bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of pituitary-gonadal suppression with a gonadotrophin-releasing hormone agonist on fetal gonadotrophin secretion, fetal gonadal development and maternal steroid secretion in the sheep
Authors: Thomas G B , McNeilly A S , Gibson F , Brooks A N
Published: December 2008

In order to investigate the regulation of the hypothalamo-pituitary-gonadal axis during fetal development, sheep fetuses at day 70 of gestation were implanted subcutaneously with a biodegradable implant containing the longacting gonadotrophin-releasing hormone (GnRH) agonist, buserelin. The treatment of fetuses with a GnRH agonist throughout the last half of gestation (term=145 days) abolished the increase in plasma LH concentrations that was seen in 2-day-old control lambs in response to an injection of GnRH. This attenuated response was associated with corresponding reductions in the pituitary content of LH and FSH. Immunolocalization studies revealed that pituitary glands from newborn lambs implanted with a GnRH agonist during fetal development were devoid of immunopositive LH- and FSH-containing cells. At birth the testicular weights of GnRH agonist-treated ram lambs were significantly decreased by 40% when compared with controls. This was associated with a 45% reduction in the total number of Sertoli cells per testis. In newborn ewe lambs GnRH agonist treatment had no effect on ovarian weight or on the morphological appearance of the ovaries. GnRH agonist treatment had no effect on the plasma concentrations of progesterone and oestrone in the maternal circulation or on the length of gestation. These results show (1) that GnRH positively regulates the synthesis and secretion of gonadotrophins in the fetus, (2) that reduced fetal gonadotrophic support during the last half of gestation results in a reduction in testicular growth, and (3) that fetal gonadotrophins do not affect maternal steroid secretion.

Journal of Endocrinology (1994) 141, 317–324
Characterization and localization of oxytocin receptors in the rat testis
Authors: Bathgate R A D , Sernia C
Published: December 2008

In this study oxytocin (OT) receptors have been characterized and localized in the testis of the rat using the radioiodinated OT receptor antagonist 125I-labelled d(CH2)5 [Tyr(Me)2,Thr4,Tyr9-NH2]-vasotocin (OTA). Receptor density and localization have been compared with the rat testis arginine vasopressin (AVP) receptor using the radioiodinated AVP V1a receptor antagonist 125I-labelled d(CH2)5Sar7-AVP and the radioiodinated linear AVP V1a antagonist 125I-labelled [(C6H5-CH2CO)-O-methyl-d-Tyr-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2]. 125I-labelled OTA bound with high affinity to membrane fractions of the rat testis (Ka = 13·8 ± 1·25 litres/nmol), mammary tissue (Ka=20·3± 4·36 litres/nmol) and uterus (Ka=27·8±0·74 litres/nmol). Competition studies with various OT and AVP receptor agonists and antagonists confirmed that the binding was to OT receptors. AVP receptors in the testis were found to be identical to AVP V1a receptors in the liver. The AVP receptor density in the testis was much higher than the OT receptor density (109 ±12·3 vs 5·2 ±0·79 (mean ± s.e.m.) fmol/mg protein). Autoradiographical localization showed that both OT and AVP receptors were present in the interstitial spaces in the testis consistent with binding to Leydig cells. AVP receptors were also localized on the epithelial surfaces of the seminiferous tubules and on testicular blood vessels. This study has, for the first time, found OT receptors in the testis of the rat which have similar ligand-binding characteristics to mammary and uterine OT receptors. The receptor localizations are consistent with binding to Leydig cells.

Journal of Endocrinology (1994) 141, 343–352
LH- and chorionic gonadotrophin-stimulated progesterone release in vitro by intact luteal tissue of the marmoset monkey (Callithrix jacchus)
Authors: Einspanier A , Hodges J K
Published: December 2008

The application of an in vitro microdialysis system (MDS) for studies on the gonadotrophic control of luteal progesterone secretion in the marmoset monkey is described. Luteal tissue collected from a total of six animals (9 ± 1 days after ovulation) was perfused with Ringer solution (without and with lipoprotein, 0·6 μg/ml). The tissue was exposed to repeated applications of human LH (hLH) and human chorionic gonadotrophin (hCG) (1, 10 and 100 IU/ml) each of 60 min duration. Perfusate was collected in 15-min fractions and assayed for progesterone content. Results showed that addition of lipoproteins to the Ringer solution had a marked effect on progesterone secretion in terms of maintaining stable baseline levels and improving reproducibility of gonadotrophin-induced responses. Progesterone secretion was significantly stimulated by both gonadotrophins at each dose tested. Maximal elevations were obtained with 10 IU/ml and there were no apparent differences in responses to hLH and hCG in terms of either magnitude or duration.

This study indicates that MDS provides a useful in vitro approach for studying the gonadotrophic control of the corpus luteum in non-human primates. The results did not demonstrate disparate actions of hLH and hCG in their ability to stimulate luteal progesterone secretion.

Journal of Endocrinology (1994) 141, 403–409
Enhancement of the granulation tissue formation in hairless mice by a potent vitamin D receptor agonist – KH 1060
Authors: Gniadecki R , Serup J
Published: December 2008

KH 1060 is a 20-epi analogue of 1,25-dihydroxyvitamin D3 and a potent agonist of the vitamin D receptor. Our recent finding that it stimulates glycosaminoglycan synthesis and transforming growth factor-β1 (TGF-β1) expression in normal skin provided a rationale for investigating its influence on the process of wound healing. Normal and betamethasone-impaired granulation tissue formation was studied in a polytetrafluoroethylene dead space model in hairless mice. The application of KH 1060 increased the indexes of fibroplasia and cellularity ([3H]thymidine incorporation and DNA concentration) of the betamethasone-impaired granulation tissue. Collagen production and deposition, measured as hydroxyproline synthesis and concentration in the granulation tissue, were also increased. The effect of KH 1060 on normal connective tissue repair was less pronounced; DNA and hydroxyproline concentrations in granulation tissue were unchanged. KH 1060 strongly stimulated the expression of TGF-β1 in betamethasone-impaired granulation tissue. Thus, it effectively reversed the deleterious effect of betamethasone on granulation tissue. The hyperproliferative response to this vitamin D analogue might be related to the direct stimulation of the vitamin D receptors in the granulation tissue, while the increased collagen synthesis and deposition was probably caused indirectly, via stimulation of TGF-β1.

