bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of ovarian inhibin secretion during the oestrous cycle of the rat
Authors: Watanabe G. , Taya K. , Sasamoto S.
Published: December 2008

Plasma and ovarian concentrations of inhibin were determined at 3-h intervals throughout the 4-day oestrous cycle of rats by a radioimmunoassay (RIA) based on a bovine RIA. Plasma concentrations of LH, FSH, progesterone, testosterone, oestradiol-17β, and pituitary contents of FSH and LH were also determined during the cycle. Plasma levels of inhibin showed a marked increase on the morning of oestrus and the afternoon of metoestrus, and a further increase was noted on the morning of pro-oestrus. These increases in plasma levels of inhibin were probably due to the following three events in the ovary, follicular recruitment on the morning of oestrus, selection of follicles on the day of metoestrus, and final maturation of follicles for ovulation on the morning of pro-oestrus with an increase in oestradiol-17β secretion. A striking decrease in inhibin secretion occurred during the process of ovulation after the preovulatory gonadotrophin surge on the afternoon of pro-oestrus. Basal levels of plasma FSH gradually decreased from metoestrus to pro-oestrus as plasma levels of inhibin increased. There was a significant inverse relationship between plasma levels of FSH and inhibin throughout the oestrous cycle (r = −0·51). The present findings suggest that changes in the plasma levels of inhibin during the oestrous cycle provide a precise indicator for follicular recruitment, selection and ovulation, and that changes in concentrations of oestradiol-17β in the plasma are associated with follicular maturation.

Journal of Endocrinology (1990) 126, 151–157
The preparation of an ovine monoclonal antibody to progesterone
Authors: Groves D. J. , Sauer M. J. , Rayment P. , Foulkes J. A. , Morris B. A.
Published: December 2008

Peripheral blood mononuclear cells were collected from a sheep immunized against progesterone-11α-hemisuccinate-ovalbumin. Following fusion with NS1 mouse myeloma or heteromyeloma cells, a large number of hybrid colonies was established. These were screened for the production of sheep antibodies to progesterone. Twenty-four cell lines were cloned and one was stabilized. This cell line, O/MP.1A9.D7B2, produced a high-affinity ovine immunoglobulin G1 (dissociation constant 4·8 pmol/l) with a high degree of specificity for progesterone. The antibody was substituted into a competitive enzyme-linked immunosorbant assay for the measurement of progesterone in bovine milk, originally established using an ovine polyclonal antibody, and the results were compared. The monoclonal antibody produced an assay with a lower limit of detection and a greater degree of discrimination than the polyclonal antiserum.

Journal of Endocrinology (1990) 126, 217–222
Atrial natriuretic peptides inhibit the release of corticotrophin-releasing factor-41 from the rat hypothalamus in vitro
Authors: Ibanez-Santos J. , Tsagarakis S. , Rees L. H. , Besser G. M. , Grossman A.
Published: December 2008

Atrial natriuretic peptide, ANP(99–126), is derived from cardiac atrial tissue and has potent effects on salt and water homeostasis, including the inhibition of aldosterone and vasopressin release. Recent studies have also suggested that it may suppress the pituitary-adrenal axis. In addition, N-truncated forms of ANP, such as ANP(103–126), have been identified within the central nervous system, with a prominent hypothalamic localization in the paraventricular nucleus. We have therefore investigated whether ANP(99–126) and ANP(103–126) are able to modulate the release of the principal ACTH-releasing factor, corticotrophin-releasing factor-41 (CRF-41), from the rat hypothalamus in vitro.

The static incubation system has been previously described in detail. Male Wistar rats were decapitated between 09.00 and 09.30 h, their hypothalami rapidly removed, and four half-hypothalami incubated for 20-min intervals following a period of stabilization. The effect of the ANP peptides on the basal (B) and KCl (28 mmol/l)-stimulated (S) release of immuno-reactive CRF-41 was studied by means of successive incubations in the absence (B1, SI) and presence (B2, S2) of the peptides. The ratios B2: B1 and S2: S1 were compared with parallel control incubations by ANOVA.

Neither form of ANP had any effect on the basal release of CRF-41. ANP(99–126) caused a dose-dependent inhibition of CRF-41 release in the concentration range 1–100 nmol (P < 0·01). ANP(103–126) also suppressed the release of CRF-41 in the concentration range 100 pmol/l–100 nmol/l (P < 0·01), with a minimum S2:S1 ratio at 10 nmol/l, and a decrease in effect at 100 nmol/l. Finally, the stimulation of CRF-41 release induced by noradrenaline (10 nmol/l and 1 μmol/l) was non-competitively antagonized by 100 nmol ANP(99–126)/l and 10 nmol ANP(103–126)/l.

It was concluded that ANP may be an important regulator of the pituitary-adrenal axis by interaction with CRF-41. As there are data indicating that ANP may also directly inhibit the pituitary corticotroph, it would appear that central ANP is intimately involved in pituitary-adrenal function.

