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M Szabo

Publications and source records attributed to M Szabo.

At least 19 recordsLinked to original sources
PubMed1992

Use of chromosomal gene fusions to investigate the role of repetitive DNA in regulation of genes involved in lipopolysaccharide biosynthesis in Haemophilus influenzae.

The lic3 locus of Haemophilus influenzae consists of four open reading frames. The derived amino acid sequences of orf2 and orf4 exhibit homology to Escherichia coli GalE and AdK, respectively. The functions of orf1 and orf3 remain unknown. orf1 contains multiple tandem repeats of the tetrameric DNA sequence CAAT near the 5' end. Two possible translational starts (ATG1 and ATG2) lie upstream. We have used lacZ fusions to investigate whether changes in the number of CAAT repeats in conjunction with differential usage of the upstream frames control the expression of lic3-orf1. Phase-variable expression of lacZ was observed for individual colonies and could be related to variable numbers of CAAT repeats. Of the three possible upstream frames, only one, containing the more downstream of the two possible ATG start codons (ATG2), is used for strong expression of lacZ. Utilization of the more upstream ATG (ATG1) or ATG2 was observed with medium-level expression, while utilization of any of the three possible frames was observed when lacZ was expressed at low to undetectable levels, indicating that other mechanisms may affect expression. To investigate this, lacZ was fused in frame with ATG2 of lic3-orf1, with concomitant deletion of the repeats. Phase-variable expression was still observed, supporting the view that an alternative level of control operates in conjunction with the repeat mechanism.

Amino Acid Sequence↗
PubMed1991

In vitro cytotoxicity of Haemophilus influenzae lipopolysaccharides for bovine aortal endothelial cells.

The cytotoxicity of purified lipopolysaccharide (LPS) from a prototype Haemophilus influenzae type b (Hib) strain (Eagan) and three transformants, differing in their LPS phenotype, for bovine aortal endothelial cells (BAOEC) was investigated. All LPS preparations caused cell disruption and release of lactate dehydrogenase (LDH), an indicator of cytotoxicity, from BAOEC monolayers but to differing extents. There was no correlation between the cytotoxicity of purified Hib LPS to BAOEC monolayers and potential to cause bacteraemia in experimental animals.

Animals↗
PubMed1990

Biphasic action of forskolin on growth hormone and prolactin secretion by rat anterior pituitary cells in vitro.

To assess the role of cAMP-mediated signal transduction processes in mediation of secretagogue-stimulated GH release, we examined the dose-related effects of the diterpene adenylate cyclase activator forskolin (FSK) in primary monolayer cultures of rat adenohypophyseal cells. In cell cultures prepared from both immature (12 days old) and adult (6 weeks to 4 months old) male or female rats, the dose-related stimulation of GH release by FSK was biphasic. With increasing FSK concentrations from 0.03-3.16 microM, GH release increased progressively to maximal values of 442 +/- 19% and 303 +/- 10% of basal release in cells from immature and adult rats, respectively. FSK concentrations above 3.16 microM induced progressively diminished GH responses, with net inhibition to below basal release evident at 100 microM FSK. FSK stimulated PRL release to a lesser degree than it did GH release; the PRL response to FSK was also biphasic. When maximal stimulatory concentrations (Emax) of FSK and GH-releasing factor (GRF; 10 nM) were added in combination, the GH response was significantly less than the individual response to either secretagogue alone. In response to FSK alone, GRF alone, and FSK plus GRF, GH release was 478 +/- 7%, 583 +/- 11%, and 244 +/- 5%; 278 +/- 4%, 283 +/- 3%, and 175 +/- 2%; and 299 +/- 12%, 351 +/- 5%, and 191 +/- 17% of basal release in cells from 12-day-old, adult male, and adult female rats, respectively (P less than 0.01 for all responses to combined addition vs. the individual responses). Submaximal stimulatory concentrations of GRF added in combination with submaximal FSK elicited partially additive GH responses; the GH response to Emax GRF, on the other hand, was inhibited in a dose-related manner by all concentrations of FSK that by themselves were stimulatory. The GH responses were also suppressed when Emax FSK was added to cultured cells of 12-day-old rats in combination with Emax cholera toxin (2.5 ng/ml) or prostaglandin E2 (10 microM), agents whose actions, like that of GRF, involve adenylate cyclase activation. In contrast, FSK did not suppress but in most cases augmented the maximal GH responses to secretagogues whose action is independent of adenylate cyclase activation: (Bu)2cAMP (0.5 mM), TRH (100 nM), phorbol myristate acetate (50 nM), the Ca2+ ionophore A23187 (250 microM), and the dihydropyridine Ca2+ channel agonist BAY K8644 (10 microM). Indeed, combined addition of FSK with the latter two agents resulted in synergistic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1990

The importance of fiberbronchoscopy in respiratory burns.