Journal of Endocrinology (1994) 141, 411–415
Regulation of 11β-hydroxysteroid dehydrogenase activity by the hypothalamic-pituitary-adrenal axis in the rat
Authors: Walker B R , Williams B C , Edwards C R W
Published: December 2008

11β-Hydroxysteroid dehydrogenase (11β-OHSD) inactivates glucocorticoids and thereby modulates their access to both mineralocorticoid and glucocorticoid receptors. Since 11β-OHSD activity influences the biological responses of the hypothalamic-pituitary-adrenal axis, it might be regulated by components of this axis. We examined 11β-OHSD activity in adrenalectomized rats treated for 9 days with dexamethasone and with or without ACTH. Adrenalectomy and low-dose (2 μg/day) dexamethasone had no effect on 11β-OHSD activity in renal cortex, hippocampus or heart, and reduced enzyme activity in aorta. High-dose dexamethasone (50 μg/day) had no effect in renal cortex but increased enzyme activity by at least 50% in all other sites. This effect of dexamethasone was unaffected by the co-administration of ACTH. We also examined the metabolism of dexamethasone by 11β-OHSD in homogenized rat tissues. Only in kidney, in the presence of NAD rather than NADP, was dexamethasone converted to a more polar metabolite previously identified as 11-dehydrodexamethasone. We conclude that: dexamethasone induction of 11β-OHSD is tissue-specific, and includes vascular tissues and hippocampus but not kidney; this tissue-specificity may be explained by contrasting metabolism of dexamethasone by the isoforms of 11β-OHSD; fluctuations of glucocorticoid levels within the physiological range may not have a biologically significant effect on 11β-OHSD activity; and the inhibitory effect of ACTH, observed previously in humans, is likely to depend on the presence of intact adrenal glands.

Journal of Endocrinology (1994) 141, 467–472
Mastoparan, a wasp venom peptide, stimulates release of prolactin from cultured rat anterior pituitary cells
Authors: Mau S E , Witt M R , Vilhardt H
Published: December 2008

Studies have shown that mastoparan and other amphiphilic peptides induce exocytosis of hormones from anterior pituitary cells. We have studied the effect of mastoparan on the secretion of prolactin from cultured rat anterior pituitary cells and on the concomitant functional status of signal-transducing pathways in lactotroph-enriched cell cultures. Mastoparan stimulation of prolactin secretion was dose-dependent, time-dependent, reversible and required the presence of calcium. Pretreatment of pituitary cell cultures with cholera and pertussis toxin had no effect on the secretory response, whereas encapsulation of guanosine 5-[β-thio]diphosphate (GDP-β-S) by reversible electropermeabilization inhibited mastoparan-stimulated secretion. Incubation of mastoparan with myo[3H]inositol-labelled lactotroph-enriched anterior pituitary cell cultures resulted in increased formation of inositol phosphates compared with control cells, and encapsulation of GDP-β-S blocked mastoparan-induced inositol lipid hydrolysis. Mastoparan caused translocation of protein kinase C activity from a soluble to a membrane-attached form. Mastoparan was able to increase the intracellular Ca2+ concentration in Fura-2-loaded individual lactotrophs. Omission of Ca2+ from the extracellular medium did not change the Ca2+ response in lactotrophs when stimulated with mastoparan.

On the basis of these results it is concluded that mastoparan-induced release of prolactin is preceded by activation of the inositol(1,4,5)trisphosphate/diacylglycerol pathway with resulting translocation of protein kinase activity and increment in intracellular Ca2+. However, other signal-transducing pathways may be involved in the secretory process.

Journal of Endocrinology (1994) 142, 9–18
Potential role for lipoxygenase products of arachidonic acid in prostaglandin F2α-stimulated oxytocin release from the ovine corpus luteum
Authors: Cooke R G , Ahmad N
Published: December 2008

Intrauterine administration of nordihydroguaiaretic acid (NDGA) will maintain luteal function in sheep and also suppress the release of both oxytocin and prostaglandin F2α (PGF2α) suggesting that 5-lipoxygenase products of arachidonic acid may be involved in ovine luteolysis. During luteolysis, uterine PGF2α is considered to be the major stimulus for the secretion of luteal oxytocin, and we report the effects of 5-lipoxygenase inhibition, via intrauterine NDGA administration, on the ability of PGF2α to effect such secretion.

In the NDGA-treated ewes, luteal function was maintained and oestrus delayed, the duration of the oestrous cycle (20 ±1 days; mean ± s.d.; n=9) being significantly (P<0·01) longer than in intact controls (15 ± 1 days, n=4). Jugular infusions of PGF2α did not stimulate luteal secretion of oxytocin, the effects being comparable with those in ovariectomized ewes. In intact ewes receiving intrauterine infusions of vehicle only, PGF2α produced marked increases in luteal secretion of oxytocin. Also, preinfusion or basal concentrations of oxytocin in this group of ewes (6·6 ± 1·9 pg/ml) were significantly (P<0·01) greater than in either the NDGA-treated (3·1 ± 1·1 pg/ml) or ovariectomized (3·0 ± 0·6 pg/ml) ewes.