Journal of Endocrinology (1990) 126, 223–228
Purification of functional lactotrophs and somatotrophs from female rats using fluorescence-activated cell sorting
Authors: Wynick D. , Critchley R. , Venetikou M. S. , Burrin J. M. , Bloom S. R.
Published: December 2008

As the secretory granules of anterior pituitary cells fuse with the cell surface, there would appear to be sufficient hormone present on the cell surface to be labelled by polyclonal hormone antibodies and thus analysed by flow cytometry. We have therefore applied fluorescence-activated cell sorting to these labelled pituitary cells. Percentage purity and depletion of other cell types was assessed by immunocytochemistry and the reverse haemolytic plaque assay (RHPA). Results demonstrate that fluorescence-activated cell sorting allows almost complete purification of functional lactotrophs and somatotrophs to 96·7 ±1·7 (s.e.m.)% and 98±1·0% respectively by immunocytochemistry, and to 95·8 ±1·1% and 97±0·8% respectively by RHPA. Depletion of other anterior pituitary cell types to less than 2% was demonstrated by both immunocytochemistry and RHPA. Fluorescence-activated cell sorting to this degree of purity was routinely possible with cell yields of 91 ±3·4%. To obtain such purity/depletion, it was necessary to use specific antisera of high titre, at concentrations which ensured maximal cell-surface labelling associated with maximal stimulation of hormonal secretion by the appropriate hypothalamic stimulatory factor. Separating cells on the basis of the intensity of prolactin cell-surface labelling demonstrated a low level of binding of the prolactin antibody to gonadotrophs (but not of sufficient fluorescence intensity to be sorted into the prolactin enriched population), raising the possibility of prolactin receptors on gonadotrophs. We were unable to demonstrate the presence of mammosomatotrophs in the normal female rat, since purified lactotrophs did not contain or secrete GH nor did purified somatotrophs contain or secrete prolactin.

Journal of Endocrinology (1990) 126, 269–274
Modulation of the biological activity of thyrotrophin by anti-human thyrotrophin monoclonal antibodies
Authors: Page S. R. , Taylor A. H. , Driscoll W. , Baines M. , Thorpe R. , Johnstone A. P. , Nussey S. S. , Whitley G. St J.
Published: December 2008

The mechanism by which monoclonal antibodies enhance the biological activity of a number of hormones is poorly understood. One such antibody (GC73), which binds to human but not bovine TSH, enhances the bioactivity of human TSH in vivo. We have investigated whether GC73 enhancement of TSH bioactivity involves potentiation of hormone-receptor activation assessed by the cyclic AMP (cAMP) responses of both primary human thyrocyte cultures and a TSH-responsive human thyrocyte cell line (SGHTL-45). GC73 had no effect on basal cAMP production. In contrast to its enhancement of the bioactivity of human TSH in vivo, it markedly inhibited the cAMP response to 1 and 10 mU human TSH/ml in primary thyrocytes. This effect was dose-dependent with neutralization of the bioactivity of TSH occurring at 2 mg GC73/ml. GC73 had no effect on the bioactivity of bovine TSH. In contrast, a second anti-TSH monoclonal antibody (TC12), which binds to both human and bovine TSH, inhibited the bioactivity of both species of TSH. Similar results were obtained using SGHTL-45 cells, although the peak concentrations of cAMP were lower. We conclude that binding of GC73 to human TSH resulted in inhibition rather than enhancement of the in-vitro biological activity of human TSH. We suggest that GC73 enhancement of human TSH bioactivity seen in vivo does not result from a mechanism involving potentiation of receptor activation by human TSH.

Journal of Endocrinology (1990) 126, 333–340
Vascular angiotensin II and atrial natriuretic peptide receptors in normal and growth-retarded human placentae
Authors: McQueen J. , Kingdom J. C. P. , Jardine A. G. , Connell J. M. C. , Whittle M. J.
Published: December 2008

Receptors for angiotensin II (AII) and atrial natriuretic peptide (ANP) were characterized in a membrane fraction from resistance-type artery from human placentae. Placentae from normal pregnancies and pregnancies complicated by intrauterine growth retardation (IUGR) were studied. High- and low-affinity receptors for AII (dissociation equilibrium constant (Kd) 1 ·7 and 15·7 nmol/l respectively) and ANP (Kd 0·2 and 55·5 nmol/l respectively) were identified; these parameters were unchanged in IUGR, but there was a reduction in high-affinity receptor number by approximately 50% for AII and 80% for ANP in this condition. Both peptides may have a role in the regulation of fetoplacental blood flow. The alterations in IUGR are consistent with sustained activation of the fetal reninangiotensin system and suggest altered vascular responsiveness to ANP.

Journal of Endocrinology (1990) 126, 341–347
Influence of mating and intra-uterine oestradiol infusion on peripheral oxytocin concentrations in the sow
Authors: Claus R. , Schams D.
Published: December 2008

Oxytocin concentrations were measured radioimmunologically in sows on the day of standing oestrus over a 6-h period (controls, n=6) or 1 h before and 5 h after mating (n=5) or transcervical infusion of either 100 ml saline (0·9% (w/v) NaCl, n=7) or saline plus 10 μg oestradiol (simulation of seminal oestrogens, n=5).

In the controls, oxytocin was low, at around 1·0 pmol/l, throughout the investigation period. Similarly, saline infusion did not lead to a noticeable change in oxytocin concentrations in six out of seven sows. In one sow, however, infusion led to a maximum of 86 pmol/l at 1 min after infusion. Oestradiol led to no immediate increase in oxytocin concentrations. Later in the post-treatment period (2–5 h) they were only slightly increased (1 pmol/l vs 3 pmol/l). All mated sows reacted with a rapid and clear increase in oxytocin. Maximal concentrations (42·0±5·1 pmol/l; mean ± s.e.m.) appeared 2 min after the onset of ejaculation. Clearly increased concentrations were found for 40 min. It was concluded that mating specifically leads to a rise in oxytocin, probably due to both mechanical and pheromonal stimuli provided by the boar.

