Does Vibration Warm-up Enhance Kinetic and Temporal Sprint Parameters?

The aim of this study was to investigate the efficacy of vibration warm-up to enhance sprint performance. 12 males involved in representative team sports performed 4 warm-up conditions in a randomised order performed at least 24 h apart; VbX warm-up (VbX-WU); Neural activation warm-up (Neu-WU); Dynamic warm-up (Dyn-WU) and Control (No VbX). Participants completed 5 m sprint at 30 s, 2:30 min and 5 min post warm-up where sprint time, kinetics, and temporal components were recorded. There was no significant (p>0.05) main effect or interaction effect between the split sprint times of 1 m, 2.5 m, and 5 m. There was a condition effect where vertical mean force was significantly higher (p<0.05) in Dyn-WU and Control compared to Neu-WU. No other significant (p>0.05) main and interaction effects in sprint kinetic and temporal parameters existed. Overall, all 4 warm-up conditions produced comparable results for sprint performance, and there was no detrimental effect on short-duration sprint performance using VbX-WU. Therefore, VbX could be useful for adding variety to the training warm-up or be included into the main warm-up routine as a supplementary modality.

Adaptation of the growth hormone and insulin-like growth factor-I axis to chronic and severe calorie or protein malnutrition.

The hierarchy of diet components (e.g., protein, carbohydrate, vitamins, and minerals) influencing growth hormone (GH), insulin-like growth factor-I (IGF-I), and their binding proteins (BP) is not well defined. Young adult rats were fed diets for 1 mo that included low protein or 60% and 40% of carbohydrate calories. We hypothesized that levels of both hormones, their dominant BPs and liver IGF-I mRNA would fall, and that part of the mechanism for decreasing serum IGF-I would be enhanced IGFBP-3 protease activity. By day 30, caloric deprivation to 40% lowered serum GH, GHBP, IGF-I and IGFBP-3, and liver IGF-I mRNA. This was the only condition resulting in body weight loss (-15%) vs 39% gain in controls. Restriction to 60% calories had no impact on BP levels, slightly lowered IGF-I (-12%) in the face of a 95% inhibition of GH levels, while allowing a modest 9% body weight gain. Protein deprivation lowered serum GH, IGF-I and IGFBP-3, and liver IGF-I mRNA, while GHBP levels were normal. The reduced total IGF-I under these dietary conditions could not be explained by an increase in IGFBP-3 protease activity, or a decrease in the association of IGF-I with IGFBP-3 and the acid labile subunit.

Growth hormone augments superoxide anion secretion of human neutrophils by binding to the prolactin receptor.

Recombinant human growth hormone (HuGH) and human prolactin (HuPRL), but not GH of bovine or porcine origin, prime human neutrophils for enhanced superoxide anion (O2-) secretion. Since HuGH, but not GH of other species, effectively binds to the HuPRL receptor (HuPRL-R), we used a group of HuGH variants created by site-directed mutagenesis to identify the receptor on human neutrophils responsible for HuGH priming. A monoclonal antibody (MAb) directed against the HuPRL-R completely abrogated O2- secretion by neutrophils incubated with either HuGH or HuPRL, whereas a MAb to the HuGH-R had no effect. The HuGH variant K172A/F176A, which has reduced affinity for both the HuGH-binding protein (BP) and the HuPRL-BP, was unable to prime human neutrophils. This indicates that priming is initiated by a ligand-receptor interaction, the affinity of which is near that defined for receptors for PRL and GH. Another HuGH variant, K168A/E174A, which has relatively low affinity for the HuPRL-BP but slightly increased affinity for the HuGH-BP, had much reduced ability to prime neutrophils. In contrast, HuGH variant E56D/R64M, which has a similar affinity as wild-type HuGH for the HuPRL-BP but a lower affinity for the HuGH-BP, primed neutrophils as effectively as the wild-type HuGH. Finally, binding of HuGH to the HuPRL-BP but not to the HuGH-BP has been shown to be zinc dependent, and priming of neutrophils by HuGH was also responsive to zinc. Collectively, these data directly couple the binding of HuGH to the HuPRL-R with one aspect of functional activation of human target cells.

Somatotroph hyperplasia. Successful treatment of acromegaly by removal of a pancreatic islet tumor secreting a growth hormone-releasing factor.

