bluuebunny/crossref_metadata_2025 huggingface dataset:
Thyroidal regulation of nuclear tri-iodothyronine receptors in the developing rat testis
Authors: Palmero S. , Prati M. , De Marco P. , Trucchi P. , Fugassa E.
Published: December 2008

Previous work has demonstrated that thyroid hormones influence testis development. Specific receptors for tri-iodothyronine (T3) have been demonstrated in Sertoli cells. The aim of the present study was to examine the possible effect of thyroid hormone on its own receptor during pubertal development by evaluating the influence of thyroid status on T3-binding capacity, -binding affinity and receptor occupancy in nuclei isolated from immature rat testes. The binding capacity for T3 of nuclei from rat testis significantly decreased during pubertal development, being 375±32, 117±15 and 44±7 fmol/mg DNA in 7-, 21-and 35-day-old rats respectively, whereas the affinity of binding, as evaluated by the dissociation constant (Kd), did not change. Early induced hypothyroidism significantly affected the time-course of the postnatal decline of nuclear T3 receptors in the testis. At 21 days of age, the binding capacity for T3 in the testis of methimazole-treated rats was significantly higher with respect to euthyroid controls, being 173 ±21 and 117 ± 15 mol/mg DNA respectively, while the Kd was unaffected. T3 replacement therapy completely prevented changes in T3 receptor number induced by hypothyroidism without modifying the Kd. Our results indicate that nuclear T3 receptors in the developing rat testis are modulated by thyroid hormone.

Journal of Endocrinology (1993) 136, 277–282
The regulation of oxidative drug metabolism by growth hormone in the dwarf goat: differences from and similarities to the mechanisms in rats
Authors: Witkamp R. F. , Nijmeijer S. M. , Van Duin C. T. M. , Noordhoek J. , Van Miert A. S. J. P. A. M.
Published: December 2008

The effects of bovine GH (BST), administered in different dose patterns, on in-vivo oxidative drug metabolism, were studied in female dwarf goats. Animals received recombinantly derived methionyl BST at a dose of 500 μg/kg body weight per 24 h for 6 days. It was administered to one group of goats as one s.c. injection per day, another group received a similar 24-h dose divided into three s.c. injections given at 8-h intervals, and the third group received 50 μg BST/kg body weight every 2·5 h by a pulsative i.v. infusion. Oxidative metabolic capacity was assessed by determining plasma sulphadimidine (SDD) elimination and urinary metabolite excretion. SDD shows a marked sex-dependent plasma elimination in dwarf goats, with male goats having a lower plasma clearance than female goats. When BST was given by daily injection, no clear effects on SDD plasma clearance or urinary metabolite excretion were observed. However, when the total dose was divided into three injections given at 8-h intervals, the plasma SDD elimination rate decreased. This was associated with a decrease in urinary excretion of the two main hydroxy SDD metabolites. When BST was given by discontinuous i.v. infusion, simulating the male endogenous plasma GH pattern, a marked decrease in SDD plasma clearance was observed. In addition, the excretion of the two urinary hydroxy metabolites was considerably reduced. These results suggest that GH can affect drug oxidation in dwarf goats via mechanisms similar to those suggested for rats. However, in the dwarf goat, the sex differences in drug metabolism are opposite to those in rats.

Journal of Endocrinology (1993) 136, 313–317
Short-term endocrine consequences of total body irradiation and bone marrow transplantation in children treated for leukemia
Authors: Ryalls M. , Spoudeas H. A. , Hindmarsh P. C. , Matthews D. R. , Tait D. M. , Meller S. T. , Brook C. G. D.
Published: December 2008

We studied 24-h hormone profiles and hormonal responses to insulin-induced hypoglycaemia prospectively in 23 children of similar age and pubertal stage, nine of whom had received prior cranial irradiation (group 1) and fourteen of whom had not (group 2), before and 6–12 months after total body irradiation (TBI) for bone marrow transplantation in leukaemia.

Fourier transformation demonstrated that group 1 children had a faster periodicity of GH secretion before TBI than group 2 children (160 vs 200 min) but the amplitude of their GH peaks was similar. There were no differences between the groups in circadian cortisol rhythm, serum concentrations of insulin-like growth factor-I (IGF-I), sex steroids and basal thyroxine (T4). The peak serum GH concentrations observed after insulin-induced hypoglycaemia were similar between the two groups but the majority of patients had blunted responses.

TBI increased the periodicity of GH secretion in both groups (group 1 vs group 2; 140 vs 180 min), but the tendency to attenuation of amplitude was not significant. There were no significant changes in the peak serum GH concentration response to insulin-induced hypoglycaemia which remained blunted. Serum IGF-I, sex steroid, cortisol or T4 concentrations were unchanged.

Low-dose cranial irradiation has an effect on GH secretion affecting predominantly frequency modulation leading to fast frequency, normal amplitude GH pulsatility. This change is accentuated by TBI. In patients with leukemia, there is a marked discordance between the peak serum GH response to insulin-induced hypoglycaemia compared with the release of GH during 24-h studies, irrespective of the therapeutic regimen used. Pharmacological assessment of GH reserve needs to be interpreted with caution in such situations.

