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Abstract
The effects of somatostatin (SRIF) on prolactin (PRL) synthesis and release were examined in primary cultured pituitary cells derived from normal and estradiol (E2)-primed male rat pituitaries. The cells were continuously incubated in a pulse medium containing [3H]leucine with or without 10−6 mol/l SRIF for a period of 15, 30, 60, 180 or 360 min. Following incubation, the medium was recovered and the cells were fractionated into cytosolic and granular fractions. PRL was isolated by SDS-PAGE and newly synthesized PRL ([3H]PRL) was identified by coincident peaks of tritium activities and PRL contents. The specific activity (SA, c.p.m./ng), a ratio of [3H]PRL to total PRL, was determined for the granular, cytosolic and medium fractions.
In control and SRIF-treated groups of non-primed pituitary cells, SAs of all three fractions significantly increased during the 6-h incubation. Cytosolic and granular SAs showed similar profiles of increasing rate in comparison to control. Medium SAs showed a significantly higher value in the SRIF-treated group than in the control group only at 180 min. These observations indicate that, in the non-primed condition, PRL synthesis is not inhibited by SRIF. Medium SAs in the E2-primed group were significantly higher than SAs in the non-primed control cells during the initial 3 h of incubation, and cytosolic and granular SAs were significantly higher than those of the non-primed control during the 3- to 6-h incubation period. These observations demonstrate that E2 enhances PRL synthesis and secretion of newly synthesized PRL. SRIF treatment of E2-primed lactotrophs resulted in a significant decrease in SAs of all three fractions as compared with those of the E2-primed control. Our results indicate that in normal male rat pituitary cells SRIF does not inhibit PRL synthesis but effectively inhibits PRL synthesis in E-primed lactotrophs. This suggests that the inhibitory action of SRIF on PRL synthesis is estrogen dependent.
Journal of Endocrinology (1996) 148, 69–76
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Search for other papers by C S-S Lee in
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Abstract
The neurohypophysial hormones, oxytocin and vasopressin, are present as non-covalently bound complexes with their designated neurophysin in the secretory granules of the posterior pituitary. The neurophysins are generally considered to be biologically inert carrier proteins for oxytocin and vasopressin. We have examined the actions of bovine neurophysin-I (bNP-I), bovine neurophysin-II (bNP-II), rat neurophysin (rat NP) and oxytocin on prolactin release using primary cultured rat pituitary cells. A dynamic perifusion system was chosen to test their stimulatory actions. The rat NP and bNP-II stimulated prolactin release. It is a new observation that rat NP and bNP-II stimulate prolactin release from primary cultured rat pituitary cells. The maximum sensitivities, the lowest concentration which stimulate prolactin release, of rat NP, bNP-II, bNP-I and oxytocin in primary cultured cells were 1 nmol/l, 1 nmol/l, 1000 nmol/l and 1 nmol/l respectively. The maximum sensitivities of rat NP and bNP-II were within the physiologically relevant concentrations.
Journal of Endocrinology (1995) 144, 225–231
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Search for other papers by C. C. LEE in
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Search for other papers by C Lee in
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Keratinocyte growth factor (KGF/FGF-7) is a stromally derived factor which exerts proliferative and differentiating effects on a variety of epithelial cells. Results of recent studies utilizing in vitro methods such as tissue culture and organ culture have suggested that KGF may act as a paracrine mediator of androgen-induced growth and development of the prostate and seminal vesicle. We undertook the present study to determine the distribution of KGF in relation to the functional regions of the rat prostatic ductal system, and whether KGF expression is influenced by androgen in vivo. Immunohistochemical staining revealed KGF to be present in the stroma throughout the prostate, regardless of the functional region, and staining for KGF remained high through 21 days post-castration. Message for KGF could also be detected by reverse transcriptase-PCR analysis of prostate stromal cells isolated from 4- and 21-day castrated animals, and no gross change in message level was observed following castration. Furthermore, no significant change in either stromal staining or message for KGF was observed in newborn rat prostates 10 days after castration, suggesting a similar regulatory mechanism for KGF in the adult and immature prostate. Epithelial staining for KGF decreased following castration, and greatly increased upon androgen replacement, possibly indicating a change in KGF internalization. These observations suggest that the presence of KGF protein is not related to functional differences in the prostate epithelium, and that expression of KGF in vivo is not greatly influenced by androgen.
