bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endocrine regulation of cytochrome P-450 in the rat brain and pituitary gland
Authors: Warner M. , Tollet P. , Strömstedt M. , Carlström K. , Gustafsson J.-Å. 
Published: December 2008

ABSTRACT
In an effort to understand the physiological functions of cytochrome P-450 in the central nervous system and pituitary gland, we evaluated changes in the level of the enzyme as a function of the endocrine status of rats and the ability of these tissues to synthesize or degrade steroids. The P-450 content of microsomes prepared from the hypothalamic preoptic area (HPOA), the olfactory lobes and the cerebrum was 0·040 ± 0·009 and in the pituitary gland 2·2 ± 0·6 (s.d.) nmol/g tissue. The P-450 content of the HPOA and olfactory lobes, but not of the rest of the cerebrum, was influenced by the endocrine status of rats. In microsomes it increased five- to tenfold over control levels during late pregnancy in the olfactory lobes and during lactation in the HPOA, and in both brain regions treatment of rats with 5α-dihydrotestosterone (DHT) caused an eight- to tenfold increase in the P-450 content. Androstenedione was not a good substrate for brain P-450. The level of androstenedione 19-hydroxylase in the olfactory lobe microsomal fraction was 0·50± 0·06 nmol 19-hydroxyandrostenedione formed/g tissue per h. This activity was tenfold lower in other brain areas and was not detectable in the pituitary gland. The rate of aromatization of androstenedione to oestradiol in the HPOA and olfactory lobe of lactating rats was 0·46 ± 0·14 and 0·38 ± 0·05 pmol/oestradiol formed/g tissue per h respectively. 5α-Androstane-3β,17β-diol (A-5α-3β,17β-diol) was a much better substrate for P-450 throughout the brain and pituitary gland. Catalytic activity was 125 ± 46 and 307 ±108 nmol triols formed/g tissue per h in the brain and pituitary gland respectively. The P-450 responsible for this catalytic activity was isolated and its substrate specificity examined. In addition to A-5α-3β,17β-diol, 5-androstene-3β,17β-diol, dehydroepiandrosterone and DHT were also substrates, with turnover numbers of 27, 8, 12 and 1 mol product/mol P-450 per min respectively. None of these catalytic activities was induced in the rat brain during pregnancy, lactation or DHT treatment. The enzyme was also present in the brains of mice but not guinea-pigs.
The yield of P-450 from the mitochondrial fraction of the HPOA and olfactory lobes in control rats was 0·01–0·02 nmol/g tissue. This increased tenfold during pregnancy. Immunological evidence for the presence of the cholesterol side-chain cleavage enzyme P-450 SCC was found in the HPOA and olfactory lobes of pregnant but not of control rats. However, no SCC catalytic activity was detectable in these brain mitochondrial P-450 fractions. From these studies we conclude that there is a major influence of the endocrine system on the content and quality of P-450 in the brain. However, the function and substrate specificities of these P-450s as well as of those in the pituitary gland remain to be characterized.
Journal of Endocrinology (1989) 122, 341–349
Cytochromes P-45011β, P-450scc and adrenodoxin gene expression during adrenocortical regeneration in the rat
Authors: Chou F.-P. , Gallant S. , Brownie A. C. 
Published: December 2008

ABSTRACT
Circulating levels of 11-deoxycorticosterone are increased during the development of adrenal-regeneration hypertension. The present studies were undertaken to examine the mechanisms involved in this increase. Plasmids containing cDNA inserts coding for cytochrome P-45011β, cytochrome P-450scc and adrenodoxin were used to determine, by Northern blot analysis, mRNA levels at 1, 2 and 3 weeks of adrenal regeneration. There was a striking decrease in mRNA transcripts for all three enzymes during the first week of regeneration when compared with intact adrenal tissue. Over the next 2 weeks the mRNA levels increased to 64% for P-450 11β, to 80% for P-450scc and to 82% for adrenodoxin. Actin mRNA levels were 70% of control levels in the first week but were back to control levels by the second week. The present findings suggest that decreased expression of steroid 11β-hydroxylase could contribute to the increased secretion of 11-deoxycorticosterone during the early stages of adrenal regeneration.
Journal of Endocrinology (1989) 122, 403–408
Increased levels of a humoral digitalis-like factor in deoxycorticosterone acetate-induced hypertension in the pig
Authors: Hamlyn J. M. 
Published: December 2008

