bluuebunny/crossref_metadata_2025_split huggingface dataset:
Androgen negative feedback during the early rise in LH secretion in bull calves
Authors: Rawlings N C , Evans A C O 
Published: December 2008

Abstract
A transient elevation in mean circulating concentrations of LH and FSH occurs in the young bull calf prior to 24 weeks of age. The functional significance of this is not clear. To see if changes in the ability of androgens to suppress gonadotrophin secretion were involved in the start of this early rise in LH secretion or the cessation of the early rise in LH and FSH secretion, bull calves were treated with flutamide (androgen receptor blocker; n=5; 9 mg flutamide/kg body weight in propylene glycol (i.m./s.c.) in three equal portions at 12-h intervals) at 8, 16 and 24 weeks of age and bled every 15 min for 12 h beginning after the third flutamide treatment; control bulls received vehicle at these times. Control bulls (n=5) were bled every 15 min for 12 h at 4, 8, 12, 16 and 24 weeks of age, and all bulls were bled weekly. Serum samples were assayed for concentrations of LH, FSH and testosterone. Based on weekly and intensive bleedings for control and flutamide-treated bulls, an early rise in LH (8–18 weeks of age) and FSH (4–24 weeks of age) secretion was seen in all bull calves (P<0·05). At 8 weeks of age flutamide treatment resulted in increased mean serum LH concentrations (P<0·05); at 16 weeks of age it resulted in increased basal and mean LH concentrations and increased LH pulse frequency (P<0·05); and at 24 weeks of age in increased mean LH concentrations, LH pulse frequency and amplitude (P<0·05) in comparison with control bulls. Flutamide treatment resulted in decreased FSH pulse amplitude at 8 weeks of age and increased mean serum concentrations of FSH and FSH pulse frequency at 24 weeks of age (P<0·05). In flutamide-treated bull calves testicular growth was greater and sexual maturity was reached earlier than in control bull calves (P<0·05). We conclude that a reduced suppression of LH secretion by androgens does not appear to be a major contributing factor to the onset of the early increase in LH secretion, but increased suppression may be involved in the termination of the early rise of both LH and FSH secretion in the bull calf. The early increase in LH secretion may be a critical initial step in postnatal reproductive development, since flutamide treatment increased early LH secretion and resulted in earlier attainment of sexual maturity.
Journal of Endocrinology (1995) 145, 243–249
Deprivation of phosphate increases IGF-II mRNA in MDCK cells but IGFs are not involved in phosphate transport adaptation to phosphate deprivation
Authors: Ernest S , Coureau C , Escoubet B 
Published: December 2008

Abstract
Phosphate (Pi) deprivation and IGFs stimulate renal Pi reabsorption. We studied the involvement of IGFs in the adaptation of Pi transport to Pi deprivation in MDCK cells.
Deprivation of Pi for 15 h increased the steady-state content of IGF-II mRNA (77 ± 12% whereas IGF-I mRNA was not detectable in MDCK cells in either control or Pi-deprived cells. IGF-II (10 −7 m) and IGF-I 10−8m) stimulated the Na-dependent Pi uptake (1·23and 1·3-fold increase at 15 h respectively). The effect of IGF-I appeared after 15 h and increased up to 40 h of treatment (2·15-fold increase). In contrast, Pi uptake was increased by Pi deprivation as early as 8 h (1·5-fold) and up to 40 h of Pi deprivation (1·9-fold increase). IGF-II mRNA was not increased before 15 h of Pi deprivation and returned to control at 40 h. The combination of IGF-I and Pi deprivation had a more than additive effect on Pi transport (fivefold increase) (P<0·001).
At variance with Pi deprivation, high concentrations of insulin stimulated Na-coupled alanine transport (6 ± 2% and 16 ± 4% in Pi-treated and Pi-depleted cells respectively). Pi deprivation and high concentrations of insulin decreased Na,K-ATPase activity (−48 and −64% respectively) and these effects were not additive.
We concluded that: (1) long-term Pi deprivation increased the content of IGF-II mRNA in MDCK cells but that the paracrine/autocrine effects of IGFs could not account for the effects of Pi deprivation on Pi transport in MDCK cells and (2) IGFs could be involved in other changes occurring during Pi deprivation such as the decrease in Na,K-ATPase activity.
Journal of Endocrinology (1995) 145, 325–331
Growth hormone and longitudinal bone growth in vivo: short-term effect of a growth hormone antiserum
Authors: Loveridge N , Farquharson C , Palmer R , Lobley G E , Flint D J 
Published: December 2008