Respiratory burns worsen considerably the prognosis of the patients. Fiberoptic endoscopy facilitated the examination of respiratory burns and determined the degree and extent of mucosal damage. At the same time, aspiration and lavage of the affected bronchi can be advantageously used in therapy. 22 patients with respiratory burns were hospitalized at the Burn Centre, Works Institute of Health Care, East Slovak Iron Works, Kosice (Czechoslovakia); 13 of them died, i.e. 59.1%. The paper analyzes fiberbronchoscopy applied to respiratory burns, anaesthetic technique and intubation, and the results are compared with post mortem findings. Some clinical findings are demonstrated, too.

Bronchoscopy↗
PubMed1989

The effect of age on prostaglandin E2 stimulation of growth hormone release from cultured rat pituitary cells.

Prostaglandin E2 (PGE2) is a potent secretagogue of GH in mature mammals. Although PGs are produced by the fetus and newborn of many species, the ontogeny of PGE2's GH stimulatory effect and the interaction of PGE2 with GHRF in the developing animal are not known. We examined the effects of 0.01-10 microM PGE2 and 0.01-10 nM rat GHRF, alone and in combination, on GH release from cultured pituitary cells of 2-day(d)-old, 7-d-old, 15-d-old, and adult (3- to 4-month-old) male rats (n = 4-7 experiments/age group). The effect of PGE2 on GH release was markedly age dependent. The GH response to all doses of PGE2 over 0.01 microM was greatest in pituitary cells of adult and 15-d-old rats and least in those of 2-d-old pups. PGE2 (0.1 microM) did not cause significant GH release from pituitary cells of 2-d-old pups (110 +/- 3% of control values), but increased that from 7-d-old, 15-d-old, and adult pituitary cells to 126 +/- 8%, 155 +/- 8%, and 156 +/- 9% of respective control values (by analysis of variance: F = 7.28; P less than 0.001). PGE2 (1 microM) increased GH release to 123 +/- 8%, 145 +/- 12%, 259 +/- 24%, and 260 +/- 17% of control values from pituitary cells of these same respective age groups (F = 12.3; P less than 0.001). The highest dose of PGE2 studied (10 microM) yielded similar results. The influence of PGE1 on GH release was also age dependent and similar to that of PGE2. In contrast to PGE2, GHRF stimulated GH release most in pituitary cells of 2-d-old pups and least in those of adults, similar to our previous observations with human GHRF-40. Coincubation with PGE2 and low dose GHRF resulted in partial additivity of GH response in adult rats, but no additivity in newborn pups. These results indicate that in rats, the sensitivity of the somatotroph to PGE2 increases with advancing age after birth. The contrasting developmental patterns of somatotroph sensitivity to PGE2 and GHRF support the concept that these GH secretagogues act, at least in part, by different intracellular mechanisms, which are subject to differential rates of maturation.

Animals↗
PubMed1988

Impaired suppression of growth hormone release by somatostatin in cultured adenohypophyseal cells of spontaneously diabetic BB/W rats.