Journal of Endocrinology (1993) 136, 331–338
Reduction of cyclic AMP in the sciatic nerve of rats made diabetic with streptozotocin and the mechanism involved
Authors: Shindo H. , Tawata M. , Onaya T.
Published: December 2008

We have investigated the relationship between cyclic nucleotides and nerve function in the sciatic nerve of rats made diabetic with streptozotocin. Cyclic AMP (cAMP) content in the sciatic nerves of diabetic rats was significantly (P < 0·05) lower than in those of normal rats, while cyclic GMP content did not differ between the two groups. Administration of the stable prostacyclin analogue iloprost or dibutyryl cyclic AMP (dbcAMP) significantly (P<0·05) restored the cAMP content in the sciatic nerves and motor nerve conduction velocity, which reflects nerve function. There was a positive correlation between cAMP content in the sciatic nerves and motor nerve conduction velocity in both normal and diabetic rats.

Endoneurial preparations of sciatic nerves obtained from normal rats were incubated in Krebs–Ringer bicarbonate buffer containing d-glucose (30 or 5·5 mmol/l). Cyclic AMP accumulation was significantly (P<0·05) suppressed in the buffer containing 30 mmol d-glucose/l compared with that containing 5·5 mmol/l. Iloprost (P<0·05) and dbcAMP (P<0·01) increased cAMP accumulations in the tissues incubated in buffer containing both 5·5 and 30 mmol d-glucose/l. When non-metabolizing hexoses, such as l-glucose or 3-O-methylglucose instead of d-glucose were used, cAMP accumulations at 30 mmol hexose/1 were not significantly different from those at 5·5 mmol/l.

Cyclic AMP phosphodiesterase activity in the sciatic nerves of diabetic rats did not change compared with that in nerves from normal rats. Although not significant, mean ATP content in the sciatic nerves of diabetic rats was about 30% lower than that in nerves of normal rats. Basal, iloprost-stimulated and forskolin-stimulated adenylate cyclase activities in the sciatic nerves of diabetic rats were significantly (P<0·05) reduced when compared with those of control rats.

We therefore conclude that reduction of cAMP content in peripheral nerves may be involved in the pathogenesis of diabetic neuropathy and is mainly caused by the impairment of adenylate cyclase activity in the diabetic state.

Journal of Endocrinology (1993) 136, 431–438
The 11β-hydroxysteroid dehydrogenase inhibitor glycyrrhetinic acid affects corticosteroid feedback regulation of hypothalamic corticotrophin-releasing peptides in rats
Authors: Seckl J. R. , Dow R. C. , Low S. C. , Edwards C. R. W. , Fink G.
Published: December 2008

Steroid-metabolizing enzymes modulate the effects of androgens on brain differentiation and function, but no similar enzymatic system has been demonstrated for adrenocorticosteroids which exert feedback control on the hypothalamus. 11β-Hydroxysteroid dehydrogenase (11β-OHSD) rapidly metabolizes physiological glucocorticoids (corticosterone, cortisol) to inactive products, thereby regulating glucocorticoid access to peripheral mineralocorticoid and glucocorticoid receptors in a site-specific manner. Using in-situ hybridization, we found expression of 11β-OHSD mRNA in neurones of the hypothalamic paraventricular nucleus (PVN) where corticotrophinreleasing factor-41 (CRF-41) is synthesized and from where it is released into hypophysial portal blood. Administration of glycyrrhetinic acid (GE), a potent 11β-OHSD inhibitor, decreased CRF-41 release into hypophysial portal blood in the presence of unchanged circulating glucocorticoid levels, suggesting that 11β-OHSD regulates the effective corticosterone feedback signal to CRF-41 neurones. These effects of GE were not observed in adrenalectomized animals, demonstrating dependence on adrenal products. In contrast, GE led to two- to threefold increases in arginine vasopressin and oxytocin release into portal blood, effects also dependent upon intact adrenal glands. These results suggest that 11β-OHSD in the PVN, and possibly other sites, may represent a novel and important control point of corticosteroid feedback on CRF-41 release in vivo.

Journal of Endocrinology (1993) 136, 471–477
The effects of dexamethasone treatment on immunoreactive and bioactive insulin-like growth factors (IGFs) and IGF-binding proteins in normal male volunteers
Authors: Miell J. P. , Taylor A. M. , Jones J. , Holly J. M. P. , Gaillard R. C. , Pralong F. P. , Ross R. J. M. , Blum W. F.
Published: December 2008

Glucocorticoids inhibit somatic growth in man and laboratory animals, and have long been regarded as suppressors of both stimulated GH secretion and insulin-like growth factor (IGF) activity. Recent evidence suggests, however, that glucocorticoids can be potent GH secretagogues in their own right with concomitant increases in circulating IGF-I levels. IGFs circulate tightly bound to a group of high-affinity binding proteins (IGFBPs) which modulate their actions. In order to investigate the effects of glucocorticoids on serum levels of IGFs and IGFBPs, normal male volunteers were sampled over 24-h periods before and directly after treatment with dexamethasone (2 mg twice daily) for 96 h. Following dexamethasone administration, all volunteers showed a marked increase in mean± s.e.m. IGF-I levels over the 24-h sampling period (292·2±31·8 before dexamethasone, 425·9 ±37 μg/l after dexamethasone, P<0·005); there was no change in mean IGF-II levels. Integrated mean insulin levels were raised by dexamethasone treatment (50 ±4·6 before dexamethasone, 117±13·4 mU/l after dexamethasone, P= 0·002) and IGFBP-1 was significantly suppressed (42·9±8·2) before dexamethasone, 28·0±7·9 μg/l after dexamethasone, P<0·001). IGFBP-2 levels were similarly suppressed after dexamethasone (319·5±24·5 before dexamethasone, 214·8±8·5 μg/l after dexamethasone, P=0·002), and there was a significant increase in IGFBP-3 levels from 3·24 ±0·25 to 3·67±0·32 mg/l (P=0·0153). Mean IGF bioactivity over the sampling period after dexamethasone was reduced by approximately 60% (0·93 ±0·39 before dexamethasone, 0·39 ±0·05 U/ml after dexamethasone, P <0·0001).

