bluuebunny/crossref_metadata_2025 huggingface dataset:
Pituitary-testicular function is suppressed by an LHRH antagonist but not by an LHRH agonist in the marmoset monkey
Authors: Lunn S. F. , Dixson A. F. , Sandow J. , Fraser H. M.
Published: December 2008

The use of pituitary desensitization by an LHRH agonist (buserelin) to examine pituitary-testicular function was investigated in a New World primate. Six adult male marmoset monkeys were injected s.c. with an LHRH agonist implant (1·5 mg in a rod 0·5 cm long). Pharmacokinetics, determined by radioimmunoassay of urinary buserelin, revealed a rapid initial release of the agonist followed by a steady decline during a 200-day period. The LHRH agonist treatment resulted in a rapid initial rise in plasma LH followed by a return to mean values similar to those seen in the control samples by 7 days after implantation. Using the present protocol, no evidence of subsequent pituitary desensitization or suppression of testicular function was observed, plasma concentrations of LH and testosterone remaining within the normal range during the 200-day study period.

In contrast, pituitary-testicular function was suppressed in the male marmoset after blockade of pituitary LHRH receptors by an LHRH antagonist. Five adults were treated with a single s.c. injection of the antagonist [Ac-d-Nal(2)1,d-pCl-Phe2,d-Trp3,d-Ser(Rha)6,AzGlyNH210]-LHRH at a dose of 300 μg/kg. The LHRH antagonist induced a marked suppression of plasma LH and testosterone by 6–8 h, the low levels being maintained for 24–48 h.

These results show that, whereas treatment with an LHRH antagonist can inhibit pituitary-testicular function in the male marmoset, it may be that desensitization cannot be induced by the LHRH agonist used.

Journal of Endocrinology (1990) 125, 233–239
Effects of corticostatin-I on rat adrenal cells in vitro
Authors: Tominaga T. , Fukata J. , Naito Y. , Nakai Y. , Funakoshi S. , Fujii N. , Imura H.
Published: December 2008

We have examined the mechanism by which corticostatin-I (CS-I) acts to attenuate ACTH-induced steroidogenesis in rat adrenal cells. CS-I inhibited ACTH-induced corticosterone production in a dosedependent manner, without any effects on the basal corticosterone level in adrenal cells. When the cells were stimulated by 100 pg ACTH/ml, the minimum effective concentration of CS-I was 100 ng/ml, and 0.3–1.0 μg CS-I/ml produced a 50% reduction of the stimulated corticosterone production. The inhibitory effect of CS-I on ACTH-stimulated corticosterone production became apparent within 15 min of incubation, and the effect was reversed quickly by the removal of CS-I from the media. CS-I had no effect on angiotensin II-stimulated aldosterone production by adrenal zona glomerulosa cells. CS-I also did not affect cyclic AMP- or forskolin-stimulated corticosterone production. In an in-vitro binding study using 125I-labelled CS-I, CS-I showed considerable specific binding to rat adrenal cells, and the binding competed with ACTH in a dose-dependent manner. These experiments suggest that CS-I competes with ACTH on their binding sites and exerts an inhibitory effect on the adrenal cells.

Journal of Endocrinology (1990) 125, 287–292
Interaction of angiotensin II with the cholinergic and noradrenergic systems in the rat pineal gland: regulation of indole metabolism
Authors: Finocchiaro L. M. E. , Goldstein D. J. , Finkielman S. , Nahmod V. E.
Published: December 2008

The pineal gland, angiotensin, and noradrenergic and cholinergic systems are involved in the regulation of tissue indole metabolism. Angiotensin II increased noradrenaline release and the production of hydroxy-and methoxyindoles by pineal slices. Electrical field stimulation (EFS) of pineal slices released angiotensin II and reproduced many of the actions of exogenous angiotensin II on serotonin and melatonin biosynthesis and release. Both sarcosine1-isoleucine8-angiotensin II ([Sar1,Ile8]-ANG II) and atropine blocked, and nadolol increased, the effect of EFS and exogenous angiotensin II on serotonin production. Nadolol blocked both the EFS-induced and the angiotensin II-induced production of melatonin. Atropine and [Sar1,Ile8]-ANG II did not modify melatonin biosynthesis in electrically stimulated slices, but the muscarinic receptor antagonist increased the stimulatory effect of angiotensin II. These data showed that EFS released angiotensin II and noradrenaline from pineal slices and that a close functional connection exists between the peptide and acetylcholine. The stimulation of serotonin biosynthesis and release by these two neurotransmitters was negatively regulated by noradrenaline acting through β-adrenergic receptors.

Journal of Endocrinology (1990) 126, 59–66
Central action of thyrotrophin-releasing hormone on growth hormone secretion in domestic fowl
Authors: Harvey S. , Lea R. W. , Ahene C.
Published: December 2008

Peripheral plasma concentrations of GH in adult chickens were increased, in a dose-related manner, between 5 and 30 min after the intracerebroventricular (i.c.v.) injection of 0·1 or 10 μg TRH. In contrast, i.v. administration of comparable doses of TRH had no significant effect on circulating GH concentrations. [3H]3-methyl-histidine2-TRH ([3H]Me-TRH) was located in the pituitary gland and peripheral plasma within 5 min of its i.c.v. administration, although in amounts that were unlikely to affect directly pituitary function. [3H]Me-TRH rapidly accumulated in the hypothalamus following its i.c.v. administration (but not after i.v. injection), and the central effect of TRH on GH secretion in birds is therefore likely to be induced by effects at hypothalamic sites.