A 21-yr-old woman with Turner's syndrome presented with signs and symptoms of acromegaly. The serum growth hormone (GH) (95+/-9.4 ng/ml; mean+/-SEM) and somatomedin C (11 U/ml) levels were elevated, and an increase in GH levels after glucose instead of normal suppression, increase after thyrotropin-releasing hormone (TRH) administration instead of no change, and decrease after dopamine administration instead of stimulation were observed. The pituitary fossa volume was greater than normal (1,440 mm(3)) and the presence of a pituitary tumor was assumed. After tissue removal at transsphenoidal surgery, histological study revealed somatotroph hyperplasia rather than a discrete adenoma. Postoperatively, she remained clinically acromegalic and continued to show increased GH and somatomedin levels. A search was made for ectopic source of a growth hormone-releasing factor (GRF). Computer tomographic scan revealed a 5-cm Diam tumor in the tail of the pancreas. Following removal of this tumor, serum GH fell from 70 to 3 ng/ml over 2 h, and remained low for the subsequent 5 mo. Serum somatomedin C levels fell from 7.2 to normal by 6 wk postoperatively. There were no longer paradoxical GH responses to glucose, TRH, and dopamine. Both the medium that held the tumor cells at surgery and extracts of the tumor contained a peptide with GRF activity. The GRF contained in the tumor extract coeluted on Sephadex G-50 chromatography with rat hypothalamic GH-releasing activity. Stimulation of GH from rat somatotrophs in vitro was achieved at the nanomolar range, using the tumor extract. The patient's course demonstrates the importance of careful interpretation of pituitary histology. Elevated serum GH and somatomedin C levels in a patient with an enlarged sella turcica and the characteristic responses seen in acromegaly to TRH, dopamine, and glucose do not occur exclusively in patients with discrete pituitary tumors and acromegaly. This condition can also occur with somatotroph hyperplasia and then revert to normal after removal of the GRF source. Thus, in patients with acromegaly a consideration of ectopic GRF secretion should be made, and therefore, careful pituitary histology is mandatory. Consideration for chest and abdominal computer tomographic scans before pituitary surgery, in spite of their low yield, may be justified.

Peripheral neuropathy in transgenic diabetic mice: restoration of C-fiber function with human recombinant nerve growth factor.

Mice (Ins.Dd1) with hypoinsulinemic diabetes were created by increased expression of syngeneic major histocompatibility complex (MHC) class I protein in pancreatic beta-cells. The diabetic state was characterized in these mice by high glucose concentrations and islet pathology. To determine whether a neuropathy would develop, motor and sensory conduction velocities (CV) were determined in the sciatic nerves of 2-, 4-, and 7-month-old control and diabetic littermate male mice. Recording bipolar electrodes were placed in the plantar muscles of the hind foot of anesthetized (ketamine/xylazine) mice. Bipolar stimulating electrodes were positioned near the sciatic nerve at the sciatic notch or near the tibial nerve at the ankle. Motor CV from alpha-motor fibers and sensory CV from proprioceptive Aalpha nerves were measured and expressed as meters per second (m/s). Group data are reported as mean +/- SE and compared by analysis of variance. The CVs from nondiabetic mice (controls) were not different across the three ages and averaged 41.3 +/- 1.7 m/s for motor and 38.7 +/- 1.7 m/s for sensory. The motor CVs from diabetic mice at 2 and 4 months were similar to controls. Sensory CVs were unchanged at 2 months but were lower at 4 months (18.9 +/- 2.4 m/s). Both sensory (23.9 +/- 2.1 m/s) and motor (18.9 +/- 1.8 m/s) CVs were significantly reduced at 7 months, which is indicative of a polyneuropathy. NGF has well-known trophic effects on sympathetic and small sensory neurons. To determine whether NGF could influence this neuropathy, 6-month-old control and diabetic mice were divided into the following groups: 1) control + vehicle, 2) diabetic + vehicle, and 3) diabetic + NGF (1 mg/kg, 3x week, s.c.). After 1 month of treatment, motor and sensory CVs were determined. In some mice, the branches of the sciatic nerve were exposed and in situ recordings from the sural nerve were performed to determine compound C-fiber CV, integral, and amplitude. Sensory CV, determined via Hoffmann's reflex (H-reflex) (A-fiber), was decreased in diabetic compared with control animals as expected (P < 0.05), and NGF did not alter this parameter. Continuing diabetes reduced the amplitude (0.9 +/- 0.2 vs. 3.2 +/- 0.7 mV x 10(-2); P < 0.05) and integral (6.9 +/- 1.9 mV/ms vs. 18.8 +/- 4.4 mV/ms; P < 0.05) of the C-fiber response versus control, suggesting fiber loss. NGF treatment normalized C-fiber amplitude (2.9 +/- 0.8 mV x 10(-2)) and integral (21.2 +/- 6.5 mV/ms) in animals with established diabetes, with no effect on blood glucose. The C-fiber CV was similar in all groups, indicating that the animals had some normally conducting small fiber sensory nerves. These studies characterized a motor and sensory polyneuropathy in transgenic diabetic mice and are the first to demonstrate directly that NGF treatment can protect or restore abnormal sensory C-fiber function.