The results suggest involvement of 5-lipoxygenase products of arachidonic acid in the release of oxytocin from the ovine corpus luteum.

Journal of Endocrinology (1994) 142, 47–52
Effects of a polyclonal antiserum to rat growth hormone on circulating insulin-like growth factor (IGF)-I and IGF-binding protein concentrations and the growth of muscle and bone
Authors: Palmer R M , Loveridge N , Thomson B M , Mackie S C , Tonner E , Flint D J
Published: December 2008

A polyclonal antiserum to rat GH (anti-rGH) injected into rats for 3 or 8 weeks markedly reduced the weight, total protein and RNA content of muscles of the hind limb. These effects were prevented when bovine GH (bGH) was administered simultaneously.

In a second experiment, the effects of 8 weeks of treatment with anti-rGH on the growth of the whole body, muscle and bone were investigated. Body weights of rats were decreased by 58% by treatment with anti-rGH; muscle weights were reduced by slightly more than the decrease in body weight (by 64%, 65% and 61% respectively for plantaris, soleus and gastrocnemius). The weight of the tibia was decreased by 54%, its length was decreased by 23%, cortical width and overall width were reduced by 26% and 18% respectively, suggesting a possible role for GH in osteoclastic activity.

Serum total insulin-like growth factor-I (IGF-I) concentrations were decreased by 80–90% in both experiments by anti-rGH; these changes were prevented in the first experiment by concurrent treatment with anti-rGH and bGH. The serum IGF-binding protein-3 (IGFBP-3) concentration was also decreased by anti-rGH in experiment 1 (by 86%); the response of the 28-32 kDa IGFBPs was smaller (−35%), and was restored to control values by simultaneous injection of bGH. Western immunoblotting using an antiserum to IGFBP-2 showed that there was a marked decrease from neonatal to adult stages which was independent of anti-rGH treatment. This clearly demonstrated a dissociation of the reciprocal relationship supposed to exist between IGFBPs-2 and -3. The 24 kDa IGFBP-4 was unaffected by anti-rGH but replacement therapy with bGH doubled its concentration.

Although the effects on body and muscle weight were prevented when rats were given anti-rGH and bGH simultaneously, the possibility of mediation by other hormones cannot be precluded.

Journal of Endocrinology (1994) 142, 85–91
Comparison of ramp and square-wave exposure to thyrotrophin-releasing hormone or depolarizing K+ on cytosolic Ca2+ concentration and prolactin secretion in GH4C1 cells
Authors: Sato N , Wang X , Greer M A
Published: December 2008

The standard method of studying hormone secretion in vitro is to make instantaneous changes in the concentration of stimulators in the medium. However, in vivo the extracellular concentration of such substances changes more gradually; secretion does not occur in square-wave bursts and agonists or antagonists transmitted through the bloodstream are diluted and diffused by plasma or tissue fluid to further decelerate the rate of change in concentration at the cell surface. We have therefore compared in GH4C1 cells the dynamics of changes in cytosolic Ca2+ concentration ([Ca2+]i) and prolactin (PRL) secretion in response to two very different secretagogues, thyrotrophin-releasing hormone (TRH) and depolarizing K+, using a square-wave or ramp exposure for 5 min. The dynamics of hormone secretion were analysed by column perifusion (2 × 106 cells/column). Ca2+ dynamics were monitored by dual excitation microfluorimetry from 20–30 optically isolated cells using the Ca2+ indicator, fura-2. With square-wave exposure, both TRH (0·1–100 nm) and K+ (10–50 mm) induced dose-dependent increases in [Ca2+]i and PRL secretion. Concentrations of TRH >1 nm caused a two-phase increase in [Ca2+]i with an initial high-amplitude first phase and a low-amplitude second phase. Depolarizing K+ induced a sharp increase in [Ca2+]i which peaked within 15 seconds, then declined gradually on a sloping plateau. Both TRH and K+ induced an acute dose-dependent PRL secretory burst peaking within 2·5 min with a subsequent rapid decline. With ramp exposure, high doses of TRH (final concentration 10–100 nm) triggered an acute rise in [Ca2+]i; however, the peaks were clearly lower than those induced by the maximum concentration reached given as a square-wave. TRH (0·1–100 nm) induced PRL secretion in a dose-dependent manner. Ramp depolarizing K+ induced dose-dependent parallel 'ramp' increases in [Ca2+]i concentration and PRL secretion without a 'burst' rise in either. These data suggest that a rise in [Ca2+]i plays a more critical role in K+-induced than in TRH-induced PRL secretion; intracellular transduction systems which do not involve [Ca2+]i appear more important for the latter.

Journal of Endocrinology (1994) 142, 145–152
Determination of lignans and isoflavonoids in human female plasma following dietary supplementation
Authors: Morton M S , Wilcox G , Wahlqvist M L , Griffiths K
Published: December 2008

Plasma levels of the lignans enterodiol and enterolactone, and also the isoflavonic phyto-oestrogens daidzein, equol and genistein, are reported for postmenopausal Australian women consuming a traditional diet supplemented with linseed, soya flour or clover sprouts. Analysis was performed by gas chromatography-mass spectrometry, after enzymatic hydrolysis and ion-exchange chromatography. Following linseed supplementation, combined levels of enterolactone and enterodiol reached 500 ng/ml, whereas after soya flour or clover sprouts the respective concentrations of equol, daidzein and genistein reached 43, 312 and 148 ng/ml. Not all subjects were able to produce equol from daidzein. The possible relationship and role of these weak dietary oestrogens as restraining factors in the development of hormone-dependent cancers in Asian populations is discussed.

