bluuebunny/crossref_metadata_2025 huggingface dataset:
Actions of somatotrophin on oxytocin and progesterone release from the microdialysed bovine corpus luteum in vitro
Authors: Liebermann J , Schams D
Published: December 2008

In the present investigation, the effect of recombinant (BST) and pituitary-derived (bGH) bovine somatotrophin on progesterone and oxytocin release was examined. Individual copora lutea (CL) were obtained from cows at different stages of the oestrous cycle (days 5–7, 8–12 and 15–18) and also from early pregnancy (days 60–120) and were implanted with an in vitro microdialysis system (MDS).

Perfusion with BST for 60 min (005, 0·5 and 5 μmol/l) induced a dose-dependent stimulation of progesterone release. Release of oxytocin from CL was significantly stimulated by BST at all dose levels. BST (0·5 μmol/l) stimulated progesterone release most during the early and mid-luteal phases and oxytocin release especially during the early luteal stage (days 5–7) of the oestrous cycle. CL from early pregnancy (days 60–120) treated with BST showed a significant response in progesterone and oxytocin release. bGH showed comparable effects.

Our results suggest that somatotrophin acts directly on the secretory function of bovine CL in the MDS, specifically during the early luteal stage (days 5–7) of the oestrous cycle and early pregnancy (days 60–120). Somatotrophin may therefore have physiologically relevant effects associated with the development and maintenance of luteal function.

Journal of Endocrinology (1994) 143, 243–250
Thyroid iodide transport is reduced by administration of monoamine oxidase A inhibitors to rats
Authors: Cabanillas A M , Masini-Repiso A M , Costamagna M E , Pellizas C , Coleoni A H
Published: December 2008

The present work was addressed to study a possible relationship between monoamine oxidase (MAO) and the thyroid iodide transport mechanism.

Normal rats treated with clorgyline (a selective MAO-A inhibitor) or tranylcypromine (a non-selective MAO inhibitor) showed a significantly diminished thyroid MAO activity, while deprenyl and pargyline (MAO-B inhibitors) did not modify the thyroidal enzyme activity with respect to the control group. Under these conditions, in vivo iodide transport was reduced both by clorgyline and tranylcypromine administration whereas it remained unchanged after treatment with MAO-B inhibitors.

The effect of MAO inhibitors on thyroid MAO activity and in vivo iodide transport was also evaluated in rats treated with exogenous thyrotrophin (TSH) after endogenous TSH secretion blockade produced by T4 administration. In this condition, thyroid MAO activity was significantly lowered by clorgyline and was not modified by deprenyl. In contrast to the results observed in normal rats, in vivo iodide transport in TSH-treated rats remained unaltered after treatment either with clorgyline or deprenyl.

MAO activity evaluated in bovine thyroid follicles in primary culture was highly sensitive to low concentrations of clorgyline (<10 nmol/l) and relatively insensitive to deprenyl, a finding that indicates a predominance of the MAO-A isoform in the follicular cells in culture. When clorgyline (0·1 and 1 μmol/l) or deprenyl (1 μmol/l) were added to the culture medium, no modifications in the active transport of iodide were observed.

These results indicate the absence of a direct linkage between thyroid MAO activity and the active iodide transport. MAO inhibitors (particularly MAO-A inhibitors) do not appear to be responsible for an in vivo diminished thyroid iodide uptake through a direct action on the iodide transport mechanism. An indirect effect of MAO-A inhibitors on thyroid iodide transport mediated by the accumulation of monoamines in neuroendocrine areas involved in TSH regulation is suggested.

Journal of Endocrinology (1994) 143, 303–308
Maternal plasma levels of human chorionic gonadotrophin, oestradiol and progesterone in multifetal pregnancies before and after fetal reduction
Authors: Johnson M R , Abbas A , Nicolaides K H
Published: December 2008

The aim of the study was to investigate the circulating levels of human chorionic gonadotrophin (hCG), oestradiol (OE2) and progesterone in multifetal pregnancies before and after embryo reduction. The levels of hCG, OE2 and progesterone were measured in plasma samples obtained from two groups of pregnant women: (i) singleton (n=17), twin (n=15) and triplet (n=15) pregnancies achieved following superovulation; and (ii) multifetal pregnancies (three to ten embryos) undergoing fetal reduction to twin pregnancies (n=31). The median value for each analyte at each gestational age in twin pregnancies was defined and used to derive multiples of the median (MoMs) for each analyte in samples obtained from multifetal pregnancies before and after reduction. The levels of hCG, OE2 and progesterone were significantly associated with the number of fetuses. Prior to reduction, the median MoMs for hCG, OE2 and progesterone were 154, 0·99 and 1·11 respectively. After reduction to twins the median MoMs decreased to 0·84 for hCG, 0·37 for progesterone and 0·51 for OE2. These data suggest that (i) the circulating levels of hCG, OE2 and progesterone increase with conceptus number; (ii) placental tissue does not remain active following fetal reduction; and (iii) the rate of steroid metabolism is increased in multiple pregnancy and remains elevated following fetal reduction.