There were strong negative correlations between both insulin and IGF-I levels and those of IGFBP-2, suggesting the presence of a novel regulation mechanism for this binding protein. The established inverse relationship between insulin and IGFBP-1 was maintained after dexamethasone. These results suggest that glucocorticoids alter the bioactivity of IGFs, possibly by induction of inhibitors, but that neither IGFBP-1 nor IGFBP-2 can be implicated as glucocorticoiddependent inhibitors of IGF bioactivity in man. The study also demonstrates for the first time a strong negative correlation between IGF-I, insulin and IGFBP-2.

Journal of Endocrinology (1993) 136, 525–533
Differential regulation of FSH and inhibin gene expression and synthesis by testosterone in immature and mature male rats
Authors: Perheentupa A. , Bergendahl M. , de Jong F. H. , Huhtaniemi I.
Published: December 2008

Direct effects of testosterone on gonadotrophins at the pituitary level were studied in intact and castrated immature (age 10 days) and mature (70 days) male rats. Gonadotrophin-releasing hormone action was blocked by treatment with a potent GnRH antagonist, Ac-d-pClPhe-d-pClPhe-d-Trp-Ser-Tyr-d-Arg-Leu-Arg-Pro-d-Ala-NH2CH3COOH (Ant; Organon 30276; 1·0 mg/kg body weight per day) injected subcutaneously. Silicone elastomer capsules were used for the testosterone treatment. Both treatments commenced on the day of orchiectomy and lasted for 7 days. In adult male rats Ant treatment suppressed serum testosterone from 9·5 ± 2·5 (s.e.m.) nmol/l to below the limit of detection (< 0·10 nmol/l; P < 0·01), and the testosterone implants reversed the decrease. Treatment with Ant decreased the pituitary content of FSH-β subunit mRNA in intact and orchiectomized rats to 14% of their respective controls (P < 0·01). These levels were increased to 80–81% of controls (not significant) in both groups by combined treatment with testosterone and Ant. Orchiectomy alone increased FSH-β subunit mRNA by 202% (P < 0·01). In intact immature rats Ant treatment decreased the level of pituitary FSH-β subunit mRNA to 21% (P<0·01), and a partial recovery (P < 0·01) to 42% of controls was observed with combined Ant + testosterone treatment. In contrast, in orchiectomized immature rats, where ANT decreased FSH-β subunit levels to 48% of controls (P < 0·01), testosterone was able to reverse these mRNA levels completely (114% of controls). No evidence for the direct pituitary effects of testosterone were found in the mRNA of the common α or LH-β subunits. In adult rats, the testicular inhibin α and βA subunit mRNA levels were increased (P < 0·01) by Ant + testosterone compared with Ant-treated animals, but there were no differences in serum immunoreactive inhibin between any of the uncastrated adult groups. In intact immature rats, Ant + testosterone treatment increased (P < 0·01) inhibin βA subunit mRNA levels compared with controls and Ant-treated animals. Ant decreased the level of peripheral inhibin immunoreactivity from 8·3 ± 2·0 U/ml to 2·1 ± 0·4 U/ml (P < 0·01) and testosterone reversed it to 5·8 ± 0·6 U/ml (not significant).

In conclusion, our observations indicated that testosterone is able to stimulate FSH gene expression and secretion directly in immature and adult rats, but the testosterone response is enhanced at both ages by orchiectomy, even more so in the immature rat. This may be explained by age differences in the contribution of testicular inhibin to the regulation of FSH synthesis and secretion at the pituitary level.

Journal of Endocrinology (1993) 137, 69–79
Growth hormone receptor gene expression in sex-linked dwarf Leghorn chickens: evidence against a gene deletion
Authors: Hull K. L. , Fraser R. A. , Marsh J. A. , Harvey S.
Published: December 2008

GH receptor (GHR) mRNA has been identified in peripheral (liver and muscle) and central (brain and hypothalamus) tissues of sex-linked dwarf (SLD) Leghorn chickens. Total RNA was extracted from the tissues of immature (1 week, 4 week), pubertal (16 week) and adult (> 24 weeks) SLD and K (the normally growing strain) Leghorn chickens. In both groups and all tissues, an mRNA moiety of 4·4 kb hybridized with cRNA probes derived from the rabbit hepatic GHR sequence. An additional low-abundance transcript of 2·8 kb was also identified in some tissues. An age-related increase in expression was observed in K and SLD hepatic GHR mRNA, suggesting normal regulation of SLD GHR gene transcription. Amplification of cDNA from K and SLD tissues in the presence of oligonucleotide primers coding for the intracellular or extracellular domains of the chicken GHR generated electrophoretically separable fragments of expected size. Restriction enzyme digestion of the products with EcoRI, BstNI, HaeIII, NcoI or BamHI produced smaller moieties of expected sizes in both strains. These results demonstrate that, in contrast to broiler SLDs, a GHR gene deletion is not responsible for the GHR dysfunction in Leghorn SLDs. Although the actual defect in GHR gene expression in SLD Leghorns remains to be identified, this study demonstrates that sex-linked dwarfism, like Laron dwarfism, is due to a heterogeneity of lesions.