ABSTRACT
Plasma levels of an endogenous digitalis-like factor (EDLF) and atrial peptides were followed in pigs confined to metabolic cages during the development of deoxycorticosterone acetate (DOCA)-induced hypertension. During the first 2 days of DOCA treatment, urinary sodium excretion decreased and the plasma levels of renin and atrial peptide fell significantly. During this period, plasma levels of EDLF increased > 30-fold from a baseline of <0·25 to 9·72 nmol ouabain equivalents/l. Between days 2 and 5 of DOCA treatment, urinary sodium returned to preDOCA levels ('mineralocorticoid escape') and during this period significant increases of atrial peptide and mean arterial pressure (MAP) and a decrease in EDLF were found. Following mineralocorticoid escape there was a secondary rise in levels of EDLF and atrial peptide and both phenomena correlated with MAP (EDLF, r = 0·87, P< 0·05; atrial peptide, r = 0·9, P< 0·05) and with each other (r = 0·96, P < 0·05) over a 20-day period. Acute expansion of extracellular fluid volume before DOCA elicited significant increments in plasma EDLF and atrial peptide. Volume loading during chronic DOCA treatment increased plasma EDLF significantly whereas no response of atrial peptide was detected. These results suggest that DOCA affects the reactivity of mechanisms involved in the perception of and/or response to acute changes in volume status. However, neither EDLF nor atrial peptide appear to be viable candidates as direct mediators of mineralocorticoid escape. Finally, the nature of the changes found in EDLF and atrial peptide levels during DOCA treatment suggest that these factors are involved in the long-term control of blood pressure in this model of low renin hypertension.
Journal of Endocrinology (1989) 122, 409–420
Adaptive responses to sustained volume expansion in hyponatraemic rats
Authors: Verbalis J. G. , Drutarosky M. D. , Ertel R. J. , Vollmer R. R. 
Published: December 2008

ABSTRACT
Studies were carried out to evaluate adaptive responses to water retention in an experimental model of the syndrome of inappropriate antidiuresis (SIAD). Hyponatraemia was induced by continuous s.c. infusions of the antidiuretic vasopressin analogue 1-deamino-[8-d-arginine]-vasopressin in rats ingesting a 5% (w/v) dextrose solution. After 48 h of sustained decreases in the plasma concentration of Na+ to 23–25% of normal levels, all body fluid compartments were significantly expanded: plasma volume estimated by changes in plasma protein concentration was increased by 26%, extracellular fluid volume estimated by 22Na volume of distribution was increased by 24%, and total body water estimated by 3H2O volume of distribution was increased by 16%. Despite marked increases in all body fluid compartment volumes, mean arterial blood pressure was only modestly increased to 110 ± 2 mmHg in conscious hyponatraemic rats. Consistent with the sustained volume expansion, both basal and stimulated plasma renin activities were significantly suppressed in the hyponatraemic rats. Plasma vasopressin levels were similarly suppressed, and the hyponatraemic rats showed a striking absence of endogenous vasopressin secretion in response to marked intravascular volume depletion (15–45%) produced by s.c. administration of polyethylene glycol. Plasma concentrations of atrial natriuretic peptide were initially stimulated four- to fivefold above basal levels in response to the water-induced volume expansion, but by 48 h fell to ranges not significantly different from basal unstimulated levels, despite continued plasma and extracellular fluid volume expansion at that time.
These results illustrate that multiple haemodynamic and hormonal adaptive responses occur with sustained dilutional hyponatraemia in rats, and suggests that these can be of sufficient magnitude to allow continued water retention without necessarily provoking either escape from antidiuresis or continued natriuresis. In contrast with previous studies in experimental animals in which hyponatraemia was maintained by continuous forced administration of hypotonic fluid, rats in this model reached a steady state with characteristics resembling many of those observed clinically in patients with SIAD.
Journal of Endocrinology (1989) 122, 421–431
Growth hormone acutely increases glucose output by hepatocytes isolated from hypophysectomized rats
Authors: Blake W. L. , Clarke S. D. 
Published: December 2008