Journal of Endocrinology (1994) 143, 309–312
The role of prolactin in the reactivation of hair follicles in relation to moulting in cashmere goats
Authors: Dicks P , Russel A J F , Lincoln G A
Published: December 2008

The effects of the suppression or elevation of plasma prolactin concentrations in spring on the timing of the reactivation of the hair follicles and the timing of the spring moult were investigated in cashmere goats. Thirty eight adult female goats, housed under conditions of natural photoperiod at 55°55′N from mid-December until May, were allocated to four groups starting on 5 January: ten served as untreated controls, eight received 2 mg ovine prolactin subcutaneously every 12 h for 7 weeks (PRL), twelve received 35 mg bromocriptine intramuscularly every 14 days for 17 weeks (BCR) and eight received injections of both ovine prolactin and bromocriptine at the above dose rates for 7 weeks (PRL+BCR). In the PRL group there was an earlier reactivation of the secondary hair follicles (PRL vs control, proportion of secondary follicles in anagen, weeks 1–5, P<0·01) associated with an earlier moult of secondary fibres (cashmere) but no significant difference in the activity of the primary hair follicles. In the BCR group there was a delay in the reactivation of both the secondary and primary hair follicles (BCR vs control, proportion of secondary and primary hair follicles in anagen, weeks 5–13, P<0·01) and a delay in the moult. In the PRL+BCR group there was an early reactivation and moult similar to the PRL group. Voluntary food intake (VFI) and liveweight were also measured. Only in the BCR group was there a decrease in VFI compared with the controls but with no effect on liveweight. It was concluded that the seasonal increase in prolactin secretion which normally occurs in spring is causally involved in the reactivation of primary and secondary hair follicles and moulting in cashmere goats.

Journal of Endocrinology (1994) 143, 441–448
11β-Hydroxysteroid dehydrogenase in the rat placenta: developmental changes and the effects of altered glucocorticoid exposure
Authors: Burton P J , Waddell B J
Published: December 2008

The enzyme 11β-hydroxysteroid dehydrogenase (11β-HSD) catalyses the interconversion of corticosterone, the major glucocorticoid of the rat, and the biologically-inactive 11-dehydrocorticosterone. In the placenta, 11β-HSD is thought to regulate glucocorticoid transport between maternal and fetal compartments, and may also affect the local action of glucocorticoids. The present study assessed whether 11β-dehydrogenase (corticosterone to 11-dehydrocorticosterone) and 11-oxoreductase (11-dehydrocorticosterone to corticosterone) activities are both present in rat placenta, and whether these activities change with advancing pregnancy. Enzyme activity was estimated on days 16, 19 and 22 of pregnancy (term=day 23) in placental fragments incubated for 6 h with either [3H]corticosterone or [3H] 11-dehydrocorticosterone. The percentage conversion of these substrates to [3H] 11-dehydrocorticosterone and [3H] corticosterone, respectively, were determined at the end of the incubation. Both 11-oxoreductase and 11β-dehydrogenase activities were clearly evident in placental tissue fragments, and while 11-oxoreductase activity declined with advancing pregnancy (P<0·01), 11β-dehydrogenase activity increased (P<0·01). Thus, 11-oxoreductase exceeded (P<0·05) 11β-dehydrogenase at day 16, but thereafter activities were similar. These changes do not appear to be glucocorticoid-induced, since pretreatment of rats with either metyrapone or dexamethasone acetate from day 15 of pregnancy did not affect placental 11β-HSD on day 22. To allow comparison with earlier studies, estimates of 11β-HSD were also made in placental homogenates at each stage of pregnancy. In contrast to observations in placental fragments, 11β-dehydrogenase was always the dominant reaction in homogenates, presumably due to the loss of 11-oxoreductase activity following tissue homogenisation.

These data demonstrate that net 11β-dehydrogenase activity in the rat placenta increases towards term, thereby increasing the capacity for placental inactivation of active glucocorticoid. This pattern of 11β-HSD is consistent with reduced transfer of active glucocorticoid between the mother and fetus near term, and thus should promote independence of their hypothalamic-pituitary-adrenal axes.

Journal of Endocrinology (1994) 143, 505–513
Changes of calmodulin concentration and cyclic 3′, 5′-nucleotide phosphodiesterase activities in cardiac muscle of hyper- and hypothyroid rats
Authors: Mano T , Iwase K , Sawai Y , Oda N , Nishida Y , Mokuno T , Itoh Y , Kotake M , Masunaga R , Nakai A , Tujimura T , Nagasaka A , Hidaka H
Published: December 2008

To investigate the effect of thyroid hormone on cardiac muscle dysfunction in hyper- and hypothyroid states, we evaluated cyclic 3′, 5′-nucleotide metabolism by measuring cyclic 3′, 5′-nucleotide phosphodiesterase activity and calmodulin concentrations in the cardiac muscles of hyper- and hypothyroid rats.

Cyclic AMP (cAMP) concentration was significantly high in the cardiac muscle of hyperthyroid rats and low in that from hypothyroid rats compared with control rats. Cyclic AMP and cyclic GMP phosphodiesterase activities were significantly decreased in the soluble fraction of cardiac muscle from hyperthyroid rats and markedly increased in this fraction in hypothyroid rats compared with normal animals. Calmodulin concentration was high in hyperthyroid and low in hypothyroid rats.

It was concluded from these findings that low cAMP-phosphodiesterase activity might, in part, bring about the high concentration of cAMP. Calmodulin was sigificantly high in the cardiac muscle of hyperthyroid rats and the reverse was the case in hypothyroid rats compared with normal rats. The implication is that, in hyper- and hypothyroid states, these changes may play an important role in cardiac function via their effect on cyclic nucleotide and Ca2+ metabolism.

