a potent angiogenic factor.

METHODS

Pituitary tumours (12 somatotroph, five lactotroph, five corticotroph and 18 non-functioning) were studied by cell culture, measuring the basal secretion of anterior pituitary hormones and VEGF in vitro. Immunocytochemistry was used to confirm the clinical diagnosis and tumour phenotype. PTTG mRNA expression was investigated by comparative RT-PCR. Tumour Volume was quantitated from pre-operative MRI scans.

RESULTS

PTTG expression was significantly increased 2.7-fold in somatotroph tumours compared with non-functioning adenomas (P<0.01, ANOVA). A positive correlation was demonstrated between PTTG expression and in vitro GH secretion (r=0.41, P<0.01, Spearman) but no correlations were found for any of the other pituitary hormones. In 16 out of 40 pituitary tumours, we were able to determine the in vitro secretion of VEGF and relate this to PTTG expression. All of the adenomas tested secreted measurable VEGF but there was no correlation between the amount of VEGF secreted and either the tumour phenotype or PTTG expression. Neither PTTG expression nor VEGF secretion correlated with tumour Volume.

CONCLUSIONS

Our studies have confirmed the presence of PTTG in pituitary adenomas and demonstrated a higher level of expression in somatotroph tumours and a significant correlation with GH secretion. We failed to demonstrate a relationship between PTTG expression and production of the angiogenic factor, VEGF, or tumour Volume. Thus, although PTTG induces angiogenesis experimentally, it seems unlikely that a VEGF-mediated angiogenic mechanism occurs during pituitary tumour progression.

Neonatal thyrotoxicosis and maternal infertility in thyroid hormone resistance due to a mutation in the TRbeta gene (M313T)

We report two unusual cases of resistance to thyroid hormone (RTH) in one family. The first case, a male infant, had clinical features of thyrotoxicosis in the neonatal period. In the fourth week of life weight gain was poor despite a daily intake of standard infant formula almost double the infant's estimated requirements. At this time serum free T4 (fT4) was 60.7 pmol/l (Normal range [NR] 11-25 pmol/l) and TSH was inappropriately normal at 1.8 mU/l (NR 0.3-4.0 mU/l). The infant responded clinically and biochemically to propylthiouracil (PTU) at a dose of 10 mg/kg/day. Following 27 days of treatment serum fT4 was 22.6 pmol/l and TSH had risen to 24.9 mU/l. As the infant was thriving treatment was discontinued. The infant, now aged 6 months old, remains clinically euthyroid and developmentally normal off treatment. The infant's mother, from whom he had inherited a mutation of the thyroid receptor beta (TRbeta) gene (M313T), presented earlier with secondary infertility and clinical features of thyrotoxicosis. Treatment with PTU restored her fertility and she spontaneously conceived. In the subsequent pregnancy, clinical and biochemical features of RTH improved, and she gave birth to a small but healthy female infant. In the next pregnancy, resulting in the birth of the affected male infant, clinical and biochemical features of RTH worsened, and high doses of PTU were required to maintain a clinically euthyroid state. To our knowledge, these are the first case reports of RTH associated with added features of a hypermetabolic state in infancy and secondary infertility.

Stimulation of extracellular signal-regulated kinase by pituitary adenylate cyclase-activating polypeptide in alpha T3-1 gonadotrophs

The putative hypophysiotropic factor pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates glycoprotein hormone alpha-subunit (alpha GSU) gene transcription and secretion in the clonal gonadotroph alpha T3-1 cell line. The specific signalling pathways regulating these actions of PACAP have not been clearly defined. We have examined the possibility that mitogen activated protein kinases (MAPKs) may play a role in mediating the effects of PACAP on alpha T3-1 gonadotrophs. Treatment of alpha T3-1 cells with PACAP (100 nM) or epidermal growth factor (EGF, 10 nM) for 5 min significantly stimulated extracellular signal-regulated kinase activity (ERK, a component of the MAPK pathway) as determined by an immunocomplex assay. Pre-treatment of alpha T3-1 cells with the specific MAPK kinase (MEK) inhibitor, U0126, blocked PACAP and EGF-induced activation of ERK. Transcriptional stimulation of a human alpha GSU-luciferase reporter construct by PACAP was unaffected by U0126 treatment. However, pre-treatment with U0126 significantly inhibited PACAP stimulation of [(3)H]-thymidine incorporation in alpha T3-1 cells. Thus our results suggest that PACAP stimulates ERK activation in alpha T3-1 cells, and that the functional effect of this ERK activation is increased DNA synthesis and cell proliferation rather then transcriptional activation of the alpha GSU gene.

Transcriptional regulators of steroidogenesis, DAX-1 and SF-1, are expressed in human skin

DAX-1 and SF-1 are members of the orphan nuclear receptor superfamily that are critical regulatory components of the hypothalamic-pituitary-adrenal-gonadal axis. In adrenal and gonadal tissues they regulate the expression of the cytochrome P450 steroid hydroxylase genes, key mediators of steroidogenesis. The identification of a number of steroid hydroxylases in human skin prompted us to investigate the presence of DAX-1 and SF-1. Immuno histochemical analysis of human skin revealed a distinctive staining pattern for DAX-1 and SF-1 in skin and its appendages. Prominent staining for DAX-1 was confined to the epidermis, sebaceous glands, sweat glands, and outer root sheath of the hair follicle with weaker expression in the inner root sheath, matrix cells, and dermal papilla cells. Similarly, SF-1 was also detected in the epidermis but displayed a scattered nuclear pattern across all layers. SF-1 immunoreactivity was also detected in the exocrine glands and was stronger than DAX-1 in the inner root sheath, matrix cells, and dermal papilla cells. Co-localization of DAX-1 and SF-1 was demonstrated by immunocytochemistry in the HaCaT keratinocyte cell line, primary keratinocytes, preadipocytes, and dermal papilla cells. Reverse transcriptase-polymerase chain reaction analysis demonstrated the expression of DAX-1 and SF-1 mRNA in whole human skin and Western analysis also confirmed the presence of DAX-1 protein in skin-derived cells. Our investigations demonstrate that two important regulators of steroidogeneisis are present in human skin and its appendages. These transcription factors may have a role in cutaneous steroidogenesis and thus be involved in hair follicle cycling or pathologies associated with steroids. Further studies are needed to determine the functional roles of DAX-1 and SF-1 in human skin.