Three-month assessment of safety and efficacy of two electric toothbrushes.

OBJECTIVE: This randomised, examiner-blind parallel group study was designed to evaluate the safety and efficacy of a rechargeable oscillating/pulsating toothbrush (Oral-B ProfessionalCare 7000, Oral-B Laboratories; PC 7000) and a battery-operated toothbrush (Crest SpinBrush Pro, Procter & Gamble Company; SBP) in the reduction of gingivitis, bleeding and plaque over a 3-month period. METHODS: After 12-18 hours of no oral hygiene, subjects had oral tissue examinations, and gingival and plaque assessments to determine eligibility in the study. Subjects were stratified and randomised into treatment groups based on initial whole mouth mean plaque (Turesky modification of Quigley Hein Plaque Index) and gingivitis (Löe & Silness Gingival Index) scores and gender. Subjects were instructed to brush twice daily with their assigned toothpaste and toothbrush. Clinical parameters were assessed at baseline, and after 1 and 3 months of use. Within treatment comparisons from baseline were analysed using t-test; between treatment comparisons were analysed using ANOVA. RESULTS: Data were obtained from 92 subjects (PC 7000 n=45; SBP n=47). No significant differences were found in baseline plaque, gingivitis and bleeding between groups. Both treatment groups had significant reductions from baseline in plaque, gingivitis and bleeding scores. PC 7000 demonstrated significantly greater reductions compared to SBP in whole mouth plaque at 1 month: 0.39 +/- 0.43 vs. 0.16 +/- 0.42 and 3 months: 0.32 +/- 0.48 vs. 0.04 +/- 0.41. PC 7000 also demonstrated significant reductions compared to SBP in gingivitis at 3 months for whole mouth: 0.14 +/- 0.09 vs. 0.10 +/- 0.10 and approximal areas: 0.11 +/- 0.08 vs. 0.08 +/- 0.09. There were no significant differences between toothbrushes in bleeding at either time point: Safety examinations revealed no apparent difference in soft and hard tissue abnormalities between groups. CONCLUSION: The PC 7000 toothbrush demonstrated significantly greater reductions in plaque and gingivitis compared to the SPB over a 3-month period.

Dopamine receptors of the monkey anterior pituitary in various endocrine states.

The anterior pituitary of adult Macaca fascicularis monkeys was removed when they were killed and the potent dopamine (DA) antagonist [3H]spiperone was used to label DA receptors. Saturation isotherms of [3H]piperone binding indicated a dissociation constant of 0.09 nM and maximal sites of 170 fmol/mg assay protein (n = 2). Competition studies validated the hypothesis that [3H]spiperone labeled DA receptors; the order of potency of 12 compounds was appropriate for a dopaminergic interaction and was similar to the order found in the anterior pituitary of other mammals. A concentration of [3H]spiperone that would label 90% of the specific binding sites (0.76 nM) was used to estimate the total DA receptor activity in the anterior pituitary of individual monkeys. [3H]spiperone binding in pregnant monkeys was greater than the binding in ovariectomized and lactating females or intact males (P less than 0.05 or 0.01). The postpartum lactating group contained more [3H]spiperone binding activity than the cycling group (P less than 0.05). Determination of the serum concentrations of PRL, estradiol, testosterone, progesterone, and dehydroepiandrosterone confirmed the predicted hormonal status of the individual monkeys at the time of sacrifice. Because DA is a PRL inhibitory hormone, it was of interest that the serum PRL concentration was positively correlated with the degree of [3H]spiperone binding (r2 = 0.74). This observation, combined with the known hypertrophy and/or hyperplasia of the mammotroph during pregnancy, supports the hypothesis that the DA receptor is associated with the PRL cell of the anterior pituitary.