Journal of Endocrinology (1990) 126, 83–88
Effects of hyper- and hypothyroidism on carbonic anhydrase, Mg2+-dependent ATPase and Mg2+-dependent, HCO3−-stimulated ATPase activities of rat duodenal mucosa and kidney cortex
Authors: Suzuki S. , Chen H. , Takahashi T. , Niwa O.
Published: December 2008

Carbonic anhydrase (CA) and Mg2+-dependent ATPase and Mg2+-dependent, HCO3−-dependent ATPase (Mg2+-HCO3−-ATPase) activities in rat duodenal mucosa and kidney cortex were examined with respect to thyroidal status. Administration of 50 and 150 μg thyroxine (T4)/kg per day s.c. for 7 days decreased duodenal cytosol CA activity to 66% of control with the former and 43% with the latter dose, while Mg2+-HCO3−-ATPase activity in brush borders of duodenal mucosa was increased to 116% of control by 150 μg T4/kg. CA and Mg2+-HCO3−-ATPase activities in the cytosol and brush border of kidney cortex did not change after administration of T4. Hypothyroidism induced by thyroidectomy for 2 and 4 weeks or administration of methimazole (2·5–20 mg/kg per day s.c. or peroral) for 2, 3 and 4 weeks all increased duodenal cytosol CA activity, to about 140% at 2 weeks and 153% at 4 weeks after thyroidectomy, and to about 136% after the oral administration of 10 mg methimazole/kg per day for 4 weeks, while brush border Mg2+-HCO3−-ATPase activity was decreased to 56% of control 4 weeks after thyroidectomy and to 74% after the s.c. administration of 20 mg methimazole/kg per day for 3 weeks. The increase in CA activity and the decrease in ATPase activity after thyroidectomy were restored to normal levels by replacement with T4. Neither enzyme activity in the kidney changed in hypothyroidism. Serum concentrations of T4 and cortisol-like material increased after administration of T4, and serum concentrations of T4, aldosterone and cortisol-like material all decreased in hypothyroidism. Correlations were observed between duodenal CA and Mg2+-HCO3−-ATPase activities and serum concentrations of T4 (P < 0·01). These results reveal that the decrease in CA activity and the increase in Mg2+-HCO3−-ATPase activity of duodenal mucosa in hyperthyroidism are reversed in hypothyroidism, while both enzyme activities in the kidney are unrelated to thyroidal status.

Journal of Endocrinology (1990) 126, 119–129
Effects of a novel 21-amino steroid, U74006F, on the rat pituitary-adrenocortical axis
Authors: Burrin J. M. , Hart G. R.
Published: December 2008

The 21-amino steroid U74006F is a potent inhibitor of lipid peroxidation and has been shown to affect beneficially the acutely injured central nervous system. Therapeutically, it is desirable for this compound to be devoid of steroid side-effects. We have demonstrated a significant (P < 0·001) inhibition of basal ACTH secretion from cultured rat pituitary cells during a 24-h incubation at concentrations (10–100 μmol/l) previously demonstrated to inhibit lipid peroxidation in vitro. U74006F also inhibited corticotrophin-releasing factor (CRF)-stimulated ACTH secretion significantly and the combination of dexamethasone and U74006F completely blocked CRF-41-stimulated ACTH secretion. Administration of U74006F in vivo (30 mg/kg, orally, every 6 h for 30 h) had no effect on ACTH levels in normal rats (84±38 vs 45±6 ng/l in control animals) but increased ACTH levels in adrenalectomized rats (1330±295 vs 464±79 ng/l in control animals, P < 0·02). This increase in ACTH was not observed when adrenalectomized animals were maintained on the same regime of U74006F for 5 days. Our data suggest that U74006F is capable of exerting inhibitory effects on ACTH secretion in vitro. In vivo, effects on ACTH secretion were stimulatory rather than inhibitory and only occurred short-term in adrenalectomized animals or chronically in adrenalectomized rats maintained on dexamethasone. No effects on the pituitary-adrenocortical axis were seen following short-term or chronic administration of U74006F in normal rats.

Journal of Endocrinology (1990) 126, 203–209
Chronic regulation of ovarian oxytocin and progesterone release by prostaglandins: opposite effects in bovine granulosa and early luteal cells
Authors: McArdle C. A.
Published: December 2008

Oxytocin is synthesized in the granulosa-derived large cells of the ruminant corpus luteum from a gene which is dramatically up-regulated in the first few days after ovulation. In this work, the regulation of granulosa and luteal cells by prostaglandins and insulin (or insulin-like growth factor-I; IGF-I) has been explored by comparing their effects on oxytocin and progesterone production in cell culture. In granulosa cells, chronic exposure to insulin (17 nmol/l) stimulated luteinization as indicated by increased release of oxytocin and progesterone. Prostaglandin F2α (PGF2α) alone had little effect, but synergized with insulin (or IGF-I) to increase the release of both these hormones. In direct contrast, insulin-stimulated oxytocin production by luteal cells was inhibited by PGF2α. The half-maximal dose (EC50) for PGF2α action in both cell preparations was similar (10–100 nmol/l). Dose–response studies revealed that PGF2α increased the potency of insulin in granulosa cells (EC50 for insulin-stimulation of oxytocin release reduced from 141 to 13 nmol/l by 1 μmol PGF2α/l), but not in luteal cells. Insulin-stimulated oxytocin release from granulosa cells was also synergistically increased by PGE1, PGE2 and forskolin, suggesting this effect to be mediated by adenylate cyclase-coupled PGE receptors. The results reveal that the effects of prostaglandins on oxytocin release are dependent on both the developmental stage of the target tissue and on the presence of other regulators of cellular differentiation. Moreover, they suggest that the increase in responsiveness to insulin and IGF-I, which appears to accompany luteinization in the cow, may be an effect of prostaglandins produced locally during the peri-ovulatory period.

