DNA regulatory sequences of the rat tyrosine hydroxylase gene direct correct catecholaminergic cell-type specificity of a human growth hormone reporter in the CNS of transgenic mice causing a dwarf phenotype

Transgenic mice bearing 4.8 kilobases (kb) of upstream rat tyrosine hydroxylase (TH) sequences linked to a human growth hormone gene (hGH) exhibited cell-specific expression of hGH in all the appropriate catecholaminergic neurons in the central nervous system (CNS), although with different penetrance in two different mouse lineages. No ectopic expression was observed in any brain or peripheral region in one founder and its progeny. In another founder there was some ectopic expression in addition to appropriate and high levels of tissue-specific expression in all catecholaminergic areas. These results identify regulatory sequences that are sufficient for targeting expression to all catecholaminergic CNS neurons. Also, expression of exogenous hGH in the hypothalamus caused a dwarf phenotype, generating a novel genetic model for GH deficiency of hypothalamic origin.

The effect of isobutylmethylxanthine, forskolin, and cholera toxin on growth hormone release from pituitary cell cultures of perinatal and mature rats

The factors that regulate growth hormone (GH) release during the perinatal period are not well understood. Circulating GH levels are markedly elevated in mammalian fetuses and newborns compared with mature animals, and the immature pituitary is highly responsive to the GH-stimulatory effect of GH-releasing factor (GHRF). The etiology of these developmental changes in GH secretion is not known. In order to investigate the mechanisms underlying GH release from immature pituitaries, we tested the effects of agents that increase intracellular cyclic adenosine 3',5' monophosphate (cAMP) production independent of the GHRF receptor on GH release from pituitaries of developing and mature rats. Pituitary cell cultures from fetal (day 20 of gestation), newborn (postnatal day 2), juvenile (postnatal day 12-15), adult male (3-4 months), and adult female (3-4 months) rats were tested with isobutylmethylxanthine (IBMX; 0.001-1.0 mM), forskolin (0.01-10 microM), and cholera toxin (0.025-25 ng/ml). IBMX, forskolin, and cholera toxin stimulated GH release in a dose-dependent manner from pituitary cultures of all age groups. However, the magnitude of the GH responses to these agents was highly age-dependent. Perinatal pituitaries exhibited markedly greater GH responses to IBMX, forskolin, and cholera toxin than did those of mature animals (P < 0.001 for age effect with each agent). GH release in response to the highest dose of IBMX (1 mM) was 301 +/- 8, 389 +/- 37, 296 +/- 33, 198 +/- 14, and 187 +/- 19% of control values from pituitary cell cultures of fetal, newborn, juvenile, adult male, and adult female rats, respectively (P < 0.001). In response to the highest dose of forskolin (10 microM) GH release was 537 +/- 46, 601 +/- 75, 274 +/- 22, 270 +/- 37, and 248 +/- 35% of control values in the same respective age groups (P < 0.001). Similarly, the highest dose of cholera toxin (25 ng/ml) stimulated GH release to 407 +/- 55, 365 +/- 43, 249 +/- 26, 186 +/- 11, and 186 +/- 1% of controls in these respective age groups (P < 0.003). The marked stimulation of GH release from perinatal pituitaries by IBMX, forskolin, and cholera toxin is consistent with the concept that cAMP is a potent mediator of GH release from immature as well as mature somatotrophs. The developmental changes in the GH secretory response to these agents further suggest that signal transduction pathways mediating GH release may undergo maturation, at least in part, at intrasomatotroph loci distal to the GHRF receptor.

PCR amplification of DNA sequences from nitrocellulose-bound, immunostained bacterial colonies

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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.

Inhibition of tumor induction in tobacco by Agrobacterium tumefaciens and nodulation induced by Rhizobium meliloti in the presence of phenothiazines and structurally related compounds

Plasmids of Agrobacterium tumefaciens and Rhizobium meliloti carrying Kanamycin resistance genes were eliminated from 1.4 to 0.2% of the growing bacterial cultures by promethazine and imipramine. As a result of plasmid elimination, the A. tumefaciens plasmidless isolate was not able to induce crown gall tumor on tobacco plants. The plasmidless R. meliloti strain failed to induce nodule formation on alfalfa plants. The efficiency of nodulation was decreased when the bacteria were grown in the presence of the drugs. The antiplasmid effects of the drugs were not prevented by opines, (nopaline and octopine) in Escherichia coli F'lac cells.

