bluuebunny/crossref_metadata_2025_split huggingface dataset:
Validation of a sensitive direct assay for melatonin for investigation of circadian rhythms in different species
Authors: Webley G. E. , Mehl H. , Willey K. P. 
Published: December 2008

ABSTRACT
The role of melatonin in animals which do not show marked seasonal changes in reproduction is disputed, in part because of the wide variation in reported concentrations. One reason for this may be the difficulties associated with the measurement of low molar concentrations of melatonin and the presence of a wide variety of potentially cross-reacting substances. The availability of a high affinity antiserum has allowed an assay, with low cross-reactivity and good sensitivity, to be established for the direct measurement of melatonin in a wide range of biological fluids, in particular serum, plasma and follicular fluid from man and rat. The high affinity of the antiserum enabled a tritium label of high specific activity to be used, removing the problems associated with the iodination of a small molecular weight compound. Melatonin concentrations in the assay were evaluated by four different methods: UV absorbance, gas chromatography, comparison of the immunoreactive concentrations of the label with the expected concentration by dilution and by comparison with a previously established assay which uses the same antiserum.
Melatonin was measured in serum from twelve healthy women over two 24-h periods; eight women with normal menstrual cycles and four taking the contraceptive pill. Concentrations were found to range from 19·8 to 215 pmol/l during the day in both groups. In women with normal menstrual cycles peak concentrations of 513·2 ± 54·1 (s.e.m.) pmol/l were recorded at 04.00 h, whereas higher concentrations were found in women taking the pill, reaching a peak of 849·12 ± 21·8 (s.e.m.) pmol/l at 04.00 h. Similar melatonin concentrations were measured in the two 24-h periods.
In the adult male rat, serum melatonin concentrations varied from 92·66 ± 37·9 (s.e.m.) pmol/l at 12.00 h, rising to 526 ± 55·6 (s.e.m.) pmol/l at 04.00 h.
This direct assay is more practical and robust than the assays currently available. The careful validation of assay characteristics allows its widespread use in both clinical studies and the investigation of the role of melatonin in different species.
J. Endocr. (1985) 106, 387–394
POSSIBLE ROLE OF UTERINE CONTRACTIONS IN THE SHORT-TERM FLUCTUATIONS OF PLASMA ACTH CONCENTRATION IN FETAL SHEEP
Authors: Lye S.J. , Wlodek M.E. , Challis J.R.G. 
Published: December 2008

ABSTRACT
Uterine contractions, induced by the administration of oxytocin to sheep between d 123-144 of pregnancy, were associated with a mean transient decrease in fetal PaO2 of 2.8 mm Hg within 5 min. These changes were associated with a rapid increase in the concentration of ACTH in fetal plasma. There was a significant (P<0.05) increase in the percentage change (+40 to +47%) over basal ACTH levels in fetal plasma at +5, +15 and +20 min after oxytocin. Administration of saline had no significant effect on intrauterine pressure, fetal PaO2 or fetal plasma ACTH levels. We speculate that increases in uterine activity and/or transient decreases in fetal PaO2 may contribute to short-term fluctuations in plasma ACTH in fetal sheep.
Homologous ligand regulation of gonadotrophin-releasing hormone receptors in vivo: relationship to gonadotrophin secretion and gonadal steroids
Authors: Naik S. I. , Saade G. , Detta A. , Clayton R. N. 
Published: December 2008