Journal of Endocrinology (1993) 137, 91–98
Steroidal interactions in the ageing endocrine system: absence of suppression and pathology in reproductive systems of old males from a mixed-sex socially stressful rat colony
Authors: Taylor G. T. , Bardgett M. , Farr S. , Womack S. , Komitowski D. , Weiss J.
Published: December 2008

A paradigm using chronic social stress and multiple measures of the reproductive system were used to assess changes with ageing in the dynamics of endogenous steroid interactions. The 22- to 24-month-old male rats lived for 8 weeks in one of four types of colony, in groups of the same sex or groups of mixed sex including familiar or unfamiliar old males. Measures of endocrinology (circulating steroid levels), behaviour (exploration and sociosexual responses), physiology (body and organ weights and epididymal sperm count) and histology (adrenal and ventral prostate glands) served as markers of activation of the hypothalamic-pituitary-adrenal (HPA) or hypothalamic-pituitary-testicular (HPT) axes. Old males living under stable conditions as familiar same-sex colonies served as the comparison group. Results indicated clear chronic activation of the HPA axis in the unfamiliar all-male colonies and of the HPT axis in the familiar males from mixed-sex colonies, whereas both steroidal axes were stimulated in colonies of unfamiliar males and females. Findings from aged males under chronic stress suggested that reproductive dysfunction may be limited to situations in which activation of the HPA axis occurs without concurrent stimulation of the HPT axis. Data on steroidal interactions from mixed-sex groups suggested that (1) chronic excitation of the HPA failed to suppress function in the reproductive system of the old males, (2) their stress responses were little affected by chronic HPT activation and (3) there was no evidence for stress-induced pathology, even in the vulnerable prostate gland. The conclusion is that increased risks for urogenital pathology with long-term exposure to stress is not an inevitable outcome for ageing male rats nor, perhaps, for other social species living under conditions in which multiple endocrine systems typically undergo simultaneous activation.

Journal of Endocrinology (1993) 137, 115–122
Measurement of insulin-like growth factor-II in human plasma using a specific monoclonal antibody-based two-site immunoradiometric assay
Authors: Crosby S. R. , Anderton C. D. , Westwood M. , Holly J. M. P. , Cwyfan Hughes S. C. , Gibson M. , Morrison C. A. , Young R. J. , White A.
Published: December 2008

An immunoradiometric assay (IRMA) for the measurement of insulin-like growth factor-II (IGF-II) in human plasma has been developed, optimized and evaluated clinically in normal subjects and patients with disorders of the GH/IGF-I axis. Six monoclonal antibodies (MAbs) to recombinant human IGF-II (rhIGF-II) were produced, all of which had low cross-reactivity with rhIGF-I (< 0·01%) and insulin (< 0·01%). Compatibility of pairs of MAbs was tested in two-site IRMAs using three radioiodinated MAbs and three MAbs linked to Sephacryl S-300 (with separation of bound and free radiolabelled MAb by sucrose layering). Seven pairs of MAbs bound rhIGF-II and the combination of 125I-labelled W3D9 and W2H1 linked to solid phase was selected. The optimized assay had a completion time of 4 h, a minimum detection limit of 30 ng/ml (2·5 standard deviations from the zero standard) and detected a single peak of endogenous IGF-II in normal plasma which co-eluted with rhIGF-II after acid gel chromatography.

IGF-II was measured in formic acid/acetone extracts of plasma from 16 normal subjects (mean 685, range 516–1008 μg/l), four acromegalic patients (mean 637, range 553–700 μg/l), fourteen patients with type-1 diabetes (mean 635, range 247–753 μg/l), nine patients with uraemia (mean 423, range 78–850 μg/l), and three patients with Laron-type GH insensitivity (75, 35 and 36 μg/l). No significant fluctuations were detected between samples obtained hourly from 08.00 to 19.00 h in normal subjects.

Low levels of IGF-binding proteins (IGFBPs) remaining in plasma extracts may interfere with the measurement of IGF-II and give rise to falsely elevated IGF-II levels in radioimmunoassays or falsely suppressed levels in IRMAs. Such interference did not occur with the IRMA when used to measure IGF-II in extracts from normal subjects, acromegalic patients and patients with type-1 diabetes, and the addition of excess rhIGF-I in order to displace IGF-II from residual IGFBPs had no effect on IGF-II measurements in these samples. However, levels of IGF-II measured in extracts from patients with Laron-type GH insensitivity and patients with uraemia increased markedly after preincubation with excess rhIGF-I. The accurate measurement of IGF-II by IRMA in extracts from these subjects therefore requires the displacement of IGF-II from IGFBPs prior to assay. We conclude that, in contrast to radioimmunoassays, the two-site IRMA developed here provides a practical, rapid and specific method for the measurement of IGF-II in human plasma.

Journal of Endocrinology (1993) 137, 141–150
The effect of the blockade of α-melanocyte-stimulating hormone on LH release in the rat
Authors: Caballero C. , Celis M. E.
Published: December 2008

We have investigated the effect of blocking α-MSH on the release of LH in rats at pro-oestrus. Continuous infusion of Pro-Leu-Gly-NH2 (PLG; 0·2 μg/h), from the afternoon of dioestrus-2 until the day of oestrus, inhibited LH at pro-oestrus and the next ovulation on the day of oestrus. Plasma α-MSH levels decreased significantly in rats treated with PLG. This inhibitory effect on LH release was not observed in rats treated with a continuous infusion of a diluted antiserum against α-MSH (0·5 μl/h, diluted 1/10) from the afternoon of dioestrus-2 until the day of oestrus. On the contrary, the administration of undiluted antiserum against α-MSH (0·5 μl/h) blocked LH release and ovulation. The release of α-MSH into the blood was also significantly blocked by this treatment.

