bluuebunny/crossref_metadata_2025 huggingface dataset:
The somatotrophic axis in young steers: influence of nutritional status on pulsatile release of growth hormone and circulating concentrations of insulin-like growth factor 1
Authors: Breier B. H. , Bass J. J. , Butler J. H. , Gluckman P. D.
Published: December 2008

The relationship between plasma GH profiles and circulating concentrations of insulin-like growth factor 1 (IGF-1) at three different planes of nutrition, chosen to represent a high, medium and low level of nutrition (3%, 1·8% and 1% dry matter of liveweight per day) was studied in 15 young Angus steers. All steers were maintained on 3% dry matter for 5 weeks, then on one of the three nutritional planes for 4 weeks and then all were returned to 3% dry matter for 3 weeks. Blood was sampled through jugular catheters at 15-min intervals for 25 h at the end of each phase of the study and additional samples were taken on 2 days each week.

Pulsatile release of GH occurred episodically with a diurnal increase during night and morning hours only in steers on high nutritional intakes. Reduced feeding at both the medium and the low plane abolished the diurnal rhythm and significantly increased mean plasma GH concentrations, the amplitude of GH pulses and the area under the GH profiles. Baseline concentrations of GH and pulse frequency did not change through nutritional manipulation. Upon realimentation, plasma GH concentrations decreased in both previously undernourished groups, with those fed 1% dry matter still having increased levels 10 days after refeeding. Plasma IGF-1 concentrations showed no periodicity. With nutritional deprivation, a decrease in IGF-1 concentration was observed only at negative energy balance (1% group). In this group plasma IGF-1 concentrations were progressively restored within 1 week of realimentation.

The different relationship between GH and IGF-1 release at each plane of nutrition suggests that at both medium and low levels of feed intake, tissue insensitivity to GH may exist peripherally and perhaps centrally. It is suggested that nutritional status may, through modulation of tissue sensitivity to GH, be a primary factor in determining growth and the regulation of the somatotrophic axis in the postnatal ruminant.

J. Endocr. (1986) 111, 209–215
Characterization of particle-associated choriomammotrophin and progesterone in ovine placentomes
Authors: Rice G. E. , Thorburn G. D.
Published: December 2008

The subcellular distribution and compartmentalization of choriomammotrophin (CM) and progesterone within ovine placentomes was investigated using differential and density gradient centrifugation techniques. Approximately 67% of placental CM and 45% of progesterone was associated with subcellular particles. The 10 000 g particulate fraction contained the highest specific activity of both CM and progesterone (19·1 ±3·8 (s.e.m.) μg/mg and 71·5 ± 9·2 pmol/mg protein respectively). This fraction was also shown to contain electron-dense granules with morphology similar to that of hormone-containing secretory granules isolated from other endocrine tissues. Particle-associated CM sedimented to a density of 1·051–1·054 g/ml in colloidal silica gradients and displayed physicochemical characteristics consistent with its storage in secretory granules. During in-vitro incubations, particle-associated CM was stable for up to 90 min, but dissociated when incubated in hypoosmotic medium. Particulate progesterone, which was also present in the CM-rich fraction and was stable for up to 90 min of incubation, was not affected by decreasing the osmolality of the incubation medium. These data suggest that ovine CM (but not progesterone) is stored within a population of secretory granules located within placentomes.

J. Endocr. (1986) 111, 217–223
The characteristics of β-adrenergic binding sites on pancreatic islets of Langerhans
Authors: Fyles J. M. , Cawthorne M. A. , Howell S. L.
Published: December 2008

The sympathetic nervous system is believed to play a part in the control of insulin release from the pancreatic islets of Langerhans. Stimulation of α-adrenoceptors is thought to inhibit the release of insulin whereas stimulation of β-adrenoceptors enhances insulin release. The present experiments were conducted to establish the existence of β-adrenergic receptors on guinea-pig and rat islet cells and to quantify them using the selective β-adrenergic ligands [3H]dihydroalprenolol (DHA) and [125I]cyanoiodopindolol (CYP).

Guinea-pig islets had 62 fmol β-adrenoceptors/mg protein using [3H]DHA, corresponding to 43 700 binding sites/cell and 25 fmol β-adrenoceptors/mg protein using [125I]CYP, corresponding to 17 400 sites/cell. Rat islet cells were found to have 4·6 fmol β-adrenoceptors/mg protein using [125I]CYP, corresponding to 7200 sites/cell. Adenylate cyclase activation exhibited a positive dose–response relationship when exposed to the β-adrenoceptor agonist isoprenaline, with a maximum response (190 ± 21% above basal) at 10 μmol isoprenaline/l. This response was abolished with 1 μmol/l of the β-adrenergic antagonist 1-alprenolol. Insulin secretion in the presence of 10 mmol glucose/l, but in the absence of the α-adrenoceptor blocker phentolamine, was not affected by 10 μmol isoprenaline/l. However, perifusion experiments showed that secretion of insulin from isolated rat islets in the presence of 10 mmol glucose/l was significantly increased (332%) by 10 μmol isoprenaline/l in the presence of 10 μmol phentolamine/l.

These results suggest that binding of selective radio-labelled ligands occurs to β-adrenergic receptors on the B cell surface of the islets of Langerhans, and that these receptors are functionally coupled to insulin secretion through modulation of adenylate cyclase activity.