The effects of the diabetic state on the somatotroph's responsiveness to the secretagogues GRF and (Bu)2-cAMP and to the inhibitor somatostatin (SRIF) were evaluated in enzymatically dissociated rat adenohypophyseal cells in primary monolayer culture. Primary cultures were prepared from pituitary tissue of spontaneously diabetic BB/W rats 23-51 days after the onset of hyperglycemia and glycosuria and of age-matched diabetes-resistant control rats. Dose-related stimulation of GH release by GRF and (Bu)2cAMP did not differ significantly in the two preparations. There was no evidence of abnormal sensitivity to TRH in cultured somatotrophs of diabetic rats. Dose-related suppression of (Bu)2cAMP (0.5 mM)-stimulated GH release by 0.01-10 nM SRIF, on the other hand, was significantly affected by diabetes, as indicated by a parallel shift of the dose-response curve to the right and an increase in the IC50 value from 76 +/- 2 to 204 +/- 5 pM (mean +/- SEM; n = 3; P less than 0.001). Maximal suppression by 10 nM SRIF was identical in the two preparations. The degree to which the cultured cells' responsiveness to SRIF was reduced was unrelated to the duration and severity of the diabetic state. Hypothalamic SRIF content did not differ significantly between diabetic and diabetes-resistant rats (186 +/- 12 vs. 178 +/- 10 ng/mg protein). Nevertheless, the SRIF concentration may be elevated in hypophysealportal blood of diabetic rats; we, therefore, examined the effect of prolonged exposure of the cell cultures to SRIF or SMS 201-995 on the subsequent suppression of (Bu)2cAMP-stimulated GH release by SRIF. Addition of either SRIF (10 nM) or SMS 201-995 (5.5 nM) to the culture medium for 4 days significantly increased the IC50 values for SRIF to values similar to those obtained in cultured cells of diabetic rats. We conclude that the somatotrophs of diabetic rats are relatively resistant to SRIF. Since prolonged exposure to SRIF in vitro produced similar resistance, the desensitization in diabetic rats may be due to elevated concentrations of SRIF in hypophyseal-portal blood. This impaired responsiveness to SRIF may contribute to aberrant GH secretion in diabetes.

Animals↗
PubMed1986

TRH and GRF stimulate release of growth hormone through different mechanisms.

Thyrotropin-releasing hormone (TRH) is an effective stimulator of growth hormone (GH) release from cultured adenohypophysial cells of chronically hypothyroid rats in vitro. The present study explored the question of cAMP and calcium mediation of the GH-stimulatory effect of TRH in this system. A maximally stimulatory concentration of TRH was added together with various concentrations of human GH-releasing factor 40 (hGRF-40) whose action is cAMP mediated, or of dibutyryl cAMP (DBcAMP), to primary monolayer cultures of adenohypophysial cells from thyroidectomized rats. The GH responses to the combined addition of TRH with all doses of GRF or DBcAMP were fully additive, causing parallel elevations of the dose-response curves. Whereas the GH response to maximally effective concentrations of hGRF-40 and DBcAMP, added together, was not greater than that to either secretagogue alone, the inclusion of TRH increased the response to a new Emax. The calcium inhibitors, verapamil, EGTA, and CoCl2, markedly suppressed basal GH release and virtually completely blocked the GH response to TRH, suggesting calcium mediation. In chronically hypothyroid, urethan-anesthetized rats, the in vivo effect of the combined administration of maximally effective doses of TRH and GRF on plasma GH levels was also additive. These findings indicate that TRH stimulates GH release in adenohypophysial cells of hypothyroid rats by a cAMP-independent, calcium-dependent mechanism.

Animals↗
PubMed1986

Differential responsiveness of the somatotroph to growth hormone-releasing factor during early neonatal development in the rat.