Journal of Endocrinology (1990) 126, 245–253
Effects of the synthetic glucocorticoid dexamethasone on reproductive function in the ewe
Authors: Phillips D. J. , Clarke I. J.
Published: December 2008

Glucocorticoids have been found to inhibit reproductive function in most domestic species studied but, in the ewe, preliminary reports suggest that glucocorticoids may have little or no effect. This study investigated the effects of the synthetic glucocorticoid dexamethasone on oestrus and ovulation rate in ewes during the breeding season and gonadotrophin secretion in the breeding and non-breeding seasons. In cyclic ewes, dexamethasone treatment at rates of up to 2 mg/day did not affect the natural or pregnant mare serum gonadotrophin-stimulated ovulation rate, or the timing and incidence of behavioural oestrus (P>0·05). Dexamethasone administration (2 mg/day) had no effect on LH secretion or the plasma LH response to a 1 μg injection of gonadotrophin-releasing hormone (GnRH) in ovariectomized ewes in the breeding and non-breeding seasons, and did not compromise the inhibition of plasma LH levels during chronic treatment with oestrogen. Similarly, dexamethasone had no effect on plasma FSH concentrations, but significantly (P<0·05) reduced the plasma FSH response to a 1 μg GnRH injection during chronic negative treatment with oestrogen in ovariectomized ewes. Collectively, these data show that in these experiments dexamethasone did not significantly modify reproductive function in the ewe, a finding that is in contrast to that found in other domestic species.

Journal of Endocrinology (1990) 126, 289–295
Inhibition of the pituitary-gonadal axis in nude male mice by continuous administration of LHRH agonists and antagonists
Authors: Redding T. W. , Schally A. V.
Published: December 2008

Analogues of LHRH can be used for the treatment of sex hormone-dependent tumours. The nude mouse is a valuable model for the investigation of transplanted human cancers, but there is a body of literature reporting that the function of the pituitary-gonadal axis in normal (immunocompetent) and nude (immunocompromized) mice, unlike that of other species, cannot be suppressed by the administration of LHRH agonists and antagonists. To explore this view further, long-term experiments were carried out in nude male mice, in which sustained-release formulations of the agonist [d-Trp6]-LHRH and of two new potent antagonists were used which permitted a continuous release of the peptides into the circulation. Nude male mice were treated for 28-30 days with 50 μg of antagonists [Ac-d-Nal(2)1,d-Phe(4Cl)2,d-Trp3,d-Cit6,d-Ala10]-LHRH (SB-30) or [Ac-d-Nal(2)1,d-Phe(4Cl)2,d-Pal(3)3,d-Cit6,d-Ala10]-LHRH (SB-75)/day delivered by osmotic minipumps. Some mice were injected twice a day with 25 μg SB-75. Other groups received microcapsule preparations of the agonist [d-Trp6]-LHRH, releasing 25 or 12·5 μg/day for 30 days. At autopsy, in mice which received 50 μg SB-30 or SB-75/day by minipumps, there was a significant decrease in weights of testes, ventral prostate and seminal vesicles compared with controls. [d-Trp6]-LHRH microcapsules at either dose also reduced weights of testes and accessory sex organs. Serum LH and testosterone were significantly reduced in all groups treated with analogues. There was a greater decrease in testicular weights and serum testosterone in nude mice which received SB-75 in a continuous fashion from minipumps than in animals injected twice a day. These results clearly demonstrate, contrary to the existing data, that the pituitary-gonadal axis of nude mice can be inhibited by LHRH agonists or antagonists if they are administered by continuous release systems. This study indicates that when the sustained-release formulations are used, nude mice can be valuable for studying the effects of analogues of LHRH on tumour biology

Journal of Endocrinology (1990) 126, 309–315
Effects of hypophysectomy and human chorionic gonadotrophin on Leydig cell function in mature rats
Authors: Stocco D. M. , Teerds K. J. , van Noort M. , Rommerts F. F. G.
Published: December 2008

The biochemical activities involved in the maintenance of Leydig cell functions, and the effects of hypophysectomy and human chorionic gonadotrophin (hCG) on these functions are largely unknown. In the present study, adult hypophysectomized rats were used as a model to determine the effects of these treatments on a number of biochemical and morphological parameters. After 33 days of hypophysectomy, the morphology of the Leydig cells had been drastically altered. In addition, α-naphthol and β-naphthol esterase activity as well as the steroidogenic capacity of the Leydig cells were greatly reduced at this time. In contrast, the level of sterol carrier protein 2 (SCP2), a Leydig cell-specific protein, was affected by hypophysectomy much less than the other parameters measured. Two daily injections of hCG to rats hypophysectomized for 31 days resulted in no change in the morphology of the Leydig cells, or in their proliferative activity. Non-specific esterase activities were also unaffected by 2 days of treatment with hCG. However, two injections of hCG to rats hypophysectomized for 31 days resulted in nearly complete restoration of steroidogenic capacity, and a 3·5-fold increase in the level of SCP2. These findings indicate that hypophysectomy results in significant morphological and biochemical changes in Leydig cells, and that hCG is capable of restoring some of these capacities within a short time.

Journal of Endocrinology (1990) 126, 367–375
Nuclear tri-iodothyronine (T3) binding in neonatal rat brain suggests a direct glial requirement for T3 during development
Authors: Hubank M. , Sinha A. K. , Gullo D. , Ekins R. P.
Published: December 2008

Tri-iodothyronine (T3) binding studies were performed on neuronal and glial nuclei prepared from developing rats brain by discontinuous sucrose gradient centrifugation. Maximum binding capacities (MBC) and dissociation constants (Kd) were obtained from Eadie-Hofstee plots of transformed data. An ontogenic study on nuclei prepared from whole brain revealed that on day 5 after birth, glial nuclear MBC was 1774±201 (s.e.m.) fmol/mg DNA compared with 974±117 fmol/mg DNA for the neurones (P<0·01). Although diminishing to 667±112 fmol/mg DNA by day 21, alterations in neuronal MBC over the neonatal period were not statistically significant, whereas glial MBC diminished steadily to 557±133 fmol/mg DNA in glial nuclei (P<0·05). Over the same period, a significant reduction in Kd was noted only in the glia, from 3·17±0·40 to 1·83±0·34 nmol/l (P<0·03). Ligand specificity of the receptor in both nuclear types on day 21 was tri-iodoacetic acid > T3 > thyroxine > 3,3′,5′-T3, but this was less clearly demonstrated at day 5.

