bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of the ACTH response to repeated pulses of corticotrophin-releasing factor and arginine vasopressin in vitro
Authors: Evans M. J. , Brett J. T. , McIntosh R. P. , McIntosh J. E. A. , McLay J. L. , Livesey J. H. , Donald R. A. 
Published: December 2008

ABSTRACT
A multi-column perifusion system was used to investigate the dynamics of the dose–response relationships of ACTH release by ovine pituitary cells when stimulated by both corticotrophin-releasing hormone (CRF) and arginine vasopressin (AVP) given alone and in combination. A dose–response relationship was obtained when 10-min pulses were given at 60-min intervals over the range of 0·002–2000 nmol CRF/l and 1–2000 nmol AVP/l, with a minimum effective concentration of 0·02 nmol CRF/l or 1 nmol AVP/l. When AVP was given together with CRF, the expected potentiation of the ACTH response occurred when compared with the summed response of these secretagogues given separately. At the higher concentrations of CRF and AVP used, the ACTH responses to repeated pulses decreased with time during the experiment. The rate of this loss of responsiveness was significantly correlated to the size of the response to the first pulse (for CRF: r = 0·89, P<0·01; for AVP: r = 0·95, P < 0·01), being greatest when the response was potentiated by adding the secretagogues together (for CRF plus AVP: r = 0·95, P <0·01). Reduced availability of receptors or changes in intracellular transduction processes may contribute to this desensitization. Reduced levels of secretable ACTH do not appear to be implicated because desensitization to pulses of one secretagogue did not cause equivalent desensitization to the other. In addition, cells stimulated continuously with submaximal levels of either secretagogue showed desensitization while more ACTH was still available for release to higher levels of stimulant. The potentiation of CRF plus AVP resulted primarily from a rapid increase in the height of the response since the width of the response (at one-third maximum height) was significantly (P < 0·001) less after AVP plus CRF than after CRF alone. Also the rapidity with which ACTH concentrations fell after removal of the stimulus from the perifusion medium was significantly (P <0·01) faster following AVP, and CRF plus AVP (P <0·05), than after CRF alone.
It is concluded that reduced ACTH responsiveness following repeated stimulation is dependent upon the type and concentration of the secretagogue. AVP had a shorter duration of action than CRF in vitro and potentiated the initial response to CRF rather than prolonging its action. Desensitization to each stimulant appeared to act by a mechanism independent of the other and therefore appeared to occur at or near the receptor level and be unrelated to the availability of ACTH.
J. Endocr. (1988) 117, 387–395
Concentrations of oxytocin-neurophysin prohormone mRNA in corpora lutea of sheep during the oestrous cycle and in early pregnancy
Authors: Jones D. S. C. , Flint A. P. F. 
Published: December 2008

ABSTRACT
Concentrations of oxytocin in corpora lutea from pregnant and non-pregnant sheep rose during luteinization to peak between days 5 and 9 after oestrus before falling to low levels on days 12 and 14. Concentrations of the 608-base mRNA encoding the oxytocin-neurophysin prohormone, measured by Northern blotting using a cRNA probe, were highest before day 5, and fell to low levels by day 9. The decline in oxytocin during the second half of the oestrous cycle and in pregnancy could therefore be accounted for by reduced luteal concentrations of oxytocin-neurophysin mRNA. The rate of decline in prohormone mRNA concentration between days 3 and 16 followed first order kinetics, suggesting that gene expression ceased early in the cycle. The lag between peak oxytocin-neurophysin mRNA and peak oxytocin concentrations may represent the time taken for post-translational processing of the prohormone.
J. Endocr. (1988) 117, 409–414
Effect of serotonin antagonists on prolactin and progesterone secretion in rats: evidence that the stimulatory and inhibitory actions of serotonin on prolactin release may be mediated through different receptors
Authors: Jahn G. A. , Deis R. P. 
Published: December 2008