The effects of human pancreatic GH-releasing factor-40 (hpGRF-40; 0.01-100 nM) and (Bu)2cAMP (0.015-1.5 mM) on GH release from primary monolayer cultures of pituitary cells were evaluated in rats of three age groups: postnatal days 2 and 12, and young adult males (3-4 months). Both hpGRF-40 and (Bu)2cAMP elicited a dose-related increase in GH release in cell cultures from each age group. However, the magnitude of the fractional increase over basal release was markedly age dependent. hpGRF-40-stimulated GH release (expressed as a percentage of control values) was greater in cultured cells of 2-day-old than of 12-day-old rats, which was, in turn, significantly greater than in cells of adult rats (P less than 0.001). Maximum hpGRF-40-stimulated GH release was 1058 +/- 50% of control values (+/- SE) in 2-day-old, 617 +/- 21% of control values in 12-day-old, and 405 +/- 6% of control values in adult pituitary cell cultures. The slopes of the dose-response curves differed significantly among the three age groups (P less than 0.001) and varied inversely with increasing age. GH release induced by (Bu)2cAMP was similarly age dependent; maximal stimulated release was 1073 +/- 20%, 414 +/- 4%, and 259 +/- 7% of control values in cultured cells of 2-day-old, 12-day-old, and adult rats, respectively (P less than 0.001 for age effect at each dose). As with hpGRF-40, the slopes of the dose-response curves for (Bu)2cAMP decreased with advancing age (P less than 0.001). Intracellular GH storage during culture, basal release of GH, and serum GH were also age dependent. Pooled serum GH was consistently elevated in 2-day-old rats (139 +/- 2 ng ml-1), became lower and more variable in 12-day-old rats (62 +/- 14 ng ml-1), and was even more variable in adult male rats (79 +/- 23 ng ml-1), owing to random sampling during spontaneous secretory pulses. These results indicate that the stimulatory effects of GRF and (Bu)2cAMP on GH secretion from cultured rat pituitaries vary with age; pituitary cells of newborn rats are relatively more sensitive to these secretagogues than those of adult rats. This increased responsiveness of the neonatal somatotroph to GRF may contribute to the elevation of the plasma GH concentration which is characteristic of the perinatal period in the rat.

Aging↗
PubMed1986

The effect of age on somatostatin suppression of basal, growth hormone (GH)-releasing factor-stimulated, and dibutyryl adenosine 3',5'-monophosphate-stimulated GH release from rat pituitary cells in monolayer culture.

To test the hypothesis that relative resistance of the somatotroph to somatostatin (SRIF) contributes to elevated circulating levels of GH in the newborn rat, we examined the effects of SRIF (0.1, 0.33, and 1 nM) on basal, human pancreatic GH-releasing factor-40 (hpGRF-40; 1 nM)-stimulated, and (Bu)2cAMP (0.5 mM)-stimulated GH release from pituitary cells of 2-day-old, 15-day-old, and adult Sprague-Dawley rats in monolayer culture. The effect of SRIF on basal GH release varied markedly with age. SRIF, in the doses studied, did not inhibit basal GH release (nanograms of GH per 10(5) cells/3 h) from pituitary cultures of 2-day-old rats. In those of 15-day-old rats, only the two higher doses of SRIF (0.33 and 1 nM) suppressed GH release. By contrast, in pituitary cell cultures of adult male and female rats, all doses of SRIF significantly inhibited basal GH release (P less than 0.001). Similarly, the degree of SRIF suppression of both hpGRF-40- and (Bu)2cAMP-stimulated GH release differed among the age groups. In pituitary cultures of 2-day-old rats, SRIF did not significantly inhibit stimulated GH release. In 15-day-old rat pituitary cells, SRIF inhibited GH release, but did not eradicate the stimulatory effect of hpGRF-40 or (Bu)2cAMP. By contrast, in pituitary cell cultures of adult male and female rats, SRIF completely abolished the stimulatory effect of both hpGRF-40 and (Bu)2cAMP. When expressed as a percentage of the control (or stimulated) value, GH release at each SRIF dose varied markedly with age (P less than 0.001). Furthermore, a similar age-associated trend was evident when, in a separate series of experiments (n = 37), we examined the suppressive effect of a single concentration of SRIF (0.33 nM) on (Bu)2cAMP (0.5 mM)-stimulated GH release in cultured pituitary cells of rats ranging in age from -1 (day 20 of gestation) to 78 days. The degree of suppression increased progressively with advancing age; GH release decreased from 82 +/- 2% (+/- SE) of stimulated values in cultured cells of perinatal rats to 20 +/- 1% of stimulated values in cultured cells of 78-day-old rats. There was a significant negative correlation between age and SRIF-inhibited GH release (r = -0.89; P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Age Factors↗
PubMed1986

Ontogeny of the in vitro growth hormone stimulatory effect of thyrotropin-releasing hormone in the rat.