Journal of Endocrinology (1990) 126, 361–365
The effect of a potent gonadotrophin-releasing hormone antagonist on ovarian secretion of oestradiol, inhibin and androstenedione and the concentration of LH and FSH during the follicular phase of the sheep oestrous cycle
Authors: Campbell B. K. , McNeilly A. S. , Picton H. M. , Baird D. T.
Published: December 2008

By selective removal and replacement of LH stimulation we sought to examine the relative importance of inhibin and oestradiol in controlling FSH secretion, and the role of LH in the control of ovarian hormone secretion, during the follicular phase of the oestrous cycle. Eight Finn–Merino ewes which had one ovary removed and the other autotransplanted to a site in the neck were given two injections of a gonadotrophin-releasing hormone (GnRH) antagonist (50 μg/kg s.c.) in the follicular phase of the cycle 27 h and 51 h after luteal regression had been induced by cloprostenol (100 μg i.m.). Four of the ewes received, in addition, i.v. injections of 2·5 μg LH at hourly intervals for 23 h from 42 to 65 h after GnRH antagonist treatment. Ovarian jugular venous blood samples were taken at 10-min intervals for 3 h before and 5 h after the injection of antagonist (24–32 h after cloprostenol) and from 49 to 53 h after antagonist (74–78 h after cloprostenol). Additional blood samples were taken at 4-h intervals between the periods of intensive blood sampling.

The GnRH antagonist completely inhibited endogenous pulsatile LH secretion within 1 h of injection. This resulted in a marked decrease in the ovarian secretion of oestradiol and androstenedione (P<0·001), an effect that was reversible by injection of exogenous pulses of LH (P<0·001). The pattern of ovarian inhibin secretion was episodic, but removal or replacement of stimulation by LH had no effect on the pattern or level of inhibin secretion. Peripheral concentrations of FSH rose (P<0·01) within 20 h of administration of the antagonist and these increased levels were maintained in ewes given no exogenous LH. In ewes given LH, however, FSH levels declined within 4 h of the first LH injection and by the end of the experimental period the levels of FSH were similar to those before administration of antagonist (P<0·01).

These results confirm that ovarian oestradiol and androstenedione secretion, but not inhibin secretion, is under the acute control of LH. We conclude that oestradiol, and not inhibin, is the major component of the inhibitory feedback loop controlling the pattern of FSH secretion during the follicular phase of the oestrous cycle in ewes.

Journal of Endocrinology (1990) 126, 377–384
Immunohistochemical localization of pituitary gonadotrophins and gonadal steroids confirms the 'two-cell, two-gonadotrophin' hypothesis of steroidogenesis in the human ovary
Authors: Kobayashi M. , Nakano R. , Ooshima A.
Published: December 2008

Ovaries from 37 women with normal menstrual cycles were analysed for localization of pituitary gonadotrophins and gonadal steroids using an immunohistochemical method. In the follicular phase, FSH and oestradiol-17β localized in the granulosa layer, and LH, progesterone and testosterone localized in the internal thecal layer. In the luteal phase, gonadotrophins and steroids localized in luteal cells. Particularly in the early luteal phase, FSH and oestradiol-17β localized in large luteal cells, and LH, progesterone and testosterone localized in small luteal cells. The results of the present immunohistochemical analysis confirm the two-cell, two-gonadotrophin hypothesis of steroidogenesis in the human ovary.

Journal of Endocrinology (1990) 126, 483–488
N-acetyltransferase activity in the Harderian glands of the Syrian hamster, Mesocricetus auratus, is regulated by androgens and by hormones of the pituitary-thyroid axis
Authors: Buzzell G. R. , Menendez-Pelaez A. , Hoffman R. A. , Vaughan M. K. , Reiter R. J.
Published: December 2008

This study tested the hypothesis that activity of the enzyme N-acetyltransferase (NAT) in the Harderian gland of the Syrian hamster is regulated both by androgens and by hormones of the pituitary-thyroid axis. To test the effects of castration and hypothyroidism, intact or castrated male hamsters were given either tap water or methimazole in their drinking water for 3 weeks. Methimazole suppresses iodination of thyroglobulin, thereby decreasing circulating levels of thyroid hormones and increasing TSH levels. Hypothyroidism or castration caused elevated or depressed Harderian gland NAT activities respectively, compared with euthyroid controls. When castration and hypothyroidism were combined, the animals exhibited high NAT activity compared with castrated euthyroid males.

To test the effects of castration and hyperthyroidism, male hamsters were given daily injections of thyroxine (T4) or diluent and were either castrated or left intact for 4 weeks. Intact animals given T4 had depressed Harderian NAT activity; serum thyroid hormone levels were elevated and TSH levels were depressed compared with those of intact controls. Castrated animals had depressed NAT activity below that of intact controls; serum thyroid hormone levels were normal but TSH levels were depressed. Castrated animals given T4 injections had NAT activity similar to that of euthyroid castrated hamsters; thyroid hormone levels were elevated but TSH levels were similar to those seen in euthyroid castrated hamsters. In another experiment, both T4 and tri-iodothyronine (T3) were equally effective in decreasing NAT activity in intact males.

To determine the effects of the removal of pituitary influences, male hamsters were hypophysectomized. NAT activity in the Harderian glands of these animals was reduced compared with intact controls. Injection of T4 in hypophysectomized male hamsters did not alter NAT activity from that of hypophysectomized hamsters.

Female hamsters given methimazole for 3 weeks had elevated Harderian NAT activity compared with controls. Injection of T4 or T3 for 4 weeks led to significantly reduced Harderian gland NAT activity compared with untreated controls. This response to thyroid hormones was the same, whether T4 or T3 was used.

These results can be explained by androgens stimulating Harderian NAT activity, as has been suggested by previous published reports, and by NAT activity being inhibited by thyroid hormones or stimulated by TSH.

