bluuebunny/crossref_metadata_2025_split huggingface dataset:
Automated repetitive microsampling of blood: growth hormone profiles in conscious male rats
Authors: Clark R. G. , Chambers G. , Lewin J. , Robinson I. C. A. F. 
Published: December 2008

ABSTRACT
A system is described for the automatic collection of small samples of blood from conscious rats. Rats bearing chronic indwelling i.v. catheters were connected via swivels to a multichannel peristaltic pump, solenoid valves and a fraction collector. A microcomputer controlled the operations involved in the removal of blood and its deposition into a fraction collector for subsequent direct radioimmunoassay for GH. Blood samples of 10–20 μl could be collected, into a total volume of 100 μl heparinized saline, from up to eight rats simultaneously every few minutes for many hours. This collection method avoided major blood loss and did not require transfusions of donor blood to maintain blood volume. Using a doublelumen cannula it was possible to inject or infuse into the animals while sampling blood. The system was used to investigate in detail the secretion of GH in conscious male rats. The 3-hourly endogenous secretory rhythm of GH was maintained for up to 44 h with episodes of GH secretion being multicomponent. Endogenous secretion was suppressed by constant i.v. infusions of somatostatin, with repetitive sampling showing in detail a rapid rebound secretion of GH after terminating the somatostatin infusions. Four injections of a fragment of GH-releasing factor, given at 3-hourly intervals, produced entrained GH responses, but the subsequent recovery of endogenous GH pulsing was delayed for up to 12 h. This method for the automatic microsampling of blood in small animals gives a very detailed description of the blood levels of hormones secreted in a highly episodic fashion, and could be widely applicable to other endocrine studies.
J. Endocr. (1986) 111, 27–35
Arginine infusion blocks the action of parathyroid hormone but not arginine vasopressin on the renal tubule in man
Authors: O'Reilly D. St.J. , Fraser W. D. , Penney M. D. , Logue F. C. , Cowan R. A. , Williams B. C. , Walters G. 
Published: December 2008

ABSTRACT
Six male volunteers were infused with arginine (0·5 g/kg body weight) over 30 min, after an overnight fast and water deprivation. There was a significant decrease in renal phosphate clearance (P<0·025) and urinary cyclic adenosine monophosphate (cAMP) output (P<0·025) during the 60- to 90-min period after the beginning of the infusion; both returned to the preinfusion basal levels within 150 min. The plasma levels of parathyroid hormone (PTH) were not affected by the infusion and remained unchanged during the subsequent 150 min. Plasma levels of arginine vasopressin (AVP) were also not significantly affected although plasma osmolality increased by 6–9 mmol/kg in all subjects. The infusion resulted in a diuresis, and a fall in urine osmolality but a decrease in free-water clearance; creatinine clearance was not affected. Six other subjects were given a bolus of 230 i.u. PTH intravenously, and 20 days later this was repeated during an infusion of arginine (0·5 g/kg body weight). There was a significant decrease in urinary phosphate (P< 0·025) and cAMP excretion (P<0·05) when PTH was given with arginine. It is suggested that arginine blocks the action of PTH on the proximal renal tubule but not that of vasopressin on the distal nephron and collecting ducts.
J. Endocr. (1986) 111, 501–506
Inhibitory effect of various radiographic contrast agents on secretion of thyroxine by the dog thyroid and on peripheral and thyroidal deiodination of thyroxine to tri-iodothyronine
Authors: Laurberg P. , Boye N. 
Published: December 2008

ABSTRACT
In previous studies we have found that the cholecystographic contrast agent ipodate induced a rapid, sustained and reversible inhibition of thyroxine (T4) secretion from perfused dog thyroid lobes. This type of inhibition of thyroid secretion has not been observed previously. To evaluate whether this effect is unique for ipodate, ten other iodine-containing radiographic contrast agents were tested. The four agents used for cholecystography (iocetamate, iodipamide, ioglycamate and iotroxate) all induced rapid inhibition of T4 secretion from TSH-stimulated perfused dog thyroid lobes, while none of six agents predominantly excreted through the kidneys (amidotrizoate, metrizamid, metrizoate, iodamide, diodone and ioxithalamate) influenced T4 secretion significantly. All the cholecystographic agents inhibited T4 deiodinases from dog thyroid and liver. Diodone also inhibited the deiodinases while none of the other compounds tested had any effect.
The results indicate that the structure necessary to inhibit thyroid secretion is common to a number of cholecystographic agents and that it could be related to the structure responsible for the inhibitory effect of cholecystographic agents on T4 deiodinases.
J. Endocr. (1987) 112, 387–390
Naloxone stimulates sexual behaviour in lactating rats
Authors: Forsberg G. , Eneroth P. , Södersten P. 
Published: December 2008