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.

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)

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.

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.

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)

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)

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.

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.

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.

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.

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.

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.

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

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.

The in-vitro caffeine contracture test: influence of the muscle histochemical profile on test results

In vitro caffeine contracture tests were carried out on whole rat muscle composed primarily of either histochemical type I or type II fibers. Muscles composed primarily of type I fibers developed contractures at lower concentrations of caffeine and had lower caffeine specific concentrations than muscles composed primarily of type II fibers. These findings indicate that the histochemical profile of a muscle can influence the results of the in-vitro caffeine contracture test.

Somatomedin-C mediates growth hormone negative feedback by effects on both the hypothalamus and the pituitary

Somatomedin-C stimulates somatostatin release to a maximum of 390 percent of basal release during short-term (20-minute) incubation of rat hypothalamus. It has no effect on basal or stimulated growth hormone release from primary cultures of rat adenohypophyseal cells during a 4-hour incubation, but inhibits stimulated release by more that 90 percent after 24 hours. These findings suggest that somatomedin-C participates in the growth hormone negative feedback loop with an immediate effect on hypothalamic somatostatin and a delayed effect on the anterior pituitary.

Ectopic production of somatostatin-like immuno- and bioactivity by cultured human pulmonary small cell carcinoma

Eleven continuous cultures of human pulmonary small cell carcinoma cells were examined, and eight were shown to secrete quantities of somatostatin-like immunoreactivity (SRIF-LI) ranging from 0.07-27 ng/ml culture medium/4 days, SRIF-LI was also found in a 2-N acetic acid extract of one of three human pulmonary small cell carcinomas obtained at autopsy as well as in the extract of a solid tumor resulting from inoculation of nude, athymic mice with SRIF-LI-producing, cultured small cell carcinoma cells. The SRIF-LI produced by one continuous cell line, DMS 53, was characterized in terms of its immunological, chromatographic, and biological properties. SRIF-LI from DMS 53 culture media and lysed cells was heat stable and exhibited parallel displacement to synthetic SRIF standard in a double antibody RIA. DMS 53 SRIF-LI was quantitatively retained on an immunoaffinity column of sheep anti-SRIF-Sepharose 4B under neutral conditions and could be eluted with 2 N acetic acid. Gel filtration chromatography of immunoaffinity-purified SRIF-LI revealed multiple molecular weight forms, the largest of which had an apparent molecular weight of 10,000-12,000 daltons and may represent a precursor form. This high molecular weight SRIF-LI form was resistant to exposure to denaturing conditions (8 M urea or 4 M urea plus 0.5% mercaptoethanol), suggesting the absence of noncovalent and/or disulfide linkages. A low molecular weight form coeluted with synthetic SRIF. Additional evidence for the identity of this form with the tetradecapeptide was provided by highly specific reverse phase high performance liquid chromatography. The rate of degradation of high molecular weight SRIF-LI by the cultures was markedly reduced in comparison to that of the SRIF monomer, resulting in a preferential accumulation of high molecular weight SRIF-LI in 4-day culture medium. Bioactivity of DMS 53 SRIF-LI was assessed in 4-day primary monolayer cultures of rat adenohypophyseal cells where 10(-10)-10(-9) M synthetic SRIF elicited a linear log-dose suppression of 5 X 10(-4) M synthetic SRIF elicited a linear log-dose suppression of 5 X 10(-4) M dibutyryl cAMP-stimulated rat GH release. Immunoaffinity-purified SRIF-LI from DMS 53 lysed cells and 1-h serum-free incubation medium, which consisted predominantly of monomeric SRIF, was equipotent to synthetic SRIF, SRIF-LI from 4-day culture medium consisted mostly of the high molecular weight form and exhibited a reduced bioassay potency ratio relative to synthetic SRIF of 0.73 (95% confidence limits, 0.99-0.53). Chromatographically purified high molecular weight SRIF-LI had significant bioactivity with a bioassay to immunoassay ratio of 0.19 (95% confidence limits, 0.33-0.09). The demonstration of ectopic SRIF, production by human pulmonary small cell carcinoma is consistent with the proposed derivation of this tumor from a cell type in the amine precursor uptake and decarboxylation cell series.