ABSTRACT
A single injection of gonadotrophin-releasing hormone (GnRH) (60 ng s.c., 42·9 nmol) induced biphasic GnRH receptor regulation in normal intact adult female mice. A transient 22% receptor decrease occurred 30–60 min after injection of GnRH when peak serum decapeptide concentrations were reached (137 ± 41 (s.e.m.) ng/l). This GnRH receptor decrease occurred shortly after the peak serum LH values at 15–30 min. The subsequent rapid (within 1 h) return of GnRH receptor levels to normal suggested transient receptor occupancy by GnRH rather than true receptor loss. At 8 h after injection of GnRH a significant 35% increase in GnRH receptors was consistently observed, when serum GnRH levels were undetectable and serum LH had returned to basal levels. This receptor increase was not due to increased receptor affinity, and was prevented by a non-specific protein synthesis inhibitor.
Ovariectomy, which caused a 50% fall in GnRH receptors (59·4 ± 4·9 fmol/pituitary gland in intact controls; 26·9 ± 2·6 in ovariectomized mice) abolished the induction by GnRH of its own receptors, although the initial transient decrease occurred over the period of the acute serum LH and FSH rise. Despite a 50% reduction in GnRH receptors in ovariectomized mice, increased serum gonadotrophin levels and responsiveness to GnRH were maintained, indicating dissociation between receptor changes and gonadotrophin levels.
No GnRH receptor up-regulation was observed 8 h after a single GnRH injection (60 ng s.c.) in either intact or orchidectomized normal male mice. However, the same treatment doubled GnRH receptors in GnRH-deficient (hpg) female mice.
While GnRH appears to up-regulate its own receptors by a direct action on pituitary gonadotrophs in the GnRH-deficient mouse its action in the normal female mouse pituitary appears secondary to stimulation of a gonadal product, presumably oestrogens.
J. Endocr. (1985) 107, 41–47
Ovarian cyclic GMP concentration and guanylate cyclase activity in immature rats after treatment with pregnant mare serum gonadotrophin
Authors: Patwardhan V. V. , Lanthier A. 
Published: December 2008

ABSTRACT
We have previously reported that the LH-induced decrease in the concentration of ovarian cyclic GMP (cGMP) in the rabbit was accompanied by a drop in ovarian guanylate cyclase activity. The present experiments were carried out to see if the increase in cGMP concentration that occurs in immature rat ovaries after stimulation with pregnant mare serum gonadotrophin (PMSG) is also accompanied by changes in guanylate cyclase activity. Total ovarian cGMP, along with ovarian weight, was found to be increased at 16 h after PMSG treatment. Ovarian concentrations of cGMP, however, increased only after that period (at 20, 24 and 48 h) and the increase was progressive. Guanylate cyclase activity was found in both the cytosol and 100 000 g particulate fractions of the immature rat ovaries. Forty-three hours after PMSG treatment, activity in the particulate fraction was found to be significantly increased. This increase in guanylate cyclase activity was also found at 20 h but not at 16 h. Thus, the increase in ovarian cGMP concentration in immature rats after PMSG treatment was accompanied by increased guanylate cyclase activity.
J. Endocr. (1985) 107, 77–81
Evidence for pituitary regulation of placental lactogen in the rat
Authors: Voogt J. L. , Pakrasi P. L. , Johnson D. C. , Dey S. K. 
Published: December 2008

ABSTRACT
The present studies examined whether the pituitary hormones, particularly prolactin, have any role in the regulation of rat placental lactogen (rPL) secretion. Total rPL was measured using a lymphoma cell bioassay. Hypophysectomy on day 13 of pregnancy increased total serum rPL levels above those of intact control rats and delayed for 3 days the decline in rPL usually seen by day 14. To test the effect of early hypophysectomy on rPL secretion, a delayed implantation model was used. Hypophysectomy was carried out on day 3, progesterone (2 mg) was given daily until day 8 and oestrone (1·0 μg) was given on day 8. This initiated implantation on day 9, which is 4 days later than normal. Rats hypophysectomized on day 3 had high serum levels of rPL (10–13 mg/l) 7 days after initiation of implantation compared with control values of 2–3 mg/l, and these levels remained raised for the duration of the experiment. Termination of maintenance injections of steroids did not affect the high levels of rPL for several days, even though there was fetal and placental resorption. When a pair of anterior pituitaries was transplanted under the kidney capsule on day 13 (day 9 of development) of rats hypophysectomized on day 3, serum rPL levels still increased for the next 3 days. However, unlike similarly treated rats not receiving transplants, rPL levels fell rapidly thereafter and were only 5% of those in control animals 1 week later. Only the intact rats and those hypophysectomized either on day 3 or 13 and given daily maintenance doses of steroids had normal pregnancies; the other two groups in which steroid injections were stopped on day 15 showed various degrees of resorption or abortion. It is suggested that the pituitary, possibly because of its prolactin secretion, is important in the regulation of rPL secretion.
J. Endocr. (1985) 107, 121–126
Steroid concentrations in fluid from human ovarian antral follicles during pregnancy
Authors: Westergaard L. , McNatty K. P. , Christensen I. J. 
Published: December 2008