The ontogenic changes in the somatotroph's responsiveness to TRH were examined in enzymatically dissociated rat pituitary cells in primary monolayer culture. Exposure to TRH (10(-8) M) caused a significant increase in GH release in cultured pituitary cells from rats ranging in age from -1 day (20 days of gestational age) to 90 days. The magnitude of the response, expressed as a percent increment above control rat GH (rGH) release, rose progressively until it reached a maximum of 209 +/- 5% (mean +/- SE) on postnatal day 12. Thereafter, the response declined to values ranging from 10-30% above control rGH release. In cultured adenohypophyseal cells of rats on postnatal day 12, the effect of TRH was dose related; the effective concentration range was 10(-10)-10(-7) M, with an EC50 of 2.5 +/- 0.6 X 10(-9) M. TRH (10(-8) M) potentiated the GH stimulatory effect of a submaximally effective concentration of human GH-releasing factor-40 (hGRF-40; 10(-9) M) in cultured pituitary cells of developing rats, aged -1 to 30 days, and that of (Bu)2cAMP (5 X 10(-4) M) in cultured pituitary cells of rats aged -1 to 45 days. The rGH response to the combined addition of TRH with either hGRF-40 or (Bu)2cAMP was up to 2 times greater (P less than 0.05) than the sum of the individual responses. When the interaction of TRH (10(-8) M) with multiple concentrations of hGRF-40 (10(-10), 10(-9), and 10(-8) M) was tested in cultured pituitary cells of 4- to 36-day-old rats at 4-day intervals, synergism was least at the lowest and greatest at the highest concentration of hGRF-40; synergistic interaction decreased progressively after 20 days of age to undetectable levels by 36 days. In cultured anterior pituitary cells of 12-day-old rats, maximally stimulatory TRH (10(-7) M) potentiated the GH stimulatory effects of both hGRF-40 and (Bu)2cAMP at concentrations at the EC50 value or greater, with synergism being most pronounced at maximally effective concentrations. Whereas the GH response to the combined addition of maximal hGRF-40 (10(-7) M) and (Bu)2cAMP (1.5 X 10(-3) M) was not greater than that to maximal hGRF alone, TRH potentiated the responses to both secretagogues whether added separately or combined.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Growth hormone response to thyrotropin-releasing hormone in the urethane-anesthetized rat: effect of thyroid status.

To evaluate the role of thyroid hormones in regulation of the GH-stimulatory effects of TRH and human pancreatic GH-releasing factor (hpGRF-40), we studied the plasma GH responses to these secretagogues under conditions of thyroid hormone deprivation and replacement in the urethane-anesthetized rat. In euthyroid control rats, TRH (1 microgram/kg) elicited a small transient rise in plasma GH, which peaked at 2-5 min and returned to basal by 20 min. In chronically hypothyroid rats (10 weeks after thyroidectomy), intrapituitary GH was markedly depleted to less than 0.1% of normal, and TRH was completely ineffective in eliciting a plasma GH response to TRH. In chronically hypothyroid rats given T4 (20 micrograms/kg daily) for 4 days, intrapituitary GH was partially repleted, and the GH response to TRH was markedly enhanced compared to that in euthyroid rats. The extent to which the GH response to TRH was enhanced by chronic hypothyroidism, followed by short term T4 treatment, depended on the duration of T4 administration. The plasma GH response was greatest after 1-3 days of T4 treatment; treatment for 7 days, on the other hand, suppressed the GH response to below that of euthyroid rats. The minimal duration of hypothyroidism which, in combination with short term (2 days) T4 treatment, enhanced the plasma GH response to TRH, was 6 weeks, with 8 weeks or longer being optimal. The effect of TRH on plasma GH was dose dependent in thyroidectomized rats given T4 for 2 days; the lowest maximally stimulatory dose was 10 times less than that in the euthyroid rat (1 vs. 10 micrograms/kg). The GH-stimulatory effect of TRH in thyroidectomized rats given T4 for 2 days was abolished by the simultaneous administration of SRIF (40 micrograms/kg). That the failure of TRH to stimulate GH release in the chronically hypothyroid rat may have been the consequence of a depletion of intrapituitary GH available for release was suggested by the finding that in parallel studies, hpGRF-40, a more potent stimulator of GH release in the euthyroid rat, was also without effect. In contrast to the GH response to TRH, the GH response to hpGRF-40 was only partially restored by T4 treatment of chronically hypothyroid rats for 2 days. We conclude that chronic thyroid hormone deficiency selectively sensitizes the somatotroph to TRH. Short term thyroid hormone replacement is needed to replete intrapituitary GH and allow the expression of this enhanced GH secretory response to TRH. More prolonged treatment with T4, on the other hand, appears to desensitize the somatotroph to TRH.