ABSTRACT
A series of experiments using isolated rat hepatocytes was carried out to establish rat liver cells in suspension as a physiological model for examining GH responses, and to determine whether acute recombinant bovine GH (rbGH) treatment of rat liver cells increased glucose output and/or suppressed fatty acid synthesis from lactate. Rat liver cells were isolated by collagenase perfusion and incubated in short-term (<60 min) suspension. The amount of insulin, glucagon or vasopressin required to elicit a half-maximal response was within the physiological range of the circulating hormone. When hepatocytes from normal rats were acutely (<60 min) treated with 0, 0·1, 10, 100 or 1000 nmol rbGH/l, rates of hepatocyte glucose output and fatty acid synthesis were unaltered. In addition, acute rbGH treatment (1000 nmol/l) did not alter hepatocyte responsiveness to insulin or vasopressin. However, acute rbGH treatment of hepatocytes isolated from hypophysectomized rats significantly (P < 0·05) increased the rate of glucose output twofold and moderately (P<0·10) enhanced fatty acid synthesis. The accelerated rate of glucose production was not accompanied by an increase in the amount of glycogen phosphorylase-a. The observations with liver cells from hypophysectomized rats are not consistent with a GH receptor-transducing mechanism which is like that for glucagon (adenylate cyclase-linked) or insulin (tyrosine kinase-linked).
Journal of Endocrinology (1989) 122, 457–464
Radioimmunoassay of inhibin in the serum of male monkeys
Authors: Fingscheidt U. , Weinbauer G. F. , Robertson D. M. , de Kretser D. M. , Nieschlag E. 
Published: December 2008

ABSTRACT
A heterologous inhibin radioimmunoassay method to measure inhibin in serum of male cynomolgus (Macaca fascicularis) and rhesus (Macaca mulatta) monkeys has been validated using a specific antibody against bovine 31 kDa inhibin and 125I-labelled 31 kDa inhibin as tracer. A serum pool from male monkeys was used as standard. Serial dilutions of normal monkey serum showed parallel logit–log dose–response curves to purified porcine and bovine inhibin as well as to a female human serum pool. The intra-assay coefficient of variation was 4·2% (n=10) and the interassay coefficient of variation 5·1% (n=10). No loss of inhibin immunoactivity was noted after storage at 23 °C for 5 days or repeated thawing and freezing of the serum samples. Serum from castrated monkeys showed undetectable levels of inhibin. Treatment with a gonadotrophin-releasing hormone agonist for 15 weeks led to a marked suppression of peripheral serum inhibin to concentrations similar to those after hypophysectomy or pituitary stalk section.
Journal of Endocrinology (1989) 122, 477–483
Testes are asymmetric in the testicular hemicastration response of the male rat
Authors: Frankel A. I. , Chapman J. C. , Cook B. 
Published: December 2008

ABSTRACT
An enquiry was made into variability in the testicular hemicastration response of the mature rat (doubling of testicular vein testosterone concentration from the remaining testis 24 h after hemicastration). The response was shown to be asymmetric, being more reliable and more robust when the left testis was removed first. Apparently the testicular hemicastration response, which has been shown to be neurally controlled, shares the asymmetry which has been reported recently in the neural regulation of unilateral ovariectomy.
Journal of Endocrinology (1989) 122, 485–488
Suppression and recovery of pituitary gonadotrophin secretion in intact and orchidectomized rats treated neonatally with a gonadotrophin-releasing hormone antagonist
Authors: Kolho K.-L. , Huhtaniemi I. 
Published: December 2008

ABSTRACT
Suppression of neonatal rat pituitary-testis function by gonadotrophin-releasing hormone (GnRH) antagonists results in delayed sexual maturation and infertility. Since the mechanism is not understood, the acute effects of a GnRH antagonist on gonadotrophin secretion in neonatal male rats has been studied in more detail. Treatment with a GnRH antagonist analogue, N-Ac-d-Nal(2)1,d-p-Cl-Phe2,d-Trp3,d-hArg(ET2)6,d-Ala10-GnRH (2 mg/kg per day) on days 1–10 of life had prolonged effects on gonadotrophin secretion; serum LH and FSH recovered in 1 week, but the pituitary content took 2 weeks to recover. Likewise, LH and FSH responses to acute in-vivo stimulation with a GnRH agonist were still suppressed 1 week after the treatment. Interestingly, a rebound (86% increase) in basal serum FSH was found 16 days after treatment with the antagonist.
Whether testis factors influence gonadotrophin secretion during treatment with the GnRH antagonist and/or in the subsequent recovery period was also assessed. Neonatal rats were castrated on days 1, 5 or 10 of the 10-day period of antagonist treatment. Orchidectomy on days 1 and 5 only marginally affected gonadotrophin secretion. When orchidectomy was performed at the beginning of the recovery period, no effects on pituitary recovery were seen within 1 week of castration. After 16 days, serum LH and FSH in the antagonist-treated and control castrated rats were equally increased but the pituitary contents of the antagonist-treated rats were still suppressed.
Finally, the effect of testosterone treatment on the recovery of gonadotrophin secretion after antagonist suppression was studied in intact and orchidectomized animals. The rats were implanted with testosterone capsules for 7 days after treatment with the GnRH antagonist in the neonatal period. Testosterone suppressed pituitary LH contents similarly in all groups of animals, but had no effects on serum LH. Paradoxically, serum FSH was suppressed 50% by testosterone in intact and castrated antagonist-treated rats and in castrated controls but not in intact controls. These findings suggest that suppression of FSH by testosterone is only seen in neonatal animals with low endogenous levels of this androgen, whether due to GnRH antagonist treatment or castration.
It is concluded that neonatal treatment with a GnRH antagonist results in prolonged suppression of LH and FSH secretion, that testis factors play only a minor role in pituitary modulation during the antagonist suppression and that more disturbances are observed in the post-treatment recovery of FSH secretion than in that of LH.
Journal of Endocrinology (1989) 122, 519–526
Stimulatory effect of caffeine on the hypothalamo-pituitary-adrenocortical axis in the rat
Authors: Nicholson S. A. 
Published: December 2008