Abstract
The control of longitudinal growth is poorly understood but GH is considered to be one of the major hormones regulating postnatal growth. However, there is dispute as to whether it has a direct or indirect action. To study the role of GH we used a polyclonal antiserum to rat GH and investigated changes in cell proliferation and enzyme activities associated with bone formation and resorption during longitudinal growth. IGF-I levels were measured by two independent RIAs, DNA synthesis by bromodeoxyuridine incorporation followed by immunocytochemistry and enzyme activities were quantified in situ by microdensitometry.
After 1 day the percentage of chondrocytes undergoing DNA synthesis within the proliferative zone was reduced but no other parameters were affected. By day 4 the labelling index was the same as in pair-fed animals but the number of chondrocytes synthesising DNA was reduced as was the total width of the growth plate and that of the proliferative zone. Alkaline phosphatase (associated with mineralisation) was unchanged but glucose 6-phosphate dehydrogenase activity (associated with cell proliferation) was decreased. Osteoclastic tartrate-resistant acid phosphatase activity (associated with bone resorption) was also significantly reduced. Similar changes were apparent after 10 days. At no time was the circulating level of IGF-I decreased.
These data suggest that, during longitudinal growth, GH affects the number of proliferating chondrocytes but not the percentage of cells undergoing DNA synthesis, indicating that its primary role may be on the commitment of prechondrocytes to a proliferative state. Furthermore, while GH does not seem to have any effect on skeletal mineralisation it may stimulate osteoclastic resorption of the primary spongiosa.
Journal of Endocrinology (1995) 146, 55–62
Follicular dynamics and secretion of inhibin and oestradiol-17β during the oestrous cycle of the hamster
Authors: Kishi H , Taya K , Watanabe G , Sasamoto S 
Published: December 2008

Abstract
Plasma and ovarian levels of inhibin were determined by a radioimmunoassay (RIA) at 3-h intervals throughout the 4-day oestrous cycle of hamsters. Plasma concentrations of FSH, LH, progesterone, testosterone and oestradiol-17β were also determined by RIAs. In addition, hamsters were injected at various times with human chorionic gonadotrophin (hCG) to determine the follicular development. The changes in plasma concentrations of FSH after injection of antisera to oestradiol-17β (oestradiol-AS) and inhibin (inhibin-AS) on the morning of day 2 (day 1=day of ovulation) were also determined.
Plasma concentrations of inhibin showed a marked increase on the afternoon of day 1, remained at plateau levels until the morning of day 4, then increased abruptly on the afternoon of day 4 when preovulatory LH and FSH surges were initiated. A marked decrease in plasma concentrations of inhibin occurred during the process of ovulation after the preovulatory gonadotrophin surges. An inverse relationship between plasma levels of FSH and inhibin was observed when the secondary surge of FSH was in progress during the periovulatory period. Plasma concentrations of oestradiol-17β showed three increase phases and these changes differed from those of inhibin. Changes in plasma concentrations of oestradiol-17β correlated well with the maturation and regression of large antral follicles. Follicles capable of ovulating following hCG administration were first noted at 2300 h on day 1. The number of follicles capable of ovulating reached a maximum on the morning of day 3 (24·8± 0·6), and decreased by 0500 h on day 4 (15·0 ± 1·1), corresponding to the number of normal spontaneous ovulations. Plasma concentrations of FSH were dramatically increased within 6 h after inhibin-AS, though no increase in FSH levels was observed after oestradiol-AS. These findings suggest that changes in the plasma levels of inhibin during the oestrous cycle provide a precise indicator of follicular recruitment, and that the changes in plasma concentrations of oestradiol-17β are associated with follicular maturation. These findings also suggest that inhibin may play a major role in the inhibition of FSH secretion during the oestrous cycle of the hamster.
Journal of Endocrinology (1995) 146, 169–176
Degradation of IGF-I in the adult rat gastrointestinal tract is limited by a specific antiserum or the dietary protein casein
Authors: Xian C J , Shoubridge C A , Read L C 
Published: December 2008