ABSTRACT
During lactation the display of sexual receptivity in response to treatment with oestradiol benzoate (OB; 2 or 10 μg) and progesterone (0·5 mg) was inhibited, but the behaviour could be activated by i.p. (5 mg) or intracerebroventricular (i.c.v.; 100 μg) but not intrathecal (i.t.; 100 or 500 μg) injections of the opioid peptide receptor antagonist naloxone. The behaviour was also inhibited in ovariectomized rats in which serum progesterone and prolactin levels had been raised by treatment with progesterone implants and the dopamine receptor antagonist domperidone, and the uterine cervix had been stimulated. Intraperitoneal injections of naloxone (1 mg) reactivated the behaviour of cervically stimulated rats. The concentration of β-endorphin-like immunoreactivity in the serum of lactating rats (42·8± 9·2 pmol/l) was not raised above that of ovariectomized rats (35·8 ± 8·4 pmol/l) nor was the concentration of β-endorphin-like immunoreactivity altered in the pituitary gland (22·5 ± 2·5 pmol/l), midbrain central grey (6·3 ± 2·2 pmol/l) or hypothalamus (5·6± 2·6 pmol/l) of lactating rats in comparison with ovariectomized rats (24·8 ± 4·4, 4·0 ± 2·0 and 4·7 ± 1·4 pmol/l respectively). Adrenalectomy facilitated the display of sexual behaviour in lactating rats treated with OB plus progesterone and caused a slight increase in serum β-endorphin-like immunoreactivity (30·5± 2·7 pmol/l) compared with that in non-adrenalectomized lactating rats (26·1 ± 2·1 pmol/l). It is suggested that an opioid peptide, but probably not β-endorphin, inhibits sexual behaviour during lactation and after cervical stimulation.
J. Endocr. (1987) 113, 423–427
Effects of injecting growth hormone or thyroxine on milk production and blood plasma concentrations of insulin-like growth factors I and II in dairy cows
Authors: Davis S. R. , Gluckman P. D. , Hart I.C. , Henderson H. V. 
Published: December 2008

ABSTRACT
Three cows received injections of thyroxine (T4; 20 mg/day), four cows GH (40 mg/day) and three cows saline (control; 10 ml/day) on days 5–8 of a 16-day experimental period during peak lactation. Milk yield increased 13% in cows given GH (from 14·6 to 16·5 kg/day) and 15% in cows given T4 (from 15·8 to 18·2kg/day) but did not change in control cows. Injection of T4 increased milkfat and lactose content but reduced milk protein content. Injection of GH was without effect on milk composition during the injection period but milk protein rose after injections ceased.
Injection of T4 increased plasma concentrations of T4 and tri-iodothyronine six- to sevenfold, with maxima occurring on day 9. Injection of GH increased the plasma concentration of GH five- to tenfold 5 h after injection. The plasma concentration of insulin-like growth factor I (IGF-I) was increased in cows given GH in both morning (08.30 h) and afternoon (14.30 h) blood samples, the difference being greatest in afternoon samples in which plasma IGF-I content increased from 3·3 to 6·8 nmol/l. Injection of T4 reduced the plasma concentration of IGF-I in morning samples but the concentration in afternoon samples remained relatively constant throughout the 16-day experimental period. The plasma concentration of IGF-II rose in morning samples in all treatment groups to reach a maximum of 200–250 nmol/l by day 9.
The galactopoietic response to injection of GH but not T4 was associated with an increase in plasma concentration of IGF-I. Changes in plasma concentration of IGF-II were not associated with changes in milk yield.
J. Endocr. (1987) 114, 17–24
Effect of different photoperiods on concentrations of 5-methoxytryptophol and melatonin in the pineal gland of the Syrian hamster
Authors: Skene D. J. , Pevet P. , Vivien-Roels B. , Masson-Pevet M. , Arendt J. 
Published: December 2008