ABSTRACT
Steroid concentrations in fluid from 138 ovarian antral follicles obtained from 30 pregnant women were measured and compared with those in aspirates of 151 follicles of similar size (i.e. diameter 2–6 mm) from 61 non-pregnant women who had normal regular menstruations. The follicles were classified as healthy or atretic by flow cytometric DNA measurement of the granulosa cells contained in the follicular fluid aspirate.
Nine (7%) of the follicles from pregnant women and 21 (14%) of those from non-pregnant women were healthy, and the remainder atretic (P>0·05). Androstenedione was the most abundant steroid in all follicles. Mean progesterone levels in follicular fluid from pregnant women were significantly (P<0·05) higher than in follicular fluid from non-pregnant women. In pregnant women progesterone levels were significantly (P<0·01) higher in fluid from healthy than from atretic follicles. In contrast, no significant differences in steroid concentrations were found between fluid from healthy and atretic follicles in non-pregnant women.
We conclude that antral ovarian follicles may develop normally to a diameter of around 6 mm during the third trimester of human pregnancy. We also conclude that these follicles accumulate steroids in the follicular fluid in amounts which equal those found in follicles of similar size in the ovaries of non-pregnant women, but that the composition of intrafollicular steroids during pregnancy is modified towards higher concentration of progesterone. The reason for this increased intrafollicular progesterone level is unclear.
J. Endocr. (1985) 107, 133–136
Progesterone receptors in rat brain and uterus: dependence on the hormonal milieu
Authors: Al-Khouri H. , Greenstein B. D. 
Published: December 2008

ABSTRACT
Cytosols were incubated from the hypothalamus and mid-brain and from the uterus, and incubated with [3H]progesterone alone or in the presence of excess radioinert steroid to reveal saturable binding sites. Bound and free hormone were separated by gel filtration. Scatchard analysis of the binding sites yielded evidence for only one class of binding sites of high affinity and limited capacity. The binding components in the hypothalamus and uterus appeared to fluctuate during the oestrous cycle, attaining a nadir at metoestrus, while those in the mid-brain were apparently unchanged. During pregnancy hypothalamic [3H]progesterone-binding sites appeared to lose affinity for the steroid while in the uterus the affinity for the steroid was unchanged but the absolute numbers of binding sites were greatly increased at day 10. It is concluded, both from studies of the properties intrinsic to the binding reaction and from endocrine correlates, that the macromolecular progesterone-binding components in the brain may be receptors for the hormone and that there may be differences between the properties of progesterone receptors in different tissues. Furthermore, during pregnancy there may be qualitative changes in the neural progesterone receptors which are not mediated by oestradiol.
J. Endocr. (1985) 107, 159–162
Oestrogen-2/4-hydroxylase activity in the rat brain during lactation and throughout the oestrous cycle
Authors: Brown C. G. , White N. , Jeffcoate S. L. 
Published: December 2008

ABSTRACT
Oestrogen-2/4-hydroxylase activity was measured in whole brain, thalamus, amygdala, hypothalamus and pituitary gland of lactating rats and in whole brain of rats on different days of the oestrous cycle. Enzyme activity was increased in whole brain and in each of the brain regions examined (with the exception of the amygdala) in lactating rats. This increase in enzyme activity was associated with an increase in serum prolactin levels. During the oestrous cycle, enzyme activity in whole brain was higher on metoestrus and dioestrus than on pro-oestrus and oestrus. The decrease in enzyme on pro-oestrus was associated with an increase in both serum oestradiol and prolactin levels. These results are consistent with the hypothesis that changes in oestrogen-2/4-hydroxylase activity are associated with changes in prolactin and oestradiol secretion and may play a regulatory role in reproduction.
J. Endocr. (1985) 107, 191–196
Progesterone and oestradiol receptor concentration and translocation in uterine tissue of rabbits treated with indomethacin
Authors: Cao Z.-D. , Jones M. A. , Harper M. J. K. 
Published: December 2008