ABSTRACT
Intraperitoneal injection of caffeine (12·5–100 mg/kg) into rats caused a significant, dose-related increase in plasma corticosterone 2 h later, when the greatest response was measured. The corticosterone response to laparotomy stress or i.v. injection of ACTH(1–24) was unaffected by prior injection of caffeine. The response to stress or caffeine was unaffected by adrenal enucleation 28 days previously.
In vitro, 10 mmol caffeine/l stimulated basal release of corticosterone from adrenal quarters and potentiated the response to a sub-maximal stimulatory concentration of cyclic AMP (cAMP). The drug had no effect on release stimulated by a sub-maximal concentration of ACTH(1–24).
Release of ACTH from pituitary fragments incubated in vitro was stimulated in a dose-related manner by caffeine (0·01–10 mmol/l), and the responses to hypothalamic extract and sub-maximal concentrations of corticotrophin-releasing factor (CRF-41) or arginine vasopressin (AVP), but not cAMP, were significantly enhanced by 10 mmol caffeine/l.
Release of immunoreactive CRF-41 (but not AVP) was significantly increased by caffeine (0·01–10 mmol/l) added to hypothalami incubated in vitro. The response to injection of caffeine in vivo was completely prevented by pharmacological blockade of endogenous CRF release.
Taken together, these results show that caffeine at high concentrations can stimulate directly the release of the hormones of the hypothalamo-pituitary-adrenocortical axis in vitro, but the fact that these concentrations are unlikely to be reached after administration in vivo suggests that the effect of caffeine may be mediated centrally.
Journal of Endocrinology (1989) 122, 535–543
Melatonin specifically stimulates type-II thyroxine 5′-deiodination in brown adipose tissue of Syrian hamsters
Authors: Puig-Domingo M. , Guerrero J. M. , Menéndez-Pelaez A. , Reiter R. J. 
Published: December 2008

ABSTRACT
The response of type-II thyroxine 5′-deiodinase (5′-DII)DII) to melatonin treatment was studied in the Syrian hamster. Male hamsters were treated for 15 days with a s.c. pellet containing melatonin, and 5′-DII activity in brown adipose tissue, anterior pituitary gland, Harderian gland and pineal gland was measured using a radioenzymatic technique. Melatonin-treated animals exhibited enhanced 5′-DII activity restricted to brown adipose tissue; the increase was threefold above the values measured in the control group. Serum concentrations of thyroid hormones were unaffected by melatonin treatment. We conclude that the stimulatory effect of melatonin on type-II thyroxine 5′-deiodination is specifically directed to the isoenzyme located in brown adipose tissue and is not accompanied by changes in serum thyroid hormones.
Journal of Endocrinology (1989) 122, 553–556
Protein metabolism in ovine primary muscle cultures derived from satellite cells – effects of selected peptide hormones and growth factors
Authors: Roe J. A. , Harper J. M. M. , Buttery P. J. 
Published: December 2008

ABSTRACT
Methods were developed for the isolation and culture of satellite cells from adult sheep muscle. Differentiated cultures of these cells were used to investigate the effects of four hormones and growth factors on protein synthesis and degradation. Insulin was found to have no effect except at supraphysiological concentrations (100 nmol/l and 1 μmol/l) where it is probably cross-reacting with the insulin-like growth factor (IGF) type-I receptor. IGF-I was found to be anabolic at lower concentrations (1–3 nmol/l). Epidermal growth factor (EGF) had a smaller effect on protein synthesis and degradation than insulin or IGF-I. The specific activity of the muscle-specific enzyme creatine phosphokinase (CPK) was increased by treatment with EGF. When both IGF-I and EGF were present in the test media an additive effect on protein synthesis was observed. However, no additive effect of IGF-I and insulin was noted. No effects of bovine GH were seen.
Journal of Endocrinology (1989) 122, 565–571
Aromatase, 5α- and 5β-reductase in brain, pituitary and skin of the sex-role reversed Wilson's phalarope
Authors: Schlinger B. A. , Fivizzani A. J. , Callard G. V. 
Published: December 2008