Tumor necrosis factor-alpha inhibits growth hormone secretion from cultured anterior pituitary cells.

Anabolic proteins such as pituitary GH enhance the function of several immune cell types. The converse could also exist, that is communication from the immune cells to GH-producing somatotrophs. To test this hypothesis, tumor necrosis factor-alpha (TNF-alpha), a product of activated macrophages, was exposed to cultured rat pituitary cells, and GH release was monitored. TNF alpha inhibited basal and GH-releasing hormone-stimulated GH accumulation, with IC50 values of 170 U/ml (5.2 ng/ml) and 50 U/ml (1.5 ng/ml), respectively. This inhibition was first measured after 6 h of TNF alpha treatment, continued for at least 3 days, and was reversible. A number of measurements (e.g. trypan blue exclusion, chromium release, and GH cell content) yielded no signs of cytotoxicity to explain the inhibition. We conclude that TNF alpha can reduce basal and stimulated pituitary GH release in vitro.

Adenosine 3',5'-monophosphate (cAMP) and calcium-calmodulin interrelation in the control of prolactin secretion: evidence for dopamine inhibition of cAMP accumulation and prolactin release after calcium mobilization.

Calcium (Ca2+) ionophore A23187 increased the intracellular cAMP content and PRL release in normal rat anterior pituitary cells. Cotreatment with dopamine reduced both control and A23187-stimulated cAMP accumulation and PRL release. The dopamine antagonist spiperone restored the response of cAMP to ionophoric stimulation after pretreatment with dopamine in the greatest concentration used. Penfluridol, a compound with Ca2+-calmodulin-blocking properties, decreased control and A23187-stimulated cAMP content and PRL release. W7, a selective calmodulin-blocking agent, reduced basal cAMP and PRL release, whereas W5, a W7 analog with only 20% of its calmodulin-blocking ability, did not affect cAMP or PRL secretion. These data indicate that the Ca2+-calmodulin and cAMP systems are interrelated in the regulation of PRL secretion. They are also consistent with the hypothesis that the inhibition of PRL release by dopamine occurs after Ca2+ is mobilized and when or before it stimulates adenylate cyclase activity.

Decreased responsiveness of GH3 cells to the dopaminergic inhibition of prolactin.

The inhibitory regulation of PRL secretion by dopamine (DA) or the dopaminergic agonists bromergocryptine (CB-154) and apomorphine was studied in cultured GH3 cells, an established rat anterior pituitary cell line which produces both PRL and GH. The basal release of PRL from GH3 cells was unaffected when incubated for 6 h with DA concentrations as high as 10(-4) M. The inability of DA to suppress PRL secretion could not be explained by the catabolism of DA or the presence of unknown inhibitors (e.g. estradiol) in the fetal calf serum present in the incubation media. Apomorphine and CB-154 were only partially effective in suppressing PRL release at high concentrations of 10(-4) and 10(-5) M, respectively. Various concentrations of the dopaminergic antagonist d-butaclamol did not reverse the inhibitory action of 10(-5) M CB-154, while equal concentrations (10(-5) M) of both d- and l-butaclamol significantly suppressed PRL release. The greatly lowered responsiveness of GH3 cells to dopaminergic inhibition of PRL is suggestive of some impairment of DA receptors. This hypothesis is supported by radioligand binding studies in which high affinity dopaminergic binding sites are absent in the same cell line used in this study.

Absence of high affinity dopamine receptor in GH3 cells: a prolactin-secreting clone resistant to the inhibitory action of dopamine.