Animals↗
PubMed1984

Thyrotropin-releasing hormone stimulates growth hormone release from the anterior pituitary of hypothyroid rats in vitro.

We have examined the interaction of thyroid hormone and TRH on GH release from rat pituitary monolayer cultures and perifused rat pituitary fragments. TRH (10(-9) and 10(-8)M) consistently stimulated the release of TSH and PRL, but not GH, in pituitary cell cultures of euthyroid male rats. Basal and TRH-stimulated TSH secretion were significantly increased in cells from thyroidectomized rats cultured in medium supplemented with hypothyroid serum, and a dose-related stimulation of GH release by 10(-9)-10(-8) M TRH was observed. The minimum duration of hypothyroidism required to demonstrate the onset of this GH stimulatory effect of TRH was 4 weeks, a period significantly longer than that required to cause intracellular GH depletion, decreased basal secretion of GH, elevated serum TSH, or increased basal secretion of TSH by cultured cells. In vivo T4 replacement of hypothyroid rats (20 micrograms/kg, ip, daily for 4 days) restored serum TSH, intracellular GH, and basal secretion of GH and TSH to normal levels, but suppressed only slightly the stimulatory effect of TRH on GH release. The GH response to TRH was maintained for up to 10 days of T4 replacement. In vitro addition of T3 (10(-6) M) during the 4-day primary culture period significantly stimulated basal GH release, but did not affect the GH response to TRH. A GH stimulatory effect of TRH was also demonstrated in cultured adenohypophyseal cells from rats rendered hypothyroid by oral administration of methimazole for 6 weeks. TRH stimulated GH secretion in perifused [3H]leucine-prelabeled anterior pituitary fragments from euthyroid rats. A 15-min pulse of 10(-8) M TRH stimulated the release of both immunoprecipitable [3H]rat GH and [3H]rat PRL. The GH release response was markedly enhanced in pituitary fragments from hypothyroid rats, and this enhanced response was significantly suppressed by T4 replacement for 4 days. The PRL response to TRH was enhanced to a lesser extent by thyroidectomy and was not affected by T4 replacement. These data suggest the existence of TRH receptors on somatotrophs which are suppressed by normal amounts of thyroid hormones and may provide an explanation for the TRH-stimulated GH secretion observed clinically in primary hypothyroidism.

Animals↗
PubMed1983

Inhibitory feedback effects of prolactin on its secretion involve central nervous system dopaminergic mediation.

Feedback regulation of basal and stimulated release of prolactin (Prl) was studied in primary cultures of rat pituitary cells and in adult male rats bearing right atrial catheters. Exposure of cell cultures to ovine (o) Prl, which does not crossreact in the radioimmunoassay for rat (r) Prl, did not affect rPrl release during in vitro incubations. oPrl, 4 mg/kg, injected subcutaneously into male rats 4 h previously, significantly suppressed basal rPrl levels and blunted the rPrl response to ether (2 min), cimetidine (25 mg/kg i.v.), thyrotropin-releasing hormone (40 or 400 ng i.v.), or a low dose of metoclopramide (25 micrograms/kg i.v.). At a higher dose of metoclopramide (500 micrograms/kg i.v.), no effect of oPrl could be observed. These data support the hypothesis that Prl feedback control occurs within the central nervous system rather than at the pituitary and involves predominantly, if not exclusively, a dopaminergic mechanism.

Animals↗
PubMed1983

Ectopic growth hormone-releasing factor stimulates growth hormone secretion in the urethane-anesthetized rat in vivo.