When serum levels of progesterone were measured at 12.00 and 14.00 h in rats in which α-MSH release was blocked by PLG or concentrated antiserum, a significant decrease was observed when compared with the levels of progesterone in control rats. These results show that the blockade of α-MSH inhibits LH release and the next ovulation in rats treated with PLG or with concentrated antiserum against α-MSH, through a blockade of progesterone of adrenal origin.

Journal of Endocrinology (1993) 137, 197–202
Two site-specific radioimmunoassays which demonstrate the presence of proteolytically modified insulin-like growth factor-binding protein-3 in the circulation
Authors: Hughes S. C. Cwyfan , Wass J. A. H. , Holly J. M. P.
Published: December 2008

The presence of proteolytic activity in the circulation directed against insulin-like growth factor binding protein-3 (IGFBP-3) was originally described in pregnancy but has subsequently been described in a number of catabolic and other pathological conditions. However, detection of this proteolytically modified IGFBP-3 has been demonstrated, in most cases, following separation using SDS-PAGE and this has led to speculation that its occurrence may be an artefact of the harsh conditions employed. Using two sitespecific antisera, one of which recognizes as its antigenic site a region of IGFBP-3 which is close to that of the IGF-binding domain, we have developed two radioimmunoassays which, when compared, can reveal alterations in the IGF-binding domain of IGFBP-3. The presence of IGFBP-3 modified by the circulating protease is denoted in this system by a divergence in the IGFBP-3 levels observed; this divergence has been shown to coincide with protease activity as determined by Western ligand blotting. The use of these assays has confirmed that the IGF-binding site of IGFBP-3 undergoes proteolytic modification in the circulation during a number of pathologies.

Journal of Endocrinology (1993) 137, 321–328
Protein kinase C activation and calcium mobilization decrease prolactin release from human decidual cells in early pregnancy
Authors: Kubota T. , Kamada S. , Taguchi M. , Sakamoto S. , Aso T.
Published: December 2008

The present study was undertaken to investigate the effects of protein kinase C (PKC) activation and calcium mobilization on the release of prolactin from human decidual cells in early pregnancy. Decidua obtained from patients in early pregnancy was enzymatically dispersed and cultured with phorbol myristate acetate (PMA) and calcium ionophore A23187 in a cell culture system. Prolactin in the medium was measured by enzyme-immunoassay.

PMA, a PKC activator, dose-dependently attenuated the release of prolactin from cultured decidual cells, while a PKC inhibitor, H7, significantly (P < 0·001) diminished the effect of PMA on prolactin release. PMA had no effect on cell numbers or DNA synthesis in the decidual cells during culture. It did not significantly increase the generation of inositol phosphate in decidual cells prelabelled with myo[3H]inositol and it had no effect on intracellular calcium concentration ([Ca2 + ]i). Calcium ionophore A23187, a Ca2 +-mobilizing agent, also significantly (P<0·001) attenuated the release of prolactin and potentiated the PMA-induced suppression of prolactin release from decidual cells.

These findings suggest that activation of PKC and mobilization of Ca2+ may be involved in regulating prolactin release from human decidual cells. The PMA-induced suppression of prolactin release is not triggered by phosphoinositide hydrolysis nor by the increase in [Ca2 + ]i in decidual cells.

Journal of Endocrinology (1993) 137, 335–340
Vasoactive intestinal peptide, but not pituitary adenylate cyclase-activating peptide, modulates the responsiveness of the gonadotroph to LHRH in man
Authors: Hammond P. J. , Talbot K. , Chapman R. , Ghatei M. A. , Bloom S. R.
Published: December 2008

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP) are hypothalamic peptides sharing considerable sequence homology which are postulated to be hypophysiotrophic releasing factors. When infused into man, PACAP has no effect on anterior pituitary hormone levels, while VIP causes a significant increase in circulating prolactin concentrations. However, PACAP has recently been shown to augment the release of LH and FSH in response to LHRH in rat anterior pituitary cell culture. In order to ascertain if either peptide has a similar effect in man, PACAP and VIP were infused at 3·6 pmol/kg per min into six healthy male volunteers, and an LHRH test was performed 30 min after the infusion was commenced. Infusion of PACAP did not alter the gonadotrophin response to LHRH significantly. However, VIP augmented the release of LH significantly, both during the infusion and for 30 min thereafter, although there was no effect on FSH release. Thus VIP, but not PACAP, potentiates the release of LH after LHRH injection in man.

Journal of Endocrinology (1993) 137, 529–532
Insulin-like growth factor-II in human fetal adrenals: regulation by ACTH, protein kinase C and growth factors
Authors: Ilvesmäki V. , Blum W. F. , Voutilainen R.
Published: December 2008