The relationship between steroidogenic factor 1 and DAX-1 expression and in vitro gonadotropin secretion in human pituitary adenomas

The orphan nuclear receptors, steroidogenic factor 1 (SF-1) and DAX-1, are involved in gonadotroph differentiation, and SF-1 has been shown to activate the LH-beta and glycoprotein hormone alpha-subunit (alpha GSU) gene promoters. Pituitary adenomas from 34 patients [13 somatotroph tumors, 4 prolactinomas, and 17 clinically nonfunctioning pituitary adenomas (NFPAs)] were enzymatically dispersed and cultured in vitro for 48 h. Tissue culture medium was collected and assayed for LH, FSH, and alpha GSU; messenger RNA was extracted from adherent cells, and expression of SF-1 and DAX-1 messenger RNA was determined by RT-PCR and verified by direct DNA sequencing. The presence of DAX-1 protein in tumor tissue was confirmed by immunocytochemistry. DAX-1 was demonstrated in all NFPAs, 7 of 13 somatotroph tumors and 0 of 4 prolactinomas. SF-1 expression occurred in 8 of 16 NFPAs, 4 of 12 somatotroph tumors, and 1 of 4 prolactinomas. LH secretion in vitro was greater in NFPAs that were SF-1 positive (P < 0.05). Neither FSH secretion nor alpha GSU secretion in vitro were significantly related to the expression of SF-1 or DAX-1. SF-1-positive somatotroph tumors immunostained positively for LH-beta and/or FSH-beta and secreted gonadotropins in vitro. SF-1 expression is associated with the in vitro secretion of LH by NFPAs. A proportion of somatotroph tumors also express SF-1 and DAX-1 and secrete gonadotropin hormones in vitro.

The release of leptin and its effect on hormone release from human pituitary adenomas

BACKGROUND

Leptin is the protein product of the obese gene, known to play an important role in body energy balance. The leptin receptor exists in numerous isoforms, the long isoform being the major form involved in signal transduction. Leptin expression has recently been demonstrated in the human pituitary, both in normal tissue and in pituitary adenomas. The long isoform of the leptin receptor has also been shown to be present in pituitary adenomas; however, contrasting results have been obtained regarding its expression in the normal human pituitary.

AIM

The aim of this study was (i) to investigate the presence and pattern of distribution of leptin mRNA and the long isoform of its receptor mRNA in the normal pituitary and in different types of pituitary adenomas with RT-PCR; (ii) to study leptin secretion from human pituitary tumours in culture and (iii) to assess in vitro pituitary hormone release following stimulation with human leptin.

RESULTS

Leptin receptor long isoform expression was detected in 2/4 GH-secreting adenomas, 12/17 non-functioning adenomas, 5/9 ACTH-secreting adenomas, 1/2 prolactinomas, 2/2 FSH-secreting adenomas and 5/5 normal pituitaries. The receptor long isoform did not segregate with any particular tumour type, and varying levels of expression were detected between the tissues studied. Leptin mRNA was detected at a low level of expression in 2/7 GH-secreting adenomas, 9/14 non-functioning adenomas, 2/3 ACTH-secreting adenomas, 1/3 prolactinomas and 1/3 FSH-secreting adenomas. We were unable to detect leptin mRNA in any of the five normal pituitaries removed at autopsy; however, immunostaining of a non-tumorous pituitary adjacent to an adenoma removed at transsphenoidal surgery showed scattered leptin positive cells. Culture of pituitary adenomas showed that 16/47 released leptin into the incubation media. Leptin release did not correlate with tumour type or with any of the other pituitary hormones released. In vitro leptin stimulation of pituitary tumours caused stimulation of FSH and alpha-subunit secretion from a non-functioning adenoma and TSH secretion from a somatotroph adenoma.

CONCLUSION

We conclude that not only is leptin stored within the pituitary, but it may also be released from pituitary cells and modulate other pituitary hormone secretion. Pituitary leptin may therefore be a novel paracrine regulator of pituitary function.

Leptin in pituitary adenomas--a novel paracrine regulatory system

A growing number of physiological and pathophysiological processes have been shown to be influenced by leptin apart from its first recognised role as a modulator of hypothalamic appetite and weight control centers. We investigated the presence and pattern of distribution of leptin mRNA and the mRNA of the long isoform of the leptin receptor in the normal pituitary and in different types of pituitary adenomas. We also studied leptin secretion from human pituitary tumors in culture, and the in vitro pituitary hormone release following stimulation with human leptin. Leptin mRNA expression was detected at a low level of expression in 50% of tumors but in none of the normal pituitaries. By immunohistochemistry, leptin was present in occasional scattered cells in the normal pituitary and in pituitary tumors. The leptin receptor long isoform was detected in the majority (65%) of pituitary tumors and in all normal pituitaries. It did not segregate with any particular tumor type, and varying levels of expression were detected between the tissues studied. 34% of pituitary adenomas showed leptin release into the incubation media during in vitro culture. Leptin mRNA, the mRNA of the long isoform of the receptor, or in vitro leptin release, did not correlate with tumor type or with any of the other pituitary hormones released. In vitro leptin stimulation of pituitary tumors caused stimulation of FSH and a-subunit secretion from a non-functioning adenoma and TSH secretion from a somatotroph adenoma. As the co-localisation of ACTH and leptin in corticotroph cells was previously suggested, we investigated whether in vivo ACTH release is accompanied by a simultaneous plasma leptin level rise (i) in peripheral plasma samples after food intake-induced ACTH rise in healthy obese and nonobese individuals and (ii) in petrosal sinus samples after CRH injection in Cushing's disease patients. Our data suggest that a rise in ACTH levels is not accompanied by detectable rise in leptin levels in peripheral and in petrosal sinus blood samples. In summary, leptin is synthesized and stored within the pituitary and may modulate other pituitary hormone secretion, although probably it does not contribute to plasma leptin level changes. Pituitary leptin may therefore be a novel paracrine regulator of pituitary function.

Potent suppression of the parathyroid glands by hydroxylated metabolites of dihydrotachysterol(2)

BACKGROUND

Dihydrotachysterol(2), a licensed pharmaceutical, is hydroxylated to 25-hydroxydihydrotachysterol(2) (25(OH)DHT(2)) and 1 alpha,25-dihydroxydihydrotachysterol(2) (1 alpha,25(OH)(2)DHT(2)) in man. We have compared the biological activity of these metabolites with calcitriol and the 'non-calcaemic' analogue, 22-oxacalcitriol (OCT) in bovine parathyroid cell cultures and in rats.

METHODS

The effect of each sterol on parathyroid hormone (PTH) secreted by primary bovine parathyroid cells was measured. High-performance liquid chromotography and gas chromotography-mass spectrometry were used to investigate in vitro 25(OH)DHT(2) metabolism. Rats were given a single intraperitoneal injection or five daily injections of each sterol, and changes in ionized calcium and PTH were measured.

RESULTS

In vitro, all sterols suppressed PTH significantly. Calcitriol and OCT were of similar potency, but 1 alpha, 25(OH)(2)DHT(2) and 25(OH)DHT(2) required higher concentrations to suppress PTH equally. We were unable to detect metabolism of 25(OH)DHT(2) to 1 alpha,25(OH)(2)DHT(2) in vitro. In rats, a single dose of 0.5 microg/rat of calcitriol increased ionized calcium at 30 and 40 h (statistically significant at 48 h). 50 microg of OCT and 1 alpha,25(OH)(2)DHT(2) did not cause significant hypercalcaemia at 48 h, although 1 alpha,25(OH)(2)DHT(2) caused hypercalcaemia at 30 h. In contrast, 50 microg of 25(OH)DHT(2) caused hypercalcaemia at 48 h but not at 30 h. Five daily doses of 0.001 microg/rat of calcitriol caused a significant rise in calcium and a 50% fall in PTH. OCT and 1 alpha,25(OH)(2)DHT(2) at 0.025 and 0.5 microg/rat respectively caused similar suppression of PTH but without hypercalcaemia.