ABSTRACT
While intrasexual competition for mates is generally considered to be an androgen-dependent characteristic of reproductively active males, in the Wilson's phalarope (Phalaropus tricolor) it is the female that acquires the brighter nuptial plumage and aggressively competes for access to the less aggressive males. Despite this pronounced sex-role reversal, circulating sex steroid hormones of breeding phalaropes are similar to those of avian species displaying traditional male–female reproductive roles. To investigate whether these behavioural and morphological steroid-dependent differences may be due to differences in target organ metabolism of circulating androgen, [3H]androstenedione in the presence of an NADPH-generating system was incubated with homogenates of brain, pituitary and skin of male and female Wilson's phalaropes collected from a naturally breeding population. Oestrone, 5α-androstanedione and 5β-androstanedione were measured as endpoints of aromatization, 5α-reduction and 5β-reduction respectively. Aromatase activity in the anterior hypothalamus/preoptic area (AHPOA) and posterior hypothalamus was greater in breeding males with high circulating concentrations of testosterone than in females, and activity in the AHPOA was greater in breeding than in non-breeding males (with low circulating testosterone). Aromatase levels did not differ in septum, archistriatum, hyperstriatum or pituitary. 5α- and 5β-reductase were detected in all neuroendocrine tissues sampled and although there were no significant male–female differences, 5α-reductase was greater in the AHPOA of breeding than of non-breeding males. We infer from this that the behavioural sex-role reversal of phalaropes is unlikely to be accounted for by differences in androgen metabolism in neural targets, although the capacity to form greater quantities of oestrogenic and 5α-reduced metabolites in the AHPOA of breeding males may be linked to the expression of masculine copulatory behaviours. Aromatase activity was not detected in skin containing a sexually dimorphic feather tract; however, 5α- and 5β-reductase activities were significantly higher in females than in males and may account for the brighter nuptial plumage of females. These data suggest that alternate determinants of neural responsiveness such as sex-steroid receptor abundance or neural circuitry may underlie atypical sexual behaviours in phalaropes.
Journal of Endocrinology (1989) 122, 573–581
Effects of infusions of various doses of bovine growth hormone-releasing factor on blood hormones and metabolites in lactating Holstein cows
Authors: Enright W. J. , Chapin L. T. , Moseley W. M. , Zinn S. A. , Kamdar M. B. , Krabill L. F. , Tucker H. A. 
Published: December 2008

ABSTRACT
In two experiments, the effects of i.v. infusions of various doses of bovine GH-releasing factor (GRF) on blood hormones and metabolites in lactating Holstein cows were determined.
In experiment 1, cows were infused with GRF (0, 3·125, 6·25, 12·5, 25·0 or 50·0 mg/cow per 24 h) for 24 h. Blood was sampled at −1, 5, 11, 15 and 23 h relative to the start of the infusion. The serum concentration of somatomedin C (SM-C) before infusion was 303 ± 8 (s.e.m.) μg/l. Doses of GRF of between 3·125 and 50·0 mg were equipotent in stimulating (P < 0·05) SM-C by 1·5- to 2·5-fold. GRF-induced increases in SM-C occurred by 11 h from the start of the infusion.
In experiment 2, primiparous cows were infused with GRF (0, 1 or 3 mg/24 h) for 20 days. Blood was sampled for 12 h on days 1, 10 and 19. The 1 mg dose of GRF increased (P < 0·05) blood concentrations of SM-C (on days 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, insulin, cortisol, tri-iodothyronine (T3), thyroxine (T4), non-esterified fatty acids (NEFA) or glucose. The 3 mg dose of GRF increased (P < 0·05) blood concentrations of SM-C (on days 10 and 19), T3 (on days 10 and 19), insulin (on day 19), NEFA (on days 1, 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, cortisol or T4.
We conclude that these data are consistent with the hypothesis that the galactopoietic effect of exogenous GRF in dairy cattle is mediated by increased secretion of GH.
Journal of Endocrinology (1989) 122, 671–679