Journal of Endocrinology (1994) 142, 251–259
The hormonal regulation of the oestrogen receptor in rat liver: an interplay involving growth hormone, thyroid hormones and glucocorticoids
Authors: Freyschuss B , Sahlin L , Masironi B , Eriksson H
Published: December 2008

The regulation of the formation of the hepatic oestrogen receptor (ER) in adult female rats was studied by assaying steady state levels of ER and ER messenger RNA under different endocrine conditions. Hypophysectomy (HX) drastically reduced ER levels from 67·5 ± 7·9 to 8·4 ± 0·5 (means ± s.e.m.) fmol/mg cytosolic protein. Continuous infusion of growth hormone (GH) to HX animals tripled ER and doubled ER mRNA levels. Treatment with triiodothyronine T3) in a high dose (10 μg/day) doubled ER mRNA levels. The effects of T3 were dose-dependent, since a lower dose (1 μg/day) increased neither ER nor ER mRNA levels. ER mRNA concentrations were increased by GH to 481 ± 44% and by T3 to 372 ± 35% of HX control levels 4 h after single injections of the hormones in HX animals. The glucocorticoid dexamethasone (DEX) alone increased neither ER nor ER mRNA levels in HX animals. DEX and GH in combination increased ER 5-fold and ER mRNA 2-fold compared with control levels in HX animals, whereas DEX and T3 in combination increased neither ER nor ER mRNA levels. Treatment with prolactin affected neither ER nor ER mRNA levels in HX rats.

Insulin-like growth factor I (IGF-I) mRNA and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA levels were measured. GAPDH mRNA levels were increased 2·5-fold in HX rats by DEX and T3 in combination and almost 2-fold by DEX and GH in combination. IGF-I mRNA levels in HX rats were increased 4·5-fold by continuous infusion of GH alone, 6-fold by GH and T3 in combination, and 2·5-fold by GH and DEX in combination.

These data indicate that both GH and T3 act directly on the liver to increase ER mRNA levels. GH, the most important of these hormones, also acts at the translational and/or post-translational level to increase ER protein levels. DEX treatment suppresses the stimulatory effects of T3, but not of GH.

Journal of Endocrinology (1994) 142, 285–298
Evidence for the presence of pro-oxytocin/neurophysin-converting enzyme in the human ovary
Authors: Guillou M-D , Camier M , Clamagirand C
Published: December 2008

The activity of pro-oxytocin/neurophysin (pro-OT/Np)-processing enzymes was determined in human granulosa cells, follicular fluids and purified secretory granules of corpora lutea. We detected the presence of an endoprotease which releases OT-Gly10-Lys -Arg12 on cleavage of the synthetic pro-OT/Np(1–20) peptide after the dibasic Lys11-Arg12 doublet. This endoprotease was inhibited by EDTA, but was not affected by phenylmethanesulfonyl fluoride and pepstatin. Enzymatic activity was markedly reduced by replacement of l-Arg by d-Arg in the basic amino acid doublet of the substrate. The molecular weight of this enzyme was estimated to be 60 kDa. These features closely resembled those of the endoprotease identified in the bovine pituitary. The endoprotease is a metalloenzyme, specific for the Lys-Arg doublet. We also detected a carboxypeptidasic activity, inhibited by guanidinoethane-mercaptosuccinic acid. In the light of our previous detection of the processing intermediates, OT-Gly-Lys-Arg, OT-Gly-Lys and OT-Gly, in human ovary, these observations are in favour of a pro-OT/Np-processing pathway in the human ovary comparable with that in the bovine ovary. Moreover, these results confirm that oxytocin post-translational processing occurs in the human ovary and strongly suggest that pro-OT/Np is synthesized locally.

Journal of Endocrinology (1994) 142, 345–352
An investigation of the effects of interleukin-1β on plasma arginine vasopressin in the rat: role of adrenal steroids
Authors: Chover-Gonzalez A J , Lightman S L , Harbuz M S
Published: December 2008

While the effects of cytokines on the hypothalamo-pituitary-adrenal axis have received a great deal of attention in recent years the effects of cytokines on posterior pituitary hormone release has been less well characterized. In the present study we have investigated the effects of a single i.p. injection of interleukin (IL)-1β on circulating levels of vasopressin (AVP) in the rat. We have found that the ability of IL-1β to increase plasma AVP is strongly influenced by circulating levels of glucocorticoid steroids. IL-1β did not affect plasma AVP in sham-operated control animals over the 4 h period of study. In contrast, following adrenalectomy we were able to stimulate AVP substantially with increases over the 4 h period. This effect was reduced by treatment of adrenalectomized rats with a low dose of dexamethasone and abolished with a high dose. These data suggest an inverse relationship between circulating levels of glucocorticoids and the ability of IL-1β to stimulate plasma AVP.

Journal of Endocrinology (1994) 142, 361–366
The effects of recombinant human insulin-like growth factor-I (IGF-I) administration on the levels of IGF-I, IGF-II and IGF-binding proteins in adolescents with insulin-dependent diabetes mellitus
Authors: Cheetham T D , Taylor A , Holly J M P , Clayton K , Cwyfan-Hughes S , Dunger D B
Published: December 2008

Insulin-dependent diabetes mellitus (IDDM) during puberty is associated with a reduction in circulating concentrations of insulin-like growth factor-I (IGF-I) and low IGF bioactivity. Altered levels of the IGF-binding proteins (IGFBPs), including low IGFBP-3 and elevated IGFBP-1, have also been described. These abnormalities have been linked to poor growth and deteriorating blood glucose control. We have therefore examined the effects of recombinant human IGF-I (rhIGF-I) administration on the levels of IGF-I, IGF-II, IGFBP-1, IGFBP-3 and IGF bioactivity in a group of 9 late-pubertal adolescents with IDDM.