Journal of Endocrinology (1990) 127, 59–67
Aromatase activity in genital skin fibroblasts from normal and androgen-insensitive individuals
Authors: Stillman S. C. , Evans B. A. J. , Hughes I. A.
Published: December 2008

Human genital skin fibroblasts were used to study aromatase activity by analysing the [3H]H2O released as [1β-3H]androstenedione is converted to oestrone. 4-Hydroxyandrostenedione was shown to be a competitive inhibitor of this aromatase activity, the concentration of inhibitor producing 50% inhibition being 1·29 nmol/l. Dexamethasone stimulated the enzyme complex in a dose-dependent manner with half-maximal stimulation at 11·5 nmol/l. A peak of induction occurred after 16 h of preincubation. Measurement of aromatase activity in normal cell strains provided a normal range for the Michaelis–Menten constant (Km) and the maximum velocity (Vmax) of 6·72±0·54 nmol/l and 215·3±33·9 fmol/mg protein per h (means ± s.e.m., n = 20) respectively. Km values obtained for partial and complete androgen insensitivity syndrome (PAIS and CAIS) patient cell strains were all within the normal range. The mean Vmax±s.e.m. in cell strains from patients with PAIS (n = 13) and CAIS (n = 11) were 127·4±19·2 and 54·8±19·3 fmol/mg protein per h respectively. Vmax values for patients with CAIS were significantly (P < 0·001) lower than normal subjects. This suggests that aromatase expression in genital skin fibroblasts is androgen-dependent.

Journal of Endocrinology (1990) 127, 177–183
Involvement of dopamine D1 receptors in the control of growth hormone secretion in the rat
Authors: Bluet-Pajot M. T. , Mounier F. , Durand D. , Kordon C.
Published: December 2008

The effects of dopamine on GH release were investigated both in vivo in freely moving intact rats and in rats with a mediobasal hypothalamic lesion, and in vitro in a perifusion system using dispersed male rat pituitary cells kept in primary culture. In vivo, dopamine (5 mg/kg body weight) induced a rapid and very transient increase in plasma GH levels in lesioned but not in intact rats. This increase was markedly inhibited by a prior injection of the D1 antagonist SCH 23390 (0·5 mg/kg) but not of the D2 antagonist domperidone (0·5 mg/kg). The D, agonist SKF 38393 induced a dose-dependent stimulation of GH release in lesioned rats, and the effect obtained with a dose of 5 mg/kg was abolished by pretreatment with SCH 23390 (0·5 mg/kg). In vitro, dopamine (0·1 μmol/l) and SKF 38393 (0·1 μmol/l) provoked a rapid and reversible release of GH from superfused rat pituitary cells; this effect was markedly inhibited by simultaneous superfusion of SCH 23390 (1 μmol/l). These findings indicate that dopamine can stimulate basal GH release at the pituitary level and that this stimulation is mediated by D1 but not by D2 receptors. They also support the hypothesis that unidentified hypothalamic neurohormones may modulate this effect.

Journal of Endocrinology (1990) 127, 191–196
Stimulation of rat renal medullary Na+/K+-ATPase by arginine vasopressin is mediated by the V2 receptor
Authors: Charlton J. A. , Baylis P. H.
Published: December 2008

In previous studies, we have demonstrated that 1–10 fmol arginine vasopressin (AVP)/l maximally stimulates the activity of the enzyme Na+/K+-ATPase in the rat renal medullary thick ascending limb (MTAL) of Henle's loop after 4 or 10 min of stimulation when measured using a cytochemical bioassay. We have tested the hypothesis that this stimulation is mediated by the V2 receptor in the MTAL. A cytochemical bioassay was used to investigate the effect of specific V1 and V2/V1 antagonists and a synthetic V2 agonist [1-deamino,8-d-arginine]-vasopressin (dDAVP), on the activity of Na+/K+-ATPase. There was no effect of the V1 antagonist (1 fmol-1 μmol/l) in inhibiting the activity of Na+/K+-ATPase stimulated by 1 fmol AVP/l. In contrast, 100 pmol of the V2/V1 antagonist/l significantly (P < 0·001) inhibited the stimulation of Na+/K+-ATPase activity by 1 fmol AVP/l from 55·5±4·3 (s.e.m.) to 31·9±1·6 mean integrated extinction (MIE) after 4 min of stimulation and from 67·0±3·2 to 36·9±0·7 MIE after 10 min of stimulation. Similarly, the stimulation of Na+/K+-ATPase by 10 fmol dDAVP/l was inhibited by the V2/V1 antagonist from 55·1±1·0 to 26·1±0·5 MIE after 4 min of stimulation.

We conclude that the stimulation of Na+/K+-ATPase by AVP is mediated by the V2 receptor in the rat renal MTAL.

Journal of Endocrinology (1990) 127, 213–216
Suckling-induced release of cholecystokinin into plasma in the lactating rat: effects of abdominal vagotomy and lesions of central pathways concerned with milk ejection
Authors: Linden A. , Eriksson M. , Hansen S. , Uvnäs-Moberg K.
Published: December 2008

Plasma levels of cholecystokinin were increased in response to suckling in lactating rats. Efferent electrical stimulation of the vagal nerve increased the concentration of cholecystokinin in plasma. Abdominal vagotomy was found to block the suckling-induced release of cholecystokinin. Furthermore, lesions to the lateral midbrain, which disrupt the oxytocin-mediated milk-ejection reflex, were shown to inhibit the increase in plasma cholecystokinin. These results show that the suckling-induced release of cholecystokinin into plasma in lactating rats is dependent upon the vagal nerves and the central neural structures concerned with milk let-down.