J. Endocr. (1986) 111, 263–270
Serotonin induces gonadotrophin release through stimulation of LH-releasing hormone release from the median eminence
Authors: Vitale M. L. , Parisi M. N. , Chiocchio S. R. , Tramezzani J. H.
Published: December 2008

The effects of serotonin (5-HT) on the release of gonadotrophins and LH-releasing hormone (LHRH) were examined in an in-vitro perifusion system using median eminences and/or anterior pituitaries obtained from male or pro-oestrous female rats. Animals were killed by decapitation between 12.00 and 13.00 h. A serial double-chamber perifusion system was employed. Three types of experiments were performed. In the first, median eminences were placed in the first chamber and one anterior pituitary in the second chamber. In the second group, only the anterior pituitary was perifused. In the third group, only five median eminences were perifused. In the first and second experiments, LH, FSH and prolactin were determined in the perifusion efflux by radioimmunoassay (RIA). In the third experiment, LHRH was determined by RIA.

Addition of 5-HT (final concentrations 0·06, 0·6 and 6·0μmol/l) into the first chamber containing the median eminences stimulated the release of LH and FSH from the pituitary, but did not affect the levels of prolactin in the effluent in the same experiment (prooestrous rats). The stimulatory effect of 5-HT was blocked by the addition of cyproheptadine (1 μmol/l) in the perifusion fluid. The introduction of 5-HT (0·6 μmol/l) into the tube connecting the first and second chambers did not modify the release of LH, nor did 5-HT added to the pituitaries perifused alone.

Injection of 5-HT into the first chamber (median eminences), containing tissue samples from male rats, stimulated LH release, but to a significantly (P< 0·001) lower degree than that found when samples from pro-oestrous females were used (P< 0·0001).

When median eminences from pro-oestrous rats were perifused alone, injection of 5-HT produced an immediate release of LHRH which peaked during the first 10 min of collection and lasted for 30 min; in these experiments, a clear relationship existed between dose of 5-HT and release of LHRH (P<0·02). The stimulatory effect of 5-HT was blocked by the addition of cyproheptadine (5 μmol/l) or methiothepin (5 μmol/l).

These results demonstrate that 5-HT stimulates gonadotrophin release by acting directly on LHRH terminals in the median eminence from pro-oestrous rats. Furthermore, the effect of 5-HT on LHRH release was dose dependent and was nullified by 5-HT receptor blockers (cyproheptadine and methiothepin).

J. Endocr. (1986) 111, 309–315
Biochemical characterization of circulating Met-enkephalins in canine endotoxin shock
Authors: Watson J. D. , Varley J. G. , Tomlin S. J. , Medbak S. , Rees L. H. , Hinds C. J.
Published: December 2008

The alterations in arterial, venous and adrenal vein levels of immunoreactive Met-enkephalins following endotoxin administration have been investigated in dogs by direct measurement and gel filtration chromatography. Animals were anaesthetized with α-chloralose and allowed to breath spontaneously. The left lumbar adrenal vein, limb vein and femoral artery were cannulated for blood sampling. Severe shock was produced by the administration of a large bolus of E. coli endotoxin followed by a continuous infusion. The production of endotoxin shock was associated with significant increases in adrenal vein and systemic venous plasma immunoreactive Met-enkephalin levels. Forty-five minutes after induction of endotoxin shock arterial immunoreactive Met-enkephalin levels were generally higher than baseline values. In resting anaesthetized animals a large 31 000 molecular weight form of Met-enkephalin, presumably proenkephalin, was found in plasma obtained from the adrenal vein, systemic and pulmonary circulations. Following endotoxin this enkephalin-containing peptide still predominated in arterial and venous plasma, whereas in the adrenal vein the proportion of Met-enkephalin immunoreactivity attributable to this large peptide fell. This was associated with the appearance of increasing amounts of smaller molecular forms (18 000, 8000, 3–5000 molecular weight and the pentapeptide itself). In this model enkephalin-containing peptides were not biochemically modified by their passage through the lungs.

J. Endocr. (1986) 111, 329–334
The distribution of immunoreactive α-melanocyte-stimulating hormone cells in the adult human pituitary gland
Authors: Coates P. J. , Doniach I. , Hale A. C. , Rees L. H.
Published: December 2008

It has been suggested that a proportion of the adenomas and the nodular hyperplasia of cells in the pituitary gland in cases of Cushing's disease are derived from cells of the pars intermedia rather than the pars anterior. The evidence can be summarized as follows: (1) the posterior site of adenoma or nodular hyperplasia in the pituitary, (2) the innervation of cells and (3) the suppressive response to the dopamine agonist bromocriptine in vivo or to dopamine in vitro. All these observations infer analogy with cells of the pars intermedia of other species, which are controlled by direct neural tonic dopaminergic inhibition. The adult human pituitary gland, however, does not possess a morphologically distinct pars intermedia, due to regression of the rudimentary fetal pars intermedia after birth, with mixing of cells into the pars anterior and pars nervosa. Since cells of the pars intermedia characteristically synthesize α-MSH, we have studied this peptide in order to assess the occurrence and distribution of intermedia-derived cells in the adult human pituitary.