Regional studies on days 15 and 21 demonstrated that for both neuronal and glial nuclei, receptors are concentrated in the cerebral cortex and diminish in a cranio-caudal direction. Cerebral glial MBC on day 21 was 2215±147 fmol/mg DNA, at this stage still exceeding the cerebral neuronal capacity of 1111±207fmol/mg DNA. The results indicate that neonatal glia may respond directly to thyroid hormones via nuclear receptor binding, and that receptors are predominantly located in the cortex. Decreases in average MBC in the late neonate may be due to increases in the numbers of cells containing fewer nuclear receptors.

Journal of Endocrinology (1990) 126, 409–415
Ageing and the sensitivity of the adrenal gland to physiological doses of ACTH in man
Authors: Roberts N. A. , Barton R. N. , Horan M. A.
Published: December 2008

Healthy men and women aged 19–38 or 67–83, in whom endogenous ACTH secretion was suppressed with dexamethasone, were given successive injections of 60 ng, 150 ng and 250 μg ACTH(1–24) at hourly intervals, and blood samples for measurement of plasma cortisol were taken every 10 min. The response to each injection was taken as the increase in cortisol concentration 20 min later, when there was a peak with the lower doses, with allowance for disappearance of cortisol produced after the previous injection. On average, the responses to 60 and 150 ng ACTH were about 0·4 and 0·7 respectively of the response to 250 μg. There were no consistent effects of age or sex on any index of adrenocortical sensitivity or responsiveness, but some groups showed isolated differences from both their age- and sex-matched counterparts: the response to 60 ng ACTH was low in young men, maximal responsiveness was low in elderly men and the slope of the dose–response curve was high in elderly women. In most of the elderly subjects, plasma ACTH was determined separately under normal conditions. It was negatively correlated with the cortisol responses to 60 and 150 ng ACTH, suggesting that differences in adrenal sensitivity between subjects contribute to the variability of plasma ACTH.

Journal of Endocrinology (1990) 126, 507–513
Growth hormone (GH) secretion in the dwarf rat: release, clearance and responsiveness to GH-releasing factor and somatostatin
Authors: Carmignac D. F. , Robinson I. C. A. F.
Published: December 2008

The new mutant GH-deficient dwarf (Dw) rat was used to study the effects of GH-releasing factor (GRF) or somatostatin (SRIF) on GH release. In anaesthetized adult Dw female rats, i.v. injections of GRF (0·031–2·0μg) elicited a dose-dependent release of GH. Although the peak plasma GH responses to maximal GRF doses were much lower in adult Dw rats compared with normal rats of this strain (AS), the responses largely reflected their relative pituitary GH contents (140±17 μg vs 2·9±0·4 μg, AS vs Dw (means ± s.e.m.), P < 0·001). Except at 20 days of age, normal AS rats were more sensitive to GRF than Dw rats despite their larger body weight. Peak GH responses to injection of 31·25 ng GRF increased nine-fold in normal rats between 20 and 40 days, whereas the GH responses to this GRF dose diminished in Dw rats over this age range, and their pituitary GH content was only 2–5% of that of age-matched AS rats. Treatment with human GH (200 μg/day for 7 days) stimulated growth in 40-day-old Dw rats and slightly increased the GH response to a low dose of GRF. Basal GH levels in adult Dw animals were sevenfold lower than in AS rats (2·4±0·3 vs 17·6±3·3 μg/l P < 0·001) and were further suppressed by i.v. infusion of SRIF (25 μg/h). As in normal rats, a rebound GH secretion occurred in Dw rats after stopping SRIF, which was blocked by injection of anti-GRF serum. The disappearance rate of 125I-labelled rat GH from plasma was identical in AS and Dw rats. We conclude that dwarf rats show GH deficiency as early as 20 days of age; they respond to GRF, but release only small amounts of GH due to their reduced pituitary GH content. Although basal GH release is reduced in Dw rats, the levels are higher than would be expected from the 50-fold reduction in pituitary stores, and may reflect a chronic reduction in SRIF and/or increase in GRF release induced by prolonged GH deficiency in the Dw rat.

Journal of Endocrinology (1990) 127, 69–75
The O-methylation of catechol oestrogens by pig conceptuses and endometrium during the peri-implantation period
Authors: Chakraborty C. , Davis D. L. , Dey S. K.
Published: December 2008

Pig conceptuses display a surge in oestrogen and catecholoestrogen synthetic activity during the periimplantation period. However, the pathways of catecholoestrogen metabolism in pig conceptuses and endometrium are unknown. O-Methylation is an important route of catecholoestrogen metabolism. Therefore, the O-methylations of 2- and 4-hydroxy-oestradiols (2- and 4-OH-oestradiol) by cytosol of pig conceptuses and endometrium during the periimplantation period were studied. Kinetic studies performed in tissues obtained on day 13 of pregnancy (day 0 = first acceptance of the male) indicated that the O-methylation of 2-OH-oestradiol displayed simple Michaelis–Menten kinetics in both tissues. In blastocysts, the apparent Michaelis constant (Km) and maximum velocity (Vmax) for the O-methylation of 2-OH-oestradiol were 1·4 μmol/l and 11·27 pmol/mg protein per min respectively, and when 4-OH-oestradiol was used as substrate, the values were 2·53 μmol/l and 9·86 pmol/mg protein per min respectively. The apparent Km and Vmax values for the O-methylation of 2-OH-oestradiol in endometrium were 0·77 μmol/l and 19·6 pmol/mg protein per min respectively, and for the O-methylation of 4-OH-oestradiol were 2·44 μmol/l and 10·38 pmol/mg protein per min respectively. Ontogenesis of catechol-O-methyltransferase (COMT) in conceptuses and endometrium was studied from day 10 to day 19 of pregnancy. Conceptus COMT activity was lowest on day 10 and increased gradually to day 19 of pregnancy. Because a surge of oestradiol-2/4-hydroxylase activity occurs on days 11–13, less COMT activity on these days than on the later days of pregnancy is consistent with a role for catecholoestrogens in conceptus-maternal signalling during pregnancy establishment. Endometrial COMT activity on day 10 was higher than that on later days of pregnancy. Therefore, a role for COMT in modulation of catecholoestrogen and oestrogen function during the peri-implantation period is possible.