This was a double-blind placebo controlled study with each individual admitted on two occasions when either rhIGF-I (40 μg/kg) or placebo was administered by subcutaneous injection in the thigh at 1800 h. Blood samples were then taken for the subsequent 22 h. The half-life of administered rhIGF-I (12·1–22·2 h) was similar to that previously described in normal subjects. There was a small increase in IGFBP-3 concentrations overnight following rhIGF-I administration when compared to placebo, whereas the levels of IGF-II decreased. Under strict euglycaemic conditions, the relationship between insulin and IGFBP-I did not appear to be affected by rhIGF-I administration although the levels of IGFBP-1 tended to be higher overnight. IGF bioactivity was low during the placebo study, and although within the normal adult range following administration of IGF-I, was still relatively low for adolescents in late puberty. Gel filtration chromatography revealed an increase in the fractions corresponding to the 150 kDa complex throughout the duration of the study and to a lesser extent the fractions corresponding to free IGF-I which reached a maximum of 7% of total IGF-I levels. In conclusion, the subcutaneous administration of rhIGF-I in a dose of 40 pg/kg to a group of adolescents with IDDM led to a sustained increase in IGF-I levels and a rise in IGF bioactivity despite a fall in IGF-II and a trend towards higher IGFBP-1 concentrations.

Journal of Endocrinology (1994) 142, 367–374
Short-term oxytocin treatment increases bovine milk yield by enhancing milk removal without any direct action on mammary metabolism
Authors: Knight C H
Published: December 2008

The milk yield-enhancing effect of oxytocin administered either before or after milking was examined using a within-animal model. Eight cows in mid-lactation were changed from normal twice daily milking to a split-milking design, whereby half of the udder was milked at 0500 and 1500 h (control half; normal milking times), and the other half at 0800 and 1800 h (test half). This continued for 3 weeks. During the second week, oxytocin was administered as an i.m. injection immediately before the 0800 and 1800 h milkings. The test half was thus milked immediately after oxytocin administration, whilst the control half was milked 3 h before oxytocin. Milk yield decreased slightly on the adoption of split-milking. The decrease did not differ between udder halves and was not, therefore, due to inadequate milk-ejection in the test half compared with the control. During the week of oxytocin treatment, the yield decreased further in the control half but increased in the test half; consequently, the yield from the test half was significantly greater than that from the control half (P<0·05). The ratio of change in the test half relative to that in the control half was 1·12, significantly different from unity (P=0·002). Analysis of variance demonstrated a significant (P<0·001) interaction between udder half and oxytocin treatment, confirming that the effect of oxytocin was restricted to the test half, treated immediately before milking. This supports the established view that oxytocin acts by enhancing the milk-ejection reflex, and refutes a recent claim that the hormone has a direct stimulatory action on mammary metabolism.

Journal of Endocrinology (1994) 142, 471–473
The development of melatonin-binding sites in the ovine fetus
Authors: Helliwell R J A , Williams L M
Published: December 2008

The pineal hormone, melatonin, is important in the timing of seasonal reproduction in the sheep. Melatonin of maternal origin readily crosses the placenta; its function in the fetal sheep is, however, unclear. To gain an insight into the role of melatonin in ovine development we have identified specific melatonin receptors throughout gestation using 2-[125I]iodomelatonin and quantitative in vitro autoradiography. Specific binding was found at the earliest time studied at 30 days of gestation, over the developing thyroid (term=145 days). At 31 days of gestation specific labelling was found over the thyroid and pituitary glands, the spinal nerves, nasal cavity and developing bronchi. This binding was diminished by over 50% in the presence of 10−4 m GTPγS (an analogue of guanosine triphosphate) indicating that the 2-[125I]iodomelatonin binding at this early stage of gestation represents a receptor coupled to a regulatory G-protein. By 40 days of gestation specific binding was found over the nasal epithelium, cochlear epithelium, regions of the brain, especially the hind brain and the vestibulocochlear and glossopharyngeal nerves, and both the pars distalis and pars tuberalis of the pituitary. As gestation proceeded, labelling over the pars distalis appeared to become more scattered in nature while that on the pars tuberalis remained consistent. Saturation studies of both the neuronal and pituitary binding sites at 121 days of gestation and in the newborn lamb revealed a single class of high-affinity binding sites with Kd values in the picomolar range. Also at 121 days of gestation, binding over the fetal pars tuberalis was diminished in a dose-dependent manner by GTPγS, again confirming that specific binding is indicative of a receptor coupled to a regulatory G-protein. These data demonstrate a potential for sensitivity to melatonin from early in gestation, as well as the developmentally specific expression of the melatonin receptor in certain tissues, and suggest a wider role for melatonin in ovine fetal development than previously considered.

Journal of Endocrinology (1994) 142, 475–484
The evolution of changes in immunoreactive serum insulin-like growth factors (IGFs), IGF-binding proteins, circulating growth hormone (GH) and GH-binding protein as a result of short-term dexamethasone treatment
Authors: Miell J P , Buchanan C R , Norman M R , Maheshwari H G , Blum W F
Published: December 2008

Inhibition of growth in man and laboratory animals by glucocorticoid treatment is well recognized, yet we have previously shown that glucocorticoids may paradoxically enhance GH secretion and increase serum insulin-like growth factor (IGF) levels. IGFs circulate bound to high-affinity binding proteins (IGFBPs) which modulate their actions, and circulating GH may be associated with two binding proteins (GHBPs) of which the high-affinity GHBP has been characterized and is structurally identical to the extracellular domain of the GH receptor.