Dopamine (DA) and DA agonists bind with high affinity to anterior pituitary receptors which mediate the inhibition of PRL release. Spiperone (SPIP), a DA antagonist, has also been successfully used to characterize pituitary DA receptors with a dissociation constant (Kd) of less than 1 nM. We studied the binding of SPIP to GH3D6 cells which secrete only PRL and GH. This clone was derived from a radiation-induced tumor of the rat anterior pituitary. Equilibrium binding of [3H]SPIP to living GH3 cells showed no high affinity receptors, but a low affinity (Kd = 0.83 microM) and saturable (0.06 fmol/cell) population of sites was observed. In addition, saturable binding with a similar affinity (Kd = 0.57 microM) was noted in broken GH3 cells. The interaction was completely reversible and temperature dependent. The concentration of various ligands required to compete for half of the [3H]SPIP binding to whole cells were: chlorpromazine, 0.17 microM; haloperidol, 0.68 microM; pimozide, 0.77 microM; d-butaclamol, 1.16 microM; 1-butaclamol, 1.30 microM; SPIP, 1.49 microM; bromergocryptine, 4.98 microM; apomorphine, 13.9 microM; and DA, 100 microM. The absence of a high affinity site in GH3 cells is consistent with the decreased effectiveness of various agonists and antagonists on PRL secretion. It is possible that the low affinity interactions observed in GH3 cells are normally present in the anterior pituitary and brain and do not simply represent an alteration of receptor affinity.

Relaxin stimulates prolactin secretion from anterior pituitary cells.

The anterior pituitary has recently been implicated as a relaxin target issue because of the cAMP elevation after relaxin treatment. We attempted to correlate this finding with an endocrine response to relaxin in rats. Anterior pituitary cells were enzymatically dispersed and subjected to the reverse hemolytic plaque assay. PRL secretion was significantly stimulated 1.31-fold by human relaxin at the lowest concentration studied (30 pM) and maximally stimulated 1.65-fold at 0.3 nM relaxin. Antibodies directed against relaxin inhibited this effect, as did the PRL inhibitory hormone, dopamine. In contrast to the response of PRL cells, there was no effect or a slight inhibition of LH release after incubation with relaxin. In conclusion, we propose that one of the pituitary cell types responsive to relaxin in culture is the PRL-secreting mammotroph.

Properties of beta-adrenergic receptors on porcine corpora lutea and granulosa cells.

The nature of beta-adrenergic binding by swine corpora lutea and granulosa cells was examined with the specific beta-adrenergic radioligand, (+/-)3-[125I]iodocyanopindolol (ICYP). Saturation analyses revealed the presence of high affinity (Kd = 15.2 +/- 2.1 pM; n = 8 experiments) and low capacity (6.7 +/- 0.8 fmol/mg protein) beta-adrenergic receptors on porcine corpora lutea membranes. The properties of beta-adrenergic binding were determined by computer modeling of competition studies with a variety of compounds selective for beta-adrenergic subtypes. These studies disclosed predominantly beta 1-adrenergic receptors on pig luteal membranes. This inference from radioligand binding studies was corroborated functionally by the approximately equipotent biological effects of L-norepinephrine and L-epinephrine on cAMP production by luteal tissue (respective EC50s of 282 +/- 31 and 187 +/- 66 nM; n = 3 experiments). Physiological regulation of specific beta-adrenergic receptor content in the swine ovary was indicated by prominent (up to 9-fold) variations in receptor concentrations among corpora lutea and granulosa cells at various stages of maturity. In addition, there was differential expression of beta-adrenergic receptor subtype. Whereas the beta-adrenergic receptor subtype was predominantly beta 1 in corpora hemorrhagica and corpora lutea, granulosa cells and corpora albicantia contained principally beta 2 receptors. This difference could not be accounted for by blood cell contamination of corpora lutea, since swine blood cells contained predominantly (greater than 98%) beta 2-receptors, which were present at less than 8.6% the concentration of total beta-receptors in luteal tissue. In summary, swine corpora lutea and granulosa cells contain specific high affinity, low capacity beta-adrenergic receptors that are functionally coupled to biological responses. Moreover, total receptor content as well as beta-adrenergic subtype exhibit significant physiological variation in relation to maturational status of ovarian follicular and luteal tissue.

Human pancreatic tumor growth hormone (GH) - releasing factor and cyclic adenosine 3',5'- monophosphate evoke GH release from anterior pituitary cells: the effects of pertussis toxin, cholera toxin, forskolin, and cycloheximide.