Sections from 100 pituitaries, removed at autopsy, were stained by an indirect immunoperoxidase technique using non-cross-reacting antisera specific for α-MSH and ACTH. Immunoreactive α-MSH (IR-α-MSH) cells were found in a total of 97 specimens. Of these, only ten cases showed a marked concentration of IR-α-MSH cells in the zona intermedia. In the majority of pituitaries, IR-α-MSH cells were more commonly seen in the pars anterior than in the zona intermedia; in 41 cases, IR-α-MSH cells were completely absent from the zona intermedia. The number of IR-α-MSH cells varied greatly, from less than ten cells per section to many hundreds, regardless of the age or sex of the individual. Additionally, no correlation could be made between the number of IR-α-MSH cells and the cause of death, treatment or the period of time between death and removal of the pituitary.

We conclude that cells containing IR-α-MSH are present in varying numbers in the normal adult human pituitary gland. These cells do not show a specific distribution pattern, but may be found in both the zona intermedia and are spread throughout the pars anterior.

J. Endocr. (1986) 111, 335–342
Release of aldosterone and corticosterone from the adrenal cortex of the Brattleboro rat in response to administration of ACTH
Authors: Brudieux R. , Krifi M. N. , Laulin J. P.
Published: December 2008

The time-course and dose–response of the in-vivo secretion of aldosterone and corticosterone after administration of ACTH(1–24) were measured in adrenal venous blood from female Brattleboro rats, homozygous for hypothalamic diabetes insipidus and lacking arginine vasopressin (AVP). Female Long–Evans rats were used as controls. All animals were pretreated with dexamethasone and anaesthetized with pentobarbital. Basal secretions of aldosterone and corticosterone were four- to sixfold lower in Brattleboro than in Long–Evans rats. Administration of ACTH consistently increased the secretion of aldosterone and corticosterone similarly in the two groups of rats; maximum values were observed 20–30 min after ACTH injection. However, for all the doses of ACTH (0·05, 0·5 and 5·0 mi.u./100 g body wt) and at every stage of response the secretion rates of aldosterone and corticosterone were twofold lower in Brattleboro than in Long–Evans rats. Furthermore the absolute increase in steroid secretion induced by ACTH was reduced by half in Brattleboro rats. These results show that the impairment of adrenal activity is largely due to a reduced capacity for corticosteroidogenesis in the adrenal cortex of Brattleboro rats. The mechanisms of action of AVP are discussed.

J. Endocr. (1986) 111, 375–381
Transient increase in prolactin secretion following hypothalamo-pituitary disconnection in ewes during anoestrus and the breeding season
Authors: Thomas G. B. , Cummins J. T. , Cavanagh L. , Clarke I. J.
Published: December 2008

Hypothalamic control of prolactin secretion was studied in ovariectomized ewes by comparing the effects of hypothalamo-pituitary disconnection (HPD) and sham-operation (sham-HPD). HPD caused a two-fold increase in plasma prolactin concentrations on days 1 and 7 following surgery during anoestrus and a tenfold increase during the breeding season. Thereafter, concentrations gradually declined to be similar to those in sham-HPD ewes by day 43 (breeding season) and day 145 (anoestrus). The maximum plasma prolactin response to HPD was similar during the two seasons (anoestrus: 128 ± 15 vs breeding season: 118 ± 13 μg/l). Sham-HPD had no effect on plasma prolactin concentrations. Prolactin pulse frequency was not affected by HPD, but increases in plasma prolactin concentrations were associated with increases in pulse amplitude. At the time of the normal anoestrus, plasma prolactin concentrations rose in both the HPD and sham-HPD ewes, raising the question of extra-hypothalamic regulation of seasonal changes in prolactin secretion. Plasma LH and FSH concentrations became undetectable in HPD ewes but were unaltered in sham-HPD ewes. We conclude that hypothalamic inhibition of pituitary prolactin secretion in the sheep can be demonstrated by HPD but that this effect is not sustained. This transience may indicate the additional requirement of hypothalamic-releasing factors in the control of prolactin release. In addition, the surgically isolated ovine pituitary of the HPD animal has an inherent pulsatile secretion of prolactin.

J. Endocr. (1986) 111, 425–431
The streaming adrenal cortex: direct evidence of centripetal migration of adrenocytes by estimation of cell turnover rate
Authors: Zajicek G. , Ariel I. , Arber N.
Published: December 2008

Thirty adult male rats were injected with 0·5 μCi [3H]thymidine/g body weight (specific activity 5 Ci/ mmol) and killed, in groups of five, 1 h and 14, 30, 60, 90 and 120 days after injection. The displacement of labelled adrenocytes with time was estimated in autoradiograms of adrenal sections. The radial distance of the labelled cell from the capsule was measured with an eyepiece micrometer and expressed in cell location units, i.e. the number of cells separating the labelled cell from the capsule. One hour after labelling, 95% of labelled cells were confined to the outer quarter of the cortex. During the following days, adrenocytes were displaced inwardly, approaching the medulla at a velocity of 0·24 locations/day. They traversed the three cortex zones, reaching the medulla after 104 days. The three adrenal zones represent three differentiation states of the adrenocyte. When young, the adrenocyte secretes aldosterone, after leaving the glomerulosa it produces corticosteroids and on reaching the reticularis it produces sex hormones. The adrenal cortex is a cell renewal system made of two compartments. A progenitor compartment extending between locations 1 and 15, and a functional compartment, covering locations 16–64. The first compartment produces 0·47 cells daily, which enter the second. Half of them die on their way while the rest are eliminated in the reticular zone. The cell stream is nourished by a subcapsular stem cell.