Journal of Endocrinology (1990) 127, 77–84
Intracellular mechanisms involved in the stimulation of growth hormone release from rat anterior pituitary cells by Russell's viper venom
Authors: Hart G. R. , Caldwell G. , Burrin J. M.
Published: December 2008

We have previously shown that a heat-stable component of Russell's viper venom (RVV) releases GH in a dose-dependent manner from cultured rat anterior pituitary cells. We have now investigated the intracellular mechanisms involved in RVV-stimulated GH release by concomitant administration of RVV with known intracellular mediators in rat pituitary cells.

3-Isobutyl-1-methylxanthine (IBMX; 0·5 mmol/l), added to cultured rat anterior pituitary cells simultaneously with RVV, at concentrations up to a maximally effective dose of 10 μg/ml, increased GH release (3·7-fold, 4·0-fold and 2·0-fold; P < 0·001) compared with the effect of venom alone. These effects were additive, indicating that RVV and IBMX stimulate through different intracellular messengers. RVV failed to increase the formation of basal or IBMX-stimulated intracellular cyclic AMP (cAMP), confirming that RVV affects GH release through a cAMP-independent pathway. 12-0-Tetradecanoylphorbol-13-acetate (TPA; 0·1 μmol/l), added simultaneously with various doses of RVV (0·1–10 μg/ml), did not increase GH release beyond the maximal effect of RVV. This result indicates that RVV might be stimulating GH release through a similar mechanism to that of TPA (by activating protein kinase C).

When pituitary cells were perifused with Ca2+-free medium or verapamil (50 μmol/l), RVV-stimulated GH release was inhibited by 65 and 42% respectively. This reflects the recognized requirement of Ca2+ for secretory processes. However, RVV (10 μg/ml) had no significant effect on intracellular free Ca2+ concentrations as measured using the fluorescent Ca2+ probe quin-2.

These findings indicate that the mechanism of action of RVV on GH release is independent of a change in both cAMP levels and intracellular free Ca2+ concentrations, and is dependent upon protein kinase C.

Journal of Endocrinology (1990) 127, 111–117
Identification and partial characterization of parathyroid hormone-related protein in human and bovine milk
Authors: Ratcliffe W. A. , Green E. , Emly J. , Norbury S. , Lindsay M. , Heath D. A. , Ratcliffe J. G.
Published: December 2008

Parathyroid hormone-related protein (PTHrP) was measured in human and bovine milk by radioimmunoassay (RIA) and bioassay, and the molecular forms characterized by gel chromatography and immunoblotting of affinity-purified PTHrP. Mean immunoreactive PTHrP(1–34) concentrations were 23 and 87 μg/l in human and bovine milk respectively. Bioactive (BIO) PTHrP concentrations determined by cyclic AMP production by ROS 17/2·8 cells correlated significantly (P< 0·001) with those obtained by RIA (BIO = 1·04RIA−3·4, r = 0·939). Gel filtration of human and bovine milk identified several peaks with immunoactivity and bioactivity. Immunoblotting of affinity-purified PTHrP revealed multiple molecular species including components with mobilities similar to those of PTHrP and its subfragments. These studies confirm the presence of immuno- and bioactive PTHrP in milk and suggest that post-translational processing is complex and variable.

Journal of Endocrinology (1990) 127, 167–176
Control of ion transport in the thyroid: prostaglandin E2 activates cation transport on the basal membrane of cultured porcine thyroid cell monolayers
Authors: Bourke J. R. , Cragoe E. J. , Huxham G. J. , Pearson J. V. , Manley S. W.
Published: December 2008

Confluent monolayers of cultured porcine thyroid cells transport fluid from the apical to the basal surface, forming circumscribed zones of detachment (domes) from the culture dish substrate. Stimulation of fluid transport by prostaglandin E2 (PGE2; 1 μmol/l) was associated with an increase in transepithelial potential (TEP). Intracellular potentials (equal to the potential difference across the apical membrane of the cell, Eapical) and the TEP were measured in individual domes so that the potential difference across the basal membrane of the cell (Ebasal) could be calculated from the relationship TEP = Eapical − Ebasal. The PGE2-induced increase in TEP was associated with hyperpolarization of the basal membrane, accompanied by a slight depolarization of the apical membrane. Lines of best fit by least-squares regression showed Eapical = −20·3 mV + 0·219 TEP (correlation coefficient r = 0·627; P < 0·001) and Ebasal = −20·3 mV − 0·781 TEP (r = 0·944; P < 0·001). Phenamil (1 μmol/l), a Na+ channel selective amiloride analogue, reduced the TEP from 13·25±0·58 (s.e.m.; n = 56) to 2·39±0·16 mV (n = 51; P < 0·001) and hyperpolarized the apical membrane potential from − 20·7±0·68 (n = 60) to −32·2±0·83 mV (n = 105; P < 0·001). The response of the TEP to phenamil was immediate, and was promptly reversed on washing; in contrast, addition of 5-(N-ethyl-N-isopropyl)amiloride (20 μmol/l; selective for Na+/H+ antiporters) resulted in a slow depolarization over 30 min with a slow recovery after washout. Exposure of the cultures to media of pH 7·04 (compared with the normal pH of 7·34) resulted in a reduced response to PGE2, and a reduction in magnitude of Ebasal. It was concluded that stimulation of ion transport by PGE2 in thyroid monolayers involves activation of cation transport across the basal membrane.