ABSTRACT
The serotoninergic regulation of prolactin release was studied in female rats in different reproductive states using ketanserin, a specific S2 receptor blocker, ICS 205-930 ((3α-tropanyl)1H-indol-3-carboxylic acid ester), a specific S3 receptor blocker and p-chlorophenylalanine (pCPA), a serotonin synthesis inhibitor. Administration of ketanserin to pro-oestrous rats inhibited the afternoon prolactin surge; this inhibition was prevented by progesterone. On day 3 of pregnancy, pCPA or ketanserin blocked the afternoon prolactin surge, and administration of oestrogen (on day 2) and progesterone (on day 3) in combination, but not alone, prevented this effect. On day 9 of pregnancy, treatment with oestrogen (on day 8) and progesterone (on day 9) induced an afternoon surge of prolactin which was prevented by administration of ketanserin or pCPA. On days 9 and 16, pCPA induced a slight increase in serum prolactin in rats not treated with steroids, but ketanserin had no effect. On day 13, ketanserin and pCPA had no effect on serum prolactin levels, but after increasing serotoninergic transmission by injecting fluoxetine and 5-hydroxytryptophan, serum prolactin levels were decreased. On day 19, ketanserin produced a transient increase in the serum concentration of prolactin, probably produced by the marked decrease in the serum concentration of progesterone induced by the S2 receptor blocker. Administration of ICS 205-930 to pro-oestrous rats or rats on day 19 of pregnancy had no effect on serum concentrations of prolactin and progesterone. These results suggest that the stimulatory action of serotonin on prolactin release is mediated through its binding to type-2 receptors, while the inhibitory action seen on the second half of pregnancy may be mediated through type-1 receptors.
J. Endocr. (1988) 117, 415–422
Effects of bovine follicular fluid on gonadotrophin secretion in intact and chronically ovariectomized ewes before and after desensitization of pituitary gonadotrophs to gonadotrophin-releasing hormone
Authors: Knight P. G. , Castillo R. J. 
Published: December 2008

ABSTRACT
Intact and chronically ovariectomized ewes were treated for 4 days with charcoal-treated bovine follicular fluid (FF) or charcoal-treated bovine serum during the late-anoestrous period, and the effects on basal and gonadotrophin-releasing hormone (GnRH)-induced secretion of LH and FSH observed. Subsequently, ewes received s.c. implants containing a sustained-release formulation of a potent GnRH agonist d-Ser(But)6-Azgly10-LHRH (ICI 118630) to desensitize pituitary gonadotrophs to hypothalamic stimulation, and the effects of bovine FF and bovine serum were re-assessed 2 weeks later. Chronic exposure (for 2–3 weeks) to ICI 118630 significantly reduced basal levels of LH and FSH in both intact and ovariectomized ewes and completely abolished both spontaneous LH pulses as well as exogenous GnRH-induced acute increases in plasma LH and FSH levels. Treatment with bovine FF significantly reduced plasma FSH levels, but not LH levels, in both intact and ovariectomized ewes before and after chronic exposure to ICI 118630. In intact ewes before exposure to ICI 118630, treatment with bovine FF actually enhanced pulsatile LH secretion and raised mean plasma LH levels by 240% (P <0·05). No such stimulatory effect of bovine FF on LH secretion was observed in intact ewes exposed to ICI 118630 or in ovariectomized ewes before or after exposure to ICI 118630, suggesting that the effect probably involved an alteration in ovarian steroid feedback affecting hypothalamic GnRH output. Treatment with bovine FF did not significantly affect the magnitude of GnRH-induced surges of LH or of FSH observed in either intact or ovariectomized ewes before exposure to ICI 118630. These observations indicate that charcoal-treated bovine FF, a rich source of inhibin, can directly suppress pituitary FSH secretion in vivo, irrespective of whether a functionally intact hypothalamo-pituitary-ovarian axis is present.
J. Endocr. (1988) 117, 431–439
Two vasopressin-like peptides in the pig testis?
Authors: Nicholson H. D. , Smith A. J. , Birkett S. D. , Denning-Kendall P. A. , Pickering B. T. 
Published: December 2008

ABSTRACT
Vasopressin (VP)-like immunoreactivity (IR) has been located in the testes of several species of mammal. There is evidence that most of this IR in the rat does not represent authentic arginine vasopressin (AVP) and that a second AVP-like peptide may exist. We have studied testis samples from the pig, which produces lysine vasopressin (LVP) in its pituitary, and have found both LVP- and AVP-like IR.
High-performance liquid chromatography (HPLC) of testis extracts showed two peaks of VP-IR. The first peak co-eluted with authentic LVP and was recognized only by antisera which cross-reacted with LVP. The second peak co-eluted with authentic AVP and was recognized by antisera raised against AVP. Both VP-like peptides bound to a neurophysin affinity column and the HPLC elution profiles of the bound peptides were similar to those of the authentic hormones. When the LVP-like material was oxidized with performic acid, a peak of IR running in the same position as oxidized authentic LVP on HPLC was produced. Similarly, the performic acid-oxidized AVP-like material co-eluted with oxidized authentic AVP.
The presence of both LVP- and AVP-like peptides in the pig testis may mean that more than one gene is involved. A second VP-like gene could also explain the anomalies of VP-IR in other species.
J. Endocr. (1988) 117, 441–446
Receptor-binding characteristics and contractile responsiveness of the myometrium following prolonged infusion of bradykinin and oxytocin in rats
Authors: Engstrom T. , Atke A. , Vilhardt H. 
Published: December 2008