Abstract
To investigate the potential of IGF-I peptides as therapeutics in the gut, the survival profiles of a bolus of 125I-labelled IGF-I (8·6 ng) in vivo in various ligated gut segments of fasted adult rats have been examined. The intactness of IGF-I tracer in the flushed luminal contents was estimated by trichloroacetic acid precipitation, antibody and receptor binding assays. It was found that IGF-I was degraded very rapidly in duodenum and ileum segments with a half-life (t1/2) of 2 min by all three methods. IGF-I was slightly more stable in the stomach (t1/2=8, 5 and 2·5 min by the above three methods), and considerably more stable in the colon (t1/2=38, 33 and 16 min as judged by the three methods). Rates of degradation in gut flushings in vitro were similar to the in vivo rates except for the colon, where IGF-I was proteolysed more rapidly in vivo.
As a means of developing gut-stable and active forms of IGF-I, several approaches were examined for their effectiveness in prolonging IGF-I survival in the upper gut. It was found that the extension peptide on the analogue, LR3IGF-I did not protect IGF-I, nor did association with IGF-binding protein-3. However, an IGF-I antiserum was effective in prolonging IGF-I half-life in duodenum fluid by 28-fold. Charge interaction between IGF-I and heparin could also protect IGF-I in the stomach but not in duodenum flushings. Furthermore, casein (a non-specific dietary protein) and to a lesser extent, BSA and lactoferrin, were effective in preserving IGF-I structural integrity and receptor binding activity in both stomach and duodenum fluids. It can be concluded that IGF-I cannot be expected to retain bioactivity if delivered orally because of rapid proteolysis in the upper gut, but the use of IGF antibodies and casein could represent useful approaches for IGF-I protection in oral formulae.
Journal of Endocrinology (1995) 146, 215–225
Expression of the prolactin receptor gene during the breeding and non-breeding seasons in red deer (Cervus elaphus): evidence for the expression of two forms in the testis
Authors: Clarke L A , Edery M , Loudon A S I , Randall V A , Postel-Vinay M-C , Kelly P A , Jabbour H N 
Published: December 2008

Abstract
The red deer is a seasonally breeding mammal with a circannual cycle of prolactin secretion which reaches its peak during the non-breeding season. This study investigated expression of the prolactin receptor gene in red deer tissues collected in the breeding and non-breeding seasons. A 562 bp fragment of the extracellular domain of the red deer prolactin receptor cDNA was amplified from red deer liver poly(A)+ RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) using primers designed from the human sequence. Northern blots were prepared using 10–20 μg poly(A)+ RNA. The blots were hybridized to the 562 bp cDNA labelled by random priming with α32P-dCTP. A main transcript of 3·5 kb was expressed in liver, heart, kidney and testis throughout the year and in epididymis during the breeding season only. In the testis an additional major transcript of 1·7 kb was present during the breeding and non-breeding seasons. Competitive binding assays using 125I-ovine prolactin (125I-oPRL) were performed on microsomal membrane fractions prepared from liver. Scatchard analyses confirmed the presence of a single class of lactogen-binding receptor with a mean Ka of 0·87 ± 0·12 × 109 m−1 and a Bmax of 73·6 ± 9·8 fmol/mg protein (n=5). Cross-linking of 125I-oPRL to liver microsomes with 0·5 mm disuccinimidyl suberate followed by SDS-PAGE revealed a major band of molecular mass 56 kDa which was displaced by ovine prolactin, suggesting a specific lactogen-binding entity of 33 kDa. This study confirms the expression of the red deer prolactin receptor gene throughout the year, characterizes the prevalent form of receptor in the liver and demonstrates the expression of a separate, short form in the testis.
Journal of Endocrinology (1995) 146, 313–321
Follicular development, steroidogenesis and gonadotrophin secretion in response to long-term treatment with a gonadotrophin-releasing hormone agonist in the rat
Authors: Srivastava R K , Krishna A , Sridaran R 
Published: December 2008