ABSTRACT
The purpose of this study was to determine whether endogenous prostaglandins are involved in the regulation of sexual steroid receptor concentration and cytosol to nucleus translocation in the rabbit uterus. The animals were injected s.c. with indomethacin (10 mg/kg) twice daily on days 5 and 6 and on the morning of day 7 of pregnancy or pseudopregnancy and killed 2 h after the last injection. The indomethacin treatment did not change progesterone and oestradiol serum concentrations compared with animals injected with vehicle only. No differences were observed either in progesterone receptor or oestradiol (pregnant animals only) receptor concentration and intracellular distribution in endometria of indomethacin-treated or control animals. In an extended experiment indomethacin given to oestrogen-pretreated ovariectomized rabbits did not inhibit the nuclear progesterone receptor accumulation induced by a single progesterone injection. These results suggest that there is no direct relationship between prostaglandins and sexual steroid receptors in the rabbit uterus.
J. Endocr. (1985) 107, 197–203
Inhibin-like activity in ovarian homogenates of prepubertal female rats and its physiological significance
Authors: Sander H. J. , Meijs-Roelofs H. M. A. , Kramer P. , van Leeuwen E. C. M. 
Published: December 2008

ABSTRACT

The presence and physiological significance of ovarian inhibin-like activity (ILA) in immature rats was studied by measuring ILA in ovarian homogenates and by studying the short-term changes in serum concentrations of FSH and LH after unilateral or bilateral ovariectomy. Inhibin-like activity in ovarian homogenates was estimated using an in-vitro bioassay system with dispersed rat anterior pituitary cells and subsequent measurement of FSH and LH levels in the spent pituitary cell medium. Inhibin-like activity, expressed in units/ovary, was undetectable in 13-day-old ovaries, was present in 18-day-old ovaries (5·8 units/ovary) and rose significantly to a value of 29·1 units/ovary on day 23. Another significant rise was seen between 28 and 33 days of age, with ILA reaching a value of 66·4 units/ovary, a value still well below that found in adult dioestrous ovaries (155·6 units/ovary). In the bioassay no systematic dose-dependent influence on LH secretion was found. Serum concentrations of FSH after unilateral or bilateral ovariectomy at 18 days of age showed no change at 5 h and a significant (P < 0·05) increase compared with sham-operated controls at 24 h after operation. At 23, 28 and 33 days of age significant increases in FSH concentration were seen at 5 and 8 h after both unilateral and bilateral ovariectomy. At 24 h after unilateral ovariectomy, FSH had returned to the control values in these rats, whereas after bilateral ovariectomy a further increase in FSH was seen. Concentrations of LH generally varied widely and, compared with the situation after sham-operation, did not show a systematic trend of change during the 24-h period after unilateral or bilateral ovariectomy.
It was concluded that ILA is present in immature rat ovaries from the age of 18 days and increases, to a still sub-adult value, until at least 33 days of age. A physiological role for ILA, as a short-term regulator of FSH secretion seems to be present from at least 23 days of age and may account for the decreasing FSH concentrations seen during the late-prepubertal period, when ovarian steroids alone cannot explain the low FSH levels measured.
J. Endocr. (1985) 107, 251–257
Endogenous opioids and the control of seasonal LH secretion in Soay rams
Authors: Ebling F. J. P. , Lincoln G. A. 
Published: December 2008

ABSTRACT
Soay rams were treated with naloxone and/or morphine at different stages of their annual reproductive cycle to study the role of endogenous opioid peptides in the control of pulsatile LH secretion. The responses in intact rams were compared with those shown by pinealectomized (PNX) or superior cervical ganglionectomized (SCGX) rams which had a different annual testicular cycle. Naloxone (4–6 mg/kg i.v.) given to intact rams at four times of the year induced significant increases in LH pulse frequency in the breeding season in September and December, but minimal responses in the non-breeding season in June. Similar treatments given to PNX or SCGX rams induced good responses in March, June and September and the poorest response in December; the different seasonal pattern between the intact and PNX/SCGX rams was correlated with differences in the timing of their testicular cycles.
Morphine (1 mg/kg i.v.) induced a significant decrease in LH pulse frequency when given to intact rams in October, but no significant effects were observed when morphine was given to sexually inactive rams in early July. Naloxone (1 mg/kg i.v.) given concurrently with morphine in October reversed the suppressive effect and resulted in an actual increase in LH pulse frequency above pretreatment levels. Morphine-treated rams showed normal LH responses to injections of LH-releasing hormone (LHRH) indicating that the site of opiate inhibition was on hypothalamic LHRH secretion rather than on pituitary LH release.
Chronic treatment of intact and PNX rams with naloxone 1 mg/kg every 4 h for 7 days) in April and October produced the expected acute increase in LH pulse frequency in the intact rams in October, and at both times of year in the PNX rams, however there was no sustained increase in LH secretion in response to chronic naloxone in any of the treatment groups. The response to the second naloxone injection was much reduced and was absent after 3 days; responsiveness to naloxone was restored within 2 days of stopping the chronic treatment.
The overall results indicate that an endogenous opioid mechanism is involved in the tonic inhibition of LH secretion and that this mechanism is most active in the breeding season when both naloxone and morphine have marked effects on pulsatile release of LH. Regulation of endogenous opioids in the hypothalamus may be part of the mechanism by which environmental factors modulate steroid negative-feedback control of LHRH and thus LH secretion in seasonally breeding mammals.
J. Endocr. (1985) 107, 341–353
Effects of intracranial androgen on the development of masculine ultrasonic vocalizations in the Mongolian gerbil (Meriones unguiculatus)
Authors: Holman S. D. , Hutchison J. B. 
Published: December 2008