J. Endocr. (1986) 111, 477–482
Differences in prolactin and LH responses to acute stress between peripuberal and adult male rats
Authors: Armario A. , Restrepo C. , Hidalgo J. , Lopez-Calderón A.
Published: December 2008

Pituitary-adrenal, pituitary-gonadal and prolactin responses to acute stress (restraint) were studied in peripuberal and adult male rats. The pituitary-adrenal response to restraint stress did not differ in peripuberal and adult rats. Prolactin increase during stress was less marked in peripuberal animals. While an increase in LH during stress was observed in adult rats, peripuberal animals did not respond to stress. Testosterone levels were also lower in peripuberal than in adult rats. Diminished LH and prolactin responses to stress in peripuberal rats did not appear to be due either to increased pituitary-adrenal activity or to altered pituitary responsiveness to LHRH and dopamine respectively. Peripuberal rats were also more sensitive to the action of morphine on LH and prolactin release than were adult rats, suggesting that endogenous opioids may be involved in the LH and prolactin responses to acute stress. Differences in the maturation of central mechanisms rather than in pituitary response appear to be responsible for the differing responses to acute stress.

J. Endocr. (1987) 112, 9–13
Enhanced corticosterone-binding capacity in plasma after stimulation of the rat adrenal cortex: the possibility of a simultaneous release of protein and corticosterone
Authors: Bassett J. R.
Published: December 2008

Exposure of rats to either footshock or handling stress produced a significant increase in both plasma corticosterone concentration and specific binding capacity. Non-specific binding was eliminated using the synthetic glucocorticoid, dexamethasone. The increase in both plasma corticosterone and specific binding capacity was biphasic following exposure to footshock. Adrenalectomy and pretreatment with betamethasone abolished both phases of the enhanced binding capacity and plasma steroid concentration. Intraperitoneal injection of ACTH (1–24) in animals pretreated with betamethasone resulted in a biphasic rise in plasma concentrations of corticosterone but only the initial increase in binding capacity. Dissociation constant (Kd) values, determined by Scatchard analysis, for adrenalectomized and betamethasone-pretreated animals were 546 and 556 pmol/l respectively. These values were significantly different from the Kd in animals with functional adrenals (631 pmol/l). The results are discussed in the light of a possible specific corticosteroid-binding globulin (CBG)-like binding protein of adrenal origin released in conjunction with corticosterone. This binding protein has a lower affinity for corticosterone and a shorter half-life than CBG.

J. Endocr. (1987) 112, 33–41
Atrial natriuretic factor inhibits the stimulated in-vivo and in-vitro release of vasopressin and oxytocin in the rat
Authors: Poole C. J. M. , Carter D. A. , Vallejo M. , Lightman S. L.
Published: December 2008

The effect of an atrial natriuretic peptide on the secretion of the neurohypophysial peptides arginine vasopressin (AVP) and oxytocin has been studied in vivo and in vitro. Atriopeptin III was administered intracerebroventricularly to conscious rats and plasma concentrations of AVP and oxytocin were determined both in controls and in rats which had their drinking water replaced by 2% NaCl. The release of both AVP and oxytocin was inhibited when basal levels were increased by the saline treatment. The inhibition of AVP release lasted for 40 min whereas oxytocin release was inhibited for 10 min only. In a further experiment the stimulated release of AVP and oxytocin from the isolated neurointermediate lobe of the rat was also inhibited by atriopeptin III.

J. Endocr. (1987) 112, 97–102
Inhibition of testosterone metabolism in the brain and cloacal gland of the quail by specific inhibitors and antihormones
Authors: Alexandre C. , Balthazart J.
Published: December 2008

The effects of antioestrogens, antiandrogens and of various inhibitors of testosterone metabolism on testosterone metabolism in the quail hypothalamus and cloacal gland were studied by an in-vitro radio-enzymatic assay. It was found that antioestrogens and antiandrogens generally had little or no effect on aromatase and 5α- and 5β-reductases of testosterone, except when used at very high doses. The 5α-reductase inhibitor, 17β-N,N-diethylcarbamoyl-4-methyl-4-aza-5α-androstan-3-one, inhibited both 5α- and 5β-dihydrotestosterone production without markedly affecting aromatase activity. Surprisingly, the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione, inhibited not only the production of oestradiol but also that of 5β-dihydrotestosterone and, to a lesser extent, 5α-dihydrotestosterone. These unexpected properties should be taken into account when interpreting the results of in-vivo experiments using these compounds.

J. Endocr. (1987) 112, 189–195
Sodium transport and the cellular sodium transport pool of colonic epithelium: effects of sodium loading, aldosterone and lithium
Authors: Edmonds C. J. , Mackenzie J.
Published: December 2008

The cellular sodium transport pool and sodium transepithelial fluxes were investigated in vivo in rat distal colon in relation to sodium loading by intravenous infusion (3·5 h), and to short (4 h) and prolonged (72 h) i.v. administration of aldosterone. Considerable natriuresis and increase in body sodium content were produced by the sodium load but there was no significant effect on the transcellular sodium flux (active absorption from lumen to plasma) or on the sodium transport pool. Both short and prolonged aldosteronism produced similar increases in the transport pool and in the transcellular sodium flux, but the transepithelial electrical potential difference (p.d.) was significantly greater in rats given the prolonged infusion. Addition of amiloride to the solution in the lumen of the colon almost completely abolished the p.d., the transport pool and the transcellular sodium flux of the rats receiving prolonged infusion, but had much less effect in those given the short infusion. The time-course of recovery of p.d. following prolonged aldosteronism was similar to that described for the turnover rate of rat colonic epithelial cells.