Journal of Endocrinology (1990) 127, 257–263
Mitosis in the oesophageal epithelium of rats during chronic antithyroid treatment with carbimazole
Authors: Tuffery A. R. , Mobarak M.
Published: December 2008

The mitotic activity of the oesophageal epithelium of male rats maintained under carefully controlled conditions was studied, using the metaphase-arrest agent, vincristine sulphate. The accumulation of metaphases was linear (r = 0·97). In untreated rats there was a clear mitotic rhythm with a peak metaphase index (expressed as a percentage) of 12·4±0·86 (s.e.m.) at 12.00–15.00 h and a trough of 1·3±0·35 at 24.00 h. The overall mean metaphase index was 5·4±0·76. The effect of treatment with the antithyroid agent, carbimazole (0·1 g/100 ml in the drinking water), for 3 weeks was to depress the higher values at 12.00–18.00 h (P <0·01), while leaving the overall index unchanged.

Carbimazole caused a significant (P <0·01), transient 40% increase in the metaphase index after 2 days; thereafter the metaphase index remained at control levels until 12 weeks of treatment when a steady decline occurred until 24 weeks.

The results are in contrast to those in previously described experiments on thyroid follicular cells which show a large increase in the first few days of treatment, followed by a steady decline towards control levels at 12 weeks. The metabolic activity of the animals is about 50% of normal at 12 weeks when both the oesophageal epithelium and the thyroid follicular cells begin to show a reduction in proliferative activity.

Journal of Endocrinology (1990) 127, 311–315
Stimulation of Na+/K+-ATPase activity by polyamines in the rat renal medullary cells of the thick ascending limb of Henle's loop
Authors: Charlton J. A. , Baylis P. H.
Published: December 2008

Previous studies have indicated that ornithine decarboxylase (ODC) may be involved in the stimulation of Na+/K+-ATPase activity by arginine vasopressin (AVP) in the rat renal medullary thick ascending limb of Henle's loop. The present study was aimed at establishing the role of the polyamines, the conversion products of ODC activity, in the stimulation of Na+/K+-ATPase by AVP. Using cytochemical methods, we have demonstrated an increase in Na+/K+-ATPase activity after stimulation with putrescine, spermidine and spermine (each 1 mmol/l) for 2·5,2 and 1·5 min respectively. The specific inhibitors of spermidine and spermine synthase, bis-cyclohexylammonium sulphate and N-alkylated-1,3-diaminopropane respectively, inhibited the stimulation of Na+/K+-ATPase by AVP, this inhibition being reversed by spermine. These findings suggest that polyamines are involved in the stimulus-response coupling of the hormone-mediated response.

Journal of Endocrinology (1990) 127, 377–382
Insulin-like growth factor-I (IGF-I) and IGF-binding proteins both decline in the rat during late pregnancy
Authors: Gargosky S. E. , Walton P. E. , Owens P. C. , Wallace J. C. , Ballard F. J.
Published: December 2008

Insulin-like growth factor-I (IGF-I), IGF-II and IGF-binding proteins (IGFBP) were examined in rat serum during pregnancy and lactation. IGF-I concentrations determined after acid column chromatography of serum were low during the last third of pregnancy. IGF-II was undetectable in pregnant and non-pregnant rats. IGF-binding protein (IGFBP) concentrations, measured as high molecular mass activity in the IGF-I RIA and the IGF-II RRA of acid column fractions, paralleled the changes observed with IGF-I. Western ligand blot analysis of serum from non-pregnant rats revealed a 40–50 kDa IGFBP aligning with IGFBP-3, a smaller 28–30 kDa doublet and 24 kDa IGFBP. Serum from rats in late pregnancy lacked IGFBP-3, whereas the smaller IGFBP persisted during late pregnancy. IGFBP-3 reappeared in postpartum animals. The fall in serum IGF-I is consistent with a maternal catabolic state during late pregnancy which may maximize substrate availability for the developing fetus.

Journal of Endocrinology (1990) 127, 383–390
Stress responsiveness of hypothalamic corticotrophin-releasing factor and pituitary pro-opiomelanocortin mRNAs following high-dose glucocorticoid treatment and withdrawal in the rat
Authors: Harbuz M. S. , Nicholson S. A. , Gillham B. , Lightman S. L.
Published: December 2008

In-situ hybridization with synthetic oligonucleotide probes was used to determine the mRNA content of corticotrophin-releasing factor (CRF) and proenkephalin A mRNA in the paraventricular nucleus, and of pro-opiomelanocortin (POMC) mRNA in the anterior pituitary gland of male rats immediately after, and during recovery from, chronic high-dose prednisolone treatment. Levels of transcripts for mRNA for both CRF and POMC were markedly reduced after the treatment, but there was a rapid return to control values for CRF mRNA within 18 h of steroid withdrawal.

In untreated animals, the stressful stimulus of i.p. hypertonic saline increased CRF and proenkephalin A mRNA within 4 h with no significant difference in response seen whether the tissues were removed at 13.00 or 20.00 h. The increase in POMC mRNA did not reach statistical significance in these animals. Although prednisolone resulted in a marked reduction of basal CRF mRNA, the stress-induced increment of CRF mRNA remained comparable with that found in untreated animals. On the day following cessation of prednisolone treatment at 09.00 h, basal and stress levels of CRF mRNA were significantly higher in rats killed at 20.00 h than at 13.00 h. Proenkephalin A mRNA transcripts were below quantifiable levels of detection in control or non-stressed prednisolone-treated animals at all the time-points studied. Stress, however, resulted in the accumulation of proenkephalin A mRNA in control animals. This response was inhibited by prednisolone treatment and only returned 18 h after withdrawal. Prednisolone treatment reduced POMC mRNA below the levels detected in untreated animals, with no detectable response to stress. However, 36 h after prednisolone withdrawal there was a significant increase in POMC mRNA in response to stress.

Prednisolone concentrations in the plasma on the morning of the day after the final administration of the steroid were very high (880 nmol/l), but these were halved by the evening of that day and had fallen to 60 nmol/l 72 h after withdrawal.

