Evidence for calcium inactivation during hormone release in the rat neurohypophysis

1976 ◽  
Vol 65 (3) ◽  
pp. 669-683
Author(s):  
J. J. Nordmann
Keyword(s):  
Hormone Secretion ◽  
Calcium Ionophore ◽  
High Rate ◽  
Hormone Release ◽  
45Ca Uptake ◽  
High K ◽  
K Concentration ◽  
The Relationship ◽  
Internal Calcium

1. A study has been made of the relationship between 45Ca uptake into and hormone release from isolated rat neurohypophyses incubated in vitro. 2. Hormone secretion is triggered by high-K (56 mM) but long exposure to the stimulus does not generate a maintained release of hormone. 3. When hormone release began to wane, addition of Ba of La increased hormone output which suggests that the decline in output did not result from depletion of the neurosecretory granules at the nerve terminals. 4. 45Ca uptake is enhanced in the presence of high-K concentration, but the initial high rate declines during long exposure to the potassium stimulus with a time constant similar to that of the decline in hormone release. 5. After a period of incubation in a K-rich, calcium-free medium, addition of calcium to the medium induced hormone release. The magnitude of this release was dependent on the time of exposure to excess potassium. 6. After inactivation of secretion, mobilization of internal calcium by means of a calcium ionophore increased hormone release.

In vitro induction of the acrosome reaction in ovine spermatozoa by calcium ionophore A23187

2003 ◽  
Vol 51 (1) ◽  
pp. 103-109 ◽  
Author(s):  
Ö. Uçar ◽  
T. J. Parkinson
Keyword(s):  
Phase Contrast ◽  
Acrosome Reaction ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Contrast Microscopy ◽  
The Relationship ◽  
In Vitro Induction ◽  
Artificial Vagina

The relationship between concentration of calcium ionophore A23187 and incubation time upon the proportion of spermatozoa undergoing acrosome reaction (AR) in vitro was investigated in rams from a commercial artificial insemination (AI) program. Two ejaculates were collected by artificial vagina from each of nine rams of three breeds (Finn Dorset, Charolais and Suffolk) aged 8-36months. Each ejaculate was diluted in a skimmed milk extender. Spermatozoa were thereafter incubated for 45 or 60min in modified Tyrode's medium (TALP) which contained either zero, 0.1 or 1.0µM/l A23187. After fixing in 10% formaldehyde, the number of spermatozoa that had undergone AR was determined by phase contrast microscopy. In pre-incubation samples, 21.3± 3.3% of spermatozoa had undergone AR. Percentages of acrosome reacted spermatozoa were significantly (P<0.001) increased after incubation with A23187. After incubation with 0.1µM/l A23187 for 45 and 60min there were 22.4±3.0% and 31.7±4.3% acrosome reacted spermatozoa, respectively. After incubation with 1.0µM/l A23187 for 45 and 60min there were 46.2±6.5% and 53.8±5.9% acrosome reacted spermatozoa, whilst corresponding numbers in control samples were 17.0±2.7% and 22.3±4.2%. There was also a significant (P<0.001) effect of individual animals upon the responses to different concentrations of A23187. These findings indicate that (i) A23187 can be used to assess the AR of ovine spermatozoa in vitro and (ii) there are effects of individual animals upon the proportion of spermatozoa undergoing AR.

scholarly journals The regulation of growth hormone secretion from the isolated rat anterior pituitary in vitro. The role of adenosine 3′:5′-cyclic monophosphate

1971 ◽  
Vol 124 (4) ◽  
pp. 815-826 ◽  
Author(s):  
R. B. Lockhart Ewart ◽  
K. W. Taylor
Keyword(s):  
Growth Hormone ◽  
Cyclic Amp ◽  
Early Phase ◽  
Late Phase ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Hormone Release ◽  
Dibutyryl Cyclic Amp ◽  
Cyclic Monophosphate