Search for other papers by S. PORS NIELSEN in
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SUMMARY
Synthetic porcine calcitonin (α-calcitonin) and its methionine-sulphoxide derivative (β-calcitonin) were given by intravenous infusion to conscious male rats. α-Calcitonin inactivated by performic acid oxidation was used as a control.
Microgram doses of α-calcitonin produced a dose-dependent decrease in the renal excretion of magnesium. The effect was not due to a secondary release of parathyroid hormone since it was also seen in parathyroidectomized animals.
A marked increase in the renal excretion of inorganic phosphate, sodium and potassium preceded the change in magnesium excretion in parathyroidectomized rats. It is concluded that the phosphaturia and natriuresis previously described after administration of extracted calcitonin preparations are true effects of the hormone.
The effect of β-calcitonin was indistinguishable from that of α-calcitonin.
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ABSTRACT
Material with the immunochemical properties of the β-core of human chorionic gonadotrophin (hCG) can be found in the urine of normal postmenopausal women. However, we have been unable to detect intact hCG (using an assay which is specific for the α–β heterodimer of intact hCG) in serum of such subjects. The levels of serum LH and urinary β-core were compared in matched samples from 28 women (serum LH: median 27 U/l, range 4-70 U/l, urinary β-core: median 0·27 μg/l, range < 0·05–0·645 μg/l). Urine (4 litres) from three postmenopausal women was concentrated, dialysed and subjected to gel exclusion chromatography on Sephadex G-100. Fractions were analysed by specific assays for LH, intact hCG, total β-hCG (free β-subunit and intact hCG), free α-subunit and β-core. Material eluting at the expected position of the β-core fragment of hCG was detected in all three samples by the β-core, β-hCG and LH assays, despite the fact that the LH antibody does not recognize the authentic β-core of pregnancy. Electrophoresis and Western blotting of the concentrated urines revealed that material of the same molecular size as β-core was recognized by the antibody to LH but not by a monoclonal antibody raised to free β-hCG which also recognizes the β-core molecule of hCG. We conclude that the predominant core-like material identified in postmenopausal urine is probably derived from the β-subunit of LH.
Journal of Endocrinology (1992) 133, 459–466
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ABSTRACT
A continuous line of somatostatin-producing medullary thyroid carcinoma cells was established from a transplantable tumour in BALB/c mice. Virtually all of the somatostatin immunoreactivity co-chromatographed with somatostatin 14. The tumour cells replicated in spinner cultures with a doubling time of approximately 4 days, and the concentration of somatostatin released into the culture medium increased in proportion to the number of cells. Two-to threefold increases in amounts of stored and released somatostatin were observed after treatment of the cells with bromodeoxyuridine. This cell line might be valuable for studies of somatostatin regulation in normal and neoplastic C-cells, and for other studies of C-cell biology which require a mouse model.
J. Endocr. (1986) 110, 309–313
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Cortisol concentration in both serum and saliva sharply increases and reaches a peak within the first hour after waking in the morning. This phenomenon is known as the cortisol awakening response (CAR) and is used as an index of hypothalamus–pituitary–adrenal (HPA) axis function. We examined whether ovarian steroid concentrations increased after awakening as with the CAR in the HPA axis. To do this, cortisol, estradiol-17β (E2), and progesterone (P4) concentrations were determined in saliva samples collected immediately upon awakening and 30 and 60 min after awakening in women with regular menstrual cycles and postmenopausal women. We found that both E2 and P4 concentrations increased during the post-awakening period in women with regular menstrual cycles, but these phenomena were not seen in any postmenopausal women. The area under the E2 and P4 curve from the time interval immediately after awakening to 60 min after awakening (i.e. E2auc and P4auc) in women with regular menstrual cycles were greater than those in the postmenopausal women. E2 and P4 secretory activity during the post-awakening period was influenced by the phase of the menstrual cycle. E2auc in the peri-ovulatory phase and P4auc in the early to mid-luteal phase were greater than in the menstrual phase. Meanwhile, cortisol secretory activity during the post-awakening period was not influenced by menstrual status or the phase of menstrual cycle. These findings indicate that, as with the CAR in the HPA axis function, ovarian steroidogenic activity increased after awakening and is closely associated with menstrual status and phase of menstrual cycle.