Abstract
Gonadotrophin-releasing hormone (GnRH) and its agonists are implicated in the local control of rat ovarian function. We have evaluated the effects of long-term administration of different doses of GnRH agonist (GnRH-Ag) in vivo (a) on reproductive cyclicity and follicular development, (b) on peripheral gonadotrophin and steroid concentrations and (c) on in vitro cAMP and progesterone production by the follicles in response to stimulatory doses of FSH or LH (1 μg/ml). GnRH-Ag (0·2, 1 or 5 μg/day) administration for 28 days had a profound impact on the oestrous cycle of rats as revealed by vaginal cytology. GnRH-Ag treatment caused a decrease in ovarian and uterine weights, which correlated very well with the decrease in the number of follicles present in the ovary. GnRH-Ag (5 μg/day) reduced the number of early preantral follicles and there was complete disappearance of early as well as late antral follicles. However, a dose of 1 μg GnRH-Ag/day was effective in the complete demise of only late antral follicles with a significant attenuation in the number of early antral follicles. There was an enhancement in serum LH concentrations in response to the highest dose of GnRH-Ag administration with serum FSH concentrations declining in rats treated with the two higher doses. However, serum prolactin concentrations were attenuated only in rats treated with the highest dose of GnRH-Ag. GnRH-Ag treatment decreased serum progesterone and oestradiol concentrations. Preantral follicles obtained from the rats treated with 0·2 or 1 μg GnRH-Ag/day resulted in an attenuated response to LH-or FSH-stimulated progesterone production, whereas antral follicles showed an exaggerated response to the stimulatory doses of FSH in vitro. Antral follicles obtained from the rats treated with 0·2 μg/day showed a robust decrease in cAMP accumulation in response to LH with a slight decrease only with FSH. In contrast, preantral follicles obtained from GnRH-Ag-treated rats did not show any significant attenuation in cAMP production. These data suggest that GnRH-Ag exerts a direct inhibitory effect on follicular development and steroidogenesis and as a result it interferes with the normal oestrous cyclicity in the rat.
Journal of Endocrinology (1995) 146, 349–357
Kaliuretic peptide and long acting natriuretic peptide as well as atrial natriuretic factor inhibit aldosterone secretion
Authors: Vesely D L , Chiou S , Douglass M A , McCormick M T , Rodriguez-Paz G , Schocken D D 
Published: December 2008

Abstract
The present investigation was designed to determine whether atrial natriuretic peptides consisting of amino acids 1–30 (long acting natriuretic peptide), 31–67 (vessel dilator) and 79–98 (kaliuretic peptide) as well as 99–126 (atrial natriuretic factor (ANF)) of the 126 amino acid ANF prohormone inhibit aldosterone secretion. Thirty healthy human subjects were studied following infusion of 100 ng/kg body weight/min for 60 min of each of the respective peptides. Kaliuretic peptide decreased plasma aldosterone concentration by the greatest amount (6-fold) and plasma aldosterone was still significantly decreased (P<0·001) three hours after stopping the infusion. In contrast, within 30 min of cessation of the ANF infusion, plasma aldosterone levels had returned to pre-infusion values. Long acting natriuretic peptide also significantly (P<0·01) decreased plasma aldosterone levels which remained significantly (P<0·001) decreased 3 h after cessation of infusion. Vessel dilator did not decrease plasma aldosterone levels. Kaliuretic peptide, ANF and long acting natriuretic peptide also decreased (P<0·01) urinary aldosterone concentrations. None of these peptides changed the plasma potassium concentration. We conclude that two new peptide hormones (long acting natriuretic peptide and kaliuretic peptide) inhibit aldosterone secretion. The length of time that aldosterone secretion is inhibited following kaliuretic peptide and long acting natriuretic peptide infusion is significantly longer (P<0·001) than following ANF infusion.
Journal of Endocrinology (1995) 146, 373–380
Blood prolactin concentrations affect prolactin transfer into goat milk: implications for maintenance of lactation
Authors: Forsyth I A , Taylor J A , Gabai G , Fleet I R 
Published: December 2008

Abstract
125I-Labelled ovine prolactin was infused for 15 min into a pudic artery supplying one mammary gland of lactating goats (n=17). Between 0 and 4·25 h significandy more total (P<0·01) and trichloroacetic acid (TCA)-precipitable (P<0·001) radioactivity appeared in the milk of the infused compared with the non-infused gland. Gel chromatography and antibody precipitation indicated the presence of undegraded 125I-labelled prolactin in milk whey. Maximum transfer occurred 60–80 min after the end of infusion suggesting passage via a transcellular route. High plasma prolactin concentrations, resulting from infusion of cold prolactin with labelled prolactin in late lactation or from seasonally elevated prolactin at peak lactation, reduced the specific activity of infused prolactin and depressed the difference in secretion of 125I-labelled prolactin into milk of infused and non-infused glands. This suggests the operation of a competitive and saturable mechanism. Together with the increase in the milk to blood ratio of prolactin in goats given long-term (3 week) bromocriptine treatment, the results suggest that the goat mammary gland has a high avidity for prolactin especially when circulating prolactin is low. There was also evidence from TCA precipitation that prolactin may be protected from degradation in these circumstances. These mechanisms may contribute to the resistance of ruminant lactation to reduction in plasma prolactin and protect lactation from seasonal prolactin fluctuations.
Journal of Endocrinology (1995) 146, 411–420
Stimulation of tyrosinase in human melanocytes by pro-opiomelanocortin-derived peptides
Authors: McLeod S D , Smith C , Mason R S 
Published: December 2008