1. The release of growth hormone from isolated fragments of rat anterior pituitary tissue incubated in vitro was studied by employing a double-antibody radioimmunoassay. 2. In the absence of added stimuli, two phases of hormone release could be distinguished, an early phase of 2h duration and a subsequent late phase. In the early phase, hormone release was rapid but could be significantly decreased by calcium depletion and by 2,4-dinitrophenol whereas the rate of release in the late phase was uninfluenced by these incubation conditions. These results have been interpreted as indicating the existence of a secretory component in the early phase of release. 3. In subsequent experiments, the effects of various agents on the rate of hormone output during the late phase of incubation were investigated. Hormone release was increased by theophylline and by dibutyryl cyclic AMP (N6-2′-O-dibutyryl-adenosine 3′:5′-cyclic monophosphate), the response to both of these agents being related to the concentration of the stimulant employed. 4. The stimulation of growth hormone output by theophylline was significantly decreased by calcium deprivation and by 2,4-dinitrophenol. The response to dibutyryl cyclic AMP was diminished by 2,4-dinitrophenol, iodoacetate and 2-deoxyglucose but not by malonate or colchicine. 5. Arginine, β-hydroxybutyrate, albumin-bound palmitate and variation in the glucose concentration of the incubation medium over a wide range were without any statistically significant effect on the rate of hormone release from either control pituitary fragments or those subject to secretory stimulation by dibutyryl cyclic AMP. 6. It is suggested that the regulation of growth hormone secretion is mediated by cyclic AMP (adenosine 3′:5′-cyclic monophosphate). The secretion observed in response to cyclic AMP requires the presence of ionized calcium and a source of metabolic energy but is independent of pituitary protein synthesis de novo. The integrity of the glycolytic pathway of glucose metabolism appears to be essential for cyclic AMP-stimulated growth hormone secretion to occur.

scholarly journals Progress of sperm IZUMO1 relocation during spontaneous acrosome reaction

Reproduction ◽  
2014 ◽  
Vol 147 (2) ◽  
pp. 231-240 ◽  
Author(s):  
Natasa Sebkova ◽  
Lukas Ded ◽  
Katerina Vesela ◽  
Katerina Dvorakova-Hortova
Keyword(s):  
Fusion Protein ◽  
Acrosome Reaction ◽  
Mating Behaviour ◽  
Calcium Ionophore ◽  
Cumulus Cells ◽  
Sperm Head ◽  
High Rate ◽  
Field Mice ◽  
Species Specific

It has been recently shown in mice that sperm undergo acrosome reaction (AR) by passing through cumulus cells; furthermore, the acrosome-reacted sperm can bind to zona pellucida and consequently fertilise the egg. During AR, the relocation of the primary fusion protein IZUMO1 into the equatorial segment is crucial for sperm–egg fusion. There is a high rate of spontaneous AR in rodents, with up to 60% in promiscuous species. The aim of this study was to clarify whether the IZUMO1 relocation in sperm after spontaneous and induced AR is the same, and whether there is a correlation between the speed of IZUMO1 relocation and species-specific mating behaviour in field mice. Immunofluorescent detection of IZUMO1 dynamics during the in vitro capacitation, spontaneous, calcium ionophore and progesterone-induced AR was monitored. Our results show that during spontaneous AR, there is a clear IZUMO1 relocation from the acrosomal cap to the equatorial segment, and further over the whole sperm head. In addition, there is positive tail tyrosine phosphorylation (TyrP) associated with hyperactive motility. Moreover, the beginning and the progress of IZUMO1 relocation and tail TyrP positively correlate with the level of promiscuity and the acrosome instability in promiscuous species. The findings that crucial molecular changes essential for sperm–egg fusion represented by dynamic movements of IZUMO1 also happen during spontaneous AR are vital for understanding fertilisation in mice.

Release of neurophysin together with vasopressin by a Ca 2+ dependent mechanism

1971 ◽  
Vol 261 (839) ◽  
pp. 379-380 ◽  
Keyword(s):  
Rabbit Antiserum ◽  
Nerve Impulse ◽  
Nerve Endings ◽  
Secretory Process ◽  
High K ◽  
K Concentration ◽  
Tracer Experiments ◽  
Dependent Mechanism

Oxytocin and vasopressin are stored with their binding proteins, the neurophysins, within neurosecretory vesicles in the nerve endings of the mammalian neurohypophysis. Depolarization of the nerve terminals, either by the arrival of a nerve impulse in vivo or by immersion of the gland in solutions of high K+ concentration in vitro , brings about a release of the hormones into the extracellular space. Douglas & Poisner (1964) have shown that this release is dependent on the entry of Ca 2+ into the nerve endings, and have proposed that Ca 2+ is necessary for coupling the stimulus of depolarization to the secretory process. Whereas Douglas (1967) suggests that Ca 2+ plays a part in emptying the neurosecretory vesicles by an exocytotic mechanism, the finding of Smith & Thorn (1965) that Ca 2+ dissociates the hormone-neurophysin complex suggests that secretion may take place by diffusion of the hormones through the vesicular and roteins. A biochemical method of distinguishing between these two mechanisms is to study whether other macromolecular constituents of the neurosecretory vesicles are specifically released by depolarizing stimuli. Fawcett, Powell & Sachs (1968) have previously shown by tracer experiments in dogs that a protein cross-reacting with a rabbit antiserum to bovine neurophysin is released from neurohypophyses stimulated by high K + solutions in vitro or by haemorrhage in vivo , but their technique did not allow a quantitation of the protein in relation to the amount of hormone released. A parallel release of neurophysin and hormone would be expected if exocytosis plays a part in the secretory mechanism.