Insulin-like growth factor-II (IGF-II) may be one of the most important local growth factors in human fetal adrenals (HFAs), where its mRNA levels are upregulated by ACTH. We have investigated whether protein kinase C (PKC)-dependent mechanisms and various polypeptide growth factors participate in the regulation of IGF-II gene expression in cultured HFA cells, and whether HFA cells secrete IGF-II peptide into the culture medium. ACTH enhanced IGF-II mRNA accumulation dose- and time-dependently, maximally four- to sixfold, and this increase was inhibited dose-dependently (0·01-100 μg/l) by 12-O-tetradecanoyl phorbol-13-acetate (TPA), a PKC activator. TPA decreased basal IGF-II mRNA levels by approximately 55%. Staurosporine, a PKC inhibitor, abolished the inhibitory effects of TPA and induced accumulation of IGF-II mRNA. Dibutyryl cyclic AMP, cholera toxin and forskolin increased IGF-II mRNA accumulation as much as ACTH, and TPA inhibited these stimulations in a similar way. ACTH increased the IGF-II peptide concentration in most experiments, but this increase was modest in comparison with IGF-II mRNA changes. TPA, although it decreased IGF-II mRNA levels, tended to increase IGF-II peptide in the medium. Additions of GH, IGF-I and IGF-II to the cell culture medium also increased IGF-II mRNA accumulation. Transforming growth factor-β1 inhibited IGF-II mRNA accumulation to the same extent as TPA. Epidermal growth factor and basic fibroblast growth factor did not change IGF-II mRNA levels. Our results confirm previous reports that ACTH is an important regulator of IGF-II in human fetal adrenals, and show that IGF-II gene expression is under multifactorial control, which includes the PKC system and polypeptide growth factors.

Journal of Endocrinology (1993) 137, 533–542
In-vitro effects of insulin-like growth factor-I on gill Na+,K+-ATPase in coho salmon, Oncorhynchus kisutch
Authors: Madsen S. S. , Bern H. A.
Published: December 2008

The effect of ovine GH (oGH) in vivo and recombinant bovine insulin-like growth factor-I (rbIGF-I) in vitro on gill Na+,K+-ATPase activity was investigated in two seasonal experiments conducted during the parr–smolt transformation period of coho salmon.

In 1991, when fish were held under a photoperiod of 12 h light: 12 h darkness, the stimulatory effect of oGH (1 μg/g) on gill Na+,K+-ATPase in vivo decreased at the time of expected parr–smolt transformation. Gill Na+,K+-ATPase from control fish was insensitive to rbIGF-I in vitro from February to June, whereas GH treatment induced sensitivity to rbIGF-I (100–1000 μg/l) in vitro in February and March, but not later in development.

In 1992, when fish were held under natural conditions, oGH (4 μg/g) stimulated gill Na+,K+-ATPase in vivo from February to July. There was, however, a pronounced developmental change in sensitivity of gill Na+,K+-ATPase to rbIGF-I in vitro. In February, gills from control fish were insensitive, but oGH treatment in vivo induced sensitivity to rbIGF-I in vitro (100–1000 μg/l). In April and May, control fish were sensitive to rbIGF-I in vitro. This sensitivity was not further potentiated by oGH treatment in vivo. In June, gills from control or oGH-treated fish were not sensitive to rbIGF-I in vitro, but in July exogenous oGH again induced gill tissue sensitivity to rbIGF-I at 1000 μg/l. Both studies showed that rbIGF-I stimulates gill Na+,K+-ATPase directly; an ability that may depend on priming by endogenous or exogenous GH. This supports the role of IGF-I as an endocrine mediator for GH action during parr–smolt transformation.

Journal of Endocrinology (1993) 138, 23–30
19-Hydroxyandrostenedione amplifies the hypertensive action of mineralocorticoids in rats
Authors: Sekihara H. , Yazaki Y. , Kojima T.
Published: December 2008

We have reported that 19-hydroxyandrostenedione (19-OH-A-dione) amplifies the sodium-retaining action of aldosterone. To evaluate whether it also amplifies the hypertensive action of small doses of aldosterone, mononephrectomized rats were given 0·5 mg aldosterone, 10 mg 19-OH-A-dione or a combination of both once a week for 19 weeks, and changes in blood pressure were evaluated. Rats were given 154 mmol NaCl/l to drink. The blood pressure of controls, rats given aldosterone alone, 19-OH-Adione alone or a combination of both in week 19 were 137±4 (s.e.m), 146±7, 147±4 and 191±8 mmHg respectively. The blood pressure of rats given the combination was significantly higher than any of the other three groups. These results indicate that 19-OH-A-dione amplifies the hypertensive action of aldosterone and may be considered a potent hypertensive agent in the presence of aldosterone. To evaluate whether 19-OH-A-dione amplifies the hypertensive action of small doses of deoxycorticosterone acetate (DOCA), another experiment was carried out in which similar rats were given 5 mg DOCA or a combination of 5 mg DOCA and 10 mg 19-OH-A-dione once a week for 8 weeks. The blood pressure of controls, rats given DOCA alone and a combination of DOCA and 19-OH-A-dione in week 8 were 139±5, 166±7 and 208±12 mmHg respectively. The blood pressure of rats given a combination of DOCA and 19-OH-A-dione was significantly higher than that of control rats or the rats given DOCA alone. These results indicate that 19-OH-A-dione can also amplify the hypertensive action of DOCA. It is concluded that 19-OH-A-dione amplifies the hypertensive action of mineralocorticoids as well as the sodium-retaining action of aldosterone.