Abstract
Human melanocytes, maintained on bovine corneal endothelium-derived extracellular matrix for at least 4 days in the absence of phorbol 12-myristate 13-acetate (PMA) and cholera toxin (CT), displayed increased tyrosinase activity when exposed to several pro-opiomelanocortinderived (POMC) peptides. Melanocytes from 9 of 14 donors showed significantly increased tyrosinase activity after treatment with adrenocorticotropic hormone (ACTH; mean increase 320±107 (s.e.m.)% of control, P<0·005), while melanocytes from 8 of 13 donors increased tyrosinase in the presence of diacetyl-melanocyte stimulating hormone (di-MSH; mean increase 223±31 (s.e.m.)% of control, P<0·005). Maximal increases in tyrosinase were seen after treatment with 10−10 m ACTH and with 10−6 m di-MSH. In two cell cultures which showed tyrosinase stimulation, melanin synthesis was similarly increased in the presence of added POMC peptides. PMA but not CT increased tyrosinase activity in melanocytes cultured under these conditions. In the presence of staurosporine, an inhibitor of protein kinase C (PKC), the magnitude of the increase in tyrosinase due to PMA, ACTH and di-MSH was significantly reduced. These results indicate that tyrosinase activity in melanocytes from most human donors, under appropriate conditions, is susceptible to the stimulatory effects of POMC peptides, that ACTH is considerably more potent than di-MSH in this test system and that in human cells the PKC pathway may be important in modulating melanogenesis.
Journal of Endocrinology (1995) 146, 439–447
Potassium chloride effects on the hormonal signal transduction mechanisms underlying phasic myometrial contractions
Authors: Phillippe M , Chien E K 
Published: December 2008

Abstract
These studies sought to test the hypothesis that potassium-stimulated phasic myometrial contractions utilize cytosolic calcium oscillation-like mechanisms comparable to those activated in response to oxytocin. Uterine tissue was obtained from pro-oestrus/oestrus Sprague-Dawley rats. In vitro isometric contraction studies were performed using longitudinal myometrial strips; computer digitalized contraction data were analyzed for contraction area, and normalized for tissue cross-section area. Dose–response studies were performed using potassium chloride with and without inhibitors of cytosolic calcium oscillation mechanisms. Qualitative inositol-phosphate production studies were performed after preloading uterine tissue with [3H]inositol; subsequently, the individual inositol-phosphates produced in response to stimulation were isolated by anion exchange chromatography. Potassium chloride over a concentration of 10 to 30 mm produced a dose-related increase in phasic contractile activity. The potassium-stimulated phasic contractions were significantly suppressed in response to inhibition of phospholipase C, stimulation of protein kinase C, inhibition of calcium-induced calcium release, and prevention of extracellular calcium influx. The qualitative inositol-phosphate production studies confirmed activation of phospholipase C in response to 20 mm potassium. These studies have provided support for the hypothesis that potassium-stimulated phasic myometrial contractions activate intracellular signal transduction mechanisms comparable to those activated in response to hormonal uterotonic agonists.
Journal of Endocrinology (1995) 146, 485–493
Estrogen increases the release of epidermal growth factor from individual pituitary cells in female rats
Authors: Mouihate A , Lestage J 
Published: December 2008

Abstract
Rat mixed anterior pituitary cells from cycling females were microscopically demonstrated to produce epidermal growth factor (EGF), in culture, using a reverse hemolytic plaque assay. Anterior pituitary cells of proestrous female rats secrete more EGF than those of metestrous rats, as evaluated by the mean area and the percentage of EGF plaque-forming cells. Estradiol-17β (10 nm) treatment of metestrous culture for 24 h increased significantly the size of EGF plaque-forming cells (from 1290±58 to 2566 ± 57 μm2, P<0·01) and the percentage of EGF plaque-forming cells (from 20·57 to 28·19%; P<0·01) to a level as high as observed in proestrous cultures (basal mean area 2171 ± 157 μm2, and basal percentage of EGF plaque-forming cells 22·71%). These results suggest that the hormonal status of female rats influences EGF secretion in the anterior pituitary gland and that estradiol is implicated in this phenomenon.
Journal of Endocrinology (1995) 146, 495–500