Cycloheximide blocks insulin-like growth factor I but not somatostatin inhibition of growth hormone secretion

1987 ◽  
Vol 65 (4) ◽  
pp. 515-519 ◽  
Author(s):  
M. S. Sheppard ◽  
R. M. Bala
Keyword(s):  
Growth Hormone ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Protein Synthesis Inhibitor ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Synthesis Inhibitor ◽  
Inhibition Of Growth ◽  
Igf I

Growth hormone secretion is controlled by the two hypothalamic hormones, growth hormone releasing factor (GRF) and somatostatin. In addition, the insulin-like growth factors (IGF or somatomedins) which are themselves growth hormone dependent, inhibit growth hormone release in vitro, therefore acting to close the negative feedback loop. The studies reported here examine some of the differences between inhibition of growth hormone secretion by somatostatin and IGF-I in vitro. The major finding is that cycloheximide, a protein synthesis inhibitor, blocks inhibition of GRF-stimulated growth hormone release caused by IGF-I, without changing the inhibition caused by somatostatin. The experiments were done by exposing mixed rat adenohypophysial cells to secretagogues with or without cycloheximide for 24 h in a short term culture. Somatostatin (0.6 nM) totally blocked rat GRF (1 nM) stimulated growth hormone release to values 48% of control (nonstimulated values), while IGF-1 (27 nM) only reduced the GRF-stimulated growth hormone release by 27 ± 3% (N = 5). Cycloheximide (15 μg/mL) totally blocked the effect of IGF-I but not somatostatin. A low concentration (0.12 nM) of somatostatin, which only partly inhibited growth hormone release, was also unaffected by cycloheximide. In purified rat somatotrophs, somatostatin (0.1 nM) inhibited GRF-stimulated cAMP levels slightly and reduced growth hormone release while IGF-I (40 nM) had no effect. We suggest that IGF-I inhibits only the secretion of newly synthesized growth hormone, while somatostatin inhibits both stored and newly synthesized growth hormone pools.

THE SEROTONIN RETAINING EFFECT OF LITHIUM IN THE RAT THYROID

1976 ◽  
Vol 82 (2) ◽  
pp. 530-534 ◽  
Author(s):  
H. Vejlsted ◽  
O. Korsgaard
Keyword(s):  
Thyroid Hormone ◽  
Inhibitory Action ◽  
Hormone Secretion ◽  
Serotonin Release ◽  
Hormone Release ◽  
Rat Thyroid ◽  
Stimulation Of

ABSTRACT The hypothesis of a lithium induced serotonin retention in the rat thyroid has been tested. It has been found that the thyroid in rats treated with lithium contains double the amount of serotonin compared with glands from untreated animals. The ability of TSH to stimulate serotonin release is inhibited by lithium. The ability of serotonin to stimulate thyroid hormone secretion in vitro is documented. The inhibitory action of lithium on both TSH and serotonin stimulation of hormone release is documented. The serotonin retaining effect of lithium as part of the goitrogenic effect of this ion is discussed.

scholarly journals Octreotide and pasireotide (dis)similarly inhibit pituitary tumor cells in vitro

2016 ◽  
Vol 231 (2) ◽  
pp. 135-145 ◽  
Author(s):  
Alejandro Ibáñez-Costa ◽  
Esther Rivero-Cortés ◽  
Mari C Vázquez-Borrego ◽  
Manuel D Gahete ◽  
Luis Jiménez-Reina ◽  
...  
Keyword(s):  
Cell Viability ◽  
Pituitary Adenomas ◽  
Somatostatin Receptor ◽  
Hormone Secretion ◽  
Somatostatin Analogs ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Molecular Features ◽  
Intracellular Ca