We have investigated the time-course of changes in GH, IGFs and their binding proteins induced by glucocorticoid treatment in normal male volunteers (n=12, age range 22–31 years) sampled at 0800 h daily before and during treatment with dexamethasone (2 mg twice daily) for 5 days. In addition, subjects were sampled at 30-min intervals over 7-h periods (0730–1430 h) during the day prior to dexamethasone (day 0), on day 1 following the first dose of dexamethasone and on day 5 following the last dose of dexamethasone. Mean serum IGF-I rose over the initial 72 h and remained elevated at 96 h (297 ± 11·5 compared with basal levels of 215·5 ± 9·3 μg/l, P<0·001) whereas IGF-II levels did not change (472·6 ± 20·5 vs 450·3 ± 21·7 μg/l, P=0·97). There was a concomitant rise in serum IGFBP-3 from basal levels of 3·69 ± 0·23 mg/l to a peak at 5 days of 4·16 ± 0·21 (P=0·003 vs day 1). Mean fasting IGFBP-1 levels fell significantly within 24 h, remaining low throughout the 5-day period whilst fasting insulin and C-peptide levels increased. IGFBP-2 rose within 24 h from basal levels of 315·5 ± 27·9 to 407·8 ± 27·3 μg/l at 24 h (P=0·01), then fell steadily to reach a nadir at 5 days of 240·4 ± 18·9 μg/l (P=0·02 vs basal levels). Peak GH secretion on day 1 (14·5 ± 3·7 μg/l) occurred between 4 and 5 h after dexamethasone administration. On day 5, the time of peak GH secretion was similar but the peak was attenuated (7·9 ± 1·2 μg/l, P<0·01 vs day 1). No morning rise in GH secretion had been observed prior to dexamethasone (day 0). GHBP fell steadily during the 5-day treatment period from basal levels of 29·3 ± 1·9% to day 5 levels of 24·4 1·6%, P=0·001.

The fall in GHBP as a result of dexamethasone treatment is in accordance with the reported inverse relationship between 24-h GH secretion and GHBP in health and disease states in man. This study has demonstrated clear temporal relationships between alterations in circulating levels of GH, IGF-I and IGFBP-1, -2 and -3 during dexamethasone treatment which support possible mechanisms whereby glucocorticoids induce a catabolic state through their endocrine and local tissue effects.

Journal of Endocrinology (1994) 142, 547–554
The effect of ovarian arterial infusion of transforming growth factor α on ovarian follicle populations and ovarian hormone secretion in ewes with an autotransplanted ovary
Authors: Campbell B K , Gordon B M , Scaramuzzi R J
Published: December 2008

Transforming growth factor α (TGFα) inhibits hormone production by cultured follicular cells but evidence of an effect of TGFα on ovarian hormone secretion in vivo is still required. Eleven ewes with an autotransplanted ovary received, by ovarian arterial infusion, either 5 μg/h recombinant rat TGFα (n=6) or placebo (n=5) for 12 h on day 10 of the luteal phase. Two hours before the start and 1 hour before the end of the infusion each ewe received a single injection of gonadotrophin-releasing hormone (GnRH; 150 ng i.v.). Two hours after the end of the infusion luteal regression was induced with prostaglandin F2α (PGF2α; 125 μg i.m.). Ovarian and jugular venous blood samples were taken at 10-min, 15-min or 4-h intervals from 2 h before the start of the infusion until 96 h after PGF2α and the rates of secretion of ovarian oestradiol, inhibin, progesterone and androstenedione were determined. Jugular venous concentrations of LH and FSH were also measured and follicle populations monitored by real-time ultrasound scanning.

Infusion of TGFα resulted in a significant (P<0.05) depression in the amplitude of the pulsatile response of oestradiol and androstenedione secretion to the GnRH-induced LH pulse at the end of the infusion. Ovarian inhibin secretion was acutely suppressed by TGFα infusion (P<0·001) and remained lower than controls for the period of the experiment. Luteal phase progesterone secretion was also acutely inhibited (P<0·001) by infusion of TGFα and in one treated ewe progesterone secretion was elevated 48–84 h after PGF2α. Jugular venous concentrations of FSH in TGFα-treated ewes were significantly (P<0·001) elevated over controls during the first 48 h of the follicular phase and the LH surge was delayed for about 10 h (P<0·05). Infusion of TGFα caused a marked decline (P<0·05) in the number of large follicles within 12 h of the end of the infusion. Two of the six treated ewes, including the one with high follicular phase progesterone, had unusually large (8·7 and 10 mm) follicles present from 48–96 h after PGF2α.

We conclude that direct arterial infusion of TGFα results in acute inhibition of ovarian steroid and inhibin secretion that is associated with induction of atresia in the population of large follicles. The lack of feedback of ovarian hormones results in a rebound increase of FSH which stimulates the growth of more ovarian follicles and the eventual re-establishment of ovarian hormone secretion and normal cyclicity.