CONCLUSION

1 alpha,25(OH)(2)DHT(2) and 25(OH)DHT(2) are potent suppressors of PTH in vitro and in vivo. 25(OH)DHT(2) may be active by virtue of its pseudo-1 alpha-hydroxyl group. Hypercalcaemia caused by a single dose of 1 alpha,25(OH)(2)DHT(2) appeared to be more transient than calcitriol. Five daily doses of 1 alpha, 25(OH)(2)DHT(2) and OCT could achieve 50% suppression of PTH without significant increments in ionized calcium. In contrast, suppression of PTH by calcitriol was associated with significant increments in ionized calcium. These data suggest that like OCT, 1 alpha, 25(OH)(2)DHT(2) can dissociate calcaemic actions from parathyroid-suppressing actions in a manner that may be therapeutically useful.

Expression of the pituitary transcription factor Ptx-1, but not that of the trans-activating factor prop-1, is reduced in human corticotroph adenomas and is associated with decreased alpha-subunit secretion

We have studied the expression of the pituitary transcription factors Ptx-1 and Prop-1 in a series of 34 pituitary adenomas fully characterized for in vitro hormone secretion and histological staining. In studies involving mammalian cell lines, the pituitary transcription factor Ptx-1 has been shown to be a pituitary hormone panactivator, whereas more recent studies have shown that it plays an important role in alpha-subunit gene expression. Its expression has not been examined previously in human pituitary adenomas characterized by in vitro hormone secretory profiles. Of the 34 pituitary adenomas studied, Ptx-1 expression was reduced by more than 50% compared to that of the housekeeping gene human glyceraldehyde-3-phosphate dehydrogenase in the 6 corticotroph adenomas, which also had significantly reduced alpha-subunit production (all 6 tumors secreting < or =0.5 ng/24 h). Mutations of the pituitary transcription factor Prop-1, which is responsible for the syndrome of Ames dwarfism in mice, are being increasingly recognized as a cause of combined pituitary hormone deficiency in humans, although ACTH deficiency has been described only once. Prop-1 expression was detected in all 34 pituitary adenomas, including 6 corticotroph adenomas and 5 gonadotroph adenomas. The expression of Prop-1 has not been described previously in these cell phenotypes.

Etomidate and the osteocalcin response to gynaecological surgery

Circulating osteocalcin is a good marker of osteoblastic activity and decreases significantly after stressful physiological states such as major surgery. Glucocorticoids are known to inhibit osteoblastic activity and result in a decline in circulating osteocalcin. We used etomidate to inhibit the cortisol response to routine gynaecological surgery to determine if this would prevent the postoperative decline in osteocalcin. Twenty-four patients were allocated randomly to receive either thiopental or etomidate for induction of anaesthesia; all other aspects of anaesthesia and perioperative management were standardized. In the thiopental group, circulating cortisol increased significantly at 2 and 6 h after the start of surgery and plasma osteocalcin concentrations decreased significantly to almost 50% of baseline values at 48 h. Etomidate abolished the cortisol response to surgery, and circulating osteocalcin concentrations did not change after operation. There was a significant difference in osteocalcin concentration between the groups at 48 h. We conclude that the cortisol response to surgery is associated with a postoperative decrease in circulating osteocalcin.

Expression and secretion of neural cell adhesion molecules by human pituitary adenomas

Neural cell adhesion molecules (NCAMs) are found predominantly in neural, muscle and endocrine cells. Recent interest has focused on their potential role in tumorigenesis. We have analysed the expression and secretion of NCAM in a series of 48 human pituitary adenomas. Immunocytochemical analysis of 19 adenomas demonstrated NCAM expression in all tumours with, in each case, diffuse cytoplasmic staining being found with variable membrane accentuation. There were no apparent differences in the expression of immunoreactivity seen on sections between individual tumours. Cell culture media from 43 dispersed human pituitary tumours were analysed by immunoassay for the secretion of soluble NCAM and all the pituitary hormones. In contrast to the immunocytochemical studies, soluble NCAM was released from only 27% of human pituitary tumours, but this was not related to tumour type nor was the amount of soluble NCAM released correlated with the amount of pituitary hormone secreted by each adenoma. NCAM expression is common to all human pituitary adenoma types and the observed differences in release of soluble NCAM between individual tumours may reflect different molecular mechanisms, altering adhesive interactions between normal and adenomatous tissue.

Steroidogenic factor 1-DNA binding: a kinetic analysis using surface plasmon resonance

Basal expression of the glycoprotein hormone alpha-subunit gene in pituitary gonadotrophs is partially dependent on a gonadotroph specific element (GSE) which binds the nuclear receptor, steroidogenic factor-1 (SF-1). We have used surface plasmon resonance (SPR) to determine the association (kappa ass), dissociation (kappa diss) and affinity (KA) constants of SF-1 binding to immobilized oligonucleotides containing either the GSE consensus motif or a GSE mutant with a 2 bp substitution in the GSE site (GSEMUT). In vitro translated SF-1 protein bound the consensus GSE with a threefold increase in affinity constant (P<0.01) compared with the GSEMUT. This was due primarily to a significant increase (P<0.05) in the kappa ass for SF-1 to the GSE and a slower kappa diss (P<0.05). The binding interaction was specific and could be significantly inhibited (P<0. 001) by either anti-SF-1 antibody or excess non-biotinylated GSE. The addition of 14 bp wild-type flanking sequences significantly reduced the affinity of SF-1 to both the GSE (P<0.05) and the GSEMUT (P<0.01). This was due to a significant (P<0.01) decrease in kappa ass for the wild-type and mutant long oligonucleotides compared with the short GSE. Nuclear extracts from alphaT3-1 gonadotroph cells also bound the GSE and GSEMUT, giving kappa diss values which were two- to threefold slower than those obtained with in vitro translated SF-1. Thus, SPR is a powerful technique for examining kinetic interaction between SF-1 and its binding site, and is able to demonstrate the effects of mutations and flanking sequences on that interaction.

Effects of new analogues of vitamin D on bone cells: implications for treatment of uremic bone disease

BACKGROUND

The use of calcitriol in the treatment of uremic hyperparathyroidism and renal osteodystrophy is limited in many patients by hypercalcemic side-effects. New less calcemic analogues of calcitriol are being developed, and some are under clinical evaluation. To investigate whether these compounds possess important differences in their action on bone cells, we have studied their effects [with and without parathyroid hormone (PTH)] on the release and synthesis of the resorptive osteotropic cytokine, interleukin-6 (IL-6).

METHODS

MG 63 and SaOS-2 human osteoblastic cell lines were cultured for 6 or 24 hours in media containing calcitriol, the sterols of interest, or 1-34 synthetic PTH. IL-6 release was assayed by commercially available enzyme-linked immunosorbent assay. IL-6 mRNA levels were assessed by reverse transcriptase-polymerase chain reaction.

RESULTS

We found that calcitriol and paricalcitol behaved in a similar fashion, resulting in increased IL-6 release only at higher concentrations (10(-7) to 10(-9) M). In contrast, 22-oxacalcitriol and 1,25-dihydroxydihydrotachysterol2 stimulated release to a similar extent but at concentrations three to four orders of magnitude lower (10(-11) to 10(-13) M), despite being less potent as suppressers of parathyroid function than calcitriol. Studies of IL-6 mRNA showed a similar pattern of concentration and cell line-dependent transcription.