Journal of Endocrinology (1994) 143, 515–520
EVIDENCE FOR A NOVEL SOURCE OF RELAXIN: ATRIAL CARDIOCYTES
Authors: Taylor Michael J. , Clark Cheryl L.
Published: December 2008

Antibody-directed, complement-induced erthrocyte lysis (reverse hemolytic plaque assay) around atrial cardiocytes was used to determine whether this cell type possesses the capacity to secrete the insulin-like hormone relaxin. After 2h of incubation, 33 ± 4% (n = 3) of cardiocytes derived from the atria of neonatal rats secreted detectable amounts of immunoreactive relaxin (i.e. formed plaques) when cultured in monolayers. Increased culture time of cardiocytes failed to increase the fraction of cardiocytes that secreted relaxin. The cumulative amount of relaxin secreted after 3h of incubation (plaque area) was 31% greater (P < 0.05) than the amount of hormone present after lh of incubation, evidence of sustained peptide secretion by cultured cardiocytes. These data suggest that the source of the endogenous ligand for the specific and high-affinity relaxin receptors located in rat atria is the atrial cardiocyte itself. Therefore, relaxin may act via autocrine and/or paracrine routes to regulate cardiovascular structure and/or function.
Porcine thyroid follicular cells in monolayer culture activate the iodide-responsive precursor form of transforming growth factor-β1
Authors: Cowin A J , Bidey S P
Published: December 2008

The release of latent transforming growth factor-β1 (TGFβ1), and conversion to the biologically active peptide, has been investigated in porcine thyroid follicular cells maintained in primary monolayer culture. Analysis by radioreceptor assay of medium conditioned for 72 h by subconfluent thyroid monolayers showed that a high proportion of the expressed TGF-β1 peptide was in the active form. Medium conditioned by iodide (10 aμmol/l)treated follicular cells contained higher levels of both active and total TGF-β1 than were present in medium conditioned by untreated cells. Exposure of cells to iodide also led to a marked decrease in [methyl-3H]thymidine incorporation that was relieved by immunoadsorption with a neutralizing antiserum against the active form of TGFβ1. Inclusion of a low dose (80 units/l) of porcine plasmin led to a small increase in incorporation of [methyl3H]thymidine, while higher doses of plasmin (1250–5000 units/l) or plasminogen (100 mg/l) significantly reduced [methyl-3H]thymidine incorporation. This inhibition was effectively reversed by immunoadsorption of TGF-β1 from the medium during the test incubations. The study therefore provides direct evidence for a stimulatory role of thyroidal iodide in enhancing the release of latent TGF-β1 peptide, and suggests that in normal thyroid follicular cells, as in other TGF-β1 producing epithelia, post-secretory processing to the biologically active molecule occurs through an endogenous cellular mechanism. It appears likely that plasmin, generated locally within the thyroid follicular microenvironment, may play a fundamental role in effecting this conversion.

Journal of Endocrinology (1995) 144, 67–73
Effect of actively immunizing sheep against growth hormone-releasing hormone or somatostatin on spontaneous pulsatile and neostigmine-induced growth hormone secretion
Authors: Magnan E , Mazzocchi L , Cataldi M , Guillaume V , Dutour A , Dadoun F , Le Bouc Y , Sauze N , Renard M , Conte-Devolx B , Oliver C
Published: December 2008

The physiological role of endogenous circulating GHreleasing hormone (GHRH) and somatostatin (SRIH) on spontaneous pulsatile and neostigmine-induced secretion of GH was investigated in adult rams actively immunized against each neuropeptide. All animals developed antibodies at concentrations sufficient for immunoneutralization of GHRH and SRIH levels in hypophysial portal blood. In the anti GHRH group, plasma GH levels were very low; the amplitude of GH pulses was strikingly reduced, although their number was unchanged. No stimulation of GH release was observed after neostigmine administration. The reduction of GH secretion was associated with a decreased body weight and a significant reduction in plasma IGF-I concentration. In the antiSRIH group, no changes in basal and pulsatile GH secretion or the GH response to neostigmine were observed as compared to controls. Body weight was not significantly altered and plasma IGF-I levels were reduced in these animals. These results suggest that in sheep, circulating SRIH (in the systemic and hypophysial portal vasculature) does not play a significant role in pulsatile and neostigmine-induced secretion of GH. The mechanisms of its influence on body weight and production of IGF-I remain to be determined.

Journal of Endocrinology (1995) 144, 83–90
Endotoxin administration decreases plasma insulin-like growth factor (IGF)-I and IGF-binding protein-2 in Angus × Hereford steers independent of changes in nutritional intake
Authors: Elsasser T H , Caperna T J , Rumsey T S
Published: December 2008

Endotoxemia and sepsis cause severe shifts in metabolism towards catabolic events. The objective of the research was to determine whether endotoxin administration changes plasma concentrations of IGF-I and IGF-binding protein-2 (IGFBP-2) in Angus × Hereford steers. In Experiment 1, mean feed intake in endotoxin-treated steers (n=6) decreased 60% within the first 24 h after endotoxin and averaged, for the duration of the 96 h test period, an intake 35·5% lower than the mean ad libitum intake recorded prior to endotoxin. Plasma concentrations of IGF-I averaged 182 ng/ml in steers before endotoxin (E. coli, 055:B5, 0·2 μg/kg, i.v. bolus) and decreased an average of 24·2% at 24 to 96 h after endotoxin. In Experiment 2, a paired feeding strategy was used to determine whether the reduced feed intake was a significant factor in changing plasma concentrations of IGF-I and IGFBP-2 after endotoxin challenge. Steers were divided into endotoxin (0·2 μg/kg, i.v., n=6) or control (saline, n=6) n=3) treatments. Each of three endotoxin-treated steers was paired to a specific control. In this fashion, the adjusted feed intake of each endotoxin-treated steer was fed to it's paired control every 24 h through 96 h after endotoxin. After endotoxin, plasma concentrations of tumour necrosis factor-α (TNF) and cortisol peaked at one and three hours, respectively. TNF returned to baseline by 8 h while cortisol returned to baseline by 24 h. Feed intake declined 60% at 24 h in endotoxin-treated steers but returned to normal by 96 h. Plasma IGF-I remained more than 28% lower in endotoxin-treated steers than in control steers through 96 h (P<0·05). IGFBP-2 was 61% lower in endotoxin-treated than control steers at 24 h (P<0·05) and gradually returned to normal levels by 96 h. The level and duration of feed offered pair-fed control steers did not affect any measured parameter. The data suggest that decreases in plasma IGF-I and IGFBP-2 which occur after endotoxin administration are not fully explained by transient changes in nutrient intake and may constitute a part of the mechanism underlying shifts in metabolism that accompany endotoxemia. The partitioning of IGFs to tissues by altered patterns of IGFBPs may be another mechanism through which the classical anabolic character of IGF-I is modified during acute disease stress.