Journal of Endocrinology (1994) 143, 13–24
Photoperiodic modulation of the dopaminergic control of pulsatile LH secretion in sheep
Authors: Tortonese D J , Lincoln G A
Published: December 2008

This study was conducted to investigate whether the photoperiodic regulation of the seasonal changes in pulsatile LH secretion in the ram involves changes in the activity of inhibitory hypothalamic dopaminergic (DA) pathways. To test this hypothesis, a series of experiments was carried out in Soay rams in which the effects of a DA-D2 receptor antagonist (sulpiride) or a DA-D2 receptor agonist (bromocriptine) on the pulsatile secretion of LH were determined under both long and short days. In each experiment blood samples were collected every 10 min for 8 h starting at the time of vehicle, sulpiride or bromocriptine injections to assess concentrations of LH. Sulpiride (0·59 mg/kg, s.c.) administered to rams under long days induced an immediate and sustained increase in the secretion of LH that lasted for approximately 4 h (P<0·05; ANOVA); this LH response reflected both a rise in mean concentrations (0·247 ± 0·03 vs.0·452 ± 0·1 μg/1) and an increase in the frequency of LH pulses (0·5±0·5 vs. 2·33±0·42 pulses/8 h; P<0·01). In contrast, under short days sulpiride had no effect. Bromocriptine (0·06 mg/kg, s.c.) administered to rams under long days, when LH concentrations were low, was without effect, but when given to rams under short days significantly (P<0·05) suppressed mean LH concentrations (0·627 ±0·08 vs. 0·320 ± 0·02 μg/l) and LH pulse frequency (4·86 ±0·46 vs. 2·43 ±0·37 pulses/8 h). In an additional experiment, pimozide (total dose: 0·16 mg/kg, i.m.), a DA antagonist less specific for DA-D2 receptors than sulpiride, was ineffective in modifying LH secretion in sexually inactive rams exposed to long days. These results are consistent with the hypothesis that an inhibitory dopaminergic system is involved in the regulation of pulsatile LH secretion in the ram. The induced changes in LH pulse frequency under long days (increased by sulpiride) and under short days (decreased by bromocriptine) indicate that, under both photoperiods, DA acts within the hypothalamus, via a specific DA-D2 receptor, to influence pulsatile GnRH secretion. A photoperiodic-induced activation of this inhibitory system may therefore represent the mechanism whereby long days suppress LH secretion and lead to the sexually inactive state characteristic of the non-breeding season.

Journal of Endocrinology (1994) 143, 25–32
Response of hepatic proteins to 3,5,3′-tri-iodo-l-thyronine in diabetic rats
Authors: Takeda T , Ichikawa K , Kobayashi M , Miyamoto T , Suzuki S , Nishii Y , Sakurai A , Nagasawa T , Katai M , Nakajima K , Hashizume K
Published: December 2008

In order to study whether peripheral action of thyroid hormones is altered in insulin deficiency and to elucidate the biological consequences of alteration of the cytosolic 3,5,3′-tri-iodo-l-thyronine (T3) binding protein (CTBP), we measured malic enzyme, T3-responsive nuclear n protein, CTBP and nuclear thyroid hormone receptor in the liver and kidney of streptozotocin (STZ)-induced diabetic rats that were treated with or without insulin and/or a receptor-saturating dose of T3. The following results were obtained. 1. Induction of malic enzyme by T3 was apparently diminished in diabetic rats. However, supplementary injection of insulin enabled previously given T3 to take effect in diabetic rats. 2. T3-responsiveness of other hepatic proteins (n protein and CTBP) was not altered by insulin in diabetic rats. 3. The level of n protein was increased by insulin in diabetic rats in vivo and in perfused rat liver, indicating that the hepatic n protein is a novel insulin-responsive protein. T3 and insulin increased the level of n protein non-synergistically in diabetic rat liver. 4. Hepatic nuclear receptor levels were not altered in diabetic rats. 5. Hepatic CTBP levels were decreased in diabetic rats. This was not due to the toxic effect of STZ. Low CTBP level was only partially increased by insulin after 30 days of diabetic period. Renal CTBP levels were not altered in diabetic rats with or without insulin treatment. These results indicate that reduction of CTBP did not influence the hepatic response to a receptor-saturating dose of T3, although CTBP may regulate the nuclear T3 transport, and that fundamental action of a receptor-saturating dose of T3 was not attenuated in diabetic rat liver.

Journal of Endocrinology (1994) 143, 55–63
Expression of the endothelin-1 gene in the rat thyroid gland and changes in its peptide and mRNA levels in goiter formation and iodide-induced involution
Authors: Colin I M , Selvais P L , Rebai T , Maiter D M , Adam E , vandenHove M-F , Ketelslegers J-M , Denef J-F
Published: December 2008

Endothelin-1 (ET-1) is a major vasoconstrictor peptide, first found in endothelial cells, and later in many other tissues, including the thyroid gland. We analysed the expression of the ET-1 gene in the rat thyroid gland and changes in ET-1 mRNA and peptide levels in goiter development and involution, two circumstances characterised by vascular changes.

Thyroid hyperplasia was induced in adult Wistar rats by feeding a low iodine diet (LID) supplemented with 0·25% thiouracil for 10 days, and LID alone for 2 further days (H.12 group). Involution was induced by injecting 100 μg iodide and refeeding a normal diet during 6 h, 12 h, and 24 h (I.6h, I.12h, 1.24 h groups). Rats fed a normal iodine diet were used as controls.

A specific 488 bp cDNA corresponding to the known sequence of pre-pro ET-1 was found by RT-PCR from RNA extracts in all thyroid experimental groups, as well as in lung and kidney which were used as positive controls. RP-HPLC analysis showed that ET-1 immunoreactivity eluted similarly as mature ET-1

During hyperplasia, ET-1 mRNA and peptide levels were increased 3·5- and 5-fold respectively. The relative volume of the vascular bed was more than doubled. During iodide-induced involution, the glandular ET-1 mRNA level remained elevated. The concentration of ET-1 peptide increased and was significantly greater at 12 h involution than in the H.12 group. At this time, the capillary reticulum reverted to individual capillaries and the vascular bed was significantly reduced.