Lithium within the lumen had no significant effect in untreated rats but after prolonged aldosterone infusion lithium reduced the p.d. and the transcellular sodium flux although the transport pool was not reduced. These findings are consistent with the hypothesis that aldosteronism renders the apical membranes of the epithelial cells permeable to lithium and that intracellular accumulation of lithium depresses active sodium transfer.

The observations are interpreted in terms of an epithelial model in which aldosterone induces amiloride-sensitive pathways (diffusion channels permeable to sodium and lithium) in the apical membrane which totally replace the amiloride-insensitive pathways when aldosteronism is prolonged; the resulting expansion of the sodium transport pool is the stimulus for increased active sodium transport across the basolateral membranes.

J. Endocr. (1987) 112, 247–252
Adrenal synthesis of corticosterone in response to ACTH in rats is influenced by leukotriene A4 and by lipoxygenase intermediates
Authors: Jones D. B. , Marante D. , Williams B. C. , Edwards C. R. W.
Published: December 2008

The possible involvement of the lipoxygenase pathway of arachidonic acid metabolism in the events which take place during ACTH-induced stimulation of corticosterone secretion has been studied using an isolated rat adrenal cell system. Incubation with arachidonic acid resulted in an inhibition of ACTH-stimulated corticosterone production. The lipoxygenase pathway inhibitors nordihydroguaretic acid (NDGA), eicosatetraynoic acid (ETYA) and compound BW755C also produced inhibition of ACTH-stimulated corticosterone synthesis. The concentrations of the inhibitors at which 50% inhibition occurred were 15, 34 and 37 μmol/l respectively. The inhibitions produced by NDGA and ETYA were independent of cyclic AMP output. NDGA also inhibited corticosterone production induced by dibutyryl cyclic AMP but had no effect on corticosterone synthesis induced by pregnenolone.

Preincubation of adrenal cells with the lipoxygenase products 5, 12 and 15 hydroxyeicosatetraenoic acid (HETE) and with leukotrienes A4, B4, C4, D4 and E4 resulted in significant inhibitions of corticosterone production in response to ACTH with leukotriene A4 (LTA4) and with 15HETE and 5HETE. Conversely, incubation with glutathione (GSH), which is known to reduce intracellular LTA4 levels, produced stimulation (at 5 mmol GSH/1) and inhibition (at 50 mmol GSH/1) of corticosterone output. These studies suggest that the lipoxygenase pathway may be involved in ACTH-stimulated corticosterone synthesis.

J. Endocr. (1987) 112, 253–258
Role of protein kinase C in the pigment cell of the lizard (Anolis carolinensis)
Authors: Lucas A. M. , Thody A. J. , Shuster S.
Published: December 2008

The role of protein kinase C in melanosome dispersion was examined using the melanophores of the lizard Anolis carolinensis and an in-vitro rate method of bioassay. The phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA), which directly activates protein kinase C, was able to potentiate the melanophore response to α-MSH in a dose-dependent manner. Similarly, the stimulatory response to forskolin, which activates the adenylate cyclase catalytic subunit, was also potentiated by TPA. The response of the melanophore to cyclic AMP, however, remained unaltered by any dose of TPA. We thus propose that the potentiation of α-MSH potency by TPA is through an interaction of protein kinase C with adenylate cyclase and, more specifically, that this interaction may be at the level of the linkage of the nucleotide regulatory subunit Ns with the catalytic moiety C of adenylate cyclase.

J. Endocr. (1987) 112, 283–287
Extraction and characterization of a cytochemically assayable Na+/K+-ATPase inhibitor/glucose-6-phosphate dehydrogenase stimulator in the hypothalamus and plasma of man and the rat
Authors: Millett J. A. , Holland S. M. , Alaghband-Zadeh J. , de Wardener H. E.
Published: December 2008

Some physicochemical properties of partially purified hypothalamic material from the spontaneously hypertensive rat, and of plasma from man and the rat, have been characterized using a validated cytochemical bioassay which measures the ability of biological fluids to stimulate fresh guinea-pig kidney glucose-6-phosphate dehydrogenase (G6PD) after 2 min of exposure to the test substance, as an indication of their ability to inhibit Na+/K+ adenosine triphosphatase (Na+/K+-ATPase) after 4–6 min of exposure.

The G6PD-stimulating activity of both hypothalamic extract and plasma is soluble in water and insoluble in chloroform. During electrophoresis the activity from both sites appears in the same fractions and travels considerably further than lysine. After high-pressure liquid chromatography the activity of hypothalamic extract appears in a discreet fraction which does not absorb u.v. light. The activity of both the hypothalamic extract and plasma survives boiling and acid hydrolysis, but is substantially inhibited by prior incubation with digoxin antibody. From ultrafiltration studies, the substance responsible for the ability to stimulate G6PD appears to have a molecular weight of less than 500. The G6PD-stimulating activity of hypothalamic extracts was destroyed by ashing and by base hydrolysis. The ability of plasma of high activity to stimulate G6PD is considerably increased by incubating at 37 °C for 15 min and destroyed by incubation for 45 min.

It is concluded that these and several other previously noted similarities suggest that the cytochemically assayable Na+/K+-ATPase-inhibiting/G6PD-stimulating activity in the plasma and hypothalamus may be due to the same ouabain-like substance.