Somatostatin-like immunoreactivity in transplantable medullary carcinoma of rat thyroid: partial chromatographic and biological characterization

Somatostatin-like immunoreactivity (SRIF-LI) has previously been demonstrated immunohistochemically in rat thyroid parafollicular cells. Studies were therefore performed to determine whether SRIF-LI was present in a transplantable medullary carcinoma of the thyroid (MCT) in the WAG/Rij strain of rat. SRIF-LI was found in MCT in significantly higher concentrations than in normal thyroid tissue. Thyroid and MCT SRIF-LI showed parallelism with the synthetic SRIF and RIA displacement curves and coeluted with synthetic SRIF on immunoaffinity chromatography. On gel filtration, thyroid SRIF-LI and the major peak of MCT SRIF-LI coeluted with synthetic SRIF. SRIF-LI of a larger molecular size was also present in the MCT. MCT and thyroid SRIF-LI coeluted with synthetic SRIF on high pressure liquid chromatography. MCT SRIF-LI purified by affinity chromatography was equipotent to synthetic SRIF in inhibiting dibutyryl cAMP-stimulated GH release by rat pituitary cells in monolayer culture. Serum SRIF-LI was elevated in tumor-bearing rats and showed characteristics similar to those of MCT SRIF-LI and synthetic SRIF on affinity and high pressure liquid chromatography (HPLC). Tumor-bearing rats showed diminished secretion of insulin after orally administered glucose and impaired secretion of GH in response to pentobarbital compared to normal control rats. The results indicate that SRIF-LI is produced in excessive quantities by a transplantable rat MCT and impairs the secretion of GH and insulin. The immunological, chromatographic, and biological properties of MCT SRIF-LI suggest that it is indistinguishable from synthetic SRIF.

Partial purification and characterization of a peptide with growth hormone-releasing activity from extrapituitary tumors in patients with acromegaly

Growth hormone (GH)-releasing activity has been detected in extracts of carcinoid and pancreatic islet tumors from three patients with GH-secreting pituitary tumors and acromegaly. Bioactivity was demonstrated in 2 N acetic acid extracts of the tumors using dispersed rat adenohypophyseal cells in primary monolayer culture and a rat anterior pituitary perifusion system. The GH-releasing effect was dose responsive and the greatest activity was present in the pancreatic islet tumor. Small amounts of activity were also found in two other tumors (carcinoid and small cell carcinoma of lung) unassociated with GH hypersecretion. Each of the tumors contained somatostatin-like immunoreactivity but the levels did not correlate with the net biologic expression of the tumor. Sephadex G-75 gel filtration indicated the GH-releasing activity to have an apparent molecular size of slightly greater than 6,000 daltons. The GH-releasing activity was adsorbed onto DEAE-cellulose at neutral pH and low ionic strength, from which it could be eluted by increasing ionic strength. The GH-releasing activity was further purified by high pressure liquid chromatography using an acetonitrile gradient on a cyanopropyl column to yield a preparation that was active at 40 ng protein/ml. Partially purified GH-releasing activity, from which most of the bioactive somatostatin had been removed, increased GH release by pituitary monolayer cultures to five times base line. Enzymatic hydrolysis studies revealed that the GH-releasing activity was resistant to carboxypeptidase, leucine-aminopeptidase, and pyroglutamate-amino-peptidase but was destroyed by trypsin and chymotrypsin, indicating that internal lysine and/or arginine and aromatic amino acid residues are required for biologic activity and that the NH2-terminus and CO9H-terminus are either blocked or not essential. The results provide an explanation for the presence of GH-secreting tumors in some patients with the multiple endocrine neoplasia syndrome, type I, and warrant the addition of GH-releasing activity to the growing list of hormones secreted by tumors of amine precursor uptake and decarboxylation cell types.

Acromegaly associated with a bronchial carcinoid tumor: evidence for ectopic production of growth hormone-releasing activity

A patient with acromegaly, pituitary enlargement, and elevated plasma GH levels also had a bronchial carcinoid tumor. Signs and symptoms of active acromegaly along with elevated GH levels persisted for 11 yr after hypophysectomy and pituitary stalk section. Resection of the bronchial carcinoid reduced plasma GH to barely detectable levels. Extracts of the frozen carcinoid tumor were devoid of significant GH, but when added to isolated pituitary cells of estrogen-primed male rats in 4-day primary culture exhibited specific GH-releasing activity in vitro. These findings strongly suggest that the patient's acromegaly resulted from continual stimulation of pituitary somatotrophs by a GH-releasing factor secreted by the bronchial carcinoid.