Journal of Endocrinology (1995) 144, 109–117
Effect of bovine GH and ovariectomy on mammary tissue sensitivity to IGF-I in prepubertal heifers
Authors: Purup S , Sejrsen K , Akers R M
Published: December 2008

Sixteen prepubertal Holstein Friesian heifers were used to study the effect of long-term administration of bovine GH (bGH; 15 mg/day for 15 weeks) and ovariectomy (at 2·5 months of age) on GH and IGF-I receptors in mammary and liver parenchymal tissue. Heifers were slaughtered on the day after the last injection of bGH or excipient. Mammary and liver parenchymal tissue was collected for preparation of crude membranes for ligand-binding assays.

Specific binding of [125I]IGF-I to mammary membranes increased linearly with increasing membrane protein concentration and was displaced by IGF-I, less effectively by IGF-II and least effectively by insulin. Linear Scatchard plots were obtained showing the presence of a single class of high-affinity binding sites for IGF-I in prepubertal mammary tissue. Specific binding of IGF-I was unaffected by bGH treatment but tended to be higher (P<0·10) in membranes from ovariectomized heifers. Hepatic binding of GH and IGF-I was unaffected by bGH treatment and ovariectomy. However, specific binding of GH tended to be lower (P<0·06) in liver tissue from bGH-treated intact heifers compared with control heifers.

The present study confirms the presence of IGF-I receptors in prepubertal mammary tissue in agreement with the suggested involvement of IGF-I in the mechanism of action of GH on mammary glands in this period. The results, however, indicate that the stimulatory effect of GH on mammary growth is mediated via increased serum concentration of IGF-I and not by increased IGF-I binding to its mammary receptors. The present study furthermore gave no clear evidence of an interaction between ovarian secretions and GH on IGF-I receptors in mammary tissue.

Journal of Endocrinology (1995) 144, 153–158
IGF-I and IGF-II receptors in the sheep placenta: evolution during the course of pregnancy
Authors: Lacroix M C , Servely J L , Kann G
Published: December 2008

The role of IGFs in placental growth is poorly understood. IGF-II receptors have been characterised in the ovine placenta and used extensively for radioreceptor assay, but their evolution during placental development has not been considered. In this study, binding sites for IGF-I were characterised in the ovine cotyledon by binding and cross-linking studies and the evolution of the number of IGF-I and IGF-II receptors on placentae collected on days 50, 75, 100 and 140 of pregnancy were compared. IGF-I bound onto placental membranes with a mean association constant of 1·7 nm−1 except on day 50 when a lower association constant was observed (0·8 nm−1). Scatchard analysis of the displacement curves led to a single binding site model. IGF-II was as potent as IGF-I at displacing the binding of 125I-labelled IGF-I on those membranes, whereas insulin cross-reaction was only 1%. IGF-II bound on our placental membrane preparations with the characteristics described previously and neither IGF-I nor insulin was able to displace this binding. Affinity cross-linking studies followed by SDS-PAGE under reducing conditions demonstrated that IGF-I was linked to a protein with a molecular weight of about 135 000 Da and IGF-II to a protein of 250 000 Da. The mean ± s.e.m. number of IGF-I receptors was significantly higher on days 50 and 75 than on days 100 and 140 (154 ± 12, 105 ± 11 vs 65 ±4, 48 ±3 fmol/mg, P<0·01). The number of IGF-II receptors followed the same pattern and also showed a decrease towards the end of the pregnancy that was significant (P<0·01) only by day 140 (days 50 and 75, 1 ± 0·08; day 100, 0·75 ±0·04; day 140, 0·51 ± 0·03 pmol/mg). IGF-I receptors were observed in the trophoblast cells of cotyledons removed on day 40 whereas IGF-II receptors were observed in mesodermal cells. These data suggest that IGFs are involved in the placental growth and differentiation processes and that some effects of IGF-II are probably mediated by IGF-I receptors.

Journal of Endocrinology (1995) 144, 179–191
Induced luteal regression: differential effects on follicular and luteal inhibin/activin subunit mRNAs in the marmoset monkey
Authors: Fraser H M , Lunn S F , Whitelaw P F , Hillier S G
Published: December 2008

During the luteal phase of the primate ovulatory cycle the predominant inhibin/activin subunit mRNAs produced by the corpus luteum and antral follicles are those for the α- and βB-subunits respectively. The control of expression of these mRNAs and the resultant nature of the endocrine and paracrine signals which they may potentially generate has yet to be elucidated. Inhibin/activin subunit mRNAs may have a role in both the paracrine regulation of follicular and luteal function and modulation of FSH secretion. The aim of this study was to investigate the expression of inhibin/activin subunit mRNAs following luteal regression induced by either withdrawal of LH support (GnRH antagonist treatment), or by a direct inhibitory action (prostaglandin administration). Marmoset monkeys with regular ovulatory cycles were treated on day 8 and 9 of the luteal phase with either GnRH antagonist, prostaglandin or vehicle (n=3 per group). Ovaries were studied 48 h after onset of treatment (on day 10 of the luteal phase) by hybridizing frozen tissue sections with radiolabelled riboprobes specific to the inhibin/activin α-, βA- and βB-subunit mRNAs. After autoradiographic exposure, grain concentrations were quantified by image analysis. In corpora lutea from control marmosets there was high expression of α-mRNA with only marginal expression of βB-mRNA. Corpora lutea in animals treated with GnRH antagonist or prostaglandin had markedly reduced expression of α-mRNA while βB-mRNA was unchanged. In controls, all healthy antral follicles exhibited a high level of expression of βB-mRNA in the granulosa cells and low expression of α-mRNA in theca cells. This was unaffected by either treatment. βA-mRNA was found at a low level in granulosa cells but was not evident at a significant level in the corpora lutea of any of the groups. These results demonstrate (1) the marmoset corpus luteum is a source of high expression of α-subunit mRNA, (2) this α-mRNA is dependent upon LH support, (3) the process of luteal regression takes place without alteration of βB-mRNA. Antral follicle α- and βB-mRNAs are independent of the process of luteal regression or gonadotrophic withdrawal during the period of the luteal-follicular phase transition.