CONCLUSIONS

Compounds stimulating IL-6 release at concentrations achievable during the treatment of uremic hyperparathyroidism might favor continuing linked bone formation and resorption and thereby avoid adynamic bone disease while still allowing profound suppression of PTH.

Serum cytokines in thyrotoxicosis

Overproduction of thyroid hormones promotes bone resorption in vivo and in vitro, and we have evaluated whether mediators of such effects could include the osteotropic cytokines. Previous studies have demonstrated raised serum interleukin (IL)-6 in thyrotoxic patients, but differentiating the contribution of the elevated thyroid hormones from that of the autoimmune inflammation present in Graves' disease (GD) has been difficult. We undertook a longitudinal study of 34 patients (19-45 yr old) with GD, toxic nodular goiter (TNG), or a history of thyroid carcinoma but no evidence of disease recurrence, receiving sufficient T4 to suppress TSH. Controls were 12 euthyroid females. The following measurements were made basally and for 6 months after carbimazole treatment: serum free T4, T3, bone-specific alkaline phosphatase (b-ALP), IL-6, IL-8, IL-1beta, tumor necrosis factor-alpha, IL-11, and urinary deoxypyridinoline (Udpd). Compared with controls (IL-6, 1.1 +/- 0.3 ng/L; IL-8, 3.2 +/- 0.8 ng/L), untreated patients with GD and TNG had elevated IL-6 (GD, 7.11 +/- 0.88 ng/L; TNG, 7.30 +/- 0.77 ng/L; P < 0.001) and IL-8 (GD, 10.3 +/- 1.23 ng/L; TNG, 9.81 +/- 1.27 ng/L; P < 0.001). These levels fell after treatment and were then indistinguishable from those in control subjects. Thyroid carcinoma patients on TSH suppressive therapy also had significantly raised levels of IL-6 (2.5 +/- 0.42 ng/L) and IL-8 (4.4 +/- 0.63 ng/L). When data from all the patients were pooled, the levels of IL-6 and IL-8 correlated with serum T3 and free T4 but not with Udpd or b-ALP. IL-1beta, IL-11, and tumor necrosis factor-alpha were not raised in any patient. The elevations in serum IL-6 and -8 that occur in hyperthyroidism seem to result from the chronic effects of thyroid hormone excess rather than the accompanying autoimmune inflammatory condition produced by Graves' thyroid or eye disease. The site of the presumed increased production of IL-6 and -8 is most likely from bone osteoblasts, despite the inability of bone markers (such as Udpd and b-ALP) to correlate with acute changes in thyroid hormone status produced by antithyroid therapy.

Expression of the growth hormone secretagogue receptor in pituitary adenomas and other neuroendocrine tumors

Synthetic GH secretagogues (GHSs; GH-releasing peptides and their nonpeptide mimetics) stimulate GH release, activate the hypothalamo-pituitary-adrenal axis, and release PRL in vivo. Patients with acromegaly show an exuberant GH response to GHSs, whereas patients with pituitary-dependent ACTH-secreting tumors show an exaggerated rise in ACTH and cortisol. We, therefore, studied the presence of GHS receptor (GHS-R) messenger ribonucleic acid (RNA) in 38 human pituitary tumors of different cell types, 3 ectopic ACTH-secreting tumors, a pancreatic gastrinoma, 3 insulinomas, and a non-secreting thymic carcinoid as well as in 7 normal pituitary glands. Certain pituitary tumors were also studied by in vitro cell culture with measurement of secreted GH, ACTH, PRL, FSH, LH, alpha-subunit, and TSH. RNA was extracted from tissue samples and, after RT, a duplex PCR reaction with primers for the GHS-R gene and for the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase was performed, allowing semiquantitation of GHS-R expression. All the somatotroph adenomas (n = 8) showed a 2-10 times higher expression of the GHS-R gene compared to normal pituitaries. Higher than normal expression was shown in 5 of 18 tumors from patients with ACTH-secreting pituitary adenomas and in 1 of 3 ectopic ACTH-secreting carcinoid tumors. Two of the pituitary ACTH-secreting adenoma samples showed completely absent expression of the GHS-R, 8 showed expression similar to that of normal pituitary tissue, and 3 of the corticotroph adenoma tissue samples and 2 ectopic ACTH-secreting tumors showed a very low level of expression. One of 4 prolactinoma samples showed a high level of expression, 1 showed expression similar to that of normal pituitary, and 2 samples showed a very low level of expression. Nonfunctioning pituitary adenoma samples showed either absent or very low level expression of the GHS-R. The pancreatic gastrinoma sample showed expression similar to that of normal pituitary tissue, whereas 3 insulinomas showed low level expression of the GHS-R gene; a nonsecreting thymic carcinoid tumor showed no detectable expression. In summary, although GHS-R messenger RNA is abundant in human somatotroph adenomas, it is also present in other pituitary adenomas, particularly ACTH-secreting tumors. These findings may explain the in vivo responses to GHSs in patients harboring such tumors. It also appears from our study that GHS-R may be expressed in other neuroendocrine tumors.

Free alpha-subunit and intact TSH secretion in vitro are closely associated in human somatotroph adenomas

OBJECTIVE

GH-secreting pituitary adenomas frequently co-secrete prolactin and glycoprotein hormone alpha-subunit (alphaSU), but expression of additional hormones is considered unusual. The aim of this study was to establish the frequency with which acromegalic tumours secrete intact glycoprotein hormones LH, FSH and TSH, in comparison with other types of pituitary adenoma.

DESIGN AND METHODS

Pituitary tumours were studied by cell culture, measuring the basal secretion of anterior pituitary hormones in vitro. Light microscopy was used to exclude tumours where normal pituitary tissue was present, and immunocytochemistry was employed to confirm the clinical diagnosis and for comparison with tissue culture data.

RESULTS

TSH secretion was observed in vitro in 15/23 somatotroph adenomas, but from only 1/8 lactotroph, 4/29 null cell, 2/12 gonadotroph and 1/10 corticotroph adenomas; moreover, somatotroph adenomas secreted the largest amounts of TSH (P < 0.(001). Somatotroph adenomas also secreted LH (7/23) and FSH (2/23) but less frequently than gonadotroph adenomas. Immunocytochemistry demonstrated glycoprotein expression in somatotroph adenomas (LHbeta: 13%, FSHbeta: 26%, TSHbeta: 30%, alphaSU: 46%) more frequently than in lactotroph, corticotroph and null cell adenomas. A strong correlation was found between alphaSU secretion and TSH secretion in somatotroph adenomas (rho= 0.683, P < 0.001.

CONCLUSIONS

TSHbeta is frequently expressed by somatotroph adenomas, often associated with alphaSU expression. Both GH and TSHbeta are dependent on the transcription factor, Pit-1, which is frequently expressed in somatotroph adenomas, although the expression of alphaSU requires an alternative explanation. Increased expression of alphaSU compared with TSHbeta may account for the secretion of free alphaSU by somatotroph adenomas.