These data show that both CRF and POMC mRNA were profoundly reduced by long-term prednisolone treatment. Stress-induced accumulation of CRF mRNA, however, persisted although the proenkephalin A mRNA responses to this stress were inhibited. No increase in pituitary POMC mRNA in response to stress was apparent until 36 h after withdrawal of prednisolone.

Journal of Endocrinology (1990) 127, 407–415
Distribution of pyroglutamylpeptide amides related to thyrotrophin-releasing hormone in the central nervous system and periphery of the rat
Authors: del Rio-Garcia J. , Smyth D. G.
Published: December 2008

A rapid and sensitive chromatographic method is presented for determining TRH and TRH-like peptides in small quantities of tissues and fluids. The procedure was applied to screen a comprehensive range of tissues from the central nervous system (CNS) and periphery of the rat. When hydrochloric acid (100 mmol/l) was used for extraction, the TRH immunoreactivity obtained was identified solely with the known tripeptide hormone. In contrast, when weakly acidic conditions were used for extraction, neutral or acidic TRH-like peptides which lacked the histidine residue at position 2 of the hormone, but reacted with TRH antibodies, were shown to be present in addition to TRH. The TRH-like peptides in the brain were located principally in the hippocampus, brain stem and dorsal colliculi. In the periphery, TRH-like peptides were shown to be present in the male reproductive system and certain endocrine tissues. In addition, the presence of TRH-like peptides was confirmed in portal blood. The results indicate that peptides with a neutral or acidic TRH-like sequence at their C-terminus are widely distributed in the CNS and periphery of the rat. These peptides appear to occur mainly or exclusively in precursor forms from which TRH immunoreactivity can be released during extraction under weakly acidic conditions.

Journal of Endocrinology (1990) 127, 445–450
Regulation of the photoperiod-induced cycle in the peripheral blood concentrations of β-endorphin and prolactin in the ram: role of dopamine and endogenous opioids
Authors: Ssewannyana E. , Lincoln G. A.
Published: December 2008

In a group of adult Soay rams housed indoors under an artificial light cycle of alternating 16-week periods of long and short days, there was a conspicuous longterm cycle in the peripheral plasma concentrations of β-endorphin and prolactin. The levels of β-endorphin were highest under short days and lowest under long days (15-fold change), and inversely related to the changes in the plasma levels of prolactin (120-fold change). The role of dopamine in the control of β-endorphin and prolactin was investigated in a series of experiments, conducted under both long and short days, in which rams were treated with dopamine receptor agonists (dopamine and bromocriptine) and antagonists (pimozide and sulpiride). Naloxone (opioid antagonist) was also administered to assess the additional involvement of endogenous opioids.

Dopamine injected i.v. (6·6 mg/kg every 10 min) did not significantly affect the mean plasma concentrations of β-endorphin and prolactin under either long or short days. Pimozide (0·08 mg/kg i.m. every 2 h) caused a large increase in the mean plasma concentrations of β-endorphin and prolactin under long days but not short days. Naloxone (1·6 mg/kg, i.v.), administered alone or in combination with dopamine or pimozide, had no effect on the mean plasma concentrations of β-endorphin and prolactin, except under short days when, combined with pimozide, it induced an increase in the plasma concentrations of the two polypeptides.

Bromocriptine (0·06 mg/kg, s.c.) caused a significant decrease in the plasma concentrations of both β-endorphin and prolactin; this effect was most marked at the times of increased secretion (under short days for β-endorphin and under long days for prolactin). Sulpiride (0·59 mg/kg, s.c.) produced the converse effect and caused an increase in the plasma concentrations of β-endorphin and prolactin with the amplitude and duration of the effect varying with the stage of the photoperiod-induced cycle.

From these results in the Soay ram, we conclude that dopamine inhibits β-endorphin and prolactin secretion by way of D2 receptors under both long and short days. Endogenous opioids interact with dopamine, augmenting this inhibition under short days. Differences in the acute responses in the secretion of β-endorphin and prolactin, and the inverse relationship between β-endorphin and prolactin during the cycle, indicate that different regulatory systems involving dopamine influence the two pituitary polypeptides.

Journal of Endocrinology (1990) 127, 461–469
Potentiation of the growth-promoting activity of porcine growth hormone (pGH) with an antibody generated in rabbits to the peptide sequence pGH110–118
Authors: Wang B. S. , Szewczyk E. , Shieh H.-M. , Hart I. C.
Published: December 2008

An effort was made to identify the antigenic epitope(s) of porcine GH (pGH) capable of inducing antibodies which would enhance the growth-promoting activity of the hormone. Several peptide sequences of the pGH molecule were synthesized and the antibodies to these peptides were generated in rabbits. The majority of these antibodies were found to be immunoreactive with both intact pGH and their respective peptide antigens. The biological activity of the antibodies was tested in growth-retarded hypophysectomized rats. Daily injections with pGH alone significantly increased their growth rate and treatment with a combination of pGH and antibody specific to the peptide sequence 110–118 further heightened the somatogenic effect. Administration of this antibody alone did not enhance the growth rate of hypophysectomized rats, neither did antibodies raised to intact pGH or the other peptide sequences. The present findings suggest that antibody with a particular pGH epitope specificity is able to increase the somatogenic activity of pGH and that the peptide corresponding to pGH amino acids 110–118 may prove useful in the development of growth promoting vaccines.