Both synthetic human pancreatic tumor GH-releasing factor (hpGRF) and prostaglandin E2 (PGE2) rapidly stimulate cellular cAMP accumulation in and GH release from primary cultures of rat anterior pituitary cells. SRIF inhibits both of these actins. A 1-h treatment with the protein synthesis inhibitor cycloheximide potentiates hpGRF-induced cAMP accumulation for hours and GH release for the first hour. This indicates that a rapidly turning over protein tonically mutes the degree of hpGRF-stimulated cAMP accumulation. Pretreatment of the cells with pertussis toxin amplifies hpGRF- and PGE2-stimulated cAMP levels and GH release; pertussis toxin also attenuates the ability of SRIF to affect these variables. This suggests that an inhibitory coupling protein contributes to these events. Finally, cholera toxin and forskolin are also potent stimulators of cAMP accumulation and GH release. We conclude that hpGRF-evoked GH release and the inhibitory action of SRIF are closely correlated with the cAMP-generating system.

Human pancreatic tumor growth hormone-releasing factor stimulates anterior pituitary adenylate cyclase activity, adenosine 3',5'-monophosphate accumulation, and growth hormone release in a calmodulin-dependent manner.

Pituitary GH secretion is regulated by Ca+2 and cAMP. We show that human pancreatic tumor GRF (hpGRF) stimulates anterior pituitary adenylate cyclase activity, cAMP accumulation, and GH release. The relationship between Ca+2 and the stimulating effects of the Ca+2 ionophore A23187 on cAMP accumulation and GH release in vitro was studied. To evaluate the role of the Ca+2-binding protein calmodulin in this system, we used the calmodulin antagonist W7, a naphthalene-sulfonamide derivative, and its less active analog W5. W7 inhibited hpGRF-stimulated adenylate cyclase activity, cAMP accumulation, and GH release, whereas W5 was either poorly effective or ineffective. Somatostatin (SRIF) also attenuated hpGRF stimulation of adenylate cyclase. These results suggest that the actions of Ca+2-calmodulin and cAMP are interrelated in modulating GH release. Calmodulin participates in hpGRF stimulation of adenylate cyclase, cAMP formation, and GH release. The attenuation of hpGRF-stimulated adenylate cyclase activity by SRIF may be one of the mechanisms for its GH inhibitory action.

"Antigonadal" activity of the neurohypophysial hormones in cultured rat testicular cells: abolition by pertussis toxin.

The intermediary role of the putative inhibitory regulatory membrane protein "Ni" in the "antigonadal" activity of the neurohypophysial hormones was investigated in vitro with the use of a primary culture of rat testicular cells. To this end, use was made of the pertussis toxin (PT) probe, an exotoxin of Bordetella pertussis presumed to modify and inactivate a membrane protein related to or identical with Ni. Testicular cells were pretreated with PT (70 ng/ml) for 24 h, a duration of exposure known to result in a maximal PT effect. Thereafter, the cells were cultured for an additional 48 h in the absence or presence of hCG (10 ng/ml), with or without a maximal inhibitory dose (10(-6) M) of the neurohypophysial principle arginine vasotocin (AVT). Although concomitant treatment of control cells with AVT produced a profound (95%) inhibition of hCG-stimulated testosterone accumulation, PT pretreatment resulted in a long-lasting (greater than 4 days) abolition of this "antigonadal" effect. Furthermore, pretreatment with PT resulted in significant (P less than 0.05) augmentation of the hCG-stimulated accumulation of extracellular cAMP (1.5- to 2.0-fold) and testosterone (1.7- to 3.8-fold), presumably as a result of abolition of the "basal" tonic inhibition of adenylate cyclase activity. Taken together, these findings constitute the first demonstration of the involvement of Ni in the "antigonadal" activity of the neurohypophysial hormones and in the regulation of testicular function, thereby raising the intriguing possibility that testicular Ni may serve as the coupling unit of inhibitory receptors other than those for the neurohypophysial hormones, integrating varied incoming signals of endocrine, paracrine or autocrine nature.

Beta-adrenergic binding and secretory responses of the anterior pituitary.