The matrix effects on kinetic rate constants of antibody-antigen interactions reflect solvent viscosity

This study describes the influence of different matrices on two model antibody-antigen interactions; that between beta2microglobulin and anti beta2microglobulin, and that of rabbit anti mouse Fc fragment (RAMFc) with mouse IgG. The matrices investigated were; phosphate-buffered saline pH 7.4 containing 0.05% Tween 20 detergent, horse serum, a 50:50 mixture of phosphate-buffered saline/Tween 20 and horse serum, and four glycerol solutions of differing concentrations. A recently developed optical biosensor, the IAsys, was used to monitor the interactions in real-time and provide precise determinations of k(ass), k(diss) and KA values. The results show that the rates of association and dissociation for the two different antibody:antigen models are significantly affected by the surrounding matrix. Glycerol of known viscosity was used as a matrix in both models to show that this effect is attributable to the viscosity as opposed to proteins present in the matrix. The viscosity of the matrix has also been shown to have an apparent influence upon the overall equilibrium/affinity constant for the interaction, with measurements of KA tending to increase with viscosity. The significant effects of matrix on kinetic rate constants for antibody-antigen interactions shown here have important implications in the use of immunoassays where non-equilibrium measurements are made in serum matrices.

Tri-iodothyronine regulates the production of interleukin-6 and interleukin-8 in human bone marrow stromal and osteoblast-like cells

Hyperthyroidism is associated with increased bone resorption but the mechanisms by which thyroid hormone (T3) affects bone cell metabolism remain unclear. Recently it has been suggested that T3 stimulates osteoclastic resorption indirectly through the release of soluble mediators from osteoblasts. The aim of the present study was to investigate whether the T3-induced increase in bone resorption could be due to the regulation of cytokine production by human osteoblasts (hOb). The effects of T3 (1, 10, 100 nM) and IL-1 beta (100 U/ml) as the positive control were examined on cytokine protein release and mRNA levels in cultured hOb cell lines (MG63, SaOs-2), primary hOb and human bone marrow stromal (hBMS) cells. T3 increased IL-6 and IL-8 mRNA levels as well as IL-6 and IL-8 protein release into the culture media from MG63 and hBMS cells in a time- and dose-dependent manner. The maximal effect on protein release in hBMS cells occurred at 24 h with a dose of T3 10 nM (IL-6 5.5 +/- 1.1-fold above controls; IL-8 3.7 +/- 0.5-fold above controls, P < 0.05). At the same time, mRNA levels in hBMS cells were increased 6.2 +/- 0.8-fold for IL-6 (P < 0.05) and 5.7 +/- 0.8-fold for IL-8 (P < 0.05). Similar results were obtained in MG63 cells but no response was seen in SaOs-2 or hOb cells despite measurable basal production. Nor was there detectable regulation of IL-1 beta, IL-3, IL-11, IL-4 or granulocyte macrophage-colony stimulating factor by T3 in any cell type. In conclusion, T3 increases IL-6 and IL-8 production by MG63 and hBMS cells, suggesting that IL-6 and IL-8 may be T3-regulated genes in osteoblasts.

Mechanism of action of pituitary adenylate cyclase-activating polypeptide on human glycoprotein hormone alpha-subunit transcription in alphaT3-1 gonadotropes

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to increase glycoprotein hormone alpha-subunit synthesis and release from pituitary cells. We have used alphaT3-1 clonal gonadotropes to investigate the intracellular mechanisms involved in PACAP regulation of alpha-subunit gene transcription; and using deletion, mutation, and heterologous constructs of the alpha-promoter linked to a luciferase reporter gene, we have defined DNA sequences responsive to PACAP. Stimulation of alphaT3-1 cells for 24 h with PACAP, GnRH, or vasoactive intestinal peptide (VIP) resulted in a time- and concentration-dependent increase in alpha-promoter transcription at 100 nM for GnRH (17.5-fold, P < 0.001), PACAP (12.7-fold, P < 0.01), and VIP (4.1-fold, P < 0.05). Incubation of alphaT3-1 cells in calcium-depleted medium suggested that the transcriptional response to PACAP was less dependent on changes in intracellular calcium concentration, in contrast to the results seen with GnRH or VIP, where alpha-subunit transcription was significantly reduced. Transfection of an alpha-promoter construct containing a mutant cAMP response element (CRE) suggested that the CRE region is involved in PACAP and VIP responsiveness, with stimulatory effects on the mutant construct by PACAP (11.1-fold) and VIP (7.6-fold) being significantly (P < 0.001) reduced, compared with their stimulatory effects (PACAP: 25.6-fold, VIP: 23.1-fold) on the native alpha-promoter. In the same experiment, the transcriptional response of the mutant CRE construct and the native CRE construct to GnRH was not significantly different. Both PACAP and VIP enhanced GnRH-stimulated alpha-subunit gene transcription, but this additive effect was lost when their combined effects on the mutant CRE were examined. Deletion analysis indicated that sequences between -244 and -195 bp were involved in mediating the response to PACAP, with a dramatic reduction in fold-stimulation by PACAP (2.0-fold) of the -195-bp construct, compared with the -244-bp construct (15.8-fold). Constructs containing only upstream alpha-promoter sequences from -517 bp to -98 bp, fused to the heterologous thymidine kinase promoter, exhibited a similar loss of responsiveness to PACAP below -298 bp. Thus, our studies show that, unlike GnRH, PACAP stimulation of alpha-subunit gene transcription in alphaT3-1 cells is less dependent on changes in intracellular calcium concentration; and full transcriptional activation of the alpha-subunit by PACAP requires an intact CRE. PACAP responsiveness involves sequences between -244 and -195 bp of the alpha-promoter. These sequences have been implicated also in GnRH-responsiveness and may thus provide a mechanism for coordinated regulation of the alpha-subunit gene by PACAP and GnRH in alphaT3-1 cells.

Pituitary-adrenal, hormonal changes during induced hypotension with labetol or isoflurane for middle-ear surgery

BACKGROUND

Pituitary-adrenal secretion during induced hypotension for middle-ear surgery has received little attention. Previous work failed to differentiate the effects of induced hypotension from surgical stimulation. We have undertaken a preliminary study examining the effects of hypotension, achieved with labetalol or isoflurane, on pituitary-adrenal secretion before, during and after middle-ear surgery.

METHODS

Twenty-four patients were allocated randomly to 3 groups. The control group were anaesthetised with isoflurane, and normotension maintained for 30 min before hypotension was induced with isoflurane and surgery started. In the labetalol group, this drug was given i.v. to obtain a mean arterial pressure (MAP) of 60 mm Hg for 30 min before surgery and hypotension maintained with labetalol during the operation. In the isoflurane group, hypotension was induced to a MAP of 60 mm Hg for 30 min before surgery and continued throughout the procedure. All 3 groups received metoprolol i.v. before hypotension was established. Blood samples were collected before induction of anaesthesia, during anaesthesia alone (normotensive or hypotensive), surgery with hypotension, and recovery. They were analysed for adrenocorticotropic hormone (ACTH), arginine vasopressin (AVP), cortisol and aldosterone.