ABSTRACT
Binding of [3H]oxytocin to purified myometrial plasma membranes was unaffected by continuous infusion of bradykinin over 5 days in rats pretreated with oestradiol 2 days before collection of tissue. In contrast, oxytocin treatment resulted in a 76% decrease in maximal binding of [3H]oxytocin and thereby in oxytocin receptor concentration without affecting the dissociation constant. The KM value (molar concentration giving half maximal contraction) of isolated uterine strips stimulated with oxytocin was increased and maximal contractile responses were reduced following oxytocin infusions.
The binding of [3H]bradykinin to purified plasma membranes was influenced by treatment with both oxytocin and bradykinin. Bradykinin infusions down-regulated the bradykinin receptor concentration by 19%, while the receptor affinity remained unchanged. Maximal contraction (Emax) values of isolated strips stimulated with bradykinin exhibited a slightly attenuated response and KM values were significantly enhanced. Long-term treatment with oxytocin down-regulated myometrial bradykinin receptors by 31%. In addition, oxytocin infusions caused Emax to decrease and KM to increase in experiments with isolated uterine strips stimulated with bradykinin.
It is concluded that the down-regulation of oxytocin and bradykinin receptors following prolonged exposure to oxytocin may result from changes in a common pathway for intracellular peptide receptor processing. Likewise, the increased KM values of isolated myometrial strips (despite unchanged dissociation constants) suggest that prolonged oxytocin treatment affects the coupling between receptor activation and contractile response.
J. Endocr. (1988) 118, 81–85
Reduced vasoactive intestinal polypeptide immunoreactivity in the pituitaries of hormone-deficient mutant mice
Authors: Noguchi T. , Sugisaki T. , Kanamatsu T. , Satoh I. , Nishikawa N. 
Published: December 2008

ABSTRACT
The prolactin-producing cells of the bovine anterior pituitary were found to contain a vasoactive intestinal polypeptide (VIP) immunoreactive substance, thus suggesting a role for VIP in the regulation of prolactin release.
The pituitaries of the dw and lit strains of mutant mice, congenitally deficient in prolactin-producing cells, and hyt mice, which were found to have reduced numbers of prolactin-producing cells, showed a markedly reduced VIP immunoreactivity. Hypothalamic VIP immunoreactivity, however, was found to be unchanged in the three strains of mutant mice, indicating that the high concentration of VIP in the hypothalamus does not derive from the adenohypophysis through retrograde flow. The deficiency in the mutant mice seems to be due to the lack of prolactin target cells in the pituitary.
J. Endocr. (1988) 118, 179–185
Correlation between myometrial receptor affinity, lipophilicity and antagonistic potency of oxytocin analogues in the rat
Authors: Atke A. , Vilhardt H. , Melin P. 
Published: December 2008

ABSTRACT
Purified myometrial plasma membrane fractions were prepared from rats treated with oestradiol to induce oestrus. The binding affinities of 11 antagonistic oxytocin analogues to the oxytocin receptor of the plasma membranes were measured. Furthermore, lipophilicity of the peptides was assessed by reversed-phase high pressure liquid chromatography. No significant correlation was found between lipophilicity of the analogues and values for antagonistic potencies or binding affinities. Also, receptor-binding affinity did not correlate with in-vitro antagonistic activity whereas a significant correlation was obtained between binding affinities and in-vivo antagonistic potency for analogues void of partial agonist properties. It is concluded that neither receptor affinity nor lipophilicity in the analogues can predict the potency of the antagonists in vitro. However, receptor affinity was found to be a relatively good predictor of the in-vivo potency, while the usefulness of measuring antagonistic potency in vitro is questioned.
J. Endocr. (1988) 118, 187–192
Effects of protein kinase C activators on the in-vitro action of thyrotrophin in pigs
Authors: Ginsberg J. , Murray P. G. 
Published: December 2008