Journal of Endocrinology (1990) 127, 197–202
Effects of altered dietary sodium intake on hormonal profiles in salt-sensitive hypertensive rats
Authors: Hazon N. , Henderson I. W.
Published: December 2008

Blood pressure and selected putatively influential hormones were measured in Brattleboro rats which were without diabetes insipidus and which were subjected to various manipulations in dietary sodium intake. Rats fed a control diet from weaning to 16 weeks of age showed a slow increase in blood pressure whereas rats fed a sodium-enriched diet for the same period exhibited sustained hypertension (115±3 versus 169±5 (s.e.m.) mmHg). In animals fed a sodium-enriched diet plasma concentrations of antidiuretic hormone (ADH) were significantly increased from 55±8 to 108±5 fmol/l. Rats fed the control diet from weaning (group A) and subsequently maintained on that diet or changed to a sodium-enriched diet or sodium-deficient diet showed no differences in their blood pressure. Plasma hormone concentrations were similar in these groups, with the exception of aldosterone suppression in rats switched from control to a sodium-enriched diet (0·26±0·04 versus 0·08±0·03 nmol/l; P <0·001). Animals fed the sodium-enriched diet from weaning to 16 weeks of age (group b) and either maintained on that diet or changed to a control diet showed little change in their established hypertension. Transfer to the control diet was associated with increased plasma renin concentrations (PRC) (13·8±2·1 to 122·6±6·2 nmol/l) and plasma aldosterone concentrations (0·04±0·01 to 0·08±0·01 nmol/l; P<0·001) but corticosteroids and ADH concentrations were unchanged. Rats maintained on the sodium-enriched diet from weaning to 16 weeks of age and transfered to a sodium-deficient diet exhibited increases in their established hypertensive blood pressures (maximally 205±4 versus 170±4 mmHg) together with significant increases in PRC (13·8 ±2·1 to 297±79 nmol/l; P< 0·001), aldosterone (0·04±0·01 to 0·23±0·07 nmol/l; P <0·001) and ADH (82·9±15·5 to 466±118 fmol/l; P <0·001), although plasma concentrations of corticosteroids were again unaffected. Thus it would appear that there is a critical developmental stage at which exposure to a sodium-enriched diet subsequently leads to hypertension. Abrupt withdrawal of the sodium-enriched diet produces an exaggerated hypertension involving changes in both ADH and the renin-angiotensin-aldosterone system.

Journal of Endocrinology (1990) 127, 243–248
Effects of a [Met]-enkephalin analogue ([d-Ala2,N-Me-Phe4,Met-(O)5-ol]-enkephalin) on canine pituitary function
Authors: Meij B. P. , Rijnberk A. , Mol J. A.
Published: December 2008

In adult healthy beagle dogs, plasma concentrations of ACTH, cortisol, α-MSH, GH, prolactin and arginine vasopressin (AVP) were measured after i.v. administration of [d-Ala2,N-Me-Phe4,Met-(O)5-ol]-enkephalin (DAMME) at doses of 0·1, 0·5, 1, 5 and 10 μg/kg body weight. Significant dose-dependent increases occurred for ACTH, cortisol and GH at dose rates of 0·5, 1, 5 and 10 μg/kg body weight. Increments in plasma concentrations of prolactin were significant only at 5 and 10 μg DAMME/kg, and there was no significant effect on plasma concentrations of α-MSH and AVP. Prior i.v. administration of the opiate antagonist naloxone (0·1 mg/kg) attenuated the DAMME (10 μg/kg)-stimulated release of ACTH and cortisol. The results demonstrate that the [Met]-enkephalin analogue DAMME stimulates the release of ACTH, cortisol, GH and prolactin in dogs, and that this stimulation is, at least in part, mediated by μ-opioid receptors. The observations for ACTH and cortisol are different from those in man, where DAMME lowers their basal concentrations.

Journal of Endocrinology (1990) 127, 265–271
Immunohistochemical localization of kallikrein within the prolactin-producing cells of the rat anterior pituitary gland
Authors: Kizuki K. , Kitagawa A. , Takahashi M. , Moriya H. , Kudo M. , Noguchi T.
Published: December 2008

The localization of tissue kallikrein in the pituitary gland of rats was investigated by an immunohistochemical technique using antiserum against rat urinary kallikrein. Kallikrein-positive cells were detected in the anterior lobe of the pituitary of both male and female rats, but were not observed in the posterior lobe of the pituitary in either sex.

The kallikrein-positive cells in the anterior pituitary of female rats in oestrus were found to correspond to the prolactin-producing cells, whereas the cells producing GH, LH and ACTH were negative for kallikrein. It is possible, therefore, that the tissue kallikrein may be involved in the production of prolactin and not that of the other anterior pituitary hormones, such as GH, LH, FSH, ACTH and TSH.

Journal of Endocrinology (1990) 127, 317–323
Binding of 125I-labelled thyrotrophin to transfected human thyrocytes (SGHTL-34 cells)
Authors: Taylor A. H. , Whitley G. St J. , Nussey S. S.
Published: December 2008

The binding of 125I-labelled bovine TSH to a human thyroid cell line (SGHTL-34) has been studied. Binding to hormonally responsive cells was time dependent, specific and reversible. Scatchard analysis of the binding data indicated the presence of a single binding site with high affinity (intrinsic dissociation constant (Kd) = 0·25 ±0·08 nmol/l; mean ± s.e.m.; n = 4) and low capacity (maximum binding (Bmax) = 104±29 fmol/mg protein; mean ± s.e.m.; n = 4). Hill plots confirmed the presence of a single site. Kinetic data demonstrated close agreement between the Kd and Bmax obtained from the competition data (Kd = 0·23±0·35 nmol/l; Bmax = 161 ±83 fmol/mg protein; n = 6).