RESULTS

Induced hypotension before surgery failed to stimulate release of ACTH, AVP and cortisol. No significant increase in these hormones occurred until the postoperative period. Aldosterone concentrations increased significantly during anaesthesia and hypotension in the labetalol and isoflurane groups (P<0.05) and continued to rise significantly in all 3 groups during surgery. However, there was no significant difference in aldosterone concentration before surgery between the control and the 2 hypotensive groups.

CONCLUSION

ACTH, AVP and cortisol secretion were not stimulated by induced hypotension to MAP of 60 mm Hg before surgery. Increased aldosterone secretion occurred and a further study with a larger sample size is needed.

Lessons for the laboratory from a general practitioner survey

AIMS

To assess the current performance of the clinical biochemistry service provided to general practitioners, with particular attention to result turnround times, and to identify and improvements required.

METHODS

Postal questionnaire survey of general practitioners in the London Borough of Tower Hamlets who used the clinical biochemistry laboratory of the Royal London Hospital. A flow analysis study of turnround times for general practitioner samples was also performed.

RESULTS

Responses to the questionnaire showed that although 82% of general practitioners thought the current quality of service provided was better than fair, the actual turnround times achieved were longer than the acceptable times required. There was also a strong demand (> 66% of responders) for additional information-such as highlighting of abnormal results-to be provided with results. There was wide variability between practitioners in their use of the laboratory (from none to > 800 requests per year), with no apparent correlation to practice size. Of the repertoire of tests requested, a surprisingly high percentage (14.3%) were for thyroid function. Flow analysis of turnround times for thyroid function tests showed that problems lay not with the time taken for analysis (only 7.8% of the total turnround time) but with the pre- and postanalytical phases, that is, the sample collection and results delivery service.

CONCLUSIONS

Increasing the proportion of health care delivered in the primary care sector will inevitably increase the requirement for pathology services. Improvements in the specimen collection and results delivery service to general practitioners are needed to meet their expectations. It remains to be determined whether increased investment in these aspects of laboratory service would result in improved patient care in the primary sector.

A longitudinal study of markers of bone turnover in Graves' disease and their value in predicting bone mineral density

Whether biochemical markers can predict improvement in reduced bone mineral density (BMD) associated with thyrotoxicosis in unclear. We investigated the relationship between serum osteocalcin (OC), bone-specific alkaline phosphatase (b-ALP), serum deoxypyridinoline (Sdpd) and pyridinoline (Spyr), 24-hour urinary deoxypyridinoline (Udpd), and BMD in 17 thyrotoxic patients during 1 yr of treatment. Coinciding with euthyroidism at 4-8 weeks, there was a peak in b-ALP and OC and a prompt fall into the normal range in Udpd and Sdpd, but not Spyr, levels. Mean b-ALP continued to be raised at week 52 when it was inversely correlated with BMD. Mean BMD rose approximately 6%, P < 0.01, over 1 yr. Coupling indices were calculated as a measure of bone balance and, at diagnosis, was [minus4.26 in favor of bone resorption and rose with treatment in favor of bone formation: weeks 2: -0.23; 4: +4.01; 8: +4.37; 12: +4.44; 24: +2.32; and 52: +1.56. Bone turnover is balanced within 2 weeks of starting treatment for thyrotoxicosis. Udpd accurately indicates thyrotoxic bone resorption. Serum b-ALP indicates continuing bone formation and, at 1 yr, may provide a marker for low BMD. OC, Sdpd, and Spyr are less sensitive in documenting bone remodeling during treatment of thyrotoxicosis.

Calcium and glycoprotein hormone alpha-subunit gene expression and secretion in alpha T3-1 gonadotropes

GnRH stimulates both transcription and secretion of the alpha-subunit in pituitary cells, but the precise role of the calcium- signaling mechanisms mediating these actions are unclear. We have examined the role of calcium using alpha T3-1 gonadotropes transfected with alpha-promoter constructs linked to a luciferase reporter gene and concomitant measurement of alpha-subunit secretion. The calcium channel agonist, BayK8644 (1 microM) significantly stimulated alpha-subunit transcription (4.9-fold, P < 0.05) but to a lesser extent than either GnRH (100 nM, 20.7-fold, P < 0.001) or phorbol-12-myristate-13-acetate (TPA, 100 nM, 8.7-fold, P < 0.05). The transcriptional response to a combination of BayK8644 and TPA was approximately additive. Despite stimulating alpha-subunit gene expression, BayK8644 had no effect on alpha-subunit secretion at 24 h, and co-addition of BayK8644 and TPA did not produce any further stimulation of alpha-subunit secretion (3.0-fold, P < 0.001) compared with TPA alone (3.2-fold, P < 0.001). Pretreatment of alpha T3-1 cells with the calcium channel blocker, nifedipine (1 microM for 5 min), essentially blocked GnRH-stimulated alpha-promoter activity without affecting GnRH-stimulated alpha-subunit release. In contrast, thapsigargin pretreatment (1 microM for 5 min), which depletes intracellular calcium stores, significantly reduced basal and GnRH-stimulated secretion without affecting the ability of GnRH to increase alpha-promoter activity. Incubation of alpha T3-1 cells in calcium-depleted media showed that the transcriptional response was dependent on extracellular calcium concentration, with maximum stimulation by GnRH seen at a calcium concentration of 1.7 mM. Deletion analysis indicated that sequences between -420 and -244 bp were involved in mediating the response to BayK8644. Constructs containing only upstream alpha-promoter sequences from -517 to -98 bp, fused to the heterologous thymidine kinase promoter, exhibited loss of responsiveness to BayK8644 below -298 bp. These upstream elements were also found to be important for basal expression of the alpha-promoter and for mediating the response to TPA but were distinct from GnRH responsiveness of the human promoter in alpha T3-1 cells. These studies suggest differential regulation of GnRH-stimulated alpha-subunit gene transcription and secretion by extracellular calcium influx and intracellular calcium mobilization. The transcriptional response to extracellular calcium influx is mediated through two or more elements between -420 and -244 bp, which are also involved in basal and TPA-stimulated expression of the alpha-subunit promoter.

Effect of different storage temperatures, sample collection procedures and immunoassay methods on osteocalcin measurement

The apparent instability of measured osteocalcin has been reported as method-dependent and related to preanalytical variables such as storage temperature, and the use of anticoagulants and protease inhibitors. The aim of this study was to determine a sample collection procedure which minimised osteocalcin degradation. Blood samples from five normal individuals were collected with or without anticoagulants and protease inhibitors (heparin, EDTA, or heparin and aprotinin) and stored at 4 degrees C, -20 degrees C or -70 degrees C for up to 7 days, 28 days and 90 days respectively. Osteocalcin was measured by both a monoclonal EIA specific for intact osteocalcin and a bovine polyclonal RIA. Osteocalcin concentrations in serum and EDTA-treated samples significantly decreased by 40% (P < 0.001) with the ELISA and 72% (P < 0.001) with the RIA after 7 days storage at 4 degrees C. Similar falls were documented in these samples when stored at -20 degrees C and -70 degrees C and measured by the ELISA. Minimal changes in osteocalcin immunoreactivity were observed in either assay when heparin-treated plasma with or without aprotinin was stored at -20 degrees C or -70 degrees C for up to 90 days. The apparent instability of measured osteocalcin can be minimised using these conditions.

