bluuebunny/crossref_metadata_2025_split huggingface dataset:
EFFECT OF LONG-TERM INFUSION OF AN LH-RELEASING HORMONE AGONIST ON TESTICULAR FUNCTION IN BULLS
Authors: Rechenberg W. v. , Sandow J. , Klatt P. 
Published: December 2008

ABSTRACT
Continuous administration of LH-releasing hormone (LHRH) agonists is an effective method of suppressing testosterone secretion in the male. The effect of the LH-releasing hormone (LHRH) agonist, buserelin, administered to bulls by constant infusion from osmotic minipumps was studied. In one experiment with four treated and one control bull, 109 pg buserelin/day were administered for 22 days. Immediately after implantation, serum testosterone concentrations rose from below 35 nmol/l to 35-105 nmol/l, and all four buserelin-infused bulls showed increased testosterone secretion during the treatment period. After removal of the minipumps, testosterone concentrations decreased to pretreatment levels. In a second experiment bulls were infused for 42 days (four treated and one control), and identical results were obtained. Testosterone secretion was stimulated (52-87 nmol/l serum) during the entire treatment period. These results demonstrate that conditions for stimulation of the pituitary-testicular axis may vary between species. Infusion of low doses of LHRH-agonists in bulls has an extended stimulatory effect without immediate desensitization of gonadotrophin release.
Effect of graded doses of gonadotrophin-releasing hormone on serum LH concentrations in mares in various reproductive states: comparison with endogenously generated LH pulses
Authors: Alexander S. L. , Irvine C. H. G. 
Published: December 2008

ABSTRACT
Luteinizing hormone release induced by a range of small (3·3–33 μg) and large (300–500 μg) i.v. doses of gonadotrophin-releasing hormone (GnRH) was measured in acyclic (n = 4), luteal phase (n = 3) and follicular phase (n = 5) mares and compared with endogenously generated LH pulses in the same reproductive states. Extrapolation from log–linear dose–response curves showed that an LH pulse comparable to an endogenous one would be simulated by i.v. injection of 7·0 (n = 4) and 4·1 (n = 6) μg GnRH in luteal and follicular phase mares respectively; a much smaller dose than the 500 μg usually given clinically or experimentally. In acyclic mares (n = 4), LH pulses occurred too infrequently to be characterized. At small doses of GnRH the amount of LH released by the same dose was similar in all three reproductive states, although the steroid hormone milieu differed markedly. This implies that observed differences between states in mean (± s.e.m.) serum LH concentrations (0·7 ± 0·01, 1·2 ± 0·03 and 11·6 ± 0·33 (μg/l) in acyclic, luteal and follicular phase mares respectively) were produced by differences in GnRH pulse frequency and/or amplitude and not by steroid-mediated changes in pituitary response to GnRH. In acyclic, luteal and follicular phase mares, LH pulse frequency was: immeasurably low, 0·09 and 1·14 pulses/h respectively, which supports the important contribution of pulse frequency to determining mean LH concentration. The LH response to large doses of GnRH was significantly greater in the luteal than in the follicular phase, and was greater than the response to 33 μg in the luteal phase but not in the other two states. Thus, to a large but not to a small dose of GnRH, the pituitary appeared most responsive in the luteal phase. Therefore, in studies of the physiology of the hypothalamic-pituitary system, small doses of GnRH, which induce physiologically sized LH responses, may be preferred to large doses, which result in a level of stimulation to which the pituitary is never naturally exposed and to which it may respond in a non-physiological manner.
J. Endocr. (1986) 110, 19–26
The origin of circulating calcitonin gene-related peptide in the rat
Authors: Zaidi M. , Bevis P. J. R. , Abeyasekera G. , Girgis S. I. , Wimalawansa S. J. , Morris H. R. , MacIntyre I. 
Published: December 2008

ABSTRACT
It is known that in addition to the calcitonin precursor the calcitonin gene also encodes a novel peptide, calcitonin gene-related peptide (CGRP). This potent vasodilator has been found in the circulation of man. This present study demonstrates that CGRP is also found in the circulation of the rat and that plasma CGRP comes from two different sources: the thyroid, a major source in old rats, and the perivascular nerves probably at all ages.
J. Endocr. (1986) 110, 185–190
Reduced affinity of intestinal receptors for 1,25-dihydroxycholecalciferol in phosphorus-deficient chicks
Authors: Bar A. , Hurwitz S. 
Published: December 2008