Journal of Endocrinology (1995) 144, 201–208
Ontogeny and ultradian rhythms of adrenocorticotropin and cortisol in the late-gestation fetal horse
Authors: Cudd T A , LeBlanc M , Silver M , Norman W , Madison J , Keller-Wood M , Wood C E
Published: December 2008

Fetal maturation and the timing of parturition in both sheep and primates are thought to be controlled by the hypothalamic-pituitary-adrenal axis but little is known about the endocrinology of the equine fetus. We investigated the ontogeny of plasma concentrations of adrenocorticotropic hormone (ACTH), cortisol and corticosteroid binding capacity in the late-gestation fetal horse. We also wished to determine whether there is ultradian rhythmic release of ACTH and cortisol in fetal horses and we compared fetuses to maternal and non-pregnant adult horses. Six fetuses, 278–304 days gestation (term ≈335), were catheterized and sampled daily until delivery. Mean (± s.e.m.) ACTH concentrations increased significantly from 159 ±21 to 246 ±42 pg/ml over the last 2 days before parturition. Fetal cortisol increased significantly from 3·1±1·0 to 13·4±3·7 ng/ml (mean±s.e.m.) over the last 9 days before delivery. The slope of regressions for ACTH and cortisol concentrations with respect to time were positive in all subjects and statistically significant in 3 of 6 for ACTH and 5 of 6 for cortisol. Fetal corticosteroid binding capacity declined from 49·5 ±20·5 to 16·1 ± 2·2 ng/ml (mean ± s.e.m.) over the last 10 days before parturition. However, the greatest changes in ACTH, cortisol and corticosteroid binding capacity occurred very late in gestation, during the last 48 to 72 h before parturition. Significant peaks and nadirs in plasma ACTH concentration were detected in all 20 experiments and in plasma cortisol concentration in 17 of 20 experiments using Cluster analysis. We found statistically significant periods of oscillation between 11 and 64 min in plasma ACTH (19 of 20 experiments) and cortisol (15 of 20 experiments) using power spectral density analysis. Statistically significant periods between 11 and 17 min were detected in 11 of 20 experiments for ACTH and in 8 of 20 for cortisol. We conclude that: 1) at the end of gestation, equine fetal plasma ACTH and cortisol concentrations increase while corticosteroid binding capacity decreases suggesting that there is a disproportionately large increase in unbound cortisol at this time; 2) the secretion of ACTH and cortisol is rhythmic in both fetal and adult horses; 3) most animals exhibit a period of oscillation between 11 and 17 min; and 4) there is no apparent developmental change from late gestation to adulthood in the ultradian oscillator influencing ACTH and cortisol secretion in this species.

Journal of Endocrinology (1995) 144, 271–283
Prolactin receptor gene expression in the fetal rat
Authors: Freemark M , Nagano M , Edery M , Kelly P A
Published: December 2008

The expression of mRNA encoding the long and short forms of the prolactin receptor (PRLR) in the fetal rat was examined using the method of reverse transcription-PCR. A 742 bp PCR product encoding the extracellular and transmembrane domains of the PRLR was detected in maternal and fetal liver and in fetal adrenal, kidney, small intestine, pancreas, brain, pituitary, thymus, lung and skin but not in fetal heart. Highest levels of the 742 bp PRLR transcript were detected in fetal adrenal (45·2% of levels in maternal liver), kidney (27·2%), small intestine (21·7%), pancreas (18·3%) and liver (10·8%), and tissue levels of the 742 bp product correlated positively (r=0·92, P<0·01) with the specific binding of the fetal lactogenic hormone rat placental lactogen II (rPL-II). These findings suggest that the PRLR may serve as a physiological binding protein for rPL-II in the rat fetus. There were striking differences in the relative expression of mRNA encoding the long and short forms of the PRLR. The long form of the receptor was expressed in maternal liver and placenta and in all fetal tissues studied except fetal heart. The short form of the receptor was also detected in maternal liver and placenta and fetal adrenal, kidney, small intestine, liver and thymus; in contrast, there was limited expression of the short-form of the receptor in fetal pancreas, pituitary and brain and no short form transcripts were detected in fetal lung, skin or heart. The results of these studies indicate widespread expression of the rat PRLR in fetal and uteroplacental tissues, implicating diverse roles for the placental prolactin-like proteins in fetal development.