ABSTRACT
Specific, sensitive and direct radioimmunoassays have been used to determine the daily patterns of 5-methoxytryptophol (ML) and melatonin in the pineal glands of Syrian hamsters kept in different photo-periods: 8 h light: 16 h darkness (8L:16D), 14L: 10D and 16L: 8D. A rhythm in pineal ML was evident in animals in all the photoperiods, with high daytime levels (641±35 (s.e.m.) fmol/gland; n=162) which dropped to 119±16 fmol/gland (n = 44) 7·1– 7·5 h after lights out. The duration of low night-time ML levels was proportional to the length of the dark phase (1·2 h in 16L:8D, 5·4 h in 14L: 10D and 8·4 h in 8L: 16D). A marked daily rhythm in melatonin was also present in hamsters in the different photoperiods, with daytime levels of 323 ± 34 fmol/gland (n = 129) and night-time peak concentrations of 3676 ± 336 fmol/gland (n = 22). The duration of high nocturnal melatonin levels was dependent upon the length of the dark phase (4·1 h in 16L: 8D, 4·5 h in 14L: 10D and 12·5 h in 8L: 16D). Linear regression analysis revealed a statistically significant inverse relationship between pineal ML and melatonin levels in 8L: 16D (P< 0·001), 14L: 10D normal (P<0·05) and 14L: 10D shifted (P<0·001) photoperiods. After advancing the lighting schedule by 10 h (14L: 10D, lights off at 04.00 h), pineal ML and melatonin rhythms became entrained to the new lighting regimen.
The daily rhythms in pineal ML and melatonin in the Syrian hamster thus depend on the prevailing photoperiod, a reciprocal relationship existing between pineal ML and melatonin concentrations.
J. Endocr. (1987) 114, 301–309
Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare
Authors: Alexander S. L. , Irvine C. H. G. 
Published: December 2008

ABSTRACT
We have developed a non-surgical technique for longterm collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2–6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae and all mares ovulated, showing that the procedure did not affect the reproductive axis. In all pituitary-cannulated mares the secretion of gonadotrophin-releasing hormone (GnRH), FSH and LH occurred almost continuously with broad, concurrent pulses of the three hormones superimposed upon this tonic background. Only 9% of the GnRH pulses appeared to be ineffective in inducing a rise in gonadotrophin levels. When measured in pituitary blood, gonadotrophin pulse frequency varied from 0·45 pulses/h early in the LH surge to 1·87 pulses/h at the time of ovulation. In contrast, mean pulse frequency measured in jugular blood did not exceed 1 pulse/h throughout the periovulatory period in cannulated or non-cannulated mares. The low amplitude of jugular pulses (< 50% fractional increase) may have caused problems in identifying the pulses. In the two mares in which pituitary venous blood was sampled during more than one period before ovulation, GnRH secretion tended to be lower on the day of ovulation (day 0) than earlier in oestrus (ratio day 0:day −1; mare WV = 0·58, mare LS = 0·66), whereas LH secretion rate was higher on the day of ovulation (ratio day 0:day −1; mare WV = 1·54, mare LS = 6·68). These studies show that the painless and non-invasive collection of pituitary venous blood, which is possible only in horses, can provide a useful tool for studying hypothalamic-pituitary interactions under completely physiological conditions.
J. Endocr. (1987) 114, 351–362
Cholecystokinin peptides as local modulators of thyroidal calcitonin secretion in the dog?
Authors: Laurberg P. , Rehfeld J. F. 
Published: December 2008

ABSTRACT
Cholecystokinin (CCK) is a heterogeneous gut hormone which is also synthetized in extra-intestinal endocrine cells and neurones. In order to examine the possibility that CCK peptides are local modulators of calcitonin secretion, we have studied the structure– activity relationship on calcitonin secretion from perfused canine thyroid lobes as well as the presence and molecular nature of CCK in the thyroid. Peptides containing the intact COOH-terminal tetrapeptide amide of CCK (CCK-4, CCK-5, pentagastrin, CCK-8 and gastrin-17) all induced dose-dependent (0·1, 3 and 100 nmol/l) increases in calcitonin release (P<0·05, n =4) with biphasic secretion during 6-min infusion periods. The deamidated tetrapeptide and the COOHterminal tripeptide were without effect. Gel chromatography of neutral water and acid–ethanol extracts of thyroid tissue, monitored by sequence-specific CCK and gastrin radioimmunoassays, disclosed a variety of CCK and gastrin peptides of which a predominant form resembled small molecular forms like CCK-4 and CCK-5. The presence in the thyroid of small CCK-like peptides and the pronounced effect of such peptides on calcitonin secretion suggest that calcitonin secretion is modulated by local release of small CCK peptides. They could originate from intrathyroidal nerves or from sub-populations of C-cells.
J. Endocr. (1987) 115,77–82
Endogenous opioid control of pulsatile LH secretion in rams: modulation by photoperiod and gonadal steroids
Authors: Lincoln G. A. , Ebling F. J. P. , Martin G. B. 
Published: December 2008