ABSTRACT
The binding of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) to its intestinal receptor was studied in chicks fed a phosphorus (P)-deficient diet. The equilibrium association constant (Ka) was determined by Scatchard analysis. Association (Kass) and dissociation (Kdis) rate constants were determined in experiments on hormone uptake and release respectively. The Ka, determined at 4, 12 and 19 °C, decreased progressively during P deficiency, due to the decrease in Kass, but Kdis was not affected. During prolonged P deficiency the concentration of binding sites (Nmax) also decreased. Duodenal calcium-binding protein (CaBP) increased during 10 days of P deficiency and then decreased.
The long-term decrease in receptor affinity and Nmax may account for the observed reduction in receptor occupancy and the decrease in the high level of intestinal CaBP stimulated during early P deficiency. The resulting decrease in Ca absorption may minimize the hypercalcaemia induced by the deficiency.
J. Endocr. (1986) 110, 217–223
Control of sex steroid-binding protein (SBP) in the male little brown bat: relationship of plasma thyroxine levels to the induction of plasma SBP in immature males
Authors: Kwiecinski G. G. , Damassa D. A. , Gustafson A. W. 
Published: December 2008

ABSTRACT
The seasonally reproductive male little brown bat (Myotis lucifugus lucifugus) exhibits marked increases in plasma concentrations of sex steroid-binding protein (SBP) in the spring following arousal from hibernation. In this species an increase in SBP levels is induced prematurely in male bats aroused during the first half of hibernation and housed under long photoperiods; however, this rise is inhibited in bats housed under short photoperiods. In order to investigate the physiological role of the thyroid gland in the regulation of plasma SBP activity, plasma total thyroxine (T4) and SBP concentrations were determined in immature male little brown bats prematurely aroused from the first half of hibernation and maintained on either a short or long photoperiod. For this purpose a radioimmunoassay for the measurement of total T4 in bat plasma was established and validated. The results showed that immature male little brown bats aroused prematurely from hibernation and housed under a long spring-like photoperiod exhibited marked increases in plasma T4 and SBP concentrations, while animals housed under a short photoperiod showed only marginal increases in SBP, and plasma T4 remained undetectable. These results suggest that the thyroid gland, through the action of T4, may normally play an important role in the control of the post-arousal rise in plasma SBP concentrations in the little brown bat.
J. Endocr. (1986) 110, 271–278
Effect of human α-atrial natriuretic polypeptide on adrenocortical function in man
Authors: Ohashi M. , Fujio N. , Kato K. , Nawata H. , Ibayashi H. , Matsuo H. 
Published: December 2008

ABSTRACT
To determine the effects of atrial natriuretic polypeptide (ANP) on plasma levels of ACTH, cortisol, aldosterone and dehydroepiandrosterone (DHEA), synthetic human α-ANP (hα-ANP) was infused i.v. into eight normotensive, disease-free volunteers, at a dose and duration previously found to be sufficient to produce apparent cardiovascular and renal effects.
The mean basal concentration of plasma ACTH determined by radioimmunoassay was 18·2 ± 3·1 ng/l. Plasma ACTH concentrations tended to be decreased during the infusion in all subjects. However, the change in plasma ACTH concentrations during infusion of hα-ANP was essentially the same as that during the infusion of saline. The mean plasma cortisol concentration was significantly suppressed from 25 to 40 min after the end of synthetic hα-ANP infusion. At 90 min after infusion, the mean plasma level of cortisol reverted to the pretreatment level. There was a non-significant increase in plasma renin activity following the infusion. The mean plasma aldosterone concentration was reduced by 15% (P < 0·05) during the infusion and returned to preinfusion levels 10 min after termination of the infusion, after which the mean plasma concentration declined to the level seen during infusion. Administration of hα-ANP had no significant influence on plasma DHEA concentrations, but there was a tendency to decrease during the infusion.
Our data suggest that synthetic hα-ANP inhibits adrenocortical steroidogenesis in man.
J. Endocr. (1986) 110, 287–292
Increase in DNA polymerase α activity associated with DNA synthesis due to FSH or oestrogen in ovaries of immature rats
Authors: Usuki S. , Shioda M. 
Published: December 2008