Journal of Endocrinology (1990) 127, 481–485
Varying dose–response characteristics of different immunoassays and an in-vitro bioassay for FSH are responsible for changing ratios of biologically active to immunologically active FSH
Authors: Jockenhövel F. , Khan S. A. , Nieschlag E.
Published: December 2008

Serum FSH levels in fertile and infertile men were determined by applying the Sertoli cell in-vitro bioassay and six different immunoassays. Bioassay and immunoassay estimates were significantly correlated (r ranging from 0·78 to 0·86; P<0·01). On average, all immunoassays measured lower FSH concentrations in samples with low FSH levels and higher FSH concentrations in those with high FSH levels compared with the bioassay. Ratios of bioactivity to immunoreactivity (B/I) were highest in fertile men and lowest in men with severe disturbances of testicular function. Depending on which immunoassay was used these differences were either significant or only marginal. Dose–response characteristics for WHO FSH standard preparation 78/549, used in the bioassay as well as in the immunoassays, were different between immunoassays and the bioassay, suggesting that decreasing B/I ratios with increasing FSH serum levels were method-related and reflected different slopes of the dose–response characteristics of the assays, rather than being true changes in the molecular composition of FSH. The present investigation underlines the necessity of choosing the immunoassay used for comparison with the bioassay carefully and of validating the system in regard to parallelism between dose–response characteristics. B/I ratios must be interpreted with great caution and previous studies which report changing B/I ratios in various endocrine situations may have to be reevaluated.

Journal of Endocrinology (1990) 127, 523–532
Parathyroid hormone-related protein in milk and its correlation with bovine milk calcium
Authors: Law F. M. K. , Moate P. J. , Leaver D. D. , Diefenbach-Jagger H. , Grill V. , Ho P. W. M. , Martin T. J.
Published: December 2008

Parathyroid hormone-related protein (PTHrP) has been shown to be present in milk of various mammals. We have assayed PTHrP in milk of various species by radioimmunoassay and estimated the molecular weights by Western blot analysis. PTHrP concentrations in bovine, ovine and human milk were 59·2±18·5, 74·1±35·0 and 36·6±20·7 μg/l (means ± s.d.) respectively, in pooled samples collected at various stages of lactation. PTHrP in mammalian milk was found to exist in two forms with molecular weights of 17·5 kDa and 21·5 kDa approximating those of PTHrP(1-108) and (1–141) respectively. In comparison, marsupial milk PTHrP appeared as a single low molecular weight form of 14·4 kDa which approximated to that of PTHrP(1–84). We performed a longitudinal study measuring the concentration of PTHrP in milk throughout lactation in cows, and found it to increase with the duration of lactation (r= 0·669, n = 91). We further examined the relationship between the concentration of PTHrP and total calcium in bovine milk, and the differences between these constituents in milk from Friesian and Jersey cows. PTHrP concentrations correlated positively with total milk calcium (r = 0·346, n = 105). The mean milk concentration of PTHrP of the Jerseys was significantly higher than that of the Friesians (52·6±5·4 μg/l compared with 41·0±4·8 μg/l, P < 0·01), as was the mean milk calcium concentration (30·5±3·0 mmol/l compared with 26·7±2·7 mmol/l, P < 0·01). We therefore postulate that production of PTHrP by the mammary gland may be associated with calcium transport from blood to milk. Also PTHrP may play a role in the development of milk fever in Jerseys which are predisposed to this condition.

Journal of Endocrinology (1991) 128, 21–26
Indirect evidence for short-loop negative feedback of insulin secretion in the rat
Authors: Ammon H. P. T. , Reiber C. , Verspohl E. J.
Published: December 2008

Feedback inhibition of glucose-mediated insulin release has repeatedly been demonstrated in isolated pancreatic islets and in the perfused pancreas. It was the aim of the present study to determine whether inhibition occurs through a long-loop (plasma concentration of insulin) or a short-loop (local concentration) action of insulin. The perfused rat pancreas was used, with different perfusion rates and different insulin concentrations in the medium. Increasing the flow rate from 1 to either 3 or 6 ml/min gradually decreased the insulin concentration in the effluent, at stimulatory concentrations of glucose (11·1 and 16·7 mmol/l). Under the same conditions, however, the integrated amount of insulin released over a period of 30 min was significantly enhanced. When exogenous insulin (2·7 and 5·4 μmol/l) was added to the perfusion medium, insulin secretion in the presence of 11·1 or 16·7 mmol glucose/l at flow rates of 3 and 6 ml/min was diminished. This effect was most prominent with 1 1·1 mmol glucose/l and 2·7 μmol exogenous insulin/l at all flow rates (except 1 ml/min), as well as at the high perfusion flow rates with other glucose concentrations. Insulin secretion was not affected by 5·4 μmol exogenous insulin/l at 1 ml/min or by 2·7 μmol exogenous insulin/l at 3 ml/min. The data support a negative feedback inhibition of insulin secretion by secreted insulin, since insulin secretion was decreased by either adding exogenous insulin or by lowering endogenous insulin as the consequence of increased flow rates. They also suggest that the local extracellular concentration of insulin is of more importance than the plasma concentration, consistent with the concept of a short-loop feedback as already claimed for other hormones and/or neurotransmitters.

Journal of Endocrinology (1991) 128, 27–34
A renin-like enzyme in rat luteal tissue: evidence of local synthesis and its regulation during pregnancy
Authors: De Vito E. , Guardia D. C. , Cabrera R. R.
Published: December 2008

Changes in the concentration of a renin-like enzyme were studied in androgenized rats in which a single luteal phase was induced by the administration of chorionic gonadotrophin. A significant increase in the luteal renin-like enzyme (RLE) concentration was found between the youngest corpora lutea (48 h old) and the oldest one studied (6 days old). The luteal RLE content varied independently of changes in plasma renin concentration. These results suggest that this enzyme was produced locally. The lack of correlation between the luteal RLE and plasma prolactin supports our previous observation that the changes in luteal renin concentration appear not to be prolactin-dependent. Furthermore, the suckling-associated hormones appear not to be related with the regulation of luteal RLE concentration, since the values were not modified in androgenized maternal rats which were suckling when compared with the controls. Changes in luteal renin concentration were also studied during pregnancy. A significant increase was found a few hours after a fertile mating which reached a peak on day 1 of pregnancy, followed by a rapid decrease to low levels throughout the remainder of the pregnancy. Because the renin-angiotensin facilitates angiogenesis, luteal renin may act as an angiogenic factor, stimulating blood vessel growth in the corpora lutea. An alternative hypothesis is that the increase in RLE could be a trigger for calcium flux redistribution and steroid biosynthesis.