Search for other papers by W M Lee in
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Abstract
Sex hormone binding globulin (SHBG) is a homodimeric plasma protein found in mammals that binds sex steroids with high affinity and regulates their bioavailability. The protein is identical in structure and properties to the androgen binding protein (ABP) found in the male reproductive tract. We have isolated a 1245-base pair rabbit SHBG cDNA encoding a reading frame for a signal peptide followed by a protein of 367 amino acids, which shares 79·0, 68·1 and 63·2% amino acid identity with the corresponding human, rat and mouse proteins respectively. Northern blot and hot-nested PCR analyses indicated that rabbit SHBG is produced from a 1·6 kilobase mRNA in the liver of both sexes and in the testis. The rabbit SHBG cDNA was inserted into pGEX-1λT for expression of a glutathione S-transferase/SHBG fusion protein in Escherichia coli. The bacterial product bound 5α-dihydrotestosterone (DHT) in the same manner as the corresponding protein in serum. The dissociation constants (Kd) for rabbit and human SHBGs produced in E. coli were 11·1 ± 1·1 nm and 2·1 ± 0·6 nm respectively, and rabbit SHBG formed a less stable protein-steroid complex (t½=5 min) than human SHBG (t½>60 min). Unlike human SHBG, rabbit SHBG does not bind estradiol with high affinity. To aid in the identification of differences in the sequences of rabbit and human SHBG, which determine species differences in steroid-binding affinity and specificity, chimeras containing the 5′-terminal half of SHBG from one species and 3′-terminal half of SHBG from the other species were constructed and expressed. It was found that the chimeric proteins assumed similar steroid-binding affinity and specificity as the wild-type proteins when the amino (N)-terminal half of SHBG was derived from the same species. Replacement of the carboxyl (C)-terminal half of rabbit SHBG by the corresponding region of the human molecule increased the integrity of its steroid-protein complex. This supports the concept that amino acids within the N-terminal half of SHBG constitute the steroid-binding domain while the C-terminal half of the molecule may provide structural stability to the protein and its steroid-binding site.
Journal of Endocrinology (1997) 153, 373–384
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ABSTRACT
5-Methoxytryptamine is a potent agonist of presynaptic 5-hydroxytryptamine autoreceptors modulating serotonin release in the central nervous system. This methoxyindole can be synthesized in the pineal gland, but its presence in vivo is still controversial, probably because of rapid catabolism by monoamine oxidase. An improved high-pressure liquid chromatography method, with coulometric detection, has been developed for the simultaneous measurement of melatonin, 5-methoxytryptamine, 5-methoxytryptophol and 5-methoxyindolacetic acid. We have demonstrated a day–night rhythmicity in the amount of 5-methoxytryptamine in the pineal gland of golden hamsters (Mesocricetus auratus) maintained under a long photoperiod (14 h light: 10 h darkness) and pretreated with the monoamine oxidase inhibitor pargyline. Levels of 5-methoxytryptamine were highest at 16.30 h and lowest at 00.30 h. The rhythm for 5-methoxytryptamine appears to be the same as for serotonin (opposite in phase to that of melatonin). The identification of 5-methoxytryptamine has been confirmed by analysis with gas chromatography–mass spectrometry.
J. Endocr. (1988) 118, 389–397