ABSTRACT
DNA polymerase activities and DNA content of ovaries from immature intact rats (4–29 days after birth), hypophysectomized rats and hormone-treated hypophysectomized rats were measured. During normal ovarian growth DNA polymerase α activity and DNA content of ovaries increased. The polymerase activity decreased gradually after hypophysectomy without any alteration in the DNA content. Administration of ovine FSH (2 μg/day) or oestradiol-17β (1 mg/day) to hypophysectomized rats enhanced ovarian DNA content and DNA polymerase α activity, whereas DNA polymerase β activity did not change significantly. These results suggest that DNA polymerase α participates in DNA synthesis in these ovaries. The specific activity of DNA polymerase α (the activity per μg DNA) in the ovaries increased between 4 and 14 days after birth, and then remained almost constant; the specific activity declined gradually after hypophysectomy. Administration of FSH or oestradiol-17β but not of ovine LH, progesterone or testosterone to hypophysectomized rats restored the specific activity. Mixing experiments with different kinds of ovarian extracts suggested that no activators of DNA polymerase α were present in the extracts.
These results suggest that FSH or oestrogen causes the induction of DNA polymerase α accompanied by DNA synthesis during cell proliferation in ovaries of immature rats.
J. Endocr. (1986) 110, 353–360
Potentiation of the somatogenic and lactogenic activity of human growth hormone with monoclonal antibodies
Authors: Aston R. , Holder A. T. , Preece M. A. , Ivanyi J. 
Published: December 2008

ABSTRACT
Monoclonal antibodies of certain epitope specificity have been shown to produce a marked dose-dependent enhancement of the somatogenic and lactogenic activity of human GH (hGH). Two antibodies (EB1 and EB2), binding to distinct antigenic determinants and expressed on both hGH and human chorionic somato-mammotrophin (hCS), significantly enhanced the hGH-stimulated uptake of 35S-labelled sulphate into cartilage. Similarly, these antibodies enhanced the lactogenic activity of both hGH and hCS in the pigeon crop sac test. Two hGH specific monoclonal antibodies (QA68 and NA71), defining a further two epitopes, exhibited only modest enhancing or inhibitory activity in these assays, whereas the binding of certain combinations of monoclonal antibodies resulted in either reversal of enhancement or inhibition of hormone activity. Univalent antibody fragments derived from EB1 were as enhancing as the intact antibody indicating that bivalency dependent mechanisms were not involved in the phenomenon. Enhancing monoclonal antibodies were relatively poor inhibitors of 125I-labelled hGH binding to liver microsomal receptors, which is in contrast with their previously described property of potent suppression of hGH interaction with lymphoid cell receptors. It is tentatively concluded that 'restriction' of hormone binding to particular hGH receptors, relevant to somatic growth or lactogenic activity, may play a role in the enhancement phenomenon of hGH in vivo.
J. Endocr. (1986) 110, 381–388
Effect of prostaglandins E2 and F2α on membrane calcium binding, Ca2+/Mg2+-ATPase activity and membrane fluidity in rat myometrial plasma membranes
Authors: Deliconstantinos G. , Fotiou S. 
Published: December 2008

ABSTRACT
Myometrial plasma membrane (MPM) preparations from rats treated with oestradiol were obtained by discontinuous sucrose-gradient centrifugation. The preparations contained calcium-stimulated and magnesium-dependent ATPase (Ca2+/Mg2+-ATPase). A dramatic decrease in the activity of Ca2+/Mg2+-ATPase was observed when preparations were treated with 0·025–10μmol protaglandins E2 and F2α (PGE2 and PGF2α)/l. In contrast, there was a marked increase in MPM-bound 5′-nucleotidase activity at low concentrations (up to 2 μmol/l) of PGE2 and PGF2α; higher concentrations (up to 10 μmol/l), however, led to a progressive inhibition of enzyme activity. Association (specific and non-specific binding) of PGE2 and PGF2α with MPM at pH 7 was found to require Ca2+ (half-maximal concentration approximately 0·7 mmol/l). Changes in the allosteric properties of MPM-bound 5′-nucleotidase by concanavalin A (as reflected by changes in the Hill coefficient) indicated a fluidization of the membrane induced by PGE2 and PGF2α. The steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene-labelled MPM decreased in PGE2- and PGF2α-treated MPM from 1·24 ± 0·04 (s.d.) to 0·66 ± 0·01 and 0·74 ± 0·01 respectively, which is consistent with a general increase in membrane fluidity. It is suggested that PGE2 and PGF2α promote changes in the physical properties of MPM which may be relevant to the induction of uterine contractions by enzymatic regulation of intracellular calcium concentrations.
J. Endocr. (1986) 110, 395–404
Reproduction in the vervet monkey (Cercopithecus aethiops): endometrial oestrogen and progestin receptor dynamics during normal and prolonged menstrual cycles
Authors: Kudolo G. B. , Mbai F. N. , Eley R. M. 
Published: December 2008