ABSTRACT
The ability of the non-phorbol protein kinase C (PKC) activator 12-hydroxy-daphnetoxin (mezerein) to modulate differentiated thyroid function was examined in vitro. A dose-dependent inhibition of TSH-stimulated iodide organification was observed in porcine thyroid cells exposed to mezerein. Under identical conditions mezerein caused the translocation of PKC from its inactive cytosolic form to an active membrane-bound form in thyroid cell extracts. The relative biological potencies of mezerein and the phorbol ester, 12-0-tetradecanoylphorbol-13-acetate (TPA), to inhibit thyroid function in vitro corresponded to their abilities to activate PKC. This effect was also observed when dibutyryl cyclic AMP was used, implying a post-receptor site of action. To provide further evidence for this concept, the effects of mezerein and TPA on receptor-related events were studied. Neither mezerein nor TPA had any effect on the binding of radiolabelled TSH to solubilized porcine thyroid membranes. However, both mezerein and TPA were capable of stimulating cyclic AMP (cAMP) production in porcine thyroid cells in the basal state but could not augment TSH or forskolin-activated cAMP release. These data provide evidence that activation of PKC plays a role in the regulation of differentiated thyroid function in vitro and suggest that the effects of PKC are complex, with independent actions on cAMP accumulation and post-receptor events.
J. Endocr. (1988) 118, 199–203
Ontogeny of catecholamine-synthesizing enzymes and enkephalins in the sheep adrenal medulla: an immunocytochemical study
Authors: McMillen I. C. , Mulvogue H. M. , Coulter C. L. , Browne C. A. , Howe P. R. C. 
Published: December 2008

ABSTRACT
An immunocytochemical staining technique was used to investigate the development of the sheep adrenal medullary cells containing enkephalins and the catecholamine synthetic enzymes dopamine β-hydroxylase (DBH) and phenylethanolamine N-methyl transferase (PNMT). No staining was observed in the adrenocortical cells with any of the antisera used in this study. Positive staining with anti-DBH was observed throughout the medulla in both adult and fetal adrenal glands from 80 days of gestation. Positive staining with anti-PNMT was observed in all glands from as early as 80 days of gestation, and staining with this antiserum was mainly confined to the peripheral medullary cells, which were adjacent to, and interdigitated between, the cells of the adrenal cortex. In the fetus between 80 and 120 days of gestation, staining for the enkephalins was observed in both the peripheral columnar and the central polygonal adrenal medullary cells. After 125 days of gestation and in the adult ewe, the peripheral columnar cells were uniformly stained with anti-enkephalin whereas many unstained cells were present in the central medullary region. Therefore, enkephalin-containing peptides are present in the catecholamine cells of the fetal and adult sheep adrenal and there appears to be a changing pattern in the distribution of the enkephalins in the fetal adrenal in late gestation.
J. Endocr. (1988) 118, 221–226
The mitogenic effects of corticotrophin-releasing factor on the anterior pituitary gland of the rat
Authors: McNicol A. M. , Kubba M. A. G. , McTeague E. 
Published: December 2008

ABSTRACT
The immunohistochemically defined corticotroph population in the anterior pituitary gland of the adult male Sprague–Dawley rat has been quantified at 2 and 6 weeks after bilateral adrenalectomy using the stereological measurement, volume density (Vv). An approximately twofold increase in corticotroph Vv was demonstrated at 2 weeks in adrenalectomized rats compared with that in sham-operated controls and this was maintained at 6 weeks. Daily i.p. injections of ovine corticotrophin-releasing factor (CRF-41) induced a significant dose-related increase in corticotroph Vv when administered at doses of 25 and 50 μg/kg body weight, but this was less than the increase following adrenalectomy.
Assessment of changes in mitotic activity of the total anterior lobe of adult Sprague–Dawley rats and of the corticotroph population was also made after daily i.p. injections of 50 μg CRF-41/kg for 2 and 7 days. There was no increase in overall mitotic index at either time. However, the numbers of mitotic corticotrophs were significantly increased in CRF-injected animals compared with those in saline-injected rats. These results indicate a role for CRF-41 in the regulation of corticotroph growth.
J. Endocr. (1988) 118, 237–241
The influence of oestrogen and progesterone on the actions of two calcium entry blockers in the rat uterus
Authors: Downing S. J. , Hollingsworth M. , Miller M. 
Published: December 2008