Journal of Endocrinology (1995) 144, 285–292
The influence of ovarian steroids on hypothalamic-pituitary-adrenal regulation in the female rat
Authors: Carey M P , Deterd C H , de Koning J , Helmerhorst F , de Kloet E R
Published: December 2008

The present study examined the association between hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-ovarian axes. HPA activity determined by plasma levels of adrenocorticotropin (ACTH) and corticosterone (B) was assessed in intact female rats as a function of oestrous cycle stage under resting conditions and after exposure to a 20 min restraint stress. To delineate the roles of oestradiol and progesterone in HPA axis modulation, plasma concentrations of ACTH and B were determined in ovariectomised (OVX) animals treated with oestradiol and/or progesterone under resting conditions and during exposure to the stress of a novel environment. The effects of these steroid treatments on the transcription and/or binding properties of the two corticosteroid receptors, the mineralocorticoid (MR) and glucocorticoid (GR) receptors, were also examined in hippocampal tissue. (i) Fluctuations in basal and stress-induced plasma ACTH and B concentrations were found during the oestrous cycle with highest levels at late pro-oestrus. (ii) In OVX steroid-replaced animals, basal and stress-induced activity was enhanced in oestradiol and oestradiol plus progesterone-treated animals compared with OVX controls. (iii) Cytosol binding assays revealed an oestradiol-induced decrease in hippocampal MR capacity. This decrease appears to be due to an effect of the steroid on MR transcription as in situ hybridisation analysis of MR mRNA showed an oestradiol-induced decrease in MR transcript in all hippocampal subfields. (iv) Treatment of oestradiol-primed animals with progesterone reversed the oestradiol-induced decrease in hippocampal MR capacity. Data from MR mRNA hybridisation in situ experiments indicate that this reversal may be due to an antagonism of the oestradiol effect on MR transcription. (v) Progesterone treatment with or without prior oestradiol-priming induced a significant decrease in the apparent binding affinity of hippocampal MR. We show that progesterone and its 11 β-hydroxylated derivative have a high affinity for the hippocampal MR. (vi) Neither oestradiol nor progesterone affected GR binding parameters in the hippocampus. In conclusion, we find that sex steroids modulate HPA activity and suggest that the observed effects of these steroids on hippocampal MR may underlie their concerted mechanism of action in inducing an enhanced activity at the period of late pro-oestrus.

Journal of Endocrinology (1995) 144, 311–321
The effects of ovine placental lactogen infusion on metabolites, insulin-like growth factors and binding proteins in the fetal sheep
Authors: Oliver M H , Harding J E , Breier B H , Evans P C , Gallaher B W , Gluckman P D
Published: December 2008

It has been suggested, but not shown, that in the fetus placental lactogen (PL) may affect the regulation of the IGFs and fetal metabolism. To examine the effects of PL on the circulating concentrations of the IGFs, IGF-binding proteins (IGFBPs), glucose, free fatty acids (FFAs) and amino nitrogen (AN), we infused late gestation sheep fetuses with recombinant ovine PL (roPL). Five chronically-catheterised sheep fetuses were infused intravenously with three 24 h infusions of saline, roPL (100 μg bolus then 500 μg over 24 h) and then saline again.

Fetal roPL infusion increased plasma oPL from 0·4 ± 0·1 to 3·3 ± 0·5 nm (mean ± s.e.m.; P<0·05; factorial analysis of variance and Scheffé's test). Fetal plasma IGF-I, IGF-II, insulin, FFAs and blood glucose were unaffected by the roPL infusion. Fetal plasma IGFBP-3, as measured by Western ligand blotting, decreased by 30% during fetal roPL infusion while other fetal plasma IGFBPs were unaffected. Fetal roPL infusion decreased fetal blood AN from 7·3 ± 0·5 to 6·6 ± 0·2 mm (P<0·05). Maternal plasma IGF-I, IGF-II, IGFBPs, insulin, FFAs, blood glucose and AN were unaffected by the fetal roPL infusion. Saline infusion had no effect on any parameter.

The data suggest that PL is not a significant determinant of plasma IGFs in the late gestation sheep fetus although there may be an indirect effect via alterations in levels of IGFBP-3. The effect of fetal roPL infusion on fetal blood AN concentrations may suggest some role for PL in the regulation of fetal amino acid metabolism.

Journal of Endocrinology (1995) 144, 333–338
Extracellular domain of prolactin receptor from bovine mammary gland: expression in Escherichia coli, purification and characterization of its interaction with lactogenic hormones
Authors: Tchelet A , Staten N R , Creely D P , Krivi G G , Gertler A
Published: December 2008

The cDNA of the extracellular domain of bovine prolactin receptor (bPRLR-ECD) was cloned and expressed at high yield as an insoluble protein in Escherichia coli. This protein was solubilized, refolded and purified to >98% homogeneity yielding 80 mg of monomeric fraction per 2 litres of induced culture. Its molecular mass was 25–7 kDa, as determined by SDS-PAGE in the absence of reducing agent and 24 kDa by gel filtration on a Superdex column. Binding experiments revealed that bPRLR-ECD binds to human (h) GH (hGH) with high affinity, whereas its affinity for ovine (o) or bovine (b) prolactins (PRLs) was lower and for bovine placental lactogen (bPL) very low. The affinity of bPRLR-ECD for the latter three hormones was, however, much higher than that of membrane-embedded or solubilized bPRLR. The stoichiometries of interaction of bPRLR-ECD with hGH, oPRL, bPRL and bPL were determined by gel-filtration chromatography. Even at a 3:1 ECD excess, only 1:1 complexes were detected at μm concentrations of ECD and ligand. At an up to 32-fold dilution, the complexes with oPRL, bPRL, and particularly bPL, underwent progressive dissociation, whereas the complex with hGH remained stable. Although all four hormones exhibited nearly identical activity in the Nb2 lymphoma cell bioassay, the ability of bPRLR-ECD to inhibit hormonal mitogenic activities differed, generally reflecting its affinity for the respective hormones. In view of these and previous results, we suggest that, unlike in the GH:GHR-ECD interaction, neither the stoichiometry of interaction of bovine or other PRLR-ECDs nor the affinity constants can predict the biological potency of the different lactogenic hormones.