Growth hormone responses to treadmill sprinting in sprint- and endurance-trained athletes

The purpose of the present study was to examine the growth hormone (GH) response to treadmill sprinting in male (M) and female (F) sprint- and endurance-trained athletes. A group of 11 sprint-trained (ST; 6M, 5F) and 12 endurance-trained (ET; 6M, 6F) athletes performed a maximal 30-s sprint on a nonmotorized treadmill. Peak power and mean power expressed in watts or in watts per kilogram body mass were higher in ST than in ET (P < 0.01) and in the men compared to the women (P < 0.01). Serum GH was greater in ST than in ET athletes, but was not statistically significantly different between the men and the women [mean peak GH: ST 72.4 (SEM 12.5) compared to ET 26.3 (SEM 4.9) mU.1(-1), P < 0.01; men 59.8 (SEM 13.3) compared to the women 35.8 (SEM 7.4) mU.1(-1), n.s.]. Plasma ammonia and blood lactate concentrations were higher and blood pH lower during 1 h of recovery after the sprint in ST compared to ET (all P < 0.01). Multiple log linear regression showed that 82% of the variation in the serum peak GH response was explained by the peak power output and peak blood lactate response to the sprint. As serum GH was still approximately ten times the basal value in ST athletes after 1 h of recovery, it is suggested that the exercise-induced increase in GH could have important physiological effects in this group of athletes, including increased protein synthesis and sparing of protein degradation leading to maintained or increased muscle mass.

Hormonal effects of thoracic extradural analgesia for cardiac surgery

We have investigated the hormonal and metabolic effects of thoracic extradural analgesia with bupivacaine in addition to sufentanil 20 micrograms kg-1 in nine patients undergoing coronary artery bypass surgery. A control group received general anaesthesia alone. The catecholamine response was inhibited for 24 h after surgery in patients who had received extradural analgesia, and the cortisol response was suppressed during cardiopulmonary bypass. Blood glucose values were unchanged until 24 h after surgery in the extradural group. There were no significant differences in cardiac index between the two groups of patients, although heart rate and mean arterial pressure decreased before surgery in patients who received extradural analgesia. The benefits of this technique in terms of a reduction in postoperative morbidity remain to be determined.

Glycoprotein hormone alpha-subunit production and plurihormonality in human corticotroph tumours--an in vitro and immunohistochemical study

Glycoprotein hormone alpha-subunit (alpha SU) is a recognized product of clinically non-functioning, glycoprotein hormone-secreting and somatotroph adenomas but has not been studied systematically in corticotroph tumours. We have performed immunohistochemistry for alpha SU in a consecutive series of four corticotroph tumours causing Nelson's syndrome, three corticotroph macroadenomas, 12 corticotroph microadenomas and one adrenocorticotrophin-secreting bronchial carcinoid tumour. In addition we have assessed alpha SU secretion in vitro in corticotroph adenomas from two subjects with Cushing's disease and two subjects with Nelson's syndrome. Immunohistochemistry, performed after microwave treatment of sections to enhance antigen retrieval, demonstrated alpha SU positivity in 3/4 Nelson's tumours, 2/3 corticotroph macroadenomas, 7/12 microadenomas and one bronchial carcinoid. Eight of the 13 tumours positive for alpha SU were also immunostained after microwave pretreatment of sections for thyrotrophin (six positive), follicle-stimulating hormone (four positive), luteinizing hormone (three positive), beta-chorionic gonadotrophin (five positive), growth hormone (three positive) and prolactin (two positive) immunoreactivity. In vitro cell cultures of all four tumours studied secreted adrenocorticotrophin and three secreted alpha SU, with the variable presence of luteinizing hormone, follicle-stimulating hormone, thyrotrophin, growth hormone and prolactin, in basal culture. The alpha SU secretion was augmented by phorbol ester (160 +/- 15%, SEM, n = 3 wells; p < 0.01) and 8-bromo-cAMP (138 +/- 8%; p < 0.05) in one tumour. These data indicate that plurihormonality and, in particular, alpha SU elaboration and secretion by corticotroph tumours is more common than hitherto recognized. Possible mechanisms include abnormal or deregulated gene expression, autocrine or paracrine effects or a stem cell origin of tumour.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic control of non-insulin-dependent diabetic patients undergoing cataract surgery: comparison of local and general anaesthesia

We studied 40 elderly patients undergoing cataract surgery. Ten non-insulin-dependent diabetes mellitus (NIDDM) patients received standardized general anaesthesia, 10 NIDDM patients received local anaesthesia using retrobulbar block, 10 non-diabetic control patients received general anaesthesia and 10 non-diabetic controls received retrobulbar block. We measured sequential changes in blood glucose, lactate and beta-hydroxybutyrate, serum cortisol and insulin, and plasma non-esterified fatty acid concentrations until 4 h after operation. The results showed that in both general anaesthesia groups, NIDDM and control, blood glucose and serum cortisol concentrations increased significantly during surgery, before returning to normal by 4 h after operation; in both local anaesthesia groups, glucose and cortisol concentrations changed little during surgery. Serum insulin concentrations increased 30 min after operation to coincide with the peak of the glucose increase in the non-diabetic patients who received general anaesthesia, but no insulin response was seen in the diabetic general anaesthesia patients. Blood glucose and insulin concentrations increased in patients who received local anaesthesia (NIDDM and controls) when they ate after operation. The results show that cataract surgery under local anaesthesia provides improved metabolic control for the diabetic patient. Its use maintains glucose homeostasis, prevents the increases in cortisol and glucose which are seen under general anaesthesia and obviates the need for postoperative starvation.

A large volume spacer significantly reduces the effect of inhaled steroids on bone formation

Inhaled steroids are increasingly advocated as first line treatment for mild asthma. Some studies suggest that inhaled steroids suppress bone formation as reflected by a fall in plasma osteocalcin. Spacers have been shown to increase the proportion of inhaled aerosol that is deposited in the lungs and to reduce the amount swallowed. We measured plasma osteocalcin levels to determine the effect on bone formation of inhaled beclomethasone dipropionate (BDP) with and without a 750 ml spacer in a double-blind, randomised, placebo-controlled, cross-over study. Twenty-six healthy male volunteers took BDP 500 micrograms (two puffs of Becloforte) together with two puffs of placebo, inhaled twice daily for seven days. One inhaler was taken directly while the other was inhaled through a 750 ml spacer. After a two week washout period, the inhalers were exchanged so that BDP was taken by the alternate route for a further seven days. Fasting plasma osteocalcin levels were measured at 09.00 h before and at the end of each week. After a week of BDP taken directly (without a spacer), osteocalcin levels fell from 11.8 (SEM 0.6) ng/ml to 9.5 (SEM 0.5) ng/ml (p < 0.001). After a week of BDP taken through a spacer, osteocalcin levels fell from 12.1 (SEM 0.5) ng/ml to 11.1 (SEM 0.5) ng/ml (p < 0.001). The fall in osteocalcin when a spacer was used was significantly less than when BDP was taken directly (p < 0.005). This is likely to be because the systemic effects on bone are caused by swallowed rather than inhaled BDP, and this is limited by the use of a spacer. Spacers should be more widely prescribed with inhaled steroids. Further prospective studies are indicated to evaluate whether spacers protect bone mass.