ABSTRACT
The role of endogenous opioid peptides in the inhibitory control of pulsatile LH secretion was studied in adult Soay rams at different stages of the seasonal reproductive cycle, entrained by an artificial lighting regimen of alternating 16-week periods of long and short days. The LH responses to the acute administration of naloxone (opioid antagonist) and morphine (opioid agonist) were measured in intact rams (n = 7), testosterone-implanted castrated rams (n = 8) and castrated rams (n = 8) to assess the interaction between photoperiod and gonadal steroids in the opioid control of LH secretion.
In the intact and testosterone-implanted castrated rams, naloxone (1·7 mg/kg i.v.) increased and morphine (1·0 mg/kg i.v.) decreased mean LH concentrations and LH pulse frequency during the sexually active phase under short days, but these effects were reduced or absent during the inactive phase under long days. The changes in the LH responses occurred in close parallel with the photoinduced changes in endogenous LH secretion. In the castrated rams receiving no supplementary testosterone, plasma LH concentrations were permanently raised and there were only minor changes related to the photoperiod. Naloxone (1·7 mg/kg) induced transient increases in LH secretion at all stages, and morphine (1·0 mg/kg) failed to suppress LH levels under both short and long days. LHRH stimulation tests revealed that there were changes in LH release related to the induced reproductive cycle in the intact and testosterone-implanted rams but not in the castrated rams; these changes in the responsiveness of the pituitary gonadotrophs to LHRH could not account for the changes in the LH response to the opiate drugs.
These results illustrate that an endogenous opioid mechanism is involved in the tonic inhibition of LH secretion acting to regulate the pulsatile release of LHRH from the hypothalamus. This system can be shown to be functional in a steroid-dependent manner in the sexually active phase of the seasonal cycle, but not in the inactive phase of the cycle when non-opioidergic mechanisms are presumed to predominate in the inhibition of LH secretion.
J. Endocr. (1987) 115, 425–438
Insulin-like growth factor-I stimulates oxytocin and progesterone production by bovine granulosa cells in culture
Authors: Schams D. , Koll R. , Li C. H. 
Published: December 2008

ABSTRACT
The effect of insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), fibroblast growth factor (FGF) and nerve growth factor (NGF) on production of oxytocin and progesterone by cultured bovine granulosa and luteal cells was studied. Secretion of oxytocin was stimulated, in a dose-dependent manner, by IGF-I at 48 and 120 h of culture to levels much higher than those after stimulation with LH, FSH, EGF, FGF or NGF. A similar effect of IGF-I was observed for progesterone but, in contrast to oxytocin, secretion of progesterone was not increased by EGF, NGF or FGF. During primary culture, for 4 h, of dispersed bovine luteal cells obtained from corpora lutea between days 4 and 10 of the oestrous cycle, all the growth factors tested failed to stimulate secretion of oxytocin or progesterone. The data suggest the relevance of growth factors (especially IGF-I) for ovarian physiology and their possible importance for differentiation of follicles and luteinization.
J. Endocr. (1988) 116, 97–100
Influence of parasitism on plasma concentrations of growth hormone, somatomedin-C and somatomedin-binding proteins in calves
Authors: Elsasser T. H. , Rumsey T. S. , Hammond A. C. , Fayer R. 
Published: December 2008

ABSTRACT
A parasitic disease model (sarcocystosis) was used to study the effects of infection and associated plane of nutrition on GH and somatomedin-C (SM-C) patterns in plasma, and SM-C binding protein patterns in plasma from 4-month-old male Holstein calves. Calves, matched by age and rate of growth before the experiment, were divided into three treatment groups (n = 7). In the first (control), animals were uninfected and food was available ad libitum; in the second, animals were infected with Sarcocystis cruzi and food was available ad libitum. The third group consisted of uninfected animals pair-fed to the level of feed intake of the infected animals. Blood samples were obtained at various times after infection for analysis of the secretory patterns of GH (day 27 after infection, samples every 10 min for 6 h), SM-C (days 27, 35 and 58 after infection) or binding protein (day 42 after infection). Samples were analysed for GH and SM-C by radioimmunoassay. Relative molecular weights of binding proteins were assessed by elution patterns from gel permeation columns.
Clinical signs of infection were manifest abruptly on day 26 after infection. Voluntary feed intakes of infected calves as a per cent of control calves were 18, 46 and 78 on days 27, 35 and 58 after infection respectively. Plasma GH concentrations were lower in infected and pair-fed than in control calves (P < 0·05). Plasma SM-C concentrations were reduced in calves with diminished feed intakes and lower still in infected calves (P < 0·05). Plasma SM-C was positively correlated with nitrogen retention across treatment groups (r = 0·81). Two classes of binding proteins differing in molecular weight were identified. The relative amounts of each binding protein in plasma were reduced during low feed intake with some differences in the endogenous saturation affected by infection.
These data suggest that altered growth and metabolism in parasitized calves may arise in part from both nutritional and infection-mediated effects on the regulation of GH, SM-C and SM-C binding proteins.
J. Endocr. (1988) 116, 191–200
Vasoactive intestinal peptide and the stimulation of lactotroph growth by oestradiol in rats
Authors: Prysor-Jones R. A. , Silverlight J. J. , Kennedy S. J. , Jenkins J. S. 
Published: December 2008