These data demonstrate that the ET-1 gene is expressed in the rat thyroid gland and that the ET-1 mRNA and peptide levels are increased during thyroid hyperplasia and remain elevated during a phase of rapid iodide-induced involution. These data suggest that changes in ET-1 production may play a role in control of thyroid gland trophic regulation and vascularity.

Journal of Endocrinology (1994) 143, 65–74
Prolactin- and testosterone-induced inhibition of LH secretion after orchidectomy: role of preoptic and tuberoinfundibular γ-aminobutyric acidergic neurones
Authors: Grattan D R , Selmanoff M
Published: December 2008

The inhibitory amino acid neurotransmitter γ-amino-butyric acid (GABA) may play an important role in the regulation of LH-releasing hormone secretion. The present study examined the effect of prolactin on GABAergic neuronal activity in microdissected brain regions of the orchidectomized rat, to determine whether inhibition of LH secretion after castration by acute hyperprolactinaemia was associated with prolactin-induced changes in GABAergic neuronal activity. The effects of prolactin were contrasted with the effects of testosterone on hypothalamic GABAergic neurones after orchidectomy. GABA concentrations were measured by high pressure liquid chromatography in eight microdissected brain regions in untreated rats and 60 min after inhibition of the GABA catabolic enzyme GABA transaminase by injection of amino-oxyacetic acid (AOAA). The rate of GABA accumulation in microdissected brain regions following injection of AOAA was taken as an index of GABAergic neuronal activity.

Rats were divided into seven experimental groups: intact controls, 2 days after castration, 2 days after castration with prolactin treatment (2·5 mg ovine prolactin injected s.c. every 12 h, starting at the time of castration), 2 days after castration with testosterone replacement (30 mm silicone elastomer implant containing crystalline testosterone), 6 days after castration, 6 days after castration with prolactin treatment, and 6 days after castration with testosterone replacement. Both 2 and 6 days after castration, plasma LH was markedly elevated above levels in intact rats, and AOAA-induced GABA accumulation was significantly decreased in the diagonal band of Broca at the level of the organum vasculosum of the lamina terminalis, in the medial preoptic nucleus and in the median eminence. Hyperprolactinaemia significantly reduced LH levels 2 days but not 6 days after castration. GABAergic neuronal activity, however, was not significantly affected by prolactin at either time. Testosterone replacement blocked the postcastration elevation in plasma LH and prevented the castration-induced suppression of GABAergic neuronal activity both 2 and 6 days after castration. There were no castration- or hormone-induced changes in GABAergic neurones observed in the medical or lateral septum, caudate nucleus, cingulate cortex or arcuate nucleus.

These results demonstrate that the activity of GABAergic neurones terminating in the rostral hypothalamus and the median eminence is positively regulated by testosterone, and that these steroid-sensitive GABAergic neurones may be important in the negative-feedback control of LH secretion. Inhibition of LH secretion by hyperprolactinaemia, however, may not be mediated by changes in GABAergic neuronal activity.

Journal of Endocrinology (1994) 143, 165–174
Production rate, metabolic clearance rate and uterine extraction of corticosterone during rat pregnancy
Authors: Waddell B J , Atkinson H C
Published: December 2008

This study examined changes in the blood concentration of corticosterone with the onset and progression of pregnancy in the rat. To identify the source of variation in blood corticosterone, the metabolic clearance rate (MCR) and production rate of corticosterone were also determined. Measurements were made in conscious rats (n=4–7 per group) in the morning of dioestrus and days 5, 10, 16 and 22 of pregnancy (term=day 23). Corticosterone levels were 713 ±38 nmol/l (mean±s.e.m.) in non-pregnant rats, remained unchanged to day 10 of pregnancy, then increased to 1036 ± 52 nmol/l by day 16 and remained high at day 22. The production rate of corticosterone appeared to increase during pregnancy from 25·6±1·7 μmol/day on day 10 to reach 36·3±3·3 mol/day on day 22, but this did not reach statistical significance (one-way ANOVA). The MCR of corticosterone was similar among all groups (overall mean 34·6±2·5 1/day), although a slight but non-significant fall was apparent at day 16. When account was taken of changes in maternal weight, the MCR decreased progressively from 139± 10 1/day per kg before pregnancy to reach a minimum of 88 ±7 1/day per kg on day 16. Transuterine extraction of corticosterone on day 22 of pregnancy was 19·2±3·1% and so, based on this and estimates of uterine blood flow, the uterus must account for around 15% of corticosterone clearance at this time. Because this uterine contribution is effectively additional clearance, it is likely that without it the MCR of corticosterone would have fallen during pregnancy. Administration of ACTH (1–24) (3·5 nmol) increased the production rate of corticosterone at dioestrus and at day 16 of pregnancy, but this effect was less marked in the pregnant group (134% and 41% increase respectively). The MCR of corticosterone also rose (17%) following ACTH(1–24) administration in pregnant but not dioestrous rats. This difference in the MCR response is likely to reflect pregnancy-induced changes in the relative levels of corticosterone, progesterone and corticosteroid-binding globulin.

In conclusion, this study shows that blood levels of corticosterone increase progressively during pregnancy in conscious rats. This increase apparently resulted from the net effects of increased production and decreased MCR, neither of which reached statistical significance. It would appear, however, that the trend toward increased production of corticosterone contributes more to the rise in blood corticosterone than does MCR, since the latter was more effectively maintained at pre-pregnancy levels. The demonstration of significant transuterine extraction of corticosterone at day 22 suggests that the maintenance of corticosterone clearance late in pregnancy is due, in part, to an additional contribution by the uterus and its contents.

Journal of Endocrinology (1994) 143, 183–190