Effects of pituitary adenylate cyclase-activating polypeptide on hormone secretion by human pituitary adenomas in vitro

Hormone release in culture in response to pituitary adenylate cyclase-activating polypeptide (PACAP) was examined in 28 human pituitary adenomas: 10 null cell adenomas, 4 gonadotropin-, 6 GH-, 6 ACTH-, and 2 PRL-producing adenomas. The effects of PACAP38 were compared with those of the classical hypothalamic releasing hormones and other activators of intracellular signaling pathways. PACAP38 significantly stimulated GH release from 1 somatotrope tumor (125 +/- 3% of control; P < 0.05) and ACTH release from 3 corticotrope tumors (134 +/- 6%, 136 +/- 7%, and 137 +/- 9% of control; P < 0.05). The effects of PACAP38 were less potent than either GHRH on GH release in the somatotrope tumor or CRH on ACTH release in the corticotrope tumors but similar to the responses seen with the cAMP analog 8-bromo-cAMP (8-Br-cAMP). No detectable effects of PACAP38 on hormone release from null cell, gonadotropin-, or PRL-producing adenomas were observed. Of the 5 somatotrope tumors that failed to respond to PACAP38, all also failed to respond to either 8-Br-cAMP, TRH, or GHRH. Of the corticotrope tumors that failed to respond, 2 of the 3 also failed to respond to CRH. In addition to eliciting hormone release appropriate to the tumor type, PACAP38 also stimulated glycoprotein hormone alpha-subunit (alpha SU) release from one somatotrope tumor (229 +/- 35% of control, P < 0.01) and one corticotrope tumor (149 +/- 4% of control; P < 0.01). This response was not mimicked by 8-Br-cAMP in the somatotrope tumor, but in the corticotrope tumor a significant alpha SU release was also seen after stimulation with the protein kinase C activator 12-O-tetradecanoyl-phorbol-13-acetate and 8-Br-cAMP. These results suggest that the novel hypothalamic peptide PACAP38 has a modest role in the regulation of GH, ACTH, and alpha SU secretion from some human tumourous pituitary corticotropes and somatotropes. Further studies are needed to elucidate the intracellular signaling pathways that mediate the effects of PACAP on hormone secretion by these tumor types.

The effect of growth hormone replacement on cortisol metabolism and glucocorticoid sensitivity in hypopituitary adults

OBJECTIVE

Growth hormone (GH) replacement therapy in hypopituitary adults is associated with sodium and water retention. The underlying mechanisms are incompletely understood and a possible contribution of altered cortisol metabolism or action has not been evaluated. We have investigated the effect of GH replacement therapy on cortisol metabolism, cortisol binding globulin and in-vitro glucocorticoid sensitivity in a group of adult hypopituitary patients.

DESIGN AND PATIENTS

We studied 19 adult hypopituitary patients (18 adult onset, M:F, 6:13), who were receiving conventional hydrocortisone (16 patients), thyroxine (14 patients), triiodothyronine (1 patient), sex steroid (9 patients), human chorionic gonadotrophin (1 patient) or desmopressin (6 patients) replacement during a 6-month, double blind controlled trial of GH therapy (active:placebo, 8:11) followed by a 6-month open phase of GH (mean dose: 0.2 IU/kg/week, range 0.051-0.27) and after a 6-week washout phase following discontinuation of GH therapy.

MEASUREMENTS

Twenty-four-hour urine free cortisol, cortisol metabolites (CoM), ratio 11-hydroxy/11-oxo CoM (F/E) and ratio 5 alpha/beta tetrahydrocortisol were measured at 6 months, 12 months and after the 6 week washout phase. Serum cortisol binding globulin was measured basally, at 6 months, 12 months and after washout. Glucocorticoid sensitivity was determined in lymphocyte preparations from 8 patients, during GH therapy and after washout, using an in-vitro technique dependent on dexamethasone suppression of phytohaemagglutinin-stimulated thymidine incorporation into DNA. Plasma renin activity and aldosterone were measured after 6-12 months GH therapy and after washout.

RESULTS

After 6 months of GH, in patients on hydrocortisone (n = 9), there were significant decreases in CoM (mean decrement 21%, P < 0.01), F/E (mean decreased from 1.27 to 1.0, P = 0.04; reference range 0.33-1.29) and 5 alpha/5 beta tetrahydrocortisol (mean decreased from 0.67 to 0.48, P = 0.01) and a subsequent increase after washout. Patients not on hydrocortisone (n = 2) demonstrated a normal basal F/E falling by 25% on GH therapy but no change in CoM. During 12 months of GH therapy, patients on hydrocortisone (n = 7) demonstrated a further trend to decrement in CoM (P = 0.09) which reversed after washout (P = 0.04). Urine free cortisol tended to fall during GH therapy and increased significantly following washout after 12 months treatment (P < 0.02). Serum cortisol binding globulin decreased by 20% (P < 0.05) during 12 months GH treatment but remained within the reference range. In-vitro studies demonstrated a trend to reduced glucocorticoid sensitivity on GH therapy; the maximum inhibition of phytohaemagglutinin by dexamethasone tended to be less on GH therapy (P = 0.052) and was also lower than in 29 normal volunteers (P < 0.05). There were no significant changes in plasma renin but there was a small increment in aldosterone in recumbent patients (P = 0.04) during the open phase of GH therapy in the placebo arm.

CONCLUSIONS

GH therapy in hypopituitary adults is associated with an apparent reduction in availability of administered hydrocortisone as measured by urine cortisol metabolites and urine free cortisol. This effect is unlikely to be clinically significant except possibly in ACTH deficient subjects on suboptimal hydrocortisone replacement. The changes in F/E suggest that GH may directly or indirectly modulate the activity of 11 beta-hydroxysteroid dehydrogenase. The apparent decrease in glucocorticoid sensitivity during GH therapy, demonstrated in vitro, merits further investigation.

Urine-free cortisol excretion: evidence of sex-dependence

Measurement of urine-free (unconjugated) cortisol (UFC) excretion is widely used in the investigation of hypercortisolaemia. We have measured 24 h UFC excretion in normal healthy individuals using a radioimmunoassay (RIA) method claimed to be suitable for unextracted urine. Significantly higher rates of excretion were found in a group of 15 men compared with a group of 18 women, with median values of 230 (range 145-334) and 149 (range 67-315) nmol/24 h, respectively (P < 0.005). This method was used to reanalyse the urine samples after extraction with dichloromethane. Although values were significantly lower than those found with unextracted urine (P < 0.001), the male:female difference remained with median values of 140 (range 96-295) and 112 (range 29-196) nmol/24 h, respectively (P < 0.02). Rates of UFC excretion were measured on the same dichloromethane-extracted urine samples using a second, different RIA, which again demonstrated the male:female difference with median values of 151 (range 116-302) and 109 (range 36-205) nmol/24 h, respectively (P < 0.001). There was no significant difference between these values and those obtained with extracted urine in the first assay. The higher rates of UFC excretion in men compared to women does not appear to be due to the presence of interfering compounds since the difference is also present using extracted urine samples and with two methods using different antibodies. These results should be borne in mind by laboratories when interpreting UFC results.