Journal of Endocrinology (1990) 127, 351–356
Autoantibody to growth hormone in a patient with myasthenia gravis
Authors: Okada S. , Saito E. , Oshima H. , Kinoshita M.
Published: December 2008

An autoantibody to GH was detected in the serum from a patient with myasthenia gravis (MG) who had never been prescribed GH. Using an immunoprecipitation technique, this autoantibody was found to belong to the IgG class and had a κ chain. The dissociation constant of the antibody was 56·8 nmol/l and the binding capacity was 37 nmol/l. Serum samples from another 130 patients, including 37 with MG, were examined, but the GH autoantibody could not be detected. To our knowledge, this is the first report demonstrating the presence of a GH autoantibody.

Journal of Endocrinology (1990) 127, 533–538
Stimulation of DNA synthesis in chicken muscle satellite cells by insulin and insulin-like growth factors: evidence for exclusive mediation by a type-I insulin-like growth factor receptor
Authors: Duclos M. J. , Wilkie R. S. , Goddard C.
Published: December 2008

Insulin-like growth factors-I and -II (IGF-I and IGF-II) stimulate proliferation, differentiation, nutrient uptake and protein accretion in muscle cells. These effects are thought to be mediated through the type-I IGF receptor although a role for the type-II IGF receptor cannot be ruled out, since it has been found in most cells studied so far. Current evidence suggests that the chicken does not have a type-II IGF receptor and therefore provides a good model to study the function of IGF peptides. We have compared the effects of insulin and insulin-like growth factors on DNA synthesis with the binding of these peptides to receptors in primary chicken muscle satellite cells.

Human IGF-I (hIGF-I), hIGF-II and porcine insulin increased thymidine incorporation into DNA by threefold in muscle satellite cells prepared from neonatal chickens. IGF-I and -II were almost equipotent, with half-maximum effective concentrations of 10 μg/l, and were 1000-fold more potent than insulin. A combination of maximum effective concentrations of all three peptides was not additive, suggesting that their effect was mediated by the same receptor.

Receptor binding studies on satellite cells demonstrated the presence of specific IGF receptors. Human IGF-I inhibited the binding of 125I-labelled hIGF-I with a much higher potency than insulin, as usually observed for a type-I IGF receptor. However, unlabelled hIGF-II exhibited a higher potency than hIGF-I in displacing 125I-labelled hIGF-I. Affinity cross-linking of 125I-labelled hIGF-I and -II, followed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, showed that hIGF-I and -II bound to a receptor with the structural characteristics of a type-I IGF receptor and confirmed the lack of a type-II IGF receptor in these cells. The concentrations of IGF-I, -II and insulin required for biological action and to displace 125I-labelled hIGF-I binding were similar, and support the hypothesis that their effects on proliferation were mediated exclusively through a type-I IGF receptor.

Journal of Endocrinology (1991) 128, 35–42
Patterns of plasma sex hormone-binding globulin, thyroxine and thyroxine-binding globulin in relation to reproductive state and hibernation in female little brown bats
Authors: Kwiecinski G. G. , Damassa D. A. , Gustafson A. W.
Published: December 2008

A sex hormone-binding globulin (SHBG), which bound both oestradiol and dihydrotestosterone, was studied in the plasma of adult female little brown bats throughout the annual reproductive cycle. This protein was present at low baseline levels from September to May inclusive, months which correspond to the periods of hibernation, ovulation and early pregnancy. During the second half of pregnancy in June, SHBG levels increased 15- to 30-fold and remained increased throughout lactation and anoestrus/pro-oestrus (July–August). Although SHBG was increased during late pregnancy, the fact that levels were also high during and after lactation indicates that this protein is not specific to pregnancy. Plasma concentrations of thyroxine (T4) and the percentage binding of T4 to thyroxine-binding globulin (TBG) also showed marked seasonal variations, with T4 levels exhibiting a biphasic seasonal pattern. A major peak in plasma concentrations of T4 occurred around the time of spring arousal from hibernation and subsequent ovulation, while a second peak of lesser magnitude was measured in August, corresponding to the time of pro-oestrus and the onset of mating. The percentage binding of T4 by TBG was increased during the summer months in parallel with the increase in SHBG concentrations. Electrophoretic analysis of plasma T4 binding revealed a single peak of TBG activity throughout most of the year; however, during the early lactational period TBG was resolved as a double peak, suggesting the presence of a molecular variant during this reproductive stage.

Journal of Endocrinology (1991) 128, 63–70
Growth of mouse endometrial luminal epithelial cells in vitro: functional integrity of the oestrogen receptor system and failure of oestrogen to induce proliferation
Authors: Uchima F.-D. A. , Edery M. , Iguchi T. , Bern H. A.
Published: December 2008

Normal endometrial luminal epithelial cells isolated from ovariectomized approximately 40-day-old BALB/cCrgl mice were purified by Percoll density gradient centrifugation and grown as primary cultures in collagen gel matrix and serum-free medium. Cells increased threefold in number during the 9-day culture period. Deletion of insulin, epidermal growth factor or bovine serum albumin resulted in decreased growth. Addition of any single factor to the unsupplemented medium had no effect. Relatively high levels of cytosolic oestrogen receptors and progestin receptors were demonstrable in the cultures. Addition of oestrogen did not enhance epithelial cell proliferation. On the contrary, all doses of oestrogen (180 fmol/l to 218 nmol/l) were inhibitory. Continuous exposure to oestradiol-17β (1·8 nmol/l) for 9 days in serum-free medium resulted in a decrease in cytosolic oestrogen receptors with an associated nuclear accumulation of oestrogen receptors. A corresponding increase in cytosolic progestin receptors was also observed, indicating that no qualitative modification of the oestrogen receptor system had occurred. Thus, as previously reported for vaginal epithelial cells, oestrogen, despite its stimulation of specific product synthesis (progestin receptors), did not increase proliferation of endometrial luminal epithelial cells in this culture system.