Journal of Endocrinology (1993) 138, 31–40
Episodic and seasonal rhythms of cortisol secretion in male Eld's deer (Cervus eldi thamin)
Authors: Monfort S. L. , Brown J. L. , Wildt D. E.
Published: December 2008

Episodic and seasonal rhythms of cortisol secretion were evaluated in six adult Eld's deer (Cervus eldi thamin) stags. Plasma cortisol was measured in serial blood samples collected via remote catheterization every 10 min for 10 h within 2 weeks of the summer solstice (21 June), autumn equinox (22 September), winter solstice (21 December) and spring equinox (20 March), and in weekly blood samples collected from sedated stags. Cortisol was secreted episodically at a rate of approximately 0·6 peaks/h. Based on quantitative peak detection analyses of each 10-h data series, no overall seasonal differences (P>0·05) were detected in the number of peaks (mean range, 5·7–6·2), maximal peak height (mean range, 30·1–40·8 nmol/l), mean peak height as per cent increase (mean range, 158–168%), mean interval between peaks (mean range, 80·1–88·6 min), mean peak width (mean range, 55·1–65·1 min) and mean peak area under the curve (mean range, 675–816 nmol/l min). Based on weekly blood sampling, spring cortisol concentrations were elevated (P<0·05) compared with summer and autumn concentrations. However, when mean cortisol concentrations derived from the 10-h quarterly data sets were analysed, no seasonal differences (P>0·05) were detected. The present study represents the first detailed confirmation of episodic cortisol secretion in any cervid. Results (1) indicate that Eld's deer stags lack a distinct seasonal rhythm of cortisol secretion and (2) clearly illustrate the need for frequent blood sampling in fully conscious individuals to ensure accurate assessment of adrenal status in cervids.

Journal of Endocrinology (1993) 138, 41–49
Growth hormone secretion in the horse: unusual pattern at birth and pulsatile secretion through to maturity
Authors: Stewart F. , Goode J. A. , Allen W. R.
Published: December 2008

A heterologous radioimmunoassay was developed and validated for the measurement of horse GH in plasma. It utilized recombinant-derived bovine GH as the radiolabelled ligand, a guinea-pig anti-porcine GH serum as first antibody and pituitary-derived horse GH as standard. Cross-reactivites were high with all of the pituitary and recombinant-derived GH preparations tested (49–140%) and very low (<0·3%) with horse FSH, LH and prolactin. A synthetic analogue of GH-releasing factor(1–29) stimulated the expected pattern of GH release in foals.

Plasma GH concentrations in foals were low at birth (<20 ng/ml) but rose sharply to a definite and, in most cases, very large peak (18–195 ng/ml) during the first 30–40 min post partum, followed by a steady decline to basal levels again by 60–100 min post partum. GH secretion was clearly pulsatile in all older foals tested (2 weeks, 1 month and 4 months of age) and in six adults (three mares and three stallions), all bled at 15-min intervals for 7–8 h. Basal levels and pulse amplitudes were higher in foals than in adults and pulse frequency was higher in stallions than in mares (3–5 pulses/8 h vs 1–2 pulses/8 h). Pulsatile secretion was further characterized in one mare by simultaneous sampling of jugular vein and pituitary cavernous sinus blood. Peak GH concentrations in cavernous sinus blood draining the pituitary gland were more than tenfold higher than the corresponding peak concentrations in peripheral circulation. The patterns of GH release in the horse therefore appear to be similar to those reported in other species with the exception of the low values at birth followed by the dramatic rise and fall in concentrations during the first hour post partum.

Journal of Endocrinology (1993) 138, 81–89
Thyrotrophin-releasing hormone-induced growth hormone secretion in domestic fowl: concomitant stimulation of dopamine turnover in the medial basal hypothalamus
Authors: Harvey S. , Lea R. W.
Published: December 2008

Thyrotrophin-releasing hormone (TRH) stimulates GH secretion in domestic fowl by actions at pituitary and central nervous system sites. The possibility that this central action might be mediated by hypothalamic catecholamines or indoleamines was therefore investigated. When TRH was administered into the lateral ventricles of anaesthetized fowl the concentration of 3,4-dihydroxyphenylacetic acid (DOPAC, a metabolite of dopamine (DA)) in the medial basal hypothalamus (MBH) was increased within 20 min. The concentrations of MBH noradrenaline (NA), DA, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were, however, unaffected by the intracerebroventricular (i.c.v.) administration of TRH, although the MBH concentrations of somatostatin and TRH were concomitantly reduced. A rapid increase in DA release into MBH extracellular fluid and its metabolism to DOPAC was also observed after i.c.v. or i.v. administration of TRH, in birds in which the MBH was perfused in vivo with Ringer's solution. Microdialysate concentrations of NA, 5-HT and 5-HIAA were not, however, affected by central or peripheral injections of TRH. Diminished GH responses to i.v. TRH challenge occurred in birds pretreated with reserpine (a catecholamine depletor), α-methyl-paratyrosine (a DA synthesis inhibitor) and pimozide (a DA receptor antagonist). These results therefore provide evidence for the involvement of a hypothalamic dopaminergic pathway in the induction of GH release following the central or peripheral administration of TRH. In contrast with its inhibitory actions at peripheral sites, DA would appear to have a central stimulatory role in regulating GH release in birds.

Journal of Endocrinology (1993) 138, 225–232
Bioactive and immunoreactive variants of prolactin in milk and serum of lactating rats and their pups
Authors: Kacsóh B. , Veress Z. , Tóth B. E. , Avery L. M. , Grosvenor C. E.
Published: December 2008