The in vivo bioactivity of ectopic growth hormone-releasing factor (GHRF) was examined in estrogen-primed, urethane-anesthetized male rats bearing intracarotid catheters. Ectopic GHRF was isolated from a carcinoid tumor metastatic to the liver from a patient with gigantism and elevated plasma growth hormone (GH) levels and was partially purified by reverse phase high performance liquid chromatography for intracarotid injection. Ectopic GHRF elicited a promt rise in plasma GH which peaked at 5 min. The time course of the response resembled that to prostaglandin E1, a known potent direct stimulator of GH secretion in vivo. The effect of ectopic GHRF was dose related in the range of 10-100 U/rat which represents approximately 30x the effective in vitro dose range/10(5) cells in rat adenohypophyseal cell cultures. The in vivo response to ectopic GHRF was completely blocked by the simultaneous intracarotid administration of the GH release inhibitory peptide, somatostatin. These findings lend further support for a role of GHRF from human tumors as a potent physiological stimulator of GH release.

Animals↗
PubMed1983

Ectopic growth hormone-releasing factor and dibutyryl cyclic adenosine monophosphate-stimulated growth hormone release in vitro: effects of corticosterone and estradiol.

Glucocorticoids and estrogens each affect GH secretion in vivo. The effects of corticosterone and estradiol (E2) were studied singly and in combination on GH secretion and cell content of primary cultures of rat adenohypophyseal cells grown in media containing intact or hormone-deficient serum. Secretion was measured under basal conditions and in response to maximally stimulatory doses of ectopic GH-releasing factor (E-GHRF) derived from a carcinoid tumor and dibutyryl cAMP [(DBcAMP) 10(-3) M]. Basal GH release measured over a 4-h period was suppressed by 40% (P less than 0.001) when hormone-deficient serum was substituted for normal serum in the growth media, and the stimulatory responses to DBcAMP and E-GHRF were markedly attenuated (P less than 0.001). The GH content of unstimulated cells was also decreased [29 +/- (SE) 7%, P less than 0.001]. The addition of corticosterone, 3 X 10(-8) M to 3 X 10(-6) M, to the 4-day growth media resulted in dose-related increases in basal and DBcAMP-stimulated GH release during the 4-h test period which was proportional to the increases in total cellular GH content. In contrast, corticosterone exposure caused a dose-related enhancement of E-GHRF-stimulated release above that accounted for by the increase in total GH content alone. Concomitant exposure to the releasing stimuli and corticosterone during a 4-h incubation, however, reduced the effects of the releasing stimuli. The addition of E2, 10(-10) M to 10(-8) M, during the 4-day growth period and/or the 4-h stimulation period did not affect the secretion of GH either basally or in response to the stimuli. E2 did increase the cell content of GH, but the effects were not additive to those of corticosterone. These studies indicate that long term (4-day) exposure to corticosterone increases net GH synthesis and E-GHRF-stimulated release, but that acute (4 h) exposure inhibits stimulated release. Although E2 also increases cellular content of GH, it exhibits no demonstrable direct effects on GH secretion or content in the presence of corticosterone.

Animals↗
PubMed1983

Somatostatin-like immunoactivity and biological activity is present in a human pheochromocytoma.

Somatostatin (SRIF)-like immunoreactivity (SRIF-LI) has previously been demonstrated immunohistochemically in sympathetic nerves and ganglia and in adrenal medullary cells. Studies were therefore performed to determine whether SRIF-LI was present in an adrenal pheochromocytoma. Acetic cid extracts of pheochromocytoma tissue contained high SRIF-LI concentrations (5.52 micrograms/g wet wt). On Sephadex G-75 gel filtration, the major peak of pheochromocytoma SRIF-LI coeluted with synthetic SRIF. SRIF-LI of a larger molecular size was also present in the tumor. Pheochromocytoma SRIF-LI coeluted with synthetic SRIF on reverse phase high pressure liquid chromatography. Pheochromocytoma SRIF-LI purified by high pressure liquid chromatography was equipotent to synthetic SRIF in inhibiting (Bu)2cAMP-stimulated GH release by rat pituitary cells in monolayer culture. Serum SRIF-LI was elevated in the patient before surgery and was restored toward normal after removal of the tumor. Serum levels of GH, TSH, and insulin were not obviously different before and after tumor removal. The results indicate that SRIF-LI is produced in excessive quantities by a pheochromocytoma. The immunological, chromatographic, and biological properties of the pheochromocytoma SRIF-LI suggest that it is indistinguishable from synthetic SRIF. This finding extends the list of peptides produced by pheochromocytoma and may provide an additional serum marker for the tumor in man.U

Adrenal Gland Neoplasms↗