Journal of Endocrinology (1991) 128, 115–120
Secretion of insulin-like growth factor-I (IGF-I) and IGF-binding proteins from bovine mammary tissue in vitro
Authors: Campbell P. G. , Skaar T. C. , Vega J. R. , Baumrucker C. R.
Published: December 2008

In vitro, insulin-like growth factor-I (IGF-I) promotes both growth and development of bovine mammary tissue. In vivo, the effects of IGF-I may encompass endocrine, paracrine or autocrine mediation. We addressed the possibility of paracrine/autocrine effects of IGF-I in the mammary gland by examining the in-vitro secretion of IGF-I and IGF-binding proteins (IGFBPs) from bovine mammary tissue. Bovine mammary explants from pregnant non-lactating and lactating non-pregnant animals were found to synthesize and secrete IGF-I and IGFBPs. Mammary acini cultures, representative of mammary secretory epithelia, secreted both IGF-I and IGFBP, but synthesized only IGFBP. Concentrations of IGF-I in conditioned media from explants were 1·54 and 0·72 fmol/μg DNA for pregnant and lactating animals respectively. Concentrations of IGFBPs in conditioned media from explants were similar for both physiological states at 2529 pmol 125I-labelled IGF-I bound/pg DNA. Ligand/Western blotting procedures identified four IGFBPs of 29, 33, 37 and 44 kDa for acini cultures and five IGFBPs of 28, 31, 36, 44 and 46 kDa for explant cultures. Similar affinities for IGF-I and IGF-II were shown by IGFBP, using 125I-labelled recombinant human IGF-I as the competing ligand (median effective dose (ED50) of 0·085 pmol). When 125I-labelled bovine IGF-II was used as the ligand, only bovine IGF-II (ED50 of 0·25 pmol) inhibited binding. The addition of prolactin, insulin and cortisol, with or without GH, did not affect secretion of either IGF-I or IGFBP. This report describes the ability of normal mammary tissue to synthesize and secrete IGF-I and IGFBPs.

Journal of Endocrinology (1991) 128, 219–228
The effect of rearing rainbow trout on black or white backgrounds on their secretion of melanin-concentrating hormone and their sensitivity to stress
Authors: Green J. A. , Baker B. I. , Kawauchi H.
Published: December 2008

Rainbow trout were reared in black or off-white coloured tanks for up to 18 months of age to achieve maximum differences in the synthesis of the neuropeptide, melanin-concentrating hormone (MCH). White-reared fish had greatly increased MCH concentrations in their pituitary glands, in their MCH perikarya and in the presumptive neuromodulatory fibres of the dorsal hypothalamus/thalamus when compared with black-reared and commercially reared trout. Following transfer to brighter white tanks, white-reared fish showed a significant increase in plasma MCH concentration and a reduction of MCH in the pituitary and MCH perikarya. The additional challenge of repeated stress further increased plasma MCH concentration in these fish and also reduced MCH in the dorsal hypothalamus/thalamus. In black-reared fish transferred to white tanks, plasma MCH concentrations were significantly raised after transfer, although they were lower after 11 days than in white-reared counterparts. Transfer from black to white background caused a fall in the MCH concentration in all regions— pituitary gland, perikarya and dorsal hypothalamus/thalamus; if transfer was accompanied by repeated stress, the hormone in the pituitary gland and MCH perikarya became so depleted that plasma MCH concentrations declined. Within each experimental situation (control, background transfer and transfer with stress) there was in inverse correlation between plasma MCH concentrations of black- and white-reared fish and the cortisol concentration. MCH had no direct effect on the secretion of cortisol by interrenal tissue but incubated hypothalami, in which endogenous MCH had been immunoabsorbed, provided evidence that MCH can depress the release of corticotrophin-releasing bioactivity.

Journal of Endocrinology (1991) 128, 267–274
The role of endothelin in the control of adrenocortical function: stimulation of endothelin release by ACTH and the effects of endothelin-1 and endothelin-3 on steroidogenesis in rat and human adrenocortical cells
Authors: Hinson J. P. , Vinson G. P. , Kapas S. , Teja R.
Published: December 2008

The rate of blood flow through the intact adrenal gland is closely linked to steroid hormone secretion, and although the mechanism involved is unknown, it is thought to involve secretory products of the vascular endothelium.

In dispersed cell preparations, endothelin-1 and -3 both caused a dose-dependent and highly sensitive increase in steroid secretion by zona glomerulosa and zona fasciculata cells of the rat and human adrenal cortex. In addition, when the perfused rat adrenal was stimulated with ACTH, significant increases in steroid secretion and perfusion medium flow rate were accompanied by significantly increased secretion of immunoreactive endothelin into the adrenal vein. It is proposed that endothelin has a role in mediating the adrenocortical response to ACTH stimulation.

Journal of Endocrinology (1991) 128, 275–280
Effects of an antiserum to rat growth hormone and bromocriptine on cholesterol-metabolizing enzymes in the lactating rat mammary gland
Authors: Shand J. H. , West D. W.
Published: December 2008

Rats in mid-lactation were treated, for 2 days, with anti-rat GH serum (anti-rGH) and/or bromocriptine before microsomes were prepared from the freeze-clamped mammary glands. The effects of these anti-hormone treatments on the concentrations of microsomal cholesterol and cholesterol esters and on the activities of acyl-CoA:cholesterol acyltransferase (ACAT), neutral cholesterol ester hydrolase and 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) were measured. HMG-CoA reductase was determined in microsomes prepared in both the presence and absence of phosphatase inhibitors to determine the expressed and total activities respectively.

Anti-rGH reduced HMG-CoA reductase and increased microsomal cholesterol and cholesterol esters. Bromocriptine reduced HMG-CoA reductase but increased all of the other parameters. The results indicate that the initial stage in the stimulation of milk secretion involves a decrease in the activity of ACAT and that the phosphorylation level of HMG-CoA reductase is modulated by both prolactin and GH acting in opposition.

Journal of Endocrinology (1991) 128, 287–295