Journal of Endocrinology (1995) 144, 393–403
Induction of immediate early gene mRNAs and proteins by hCG in interstitial cells of rat testis
Authors: Schultz R , Kononen J , Pelto-Huikko M
Published: December 2008

In the present study we have investigated the induction of immediate early gene (IEG) c-fos, c-jun, junB and junD mRNAs and proteins in interstitial cells of rat testis after hCG treatment in vivo using in situ hybridization and immunocytochemistry. The basal levels of all IEGs were barely detectable with our methods. A prominent induction of c-fos, c-jun and junB mRNAs and proteins in Leydig cells was seen after hCG treatment. The induction of these IEG mRNAs and proteins demonstrates that their expression is an early transcriptional response to the extracellular stimulus of hCG and that they are involved in transcriptional processes which may mediate the effects of LH on cellular adaptive responses or steroid biosynthesis.

Journal of Endocrinology (1995) 144, 417–424
Dietary ω6 fatty acids and the effects of hyperthyroidism in mice
Authors: Deshpande N , Hulbert A J
Published: December 2008

The influence of the type of dietary fat on the effects of thyroid hormones was investigated in mice. Hyperthyroidism was achieved by providing thyroid hormones (T3 and T4) in the drinking water. Both hyperthyroid and euthyroid mice (Mus musculus) were fed isoenergetic diets containing 18% (w/w) total lipid but differing in fatty acid composition. Diets were either low in the polyunsaturated linoleic acid (18:2, ω6) and high in saturated fatty acids (SFAs) or low in saturated fats and high in the polyunsaturated fatty acid (PUFA), linoleic acid. Treatments were maintained for 21–22 days. Plasma thyroid hormone levels, standard metabolic rate (SMR), changes in body mass, specific activities of malic enzyme (ME), Na-K-ATPase and glycerolphosphate dehydrogenase (GPDH) of the liver were measured. Fatty acid composition of the liver phospholipids was also determined. Levels of T3 (15–17 nm) and T4 (250–255 nm) were significantly higher in the respective hyperthyroid groups. There was no significant influence of the diet on hormone levels. Hyperthyroidism increased the SMR 37–44% above the euthyroid levels. A significant body weight loss of 14–18% was observed in hyperthyroid mice on the PUFA diet but not in those on the SFA diet. PUFA diet significantly reduced the activity of ME but had no effect on Na-K-ATPase or GPDH activity. Activities of Na-K-ATPase and GPDH were significantly elevated in all hyperthyroid groups. Mice on T4 and PUFA diet showed a highly significant 399% increase in GPDH activity above the euthyroid level. The overall degree of unsaturation of the fatty acids in the liver phospholipids was comparable in all groups. Dietary treatment substantially changed liver membrane fatty acid composition whilst hyperthyroidism resulted in only small changes. The only parameters to show an interaction between dietary fat profile and hyperthyroidism were ME activity, changes in body mass and liver phospholipid fatty acid composition.

Journal of Endocrinology (1995) 144, 431–439
Effects of hemitransection of the midbrain on milk-ejection burst of oxytocin neurones in lactating rat
Authors: Wang Y-F , Negoro H , Honda K
Published: December 2008

Unilateral knife cuts were performed in the midbrain of lactating rats and the activities of oxytocin neurones were recorded extracellularly from the supraoptic nuclei (SON) in order to investigate the location of the neural mechanism responsible for the synchronization of milk-ejection bursts of oxytocin neurones in different magnocellular nuclei of the hypothalamus. The lesions involved the mesencephalic lateral tegmentum, the intermedial tegmentum and the central grey. Ninety-six SON neurones were antidromically activated by neurohypophyseal stimulation and were also identified as oxytocin neurones, which included 17 pair-recorded neurones. First, the response of oxytocin neurones recorded from the unilateral SON to bilateral or unilateral suckling was tested. During bilateral suckling, not only the oxytocin neurones recorded from the SON on the intact side (n=34) but also those recorded from the SON on the lesioned side (n=58) displayed milk-ejection bursts. When only the nipples ipsilateral to the lesion were suckled (ipsilateral suckling), bursts were induced in most of the oxytocin neurones on the intact (83·3%, n=12) and lesioned side (88·9%, n=27). In contrast, none of the oxytocin neurones (n=37) produced bursts and none of the rats tested (n=23) showed milk ejections during contralateral suckling. Secondly, some characteristics of the bursts of pair-recorded neurones during bilateral suckling and their response to different modes of suckling were investigated. When oxytocin neurones on both sides displayed milk-ejection bursts, they were always well synchronized but the mean burst amplitude of the neurones on the lesioned side (55·6 ±4·9 spikes, n=43) was significantly (P<0·05) lower than that of the neurones on the intact side (65·7 ±5·6 spikes, n=43). Late-recruited neurones were observed in 6 pairs of oxytocin neurones, and these mainly occurred in the neurones on the lesioned side (5/6). In 5 pair-recorded oxytocin neurones, bursts could also be induced synchronously by ipsilateral suckling but not by contralateral suckling. Thus it is very likely that the major mechanism synchronizing the milk-ejection bursts of oxytocin neurones in the bilateral SON is located in the region rostral to the midbrain.