Somatostatin analogs (SSA) are the mainstay of pharmacological treatment for pituitary adenomas. However, some patients escape from therapy with octreotide, a somatostatin receptor 2 (sst2)-preferring SSA, and pasireotide, a novel multi-sst-preferring SSA, may help to overcome this problem. It has been proposed that correspondence between sst1-sst5 expression pattern and SSA-binding profile could predict patient’s response. To explore the cellular/molecular features associated with octreotide/pasireotide response, we performed a parallel comparison of their in vitro effects, evaluating sst1-sst5 expression, intracellular Ca2+ signaling ([Ca2+]i), hormone secretion and cell viability, in a series of 85 pituitary samples. Somatotropinomas expressed sst5>sst2, yet octreotide reduced [Ca2+]i more efficiently than pasireotide, while both SSA similarly decreased growth hormone release/expression and viability. Corticotropinomas predominantly expressed sst5, but displayed limited response to pasireotide, while octreotide reduced functional endpoints. Non-functioning adenomas preferentially expressed sst3 but, surprisingly, both SSA increased cell viability. Prolactinomas mainly expressed sst1 but were virtually unresponsive to SSA. Finally, both SSA decreased [Ca2+]i in normal pituitaries. In conclusion, both SSA act in vitro on pituitary adenomas exerting both similar and distinct effects; however, no evident correspondence was found with the sst1-sst5 profile. Thus, it seems plausible that additional factors, besides the simple abundance of a given sst, critically influence the SSA response.

scholarly journals Effects of veratridine on Ca fluxes and the release of oxytocin and vasopressin from the isolated rat neurohypophysis.

1978 ◽  
Vol 72 (3) ◽  
pp. 297-304 ◽  
Author(s):  
J J Nordmann ◽  
R E Dyball
Keyword(s):  
Calcium Antagonists ◽  
Incubation Medium ◽  
Hormone Release ◽  
45Ca Uptake ◽  
Regulation Of Secretion ◽  
45Ca Efflux ◽  
Isolated Rat

Uptake of radioactive calcium, 45Ca efflux, and hormone release from the isolated rat neurohypophysis were monitored in vitro after the addition of veratridine to the incubation medium. Veratridine dramatically increased hormone release, but the release was not sustained and had declined by about 90% after 2 h. Removal of external Na+ prevented hormone release as did addition to the incubation medium of tetrodotoxin or the calcium antagonists D600 and Mn2+ ions. Veratridine increased 45Ca uptake into the isolated neurohypophysis and the increase could be prevented by addition of tetrodotoxin or D600 to the medium. Efflux of 45Ca was not changed by addition of veratridine. The results underline the importance of both Na+ and Ca+2 channels in the regulation of secretion of neurosecretory products.

ROLE OF THE HETEROGENEITY OF THYROGLOBULIN IN THE SECRETION OF THYROID HORMONE IN MICE

1980 ◽  
Vol 86 (3) ◽  
pp. 413-418 ◽  
Author(s):  
N. BAGCHI ◽  
T. R. BROWN ◽  
B. SHIVERS ◽  
R. E. MACK
Keyword(s):  
Drinking Water ◽  
Chromatographic Analysis ◽  
Hormone Secretion ◽  
Hormone Release ◽  
Basal Rate ◽  
Thyroid Glands ◽  
Hydrolysis Of ◽  
Mouse Thyroid

The rates of thyroglobulin hydrolysis and iodothyronine release from mouse thyroid glands were studied in vitro. Recently iodinated thyroglobulin ('new pool') had been labelled during life by injection of 131I 3 h before removal of the thyroid, 'old pool' thyroglobulin had been labelled by the administration of 125I in the drinking water for 1 week starting 3 weeks earlier. Chromatographic analysis of pronase digests of the thyroid glands showed that the iodothyronine content of the old and new pools were 19·5 and 7·4 per cent respectively. In the basal state the rate of thyroglobulin hydrolysis was lower from the old pool but the rate of hormone secretion was similar from both pools. Thyrotrophin (TSH) increased the rate of thyroglobulin hydrolysis and hormone release from both pools by up to four to six times the basal rate, the effect being maximal 2 h after administration of TSH and lasting for 6–8 h. The rate of thyroglobulin hydrolysis after TSH was similar in both pools but the rate of release of labelled iodothyronines was significantly higher from the old pool. These studies have indicated that although hydrolysis of thyroglobulin proceeds faster in the new pool than in the old ('last come, first served' hypothesis) nevertheless there is no difference in the rate of hormone secretion from the two pools, and hydrolysis in both pools is affected by TSH.

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