J. Endocr. (1987) 112, 299–303
Indomethacin treatment prevents prolactin-induced luteolysis in the rat
Authors: Sánchez-Criado J. E. , Ochiai K. , Rothchild I.
Published: December 2008

Adult female rats were hypophysectomized and their pituitary glands autotransplanted beneath the left kidney capsule on day 2 (day 1 was the day of ovulation). In such rats the pituitary secretes prolactin fairly constantly and the corpora lutea secrete progesterone for several months. To induce the luteolytic effect of prolactin the rats were first injected s.c. with 2-bromo-α-ergocryptine (CB-154) on cycle days 12, 13 and 14 (i.e. 10, 11 and 12 days after operation) to depress prolactin secretion, and then with CB-154 vehicle (70% ethanol) daily until cycle day 21, to allow prolactin secretion to resume. One ovary was removed from each rat on day 15 and the remaining one on day 22. The mean (± s.e.m.) weight of the corpora lutea on day 15 was 1·46±0·06 mg and 0·98±0·07 mg on day 22 (n = 17). In contrast, rats in which the CB-154 treatment was maintained to day 21 had corpora lutea which weighed 1·31 ±0·09 on day 15 and 1·47 ±0·08 mg on day 22 (n = 15). To investigate whether indomethacin, a prostaglandin synthesis inhibitor, affected the luteolytic action of prolactin, the experiment was repeated, but on day 15 (after the removal of one ovary) the groups in which CB-154 treatment was stopped, as well as the group in which CB-154 treatment was maintained, were each divided into two groups. In one, indomethacin-containing silicone elastomer wafers and, in the other, blank silicone elastomer wafers, were placed within the bursa of the remaining ovary. There were no differences in corpus luteum weight on day 15 among any of these groups and the two groups of the first experiment.

There was no significant difference in corpus luteum weight between day 15 and day 22 in any of the six groups except for the two groups treated with the CB-154 vehicle and not with indomethacin. Thus, treatment with indomethacin prevented the fall in corpus luteum weight associated with the discontinuation of CB-154 treatment.

Serum prolactin levels fell until day 15 in all rats and remained low in those in which the CB-154 treatment was maintained to day 21, but returned to control values in those treated with vehicle after day 14. Serum progesterone levels fell and remained low in all groups. Indomethacin treatment had no effect on the levels of either serum prolactin or progesterone. We conclude that some of the pharmacological effects of indomethacin are to prevent prolactin-induced luteolysis, and we suggest that prolactin induces rapid regression of the corpus luteum by stimulating intraluteal prostaglandin production or by being necessary for the effect of luteolytic prostaglandins.

J. Endocr. (1987) 112, 317–322
A quantitative study of steroid bioconversions in the testis of the African catfish, Clarias gariepinus (Burchell), under natural spawning and natural and cultivated non-spawning conditions
Authors: Schoonen W. G. E. J. , Lambert J. G. D. , Resink J. W. , Viveen W. J. A. R. , Van Oordt P. G. W. J.
Published: December 2008

Quantitative aspects of bioconversions in the testes of the African catfish (Clarias gariepinus) were studied in vitro by incubation of tissue with [3H]pregnenolone or [3H]androstenedione. During the breeding period, spawning and non-spawning animals were collected from their natural habitat, the Hula nature reserve, in northern Israel. In the same period, non-spawning animals were collected from a fish pond in the same region. It was shown that spawning was accompanied by significant changes in steroid bioconversions, i.e. a reduction in androgen synthesis, especially of 11β-hydroxyandrostenedione and 11β-hydroxytestosterone and an increase in the production of C21-steroids, especially progesterone, 17α-hydroxyprogesterone and a pregnenolone ester. These changes resulted from a decreased contribution of the cytochrome P-450 enzymes 17α-hydroxylase, C17–20-lyase and 11β-hydroxylase. A rise in plasma gonadotrophin concentration was observed only in spawning catfish. In the absence of such an increase in plasma gonadotrophin, steroid synthesis in the testes of non-spawning feral and pond catfish was primarily directed towards the production of 11-oxygenated androgens and 5β-pregnane-3α,17α,20α-triol. It is suggested that spawning is induced by gonadotrophin and the ensuing change in steroidogenesis. It is possible that husbandry conditions inhibit the necessary increase in gonadotrophin release.

J. Endocr. (1987) 112, 323–332
Comparison of the cellular composition and steroidogenic properties of preparations of interstitial cells isolated from immature and mature rat testis
Authors: Themmen A. P. N. , Molenaar R. , Visser W. J. , Jongkind J. F. , Rommerts F. F. G. , van der Molen H. J.
Published: December 2008

The morphological and steroidogenic properties of preparations of interstitial cells isolated by collagenase treatment from testes of immature and mature rats have been compared.

After additional purification on a Ficoll gradient, 80% of cells from mature rat testes were found to be Leydig cells; 20% were macrophages. Forty to sixty per cent of collagenase-dispersed cells isolated from immature rats were Leydig cells, 37% were mesenchymal cells and there were no macrophages. A preparation in which 90% cells were Leydig cells could be obtained from immature testes after further purification by centrifugation through a Percoll gradient. The distribution of steroidogenic enzymes through the gradient corresponded to the distribution of LH-dependent steroid production. The results indicate that the steroidogenic activity per Leydig cell from mature rats is fourfold greater than the activity in immature rat Leydig cells in control incubations or after stimulation with LH, dibutyryl cyclic AMP or in the presence of 22R-hydroxycholesterol.