Prolactin (PRL)-like bioactivity (in Nb2 lymphoma assay) and immunoreactivity (in radioimmunoassay (RIA)) in rat milk, maternal and neonatal sera and in neonatal rat pituitary cultures were investigated. The PRL-like bioactivity in the water-soluble fraction of rat milk was high and exceeded its immunoreactivity 5·8-, 4·0- and 2·1-fold, on days 2, 12 and 22 of lactation respectively. The elevated bioactivity to immunoreactivity (B/I) ratio of PRL in milk was not due to the presence of interleukin-2 (IL-2) in milk, since the proliferation of the CTLL-2 murine T cells, which are not sensitive to PRL, was promoted by IL-2 but not by milk. Serum levels of immunoreactive PRL were low in sera of non-weaned rat pups on days 2, 12 and 22 postpartum. Similar to milk, the B/I ratio of PRL in sera of rat pups was high and decreased with time postpartum. Pituitary glands of pups obtained on days 2, 12 and 22 secreted progressively increasing amounts of PRL in vitro; the B/I ratio ranged between 1·2 and 2·1 without a significant change. The relative concentrations of size variants in milk were not proportional to those in serum of lactating rats on day 2 postpartum as assessed by Sepharcryl S-100 HR gel permeation chromatography and Nb2 bioassay or RIA. Size variants of biologically active PRL were abundant in early milk and gradually diminished as lactation progressed: a partially resolved peak representing monomeric to dimeric PRL variants (relative molecular weights ranging between 18 k and 42 k) became progressively narrower between days 2 and 22. Biologically active and immunoreactive PRLs displayed disparate elution profiles. The elution profile of PRL in sera of neonatal rats on day 2 postpartum was different from that of maternal serum or milk. The major immunological (and possibly biological) PRL-like activity eluted as two adjacent peaks at 2·2 k and 1·5 k, raising the possibility that fragments of milk-borne PRL were absorbed from the gut after partial proteolytic degradation. In contrast with PRL, GH (which is present in rat milk only in minute concentrations) did not show heterogeneity in sera of 2-day-old rat pups in gel permeation chromatography.

The present results demonstrate that the concentrations of PRL-like activity in rat milk and newborn rat serum have been grossly underestimated because levels have been measured by RIA. The high B/I ratio of PRL in milk and neonatal sera is due to the presence of PRL-related compounds. The difference between the ontogeny in the B/I ratio of serum and in-vitro secreted PRL might be related to absorption of PRL variants from milk during the early postpartum period. The data suggest that PRL might be modified by the mammary gland and the neonatal gut during its passage from the circulation of the mother to that of the neonatal rat.

Journal of Endocrinology (1993) 138, 243–257
The effect of dietary protein restriction on the secretory dynamics of 1α-hydroxycorticosterone and urea in the dogfish, Scyliorhinus canicula: a possible role for 1α-hydroxycorticosterone in sodium retention
Authors: Armour K. J. , O'Toole L. B. , Hazon N.
Published: December 2008

The putative osmoregulatory role of the unique elasmobranch corticosteroid, 1α-hydroxycorticosterone (1α-OH-B), was investigated using dietary protein restriction as a means of limiting urea biosynthetic ability. Groups of dogfish (Scyliorhinus canicula) were adapted to either a high or a low protein diet (HPD and LPD respectively) and the secretory dynamics of urea and 1α-OH-B were determined following acclimation to normal (100%), 130% and 50% sea water.

In normal sea water, LPD fish showed significantly decreased blood production of urea compared with fish fed a HPD (P <0·05), and the plasma urea concentration required to maintain iso-osmolality was achieved only by a substantial decrease in urea clearance from the plasma. Unlike HPD fish, LPD fish in 130% sea water had no apparent ability to increase plasma urea concentration. An alternative strategy adopted by these animals was the retention of high plasma concentrations of Na+ and Cl−, which increased plasma osmolality and tended to decrease osmotic water loss. Concomitant with the increased ion concentrations, plasma 1α-OH-B concentration was also greatly elevated in LPD fish indicating that the steroid may be acting to minimize Na+ (and Cl−) excretion at osmoregulatory sites such as the rectal gland, kidney and gills.

This and a previous study have also demonstrated that 1α-OH-B concentration is elevated in 50% sea water. Decreases in plasma Na+ concentration are tolerated down to 75% sea water, whereafter Na+ is preferentially retained and further decreases in osmolality are achieved by reductions in plasma urea concentration. Increased 1α-OH-B concentration in 50% sea water corresponds to Na+ retention and regulation around a lower set point.

The results of this study are consistent with a mineralocorticoid role for 1α-OH-B in elasmobranchs, with 1α-OH-B acting preferentially to maintain plasma Na+ concentrations under certain osmotic conditions.

Journal of Endocrinology (1993) 138, 275–282
Timing of exposure to somatostatin relative to growth hormone-releasing factor dictates the rat anterior pituitary cell growth hormone response
Authors: Richardson S. B. , Twente S.
Published: December 2008

The temporal interactions of rat GH-releasing factor (GRF) and somatostatin (SRIF) on the secretion of GH from perifused rat anterior pituitary cells have been studied. SRIF and GRF were employed at concentrations in a range close to levels reported in the hypophysial circulation of the rat.

GH secretion was inhibited by pulses of 1 nmol SRIF/1 (6 min) or 0·3 nmol SRIF/1 (6 or 20 min). No rebound GH stimulation was observed. Exposure of cells to 6-min pulses of 0·3 nmol rat GRF/1 repeated three times resulted in rapid stimulatory responses which became attenuated. Concomitant exposure to 0·3 nmol SRIF/1 during a GRF pulse resulted in transient inhibition followed by a delayed and enhanced GH response, measured as the area under the curve but not peak height, whereas continuation of SRIF after a GRF pulse abolished the GH response. Exposure to 0·3 nmol SRIF/1 prior to but not during a GRF pulse did not delay or inhibit the GH response. The area under the curve was increased under these conditions because of the lowered baseline in cells perifused with SRIF.

SRIF alters somatotroph responsivity to equimolar concentrations of rat GRF and under different temporal conditions and can inhibit, enhance or delay GH secretion.

Journal of Endocrinology (1993) 138, 369–377