ABSTRACT
Sixteen individually caged adult female vervet monkeys (Cercopithecus aethiops), whose reproductive parameters had been studied for 5 years, were hysterectomized/ovariectomized during three reproductive states; i.e. the late follicular (15·4 ± 4·7 (s.d.) days) and luteal (27·8 ± 4·7 days) phases of the normal cycle (20–50 days), and during prolonged intermenstrual intervals (PII; 99·0 ± 2·5 days since the previous menses). These latter animals showed characteristics of both follicular and luteal phases; i.e. their ovaries contained both corpora lutea and large antral follicles and systemic oestradiol and progesterone concentrations were raised. Analysis of cytoplasmic oestrogen and progestin receptors (CER and CPR) revealed that endometrium during PII had CER levels of 0·58 ± 0·07 pmol/mg protein, similar to those of the follicular phase (0·60 ± 0·12); CPR levels (1·20 ± 0·87) were not different from those of the luteal phase (1·05 ± 0·45). The ratio of CPR to CER during the luteal phase was about tenfold higher than that of the follicular phase. Levels during PII were intermediate between the two phases. Under receptoractivating conditions, the DNA-binding components of the PII cytoplasmic fraction underwent over 40% loss while those present during both phases of the normal cycle doubled. The hormone-binding sites at all times remained intact indicating that the DNA and hormone-binding sites are distinct on both CER and CPR.
Less than 50% interaction of CER/CPR with DNA-cellulose was obtained, indicating the presence of only limited quantities of cytoplasmic activating factors which may be a prerequisite for receptor binding to the genome. During PII, factors which deactivate DNA-binding sites may also have been induced. Extensive accumulation of nuclear oestrogen receptor was evident in PII endometrium with 80% being salt-resistant. This level is higher than that in the follicular and luteal phases (37 and 52% respectively). These data, suggesting a possible aberration of receptor activation in vitro and receptor processing in vivo, may be indicative of endometrial dysfunction during PII. This could lead to a delay in menstruation.
J. Endocr. (1986) 110, 429–439
Microheterogeneity of anterior pituitary FSH in the male rat: isoelectric focusing pattern throughout sexual maturation
Authors: Ulloa-Aguirre A. , Mejia J. J. , Dominguez R. , Guevara-Aguirre J. , Diaz-Sánchez V. , Larrea F. 
Published: December 2008

ABSTRACT
Anterior pituitary glands were removed from male rats at 5, 10, 15, 18, 21, 28, 30, 40, 45, 50 and 90 days of age, and the multiple forms of FSH present within them were separated by polyacrylamide gel–isoelectric focusing (PAGE–IEF; pH range 3·0–8·0). Gel eluents were analysed for FSH content by radioimmunoassay (RIA) and a specific radioreceptor assay (RRA). All pituitaries studied exhibited one or more peaks of immunoactive FSH within a pH range of 7·0–3·0; the major peak exhibited an isoelectric point (pi) of 4·9–4·0. Between 25 and 56% of anterior pituitary FSH obtained from rats 5–30 days old focused within a pH range of 4·9–4·5, whilst in older animals (≥40 days) this pH range contained 17–27% of the total FSH recovered. In contrast, in animals 40–90 days old, the greatest proportion of immunoactive FSH (42–62% of the total immunoactivity recovered) focused within a pH range of 4·4–4·0; further, only these groups of animals exhibited a significant proportion of anterior pituitary FSH with a pI ≤3·9. Between 14 and 21% of total FSH from 5- to 30-day-old rats focused within a pH range of 5·4–5·0, whereas in older animals this pH range contained 6–9% of the total FSH recovered. These shifts in FSH pI occurred at the time of appearance of spermiogenesis, at 45 days of age.
Although the ratio of the concentration of FSH measured by RRA to that measured by RIA declined as the pI of the anterior pituitary FSH decreased throughout a pH range of 7·0–4·0, the most acidic FSH molecules (pI <4·0) showed an abrupt increase in that ratio.
These results demonstrate that the transition from sexual immaturity to adulthood is accompanied by qualitative changes of intracellular pituitary FSH. They contrast with previous findings in female rats in which a shift to less acidic anterior pituitary FSH forms was detected at the time of vaginal opening, thus indicating the existence of a sexual dichotomy in terms of the action of gonadal steroids on the type of FSH molecule synthesized by the anterior pituitary gland.
J. Endocr. (1986) 110, 539–549
1,25-DIHYDROXYCHOLECALCIFEROL STIMULATES CONVERSION OF ANDROSTENEDIONE INTO OESTRONE BY HUMAN SKIN FIBROBLASTS IN CULTURE
Authors: Hodgins M.B. , Murad S. 
Published: December 2008