ABSTRACT
The potency and maximum effect of the calcium entry blocker nifedipine as an inhibitor of uterine contractions in vivo are increased in rats in late pregnant compared with non-pregnant rats. The influence of ovarian steroids produced during pregnancy (oestrogen and progesterone) on the potency and maximum effect of two calcium entry blockers (nifedipine and diltiazem) against uterine contractions during i.v. infusion was therefore investigated in anaesthetized non-pregnant rats. The influence of pregnancy on the relationship between serum concentrations of diltiazem during i.v. infusion and uterine and cardiovascular effects was also investigated.
A twofold increase in the potency of nifedipine as an inhibitor of uterine contractions was observed in rats treated with oestrogen or oestrogen plus progesterone compared with rats treated with corn oil. There was no change in potency in rats receiving progesterone alone. Maximum inhibition of uterine contractions by nifedipine was significantly increased by all three hormone treatments.
A twofold increase in the potency of diltiazem and a significant increase in maximum inhibition of uterine contractions was observed in rats in late pregnancy compared with non-pregnant rats. No increase in potency of diltiazem in reducing blood pressure or heart rate was observed in rats in late pregnancy. No significant difference in potency of diltiazem against uterine contractions was observed in rats treated with oestrogen, progesterone or oestrogen plus progesterone.
In order to determine if the hormone-induced changes in the potency of nifedipine against contractions in vivo were due to a direct effect of the ovarian steroids on voltage-operated calcium channels of the uterus or were mediated by extra-uterine mechanisms, the potency of nifedipine as a relaxant of uterine spasms in vitro was investigated. The potency of nifedipine in the isolated uterus as a relaxant of the spasm induced by KC1 did not differ between rats which received oestrogen, progesterone or oestrogen plus progesterone or corn oil. Additionally, the potency of nifedipine to inhibit oxytocin-driven phasic tension development was not affected by treatment with oestradiol.
These findings suggest that the increase in potency and maximum effect of nifedipine against uterine contractions observed previously in rats in late pregnancy can be ascribed, in part, to the action of the ovarian steroids (oestrogen and progesterone). The increase in potency of diltiazem observed in rats in late pregnancy, however, is due to factors other than oestrogen and progesterone. The lack of effect of hormonal manipulations on the potency of nifedipine on the isolated uterus suggests that the changes in potency in vivo due to oestrogen and progesterone are mediated by extra-uterine mechanisms.
J. Endocr. (1988) 118, 251–258
Relationships between prolactin, LH and broody behaviour in bantam hens
Authors: Sharp P. J. , Macnamee M. C. , Sterling R. J. , Lea R. W. , Pedersen H. C. 
Published: December 2008

ABSTRACT
The interactions between broody behaviour and changes in concentrations of plasma prolactin and LH were investigated in bantam hens. Adoption of newly hatched chicks caused incubating hens to leave their nests and prevented plasma prolactin decreasing as rapidly as in hens deprived of their nests and not given chicks. Further, the hens allowed to rear chicks came back into lay later (P< 0·001) than the hens not allowed chicks. Plasma prolactin decreased and plasma LH increased in hens deprived of their nests: these changes were reversed when the hens re-nested. The changes in plasma LH and prolactin in nest-deprived and re-nesting birds were not always synchronous; this was particularly clear immediately after nest deprivation when the increase in plasma LH preceded the decrease in the plasma prolactin. Readiness to incubate disappeared between 48 and 72 h after nest deprivation and corresponded with the time when plasma prolactin decreased to baseline values. Administration of ovine prolactin depressed (P<0·01) the initial increase in plasma LH after nest deprivation, but repeated administration of prolactin for up to 72 h failed to suppress plasma LH to the values found in incubating hens. Repeated administration of ovine prolactin at 5- to 8-h intervals for 72 h maintained readiness to incubate in nest-deprived hens. It is concluded that the secretion of prolactin in broody hens is facilitated by the presence of chicks and that increased concentrations of plasma prolactin maintain incubation behaviour. In incubating hens the secretion of LH and prolactin may be partly regulated independently. In addition, LH secretion may also be inhibited by increased plasma prolactin.
J. Endocr. (1988) 118, 279–286