Dissociation of prolactin-releasing activity from thyrotropin-releasing hormone in porcine stalk median eminence

The prolactin (PRL)-releasing activity of porcine stalk median eminence (pSME) was characterized by an in vivo bioassay and concomitant radioi-munoassay of plasma PRL and thyrotropin (TSH) levels. Methanol extracts of pSME stimulated PRL release in 3-day estrogen-primed rats when administered by the intracarotid route in doses ranging from 0.1 to 2.0 pSME equivalents. Synthetic thyrotropin-releasing hormone (TRH) stimulated the release of PRL and TSH in the dose range of 10 to 300 ng. PRL release was greater in response to a maximally effective dose of pSME than the release elicited by a maximal dose of TRH, and pSME administered together with a greater than mazimally effective dose of TRH caused additional PRL but not TSH secretion. Lysine vasopressin and prostaglandin E1 and E2 stimulated PRL release only at doses several orders of magnitude greater than the dose present in pSME. Somatostatin inhibited the release of TSH but not that of PRL whether the stimulus employed was pSME or TRH. The effective inhibitory dose of somatostatin was also significantly greater than the reported hypothalamic content. When pSME was subjected to incubation with plasma, a treatment reported to inactivate TRH, TSH-releasing activity was destroyed to a greater extent than was PRL-releasing activity. When pSME was adsorbed onto charcoal, the supernatant solution was devoid of TRH, as determined by complete removal of a [3H]TRH marker, yet substantial PRL-releasing activity was retained. TSH-releasing activity eluted from the charcoal with methanol was considerably greater than that expected on the basis of the recovery of [3H]TRH, suggesting the presence in the crude extract of a TSH-release inhibitor or of a TSH-releasing factor other than TRH. Based on the above evidence, we conclude that crude pSME contains PRL-releasing substance(s) distinct from the tripeptide TRH.

Big growth hormone (GH): conversion to small GH without peptide bond cleavage

Mercaptoethanol treatment of big growth hormone (GH) obtained from human pituitary resulted in a 60% conversion to small GH. Further dissociation was obtained by combined treatment with the reducing agent plus urea. The results indicate that the existence of big GH is dependent upon the formation of inter-polypeptide chain disulfide bonds.

Effects of porcine stalk median eminence and prostaglandin E2 on rat growth hormone secretion in vivo and their inhibition by somatostatin

The studies described were performed to develop a technically simple, yet sensitive in vivo model for growth hormone (GH) releasing activity in porcine stalk median eminence (pSME) extracts, to compare the GH releasing effects of pSME with those of prostaglandin E2 (PGE2), and to study the effect of somatostatin (SRIF) on the above stimuli. The use of the one day estrogen-primed male rat in conjunction with intracarotid injection of test materials provided a model sensitive to the injection of one pSME. Neither increasing the duration of estrogen pre-treatment nor reserpine resulted in a greater response. The GH releasing effects of pSME were directly related to the preinjection GH level. Two successive injections of pSME at 30 minute intervals evoked similar responses. In contrast, PGE2 effects were not potentiated by estrogen pre-treatment and were independent of the preinjection GH level. The GH releasing effect of pSME was not related to its content of TRH or K+. Extracts of porcine cerebral cortex also contained GH releasing activity, although at a lower concentration than in pSME. Somatostatin inhibited the GH releasing effects of pSME, PGE2, and cerebral cortex extract. These results provide evidence for the direct inhibitory effect of SRIF on GH secretion in vivo and suggest that SRIF is capable of blocking a variety of different stimuli to GH release.

Thyrotropin and cyclic nucleotide effects on prostaglandin levels in isolated thyroid cells

Thyrotropin increases prostaglandin levels in isolated thyroid cells. Since comparable results were obtained with butyrated cyclic adenosine monophosphate derivatives as well as with the phosphodiesterase inhibitors quazodine and theophylline, it appears that cyclic adenosine monophosphate mediates this effect of thyrotropin. These observations suggest that intracellular prostaglandins play a role in modulating thyrotropin action on thyroid.

Sensitivity in electron microscope autoradiography. I. The effect of radiation dose

Sensitivity in electron microscope autoradiography using Ilford L4 emulsion was shown to be affected by radiation dose ( i.e., number of decays in test specimen per unit surface area). The sensitivity tended to be higher with lower doses. This dose dependence was most marked with Microdol X and least with gold latensification-Elon ascorbic acid development. Possible consequences for quantitation in electron microscope autoradiography are discussed.