ABSTRACT
Pre-incubation of monolayer cultures of human skin fibroblasts with 1,25-dihydroxycholecalciferol (1,25-D3; 0.1-10 nmol/l) increased the rate of conversion of androstenedione into oestrone (aromatase activity) when measured subsequently in the presence of a 5α-reductase inhibitor (10 umol/l). Maximal stimulation (14- to 89-fold with 10 nmol 1,25-D3/l) occurred 12 h after addition of the hormone and was maintained for up to 48 h. Stimulation was prevented by cycloheximide. In one cell line high 1,25-D3 concentrations (>30 nmol/l)prevented the increase in aromatase activity; this did not appear to result from direct enzyme inhibition by 1,25-D3. The possibility is considered that 1,25-D3 could act as a physiological regulator of peripheral aromatase. As oestrogens can prevent postmenopausal bone loss, it is speculated that 1,25-D3 might protect against bone resorption by maintaining peripheral oestrogen biosynthesis.
Ontogeny of hypothalamic pituitary function in the pig: pituitary thyrotrophin in the fetus and neonate
Authors: McNamara M. , Vandalem J. L. , Hennen G. , Colenbrander B. , MacDonald A. A. , Van de Wiel D. , Meijer J. 
Published: December 2008

ABSTRACT
Thyrotrophin in individual pituitaries obtained from fetal and prepubertal pigs was quantified by homologous radioimmunoassay (RIA) and heterologous radioreceptor assay (RRA). Relative evolution of pituitary TSH contents and concentrations with age were in good agreement as measured by both assay systems although the quantity of TSH detected by RRA appeared consistently lower than that measured by RIA. Thyrotrophin was first detected in pituitaries of fetal pigs at day 75 of gestation. Thereafter the pituitary content of TSH increased to approximately 45 μg/pituitary in the oldest group tested (6 weeks of age). The pituitary TSH concentration rose sharply until birth (114±1 day post coitum) and thereafter remained increased at a concentration of approximately 400 ng/mg wet weight.
J. Endocr. (1986) 111, 111–115
Effects of an antiserum to rat growth hormone on lactation in the rat
Authors: Madon R. J. , Ensor D. M. , Knight C. H. , Flint D. J. 
Published: December 2008

ABSTRACT
A highly specific antiserum to rat GH (anti-rGH) was used to assess the role of GH in lactation in the rat. When administered alone, anti-rGH had no effect on litter weight gain, whereas bromocriptine reduced serum prolactin concentrations and litter weight gain for up to 7 days when given on day 4 of lactation. When bromocriptine and anti-rGH were given in combination, however, litter weight gain declined even more dramatically so that pups were receiving virtually no milk 2–3 days after treatment. Daily litter exchange failed to prevent this effect. Concurrent injections of highly purified GH (prolactin contamination undetectable) prevented the dramatic decline in litter weight gain induced by combined bromocriptine and anti-rGH treatment, so that these litters grew as well as those receiving bromocriptine alone. Growth hormone did not act by influencing serum prolactin concentrations, which remained low during GH therapy.
Direct effects of anti-rGH or GH on the pups (transferred through the milk) were ruled out since virtually identical results were obtained when milk yield was estimated during a 30-min suckling period after a 3-h separation of mother and pups.
Lactation had virtually ceased 3 days after treatment with both bromocriptine and anti-rGH, but it could be reinitiated by a single injection of prolactin or GH, and subsequent recovery was virtually complete.
The results of this study show that (1) prolactin can maintain a full milk yield in the absence of GH, (2) milk yield is reduced by approximately 50% in the absence of prolactin and (3) milk yield is totally stopped in the absence of prolactin and GH.
Growth hormone therefore appears to play an auxiliary role in lactation which may be important in times of prolactin insufficiency.
J. Endocr. (1986) 111, 117–123
Episodic prolactin and growth hormone secretion not related to the actual suckling activity in lactating rats
Authors: Nagy G. , Kacsóh B. , Halász B. 
Published: December 2008

ABSTRACT
In order to characterize the secretion pattern of prolactin and GH in freely behaving lactating rats, frequent serial blood samples were collected through indwelling atrial cannulae and their prolactin and GH concentrations determined by radioimmunoassay. At the time of blood sampling, physical contact with the pups was recorded. Plasma prolactin and GH levels showed episodic changes which were independent of each other and there was no apparent correlation between hormone levels and contact between mother and pups. The data suggest that there are episodic fluctuations in plasma prolactin and GH concentrations in lactating rats. These changes do not appear to be closely correlated with the proximity of the mother to her pups.
J. Endocr. (1986) 111, 137–142