J. Endocr. (1987) 112, 361–366
Mammary resistance: a possible controlling factor in milk ejection
Authors: Lau C. , Henning S. J.
Published: December 2008

At 8 and 13 days post partum, rats have the same total milk availability; yet, in response to suckling they release a greater amount of milk on day 13 than on day 8. Increased sensitivity to suckling in the more advanced lactators may result from a greater release of oxytocin or from changes in the mammary glands as lactation advances. The present study explores this latter possibility in anaesthetized dams at 8–9 and 13–15 days of lactation. Milk release and intramammary pressure were measured in anaesthetized dams in response to various doses of oxytoxin. Milk release was determined from the body weight gain of pups which had been fasted for 5 h before suckling on dams which had been isolated for 5 h. This parameter was significantly greater in 13- to 15-day lactators than in 8- to 9-day lactators over the range of oxytocin doses examined. In contrast, intramammary peak pressure and its dissipation time were significantly larger in the 8- to 9-day lactators than in the 13- to 15-day lactators. The compliance of the mammary glands was indirectly assessed at the two stages of lactation. When a constant pressure pulse was introduced into a cannulated gland, the resulting pressure peak was significantly greater in 8-day than in 13-day lactators, indicating a greater resistance in the former. Taken together, these results indicate that when endogenous oxytocin is inhibited (by anaesthesia) the greater milk release observed at the later stage of lactation in response to various doses of oxytocin may be due to a decline in mammary resistance as lactation progresses.

J. Endocr. (1987) 112, 379–385
Inhibition of first ovulation: administration of an LHRH antagonist to immature female rats
Authors: Meijs-Roelofs H. M. A. , Kramer P. , van Cappellen W. A. , Schuiling G. A.
Published: December 2008

Subcutaneous injections of an LHRH antagonist (ALHRH; Org.30093) were administered to immature female rats. Neither a single high dose (50 μg) nor repeated daily doses of 5–30 μg ALHRH/day, administered between 28 and 38 days of age, influenced the age and body weight at the time of vaginal opening or first ovulation. If repeated daily doses of 2 × 10 μg ALHRH were given from 32 to 42 or from 37 to 47 days of age, first ovulation was delayed by 3·0 and 6·3 days respectively. Administration of 10 μg ALHRH at 09.00 h and again at 17.00 h on the day of first pro-oestrus was found to be sufficient to block the expected first ovulation in 36 out of 38 rats. This effect could be repeated by administering the same doses of ALHRH at pro-oestrus and again on the next day: ovulation was blocked in eight out of eight rats. A single dose of 10 μg ALHRH, administered on the morning of pro-oestrus, blocked ovulation in five out of twelve rats. Both the preovulatory LH and FSH surge, as measured at 16.00 h on pro-oestrus, were found to be inhibited by ALHRH treatment.

On the day after pro-oestrus no recruitment of new small antral follicles had occurred in rats with ovulatory blockade. Delayed ovulation took place 2–5 days after ALHRH injection at pro-oestrus; until 3 days after injection rats were able to ovulate their original preovulatory follicles, thereafter newly developed follicles ovulated and large ovarian cysts were found in the ovaries, next to fresh corpora lutea.

Chronic administration of two injections daily of 10 μg ALHRH from 34 days of age until the morning of first pro-oestrus had marginal effects on the timing of first pro-oestrus and on follicle dynamics.

It was concluded that with the ALHRH compound used, and in chronic as well as in acute experiments, first ovulation could only be delayed by its administration on the day of first pro-oestrus and that the effect was due to acute inhibition of the preovulatory gonadotrophin surge.

J. Endocr. (1987) 112, 407–415
Antidiuretic antagonism and agonism of 1-deamino-pentamethylene-2-d-phenylalanine-4-isoleucine-arginine vasopressin in rats with diabetes insipidus
Authors: Vilhardt H. , Lundin S.
Published: December 2008

Using implanted minipumps it was shown over a period of 7 days that the vasopressin antagonist, 1-deamino-pentamethylene-2-d-Phe-4-Ile-arginine vasopressin, caused increased diuresis in normal rats and reversed vasopressin- or oxytocin-induced antidiuresis in Brattleboro rats. When the antagonist was infused alone in Brattleboro rats it induced a marked antidiuretic response, indicating that the analogue also possessed agonistic properties. The agonist action could not be demonstrated in anaesthetized, hydrated normal rats. In these animals the analogue behaved as a pure antagonist. It is concluded that analogues which behave as antagonists in one test model may display agonistic properties under different experimental conditions.

J. Endocr. (1987) 112, 439–442
Influence of administration of ovarian steroids on the function of neutrophils isolated from the blood and uterus of ovariectomized mares
Authors: Watson E. D. , Stokes C. R. , Bourne F. J.
Published: December 2008

The function of blood and uterine luminal neutrophils from ovariectomized mares treated with ovarian steroids was investigated 18 h after intrauterine infusion of 1 × 109 Streptococcus zooepidemicus. Random migration of blood neutrophils under agarose was reduced by treatment with progesterone compared with that of neutrophils from oestradiol-treated and control mares. In-vitro addition of progesterone to blood neutrophils from acyclic ponies also reduced migration. Uterine neutrophils did not migrate under agarose which was probably an effect of bacterial phagocytosis. Hormone treatment had little effect on phagocytosis of yeast blastospores by blood neutrophils. Phagocytosis by uterine neutrophils from oestradiol-treated and control mares was significantly better than that by blood neutrophils. In progesterone-treated mares, however, phagocytosis by uterine neutrophils was significantly lower than that in the other two treatment groups and was similar to that measured in blood neutrophils.