Journal of Endocrinology (1995) 144, 463–470
Effects of catecholamine synthesis inhibitors and adrenergic receptor antagonists on restraint-induced LH release
Authors: Martín A I , Fernández-Ruiz J , López-Calderón A
Published: December 2008

Acute stress is known to increase LH secretion and the release of central norepinephrine (NE) in intact rats. Studies were performed to analyse the role of catecholamines in acute stress-induced LH release in male rats. Injection of α-methyl-p-tyrosine (αMPT) and diethyldithiocarbamate (DDC), catecholamine synthesis inhibitors, significantly decreased both hypothalamic concentration of NE and serum LH. Restraint for 30 min evoked an increase in serum LH in saline-treated rats, whereas αMPT and DDC administration blocked the stress-induced LH release. The effects of α1-, α2- and β-adrenoreceptor antagonists on the LH response to restraint stress were also studied. Propranolol treatment did not modify serum LH in either unstressed or stressed rats. The two α-adrenergic receptor antagonists prazosin and yohimbine prevented the restraint-induced LH release; however, prazosin but not yohimbine significantly decreased the serum concentration of LH in unstressed rats. These data suggest that the acute stress-induced increase in LH secretion is mediated through the activation of α2-adrenergic receptors.

Journal of Endocrinology (1995) 144, 511–515
Expression of mRNA and immunocytochemical localization of inhibin α- and inhibin βA-subunits in the fetal sheep testis
Authors: Thomas G B , Davidson E J , Engelhardt H , Baird D T , McNeilly A S , Brooks A N
Published: December 2008

In order to investigate the ontogeny of gonadal inhibin production in the male fetal sheep, testes were collected from male fetuses at days 70, 100, 130 and 140 of gestation (term=145 days). The expression and localization of inhibin α- and inhibin βA-subunit mRNA and protein were evaluated using in situ hybridization and immunocytochemistry. The expression of inhibin α-subunit mRNA was localized within the seminiferous cords of the developing fetal testis and progressively increased with gestational age. Immunostaining corresponding to immunoreactive inhibin α-subunit was detected in Sertoli cells within the seminiferous cords at days 100, 130 and 140 of gestation. In addition, immunostaining was detectable in a small proportion of Leydig cells. No expression of inhibin βA-subunit mRNA or immunoreactivity was detected in any testicular tissue at any stage of gestation. These data show that the Sertoli cells of the developing fetal sheep testis have the capacity to produce inhibin α-subunit by day 100 of gestation and that production increases during late gestation.

Journal of Endocrinology (1995) 145, 35–42
Effect of systemic glucagon administration on ACTH secretion in anaesthetized rats
Authors: Rao R H
Published: December 2008

The effect of glucagon on ACTH secretion was studied in anaesthetized rats injected with either saline (0·1 ml i.m.) or glucagon (0·02 mg/kg i.m.). For the first 90 min after glucagon injection, plasma ACTH fell by 50% from the basal value of 23 ±4 pmol/l (mean ± s.e.m.) to 11 ±2 (P=0·011), after which an abrupt return to baseline occurred (120 min value: 26 ± 2 pmol/l). In saline injected rats, the baseline ACTH value was not significantly different from either the 90 min value or the 120 min value (27 ±3 vs 21 ± 4 and 24 ± 3 pmol/l respectively; P>0·10). Plasma glucose after glucagon peaked at 11·6 ± 1·1 mmol/l by 15 min but subsequently fell rapidly, attaining the baseline by 60 min. Insulin levels increased sharply after glucagon, from 381 ±78 pmol/l to 3172 ±668 pmol/l at 15 min, and plateaued at approximately 1000 pmol/l thereafter. No changes in glucose or insulin were seen in saline injected rats. The magnitude of suppression of ACTH after glucagon was not affected either by sustained hyperinsulinaemia (≃ 1400 pmol/l), induced with continuous glucose infusion to maintain plasma glucose>12 mmol/l, or by pretreatment with the long-acting somatostatin analogue octreotide (50 μg/kg s.c.). However, the return to baseline between 100 and 120 min was prevented both by hyperinsulinaemia induced with sustained hyperglycaemia, and by octreotide. It is postulated that glucagon may inhibit ACTH secretion either by a direct effect on the hypothalamus or indirectly through insulin, which is known to stimulate endogenous somatostatin release.

Journal of Endocrinology (1995) 145, 51–58
Effect of gonadectomy on growth and GH responsiveness in dwarf rats
Authors: Gevers E F , Wit J M , Robinson I C A F
Published: December 2008

Normal rats are sexually dimorphic in their growth and GH secretion. Gonadectomy (Gnx) changes the GH secretory pattern and this could explain differential growth rates in male and female rats. Gonadal steroids may also affect tissue growth directly, or by changing their responsiveness to GH. The effects of Gnx on growth, GH responsiveness, and hepatic GH receptors have now been studied in young (4–7 weeks old) GH-deficient dwarf rats in which the effects of steroid-induced alterations in residual endogenous GH secretion will be much less pronounced. Groups of intact and Gnx dwarf rats (n=5–7) were infused with recombinant human GH (144 μg/day) either continuously or in a pulsatile pattern (every 3 h) for 7 days, whilst control groups received saline infusions. Gains in weight, length and tibial bone growth were measured. Female dwarf rats grew significantly more slowly than male dwarfs. Gnx in male dwarfs inhibited growth significantly, whereas ovariectomy had a lesser stimulatory effect in females. Hepatic lactogenic and somatogenic receptors were higher in females and ovariectomy lowered their values towards male levels. Pulsatile GH infusions were more effective than continuous infusions of the same daily GH dose, but when the different underlying growth rates (measured in saline-infused Gnx animals) were taken into account, the responsiveness to pulses of hGH was not different between males and females or between intact and Gnx animals. We have concluded that Gnx in dwarf rats does affect growth, but the effects are small in comparison with those seen in normal rats. Since pulsatile GH infusions stimulated growth more effectively than continuous GH, irrespective of the gonadal steroid status, and the responsiveness to exogenous GH was not changed by Gnx, the results imply that changes in the GH secretory pattern induced by gonadal steroids may have a larger impact on the growth rate than direct effects at the tissue level, at least in the rat.

Journal of Endocrinology (1995) 145, 69–79