Our studies demonstrated that beta-adrenergic agonists stimulate the release of GH from rat anterior pituitary (AP) cells in vitro. Concentration-response experiments with beta-adrenergic agonists demonstrated that beta 2-adrenergic receptors mediated this phasic GH release, while having no apparent effect on PRL or LH release. The ACTH response to beta-adrenergic agonists was equivocal. Half-maximal stimulation of GH release occurred at 14 +/- 2 (+/-SE) nM isoproterenol, 160 +/- 30 nM epinephrine, and over 1 microM l-norepinephrine (n = 4). Direct binding studies in membrane particulates of rat AP confirmed receptors of the beta 2-subtype. Iodocyanopindolol binding to beta-adrenergic receptors of rat AP yielded a dissociation constant of 4.6 +/- 0.1 pM and a maximal capacity of 1.9 +/- 0.4 fmol/mg protein (n = 3). In contrast, porcine AP contained beta 1-adrenergic receptors. These results support the hypothesis that the endogenous beta 2-adrenergic agonist l-epinephrine may be a GH-releasing factor of physiological significance in the rat.

Pertussis toxin blocks the somatostatin-induced inhibition of growth hormone release and adenosine 3',5'-monophosphate accumulation.

A protein toxin synthesized by the bacterium Bordetella pertussis has the unique property of blocking a number of receptor-mediated inhibitory systems which are linked to adenylate cyclase. We found that pertussis toxin (PT) eliminates the ability of somatostatin to reduce both basal and GH-releasing factor-stimulated GH release in primary cultures of rat pituitary cells. Furthermore, the ability of somatostatin to reduce GH-releasing factor-induced cAMP accumulation in the cells is significantly attenuated after PT treatment. The PT effect, which is dose dependent and prevented by pretreatment with anti-PT antibodies, represents an alteration in somatostatin efficacy rather than potency. The modification of somatostatin responsiveness persists for at least 5 days after toxin removal. The PT actions on the somatotroph are similar to the effects on other eukaryotic cell types. The combination of available data indicates that the toxin acts on a highly conserved component(s) that is obligatory for transducing the inhibitory hormone message into the cell.

Growth hormone stimulates the formation of sn-1,2-diacylglycerol in rat hepatocytes.

The transmembrane signaling events of GH were investigated in the liver, a major target organ of GH action. Recombinant human GH when added to freshly isolated rat hepatocytes rapidly stimulated the production of sn-1,2-diacylglycerol (DAG). The generation of DAG was biphasic with the first transient peak observed at 2 min and the second peak at 15 min (1.2-fold and 1.4-fold over control, respectively). Levels of DAG continued to be elevated above those in control cells at 30 min. The response was dose-dependent with an EC50 of 0.15 nM. Both bovine GH and rat GH, which bind to the rat GH receptor but not to the PRL receptor, also stimulated DAG production. Similarly, human PRL, which binds to the PRL but not GH receptor, stimulated DAG formation to a comparable extent. These results suggest that production of DAG may be an early signaling event mediated by hormone stimulation of both the GH and PRL receptors.

Beta-adrenergic stimulation of growth hormone (GH) release in vivo, and subsequent inhibition of GH-releasing factor-induced GH secretion.

In vivo and in vitro studies of beta-adrenergic influences on GH secretion have produced apparently conflicting data in which the in vivo effect seems to be inhibitory and the in vitro effect to be stimulatory. The present studies were designed to observe the in vivo effect of isoproterenol (ISO), a beta-adrenergic agonist, on 1) GH release during a brief interval after intraatrial infusion, and 2) GH release in response to GRF infused 10 min after ISO. ISO was found to stimulate GH release in both intact and hypothalamus-lesioned animals within 2 min after infusion, but GH returned to control levels within 10 min. ISO also profoundly inhibited the release of GH in response to GRF. Pretreatment of animals with somatostatin (SRIF) antiserum prevented the inhibitory action of ISO on GRF-induced GH release. No change in peripheral levels of SRIF was detected. Also, there was no suppression of GRF-induced GH release by ISO when the treatments were applied in vitro to dispersed perifused pituitary cells. These data show that beta-adrenergic systems can stimulate a rapid but brief release of GH in vivo, and that the subsequent inhibitory action on GRF-induced GH release might be by means of SRIF release.