ABSTRACT
Treatment with a high dose of oestradiol for 6 months caused hyperprolactinaemia and pituitary hyperplasia in female Wistar–Furth rats. Changes in the vasoactive intestinal peptide (VIP) and dopamine content of the hypothalamus and pituitary were also found. The hypothalamic dopamine concentration was only slightly reduced and, although the concentration of dopamine in the pituitary was less in treated animals, the total pituitary content was increased. The concentration of VIP in the pituitary was increased by oestradiol treatment but decreased in the non-median eminence hypothalamus. In the median eminence the VIP content was increased by oestradiol treatment and the amount present correlated positively and significantly with pituitary wet weight in animals treated with both oestradiol and fluphenazine. In Fischer 344 rats, oestradiol produced greater incremental changes in pituitary wet weight and plasma concentrations of prolactin than in Wistar controls and the increase in the pituitary concentration of VIP was five times greater. Although peptide turnover has not been measured, these results suggest that oestradiol, as well as having a direct action, stimulates pituitary lactotrophs by increasing pituitary concentrations of VIP.
J. Endocr. (1988) 116, 259–265
Diurnal variation in the effect of potassium depolarization on vasoactive intestinal polypeptide release from rat hypothalamus: a possible role for adrenaline
Authors: Burns G. , Brown B. L. , Dobson P. R. M. 
Published: December 2008

ABSTRACT
We have previously reported a lack of effect of a depolarizing concentration of K+ on the release of vasoactive intestinal polypeptide (VIP) from the perifused rat hypothalamus, and suggested that this was due to the presence of an endogenous inhibitor of the release of VIP. In this study we report that the VIP response to K+ was restored if the hypothalami were obtained from animals killed during the dark phase of the light–dark cycle. Adrenaline blocked the K+-stimulated release of VIP when used at a concentration of 0·1 μmol/l; however, at a higher concentration (10 μmol/l) adrenaline stimulated the basal release of VIP. The use of specific receptor antagonists indicated that this dual effect of adrenaline was mediated through two distinct receptors, a stimulatory β-receptor and an inhibitory α2-receptor. The suggestion that adrenaline might be the endogenous inhibitor of the release of VIP, mediating the diurnal variation in the effect of K+, was supported by studies where 50 mmol K+/l was perifused concomitantly with an α2-antagonist, restoring the VIP response to K+ in light-phase hypothalami. In conclusion, adrenaline has a dual role in the control of VIP release and may function to inhibit the K+-stimulated release of VIP in our system.
J. Endocr. (1988) 116, 335–341
Quantitative in-situ hybridization histochemistry in the rat pituitary gland: effect of bromocriptine on prolactin and pro-opiomelanocortin gene expression
Authors: Levy A. , Lightman S. L. 
Published: December 2008

ABSTRACT
The temporal effect of orally administered bromocriptine on pro-opiomelanocortin (POMC) and prolactin gene expression in male Sprague–Dawley rats was examined using in-situ hybridization histochemistry. Messenger RNA in the anterior and intermediate lobes could be clearly delineated in each section. Administration of bromocriptine resulted in a reduction in hybridization of 35S-labelled cDNA probe to prolactin mRNA from 0·69 × 1012 to 0·29 × 1012 copies bound/g after 150 h. POMC mRNA in the anterior lobe remained unchanged with 0·08 × 1012 copies of probe bound/g for the duration of the experiment, while in the intermediate lobe it decreased from 2·44 × 1012 to 0·44 × 1012 copies of probe bound/g at 150 h. The rate of reduction in intermediate lobe POMC mRNA was similar to that of prolactin mRNA for the first 24 h but was subsequently more rapid and more profound, falling to 20% of the control value at 84 h and to 18% at 150 h.
J. Endocr. (1988) 118, 205–210