The results indicate a marked effect of progesterone in reducing both migration of blood neutrophils and phagocytosis by uterine neutrophils.

J. Endocr. (1987) 112, 443–448
Effects of the uterus and the ovaries on growth, somatotrophin and somatomedin A in developing rats
Authors: Biro J. C. , Eneroth P.
Published: December 2008

The effects of hysterectomy and ovariectomy on plasma concentrations of GH, somatomedin A, TSH and thyroxine (T4) were studied in developing rats. Four groups of 24-day-old rats were ovariectomized, ovohysterectomized, hysterectomized or sham-operated. Their weights, lengths and plasma hormone concentrations were measured at 26, 43, 64, 78 and 92 days of age to investigate pre- and postpubertal differences caused by the uterus or ovaries. Plasma concentrations of the hormones examined showed a successive rise with time, but GH and somatomedin A concentrations rose mainly after the opening of the vagina (days 50–55). Higher GH and somatomedin A concentrations were found in the plasma of ovariectomized animals than in ovohysterectomized controls before puberty (GH: 260–300%, P<0·01; somatomedin A: 25–30%, P<0·05). Ovariectomized animals weighed more than ovohysterectomized females after puberty (4·5–6%, P<0·01). This indicated that the uterus exerted a stimulatory effect on GH-somatomedin A regulation and body weight gain in the absence of the ovaries.

Significantly lower plasma somatomedin A (but not GH) concentrations were found in hysterectomized and sham-operated animals than in their respective controls after puberty (30–39%, P<0·01) and their final body weight was lower (22–26%, P<0·001). There were no consecutive uterus- or ovary-related changes in plasma TSH and T4 levels.

It was concluded that both the uterus and ovaries had significant as well as opposite effects on somatomedin A and body weight with the effects of the ovaries being greater than those of the uterus.

J. Endocr. (1987) 113, 21–26
High-affinity receptor for insulin-like growth factor II in rat liver: properties and regulation in vivo
Authors: Bryson J. M. , Baxter R. C.
Published: December 2008

Receptors for insulin-like growth factor II (IGF-II) have been identified in many tissue types and have been shown to differ widely in their specificities and affinities. We have characterized the IGF-II receptor in rat liver microsomal membranes, both in the intact membrane and in a solubilized extract. Binding was time- and temperature-dependent and was unaffected by changes in pH in the range 6–9. Half-maximal displacement was obtained with 0·33 ng IGF-II/ml standard, and Scatchard analysis showed a class of receptors with an affinity for IGF-II of 1·33 ± 0·36 × 1010 litres/mol which increased threefold in the presence of Ca (1 mmol/l) to 3·74 ± 0·89 × 1010 litres/mol. There was also a threefold decrease in the rate of dissociation in the presence of Ca. Cross-reactivity with IGF-I was < 1% and there was no cross-reactivity with insulin.

Infusion of rat GH or prolactin for 1 week, at the rate of 175–200 μg/day, into female rats had no effect on IGF-II binding in control animals, but rat GH infusion caused a 60% increase (P< 0·001) in binding in hypophysectomized rats by increasing the number of receptors.

These studies demonstrate that rat liver microsomal membranes contain a highly specific, high-affinity receptor for IGF-II which may be under partial GH control

J. Endocr. (1987) 113, 27–35
Recovery of the components of the hypothalamo-pituitary-adrenocortical axis in the rat after chronic treatment with prednisolone
Authors: Nicholson S. A. , Campbell E. A. , Gillham B. , Jones M. T.
Published: December 2008

Male Wistar-derived rats (200–250 g) were treated for 14 days with prednisolone 21-sodium succinate at a concentration of 1035 μmol/l in their drinking water. The drug was then replaced with normal tap water and groups of animals were killed at various times during recovery, trunk blood being collected after decapitation. At the same time, hypothalamic slices, anterior pituitary gland fragments and adrenals were removed and their responsiveness assessed by exposure to appropriate stimuli in vitro. Tissues were also extracted to measure changes in content of hormones during recovery. Treatment with prednisolone produced marked reductions in body weight gain, adrenal weight and pituitary ACTH content, but no significant change in hypothalamic corticotrophin-releasing factor (CRF) bio- or immunoreactivity. The ACTH content was restored by 5 days after withdrawal but adrenal weight remained significantly reduced after 9 days of recovery. The responsiveness of the hypothalamus to acetylcholine in vitro was markedly inhibited and was still significantly reduced 7 days after withdrawal. The responsiveness of the anterior pituitary gland to synthetic CRF or arginine vasopressin and that of the adrenal gland to ACTH added in vitro were restored simultaneously after 7 days of withdrawal. In vivo, recovery was assessed by measurement of the response to laparotomy stress. Treatment with prednisolone prevented the increase in the plasma concentrations of ACTH and corticosterone produced by stress, and these responses recovered by 5 days (corticosterone) and 7 days (ACTH) after withdrawal. The abolition of the circadian rhythms of ACTH and corticosterone by treatment was also reversed by 5 days after withdrawal. This pattern of recovery is different from that which we observed after long-term treatment with dexamethasone, where the responsiveness of the hypothalamus and adrenal gland in vitro recovered before that of the anterior pituitary gland.

J. Endocr. (1987) 113, 239–247