Journal of Endocrinology (1991) 128, 43–49
Distribution of 125I-labelled insulin-binding sites in peripheral tissues of the normal and diabetic rat: an autoradiographic study
Authors: Thompson C. S. , Sykes R. M. , Muddle J. , Dashwood M. R.
Published: December 2008

In-vitro autoradiography was used to demonstrate the regional distribution of 125I-labelled insulin-binding sites in the liver, kidney and heart of normal rats and rats made diabetic with streptozotocin.

The distribution of insulin-binding sites in the liver of control rats was uniformly high, while in the kidney of control rats there was weak 125I-labelled insulin binding in the medulla and dense binding in the cortex. In the hearts of control rats a high density of 125I-labelled insulin-binding sites was evident both in the atrial and ventricular muscle.

Non-ketotic diabetes mellitus caused a marked increase in 125I-labelled insulin-binding sites in both the liver and kidney with the former tissue exhibiting a time-dependent (7 to 62 days) increase. There was no apparent effect of diabetes on insulin-binding sites in the heart.

Since experimental diabetes causes (1) a decrease in circulating insulin concentration and (2) impaired insulin action at many target tissues, the increase in 125I-labelled insulin-binding sites observed in the present study may represent a compensatory 'up regulation' of insulin receptors.

Journal of Endocrinology (1991) 128, 85–89
Characterization of a factor(s) from partially purified human gonadotrophin preparations which inhibit(s) the binding of radiolabelled human LH and human chorionic gonadotrophin to Candida albicans
Authors: Bramley T. A. , Menzies G. S. , Williams R. J. , Kinsman O. S. , Adams D. J.
Published: December 2008

We have shown previously that partially purified human chorionic gonadotrophin (hCG) preparations inhibited the specific binding of I-labelled hLH or hCG to Candida albicans membranes at much lower concentrations than did highly purified hLH or hCG preparations. We now describe the characterization and partial purification of a heat-labile glycoprotein from commercially available gonadotrophin preparations. The factor strongly inhibited LH binding to Candida membranes, but not to sheep or pig luteal LH receptors. This material had a molecular weight of 16 000–21 000 daltons, bound strongly to CM-Sepharose at physiological pH, and could be resolved completely from hCG and from epidermal growth factor-like factors present in commercial gonadotrophin preparations. Its activity was not attenuated by a range of inhibitors specific for the four major classes of proteolytic enzymes, nor did it inhibit hormone binding by causing degradation of 125 I-labelled hLH or hCG tracers. Factors which inhibited hLH binding to Candida membranes were also present in partially purified human urinary and equine serum gonadotrophin preparations and in placental extracts, but were not detected in highly purified CG of hLH preparations. The properties of this factor were similar to those described for β-core protein, a cleavage product of the β subunit of hCG which is a contaminant of commercial gonadotrophin preparations. Highly purified β-core protein inhibited 125I-labelled hLH binding to Candida membranes, but not to sheep luteal binding sites.

Preparations of hCG depleted of inhibitor activity could stimulate adenylate cyclase activity in Candida membranes almost five fold. In contrast, partially purified inhibitor preparations strongly inhibited basal adenylate cyclase activity (to 18% of control levels). These observations suggest that endogenous LH-like factors, perhaps similar to β-core proteins of hCG, may play a role in the regulation of morphogenesis in Candida species.

Journal of Endocrinology (1991) 128, 139–151
Pharmacokinetics of thyrotrophin-releasing hormone in patients in different thyroid states
Authors: Iversen E.
Published: December 2008

In view of recent reports suggesting that thyroid hormone control of TRH degradation occurs outside the central nervous system in animals, the effect of thyroid status on serum and tissue degradation of TRH in man was investigated. In six patients with hyperthyroidism and six patients with hypothyroidism, constant TRH infusions were carried out for determination of plasma clearance rate (PCR) and half-life of disappearance (t½) of TRH, with simultaneous determination of half-life of disappearance in serum in vitro (t½p). Using a kinetic model, this enabled the calculation of the half-life of disappearance in the extravascular tissue compartment (t½t). All patients were reinvestigated after they had become euthyroid. PCR, t½ and t½p were 22·1 ±3·4 ml/kg per min, 6·8±1·1 min and 17·3±6·7 min (means ± s.d.) respectively in the euthyroid patients. The t½p was slightly but significantly prolonged during hyperthyroidism. The t½ was 5·6 min in the hyperthyroid patients compared with 9·4 min in the hypothyroid patients. The calculated t½t was 6·5 min in the euthyroid patients. In the patients with untreated hyperthyroidism, t½t was significantly reduced (22·7±10·7%; mean ± s.d.), while it was considerably prolonged (41·1±24·6%) in patients with untreated hypothyroidism. The percentage reduction or prolongation of t½t was negatively correlated with the logarithm of the serum concentrations of thyroxine (r = 0·92) and tri-iodothyronine (r= 0·91) in the untreated patients. Thus, thyroid hormones induce alterations in the pharmacokinetics of TRH. This may partly be due to induction by thyroid hormones of membrane-bound pyroglutamyl aminopeptidase.

Journal of Endocrinology (1991) 128, 153–159