ABSTRACT
The effects of testosterone propionate (TP) on brain mechanisms involved in the sexual differentiation of ultrasonic vocalizations were examined in Mongolian gerbils (Meriones unguiculatus). Treatment of neonatal females with TP fully masculinized the rate of emission of the upsweep precopulatory ultrasound during adult sexual interactions with oestrous females. Intracranial implantation of small crystals of TP mixed with cholesterol (65 ng) into females 1–15 h after birth also masculinized the upsweep vocalization emitted in adulthood. Implants of TP positioned in the hypothalamic area had a significantly greater masculinizing effect than TP implants outside this region, or pure cholesterol implants. Two other sexually dimorphic vocalizations, the modulated (mainly precopulatory) and unmodulated (mainly copulatory) calls were masculinized by systemic TP, but intracranial TP had no significant masculinizing action on these calls. Genital structures of females which received neonatal injections of TP were strongly virilized in that their clitorides were lengthened and male-type cornified spines were present on the glans. Females which had received intracranial implants of TP were not virilized peripherally in adulthood. We conclude that testosterone or its metabolites have a direct hypothalamic effect on the development of masculine upsweep vocalizations. Because the other vocalizations were insensitive to intracranial TP, the underlying neural tissues may have different thresholds of response to androgen.
J. Endocr. (1985) 107, 355–363
Circadian variations in plasma calcium and calcitonin: effect of calcium deficiency and fasting
Authors: Lausson S. , Staub J. F. , Milhaud G. , Perault-Staub A. M. 
Published: December 2008

ABSTRACT
Circadian fluctuations of plasma calcium and immunoassayable calcitonin levels were studied in normal and calcium-deficient 2-month-old rats. The relationship between these parameters was also studied in animals which had been fasted for short periods. The plasma calcium rhythm persisted and was even amplified in rats placed on a 4-week calcium-deficient diet. In these rats, as in normal rats, the plasma calcium concentration diminished during the dark period. Calcitonin levels increased at the onset of the feeding period in normal rats but, in calcium-deficient rats, the pattern changed completely, with a major peak at the end of the light period and remaining at a low level during the dark feeding period. This modification of calcitonin rhythmicity appeared to be dependent on the degree of calcium deficiency. Fasting had little effect on calcitonin rhythms in either normal or calcium-deficient rats.
It is concluded that the calcitonin rhythm is relatively independent of feeding per se and that there appears to be no simple relationship between plasma calcium and calcitonin concentrations. It is suggested that the results may best be interpreted as reflecting the presence of rhythmic endogenous phenomena which are intrinsic to calcium metabolism and its regulation in the rat.
J. Endocr. (1985) 107, 389–395
MONOCLONAL ANTIBODY-MEDIATED ENHANCEMENT OF GROWTH HORMONE ACTIVITY IN VIVO
Authors: Holder A. T. , Aston R. , Preece M.A. , Ivanyi J. 
Published: December 2008

ABSTRACT
This work demonstrates that complexing hGH with monoclonal antibody EBl (MAB-EBl) can produce a striking potentiation of the somatogenic actions of hGH in vivo in Snell dwarf mice. In short-term experiments significant increases in cartilage metabolism and body weight were noted; these responses were dose-dependent for both MAB-EBl and hGH concentration. Increased growth was also observed in long-term experiments. In marmosets where MAB-EBl cross-reacts with endogenous GH, MAB-EBl alone enhanced the actions of endogenous GH. A new perspective may be necessary to incorporate these results into the current concept of antibody action.