Growth hormone and insulin-like growth factor-I: effects on the growth of glioma cell lines.

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) are known to be mitogens for many types of neoplasms. To investigate their role in tumors of glial origin, in vitro and in vivo experiments were performed with a panel of immortalized glioma cell lines (D54, SNB-19, U87, U251 and U373). Initial analysis for mRNA expression demonstrated the following: GH receptor (5/5 cell lines positive), IGF-I (0/5), IGF-II (0/5), IGF-I receptor (5/5), IGF-II receptor (2/5). Thus, each cell line expressed the necessary receptors to respond to GH and the IGFs but there was no autocrine IGF production by the tumors themselves. IGF-I stimulated mitogenesis as measured by [(3)H]thymidine uptake experiments in U251 and U373 cells. However, when these two IGF-responsive cell lines were xenografted into mice, tumor development and growth rates were not significantly different in GH-deficient animals (despite having IGF-I serum concentrations only 31% of normal). Because our studies were performed in immunocompromised animals, GH or IGF effects on immune surveillance, known to be important from some syngeneic glioma models, would not be likely to contribute to our findings. Nevertheless, these studies are important because they demonstrate that the growth of glioma cell lines in an in vivo environment can remain robust in a GH/IGF-I-deficient setting, even if in vitro experiments indicate that IGF-I is mitogenic.

Corticosteroid-induced inhibition of adrenal androgen production in selected patients with prostate cancer.

OBJECTIVE: To determine the effect of administration of corticosteroids on adrenal androgen production and the serologic markers of prostate cancer. METHODS: Six patients with prostate cancer who had a serum testosterone concentration that exceeded 20 ng/dL despite treatment with medical or surgical castration were treated with dexamethasone. All patients were asymptomatic, but four were demonstrating progressive increases in serum prostate-specific antigen (PSA) concentrations. Dexamethasone, 1 mg at bedtime, was given initially and then increased to 1 mg twice daily if serum testosterone concentrations remained > or =10 ng/dL. The effect of treatment on PSA concentration was monitored. RESULTS: The mean testosterone concentration (and standard error of the mean) was 47.5 +/- 7.9 ng/dL before administration of dexamethasone; this decreased to 5.2 +/- 3.0 ng/dL during therapy (P = 0.002). The effect was rapid (overnight) and sustainable (for 6 months). Although the duration of follow-up is limited, PSA concentrations generally stabilized (23.5 +/- 6.1 ng/mL at baseline in comparison with 15.6 +/- 1.1 ng/mL approximately 2 months after initiation of dexamethasone therapy; P = 0.24). Two patients required 1 mg of dexamethasone twice daily to suppress serum testosterone levels to <10 ng/dL. CONCLUSION: Administration of corticosteroids in a manner opposing the normal circadian glucocorticoid production effectively and rapidly decreases adrenal androgen production in patients with prostate cancer treated with orchiectomy or luteinizing hormone-releasing hormone agonists. This reduction of androgen production was generally associated with a decrease or stabilization of PSA concentrations in all patients with increased PSA levels. Overnight dexamethasone suppression testing is useful in determining the minimal effective dose.

Coadministration of intrathecal strychnine and bicuculline effects synergistic allodynia in the rat: an isobolographic analysis.

Tactile allodynia can be modeled in experimental animals by acutely blocking spinal glycine or GABA(A) receptors with intrathecal (i.t.) strychnine (STR) or bicuculline (BIC), respectively. To test the hypothesis that glycine and GABA effect cooperative (supra-additive) inhibition of touch-evoked responses in the spinal cord, male Sprague-Dawley rats, fitted with chronic i.t. catheters, were used. Following i.t. STR, BIC, or STR + BIC, hair deflection evoked cardiovascular (increased blood pressure and heart rate), motor (scratching, kicking and rippling of the affected dermatomes), and cortical encephalographic responses. Hair deflection was without effect in i.t. saline-treated rats. Isobolographic analysis of STR (ED(50) = 25.1-36.9 microg), BIC (ED(50) = 0.5-0.6 microg), and BIC:STR combination (ED(50) = 0.026-0.034:2.6-3.4 microg) dose-response curves confirmed a supra-additive interaction between BIC and STR in this model. BIC-allodynia was reproduced by i.t. picrotoxin. Pretreatment with i.t. scopolamine, or i.t. muscarine had no effect. STR-allodynia was dose dependently inhibited by i.t. muscimol but not baclofen. The results of this study indicate that 1) glycine and GABA effect cooperative inhibition of low-threshold mechanical input in the spinal cord of the rat; and 2) BIC-allodynia arises from the blockade of GABA(A) receptors and is unrelated to any secondary anticholinesterase activity. The allodynic state induced by the blockade of glycine or GABA receptors is clearly exacerbated by the removal of both inhibitory systems. Their combined loss after neural injury may explain the exaggerated sensitivity to and subsequent miscoding of tactile information as pain.

The effects of insulin-like growth factors on tumorigenesis and neoplastic growth.

Several decades of basic and clinical research have demonstrated that there is an association between the insulin-like growth factors (IGFs) and neoplasia. We begin with a brief discussion of the function and regulation of expression of the IGFs, their receptors and the IGF-binding proteins (IGFBPs). A number of investigational interventional strategies targeting the GH or IGFs are then reviewed. Finally, we have assembled the available scientific knowledge about this relationship for each of the major tumor types. The tumors have been grouped together by organ system and for each of the major tumors, various key elements of the relationship between IGFs and tumor growth are discussed. Specifically these include the presence or absence of autocrine IGF-I and IGF-II production; presence or absence of IGF-I and IGF-II receptor expression; the expression and functions of the IGFBPs; in vitro and in vivo experiments involving therapeutic interventions; and available results from clinical trials evaluating the effect of GH/IGF axis down-regulation in various malignancies.

Inhibition of strychnine-allodynia is mediated by spinal adenosine A1- but not A2-receptors in the rat.

Intrathecal (i.t.) strychnine produces localized allodynia in the rat without peripheral or central nerve injury. Intrathecal CPA (A1-selective agonist) and CGS-21680 (A2-selective agonist) dose-dependently inhibited strychnine-allodynia but with a 50-fold difference in potency (0.02-0.07 vs. 2.7-3.1 microgram, respectively). The anti-allodynic effect of CPA and CGS was completely blocked by pretreatment with the A1-selective antagonist, DPCPX (10 microgram i.t. ), but unaffected by the A2-selective antagonist, CSC (2 microgram i.t. ). The results indicate that spinal A1-, but not A2-, receptors modulate abnormal somatosensory input in the strychnine model, and suggest a difference in spinal purinergic modulation in injury vs. non-injury models of allodynia.

Comparable dose-dependent inhibition of AP-7 sensitive strychnine-induced allodynia and paw pinch-induced nociception by mexiletine in the rat.

The blockade of spinal glycine receptors with intrathecal (i.t.) strychnine produces segmentally-localized allodynia in the rat; a reversible and highly reproducible effect that is attained without peripheral or central nerve injury. We investigated the effect of i.v. mexiletine, an orally active congener of lidocaine, on strychnine allodynia and compared the dose-response relationship of mexiletine in normal (noxious paw pinch) versus abnormal (i.t. strychnine) nociceptive conditions. In addition, we determined the dose-response effect of i.t. AP-7 (an NMDA antagonist) on strychnine allodynia. Male, Sprague-Dawley rats, fitted with chronic i.t. catheters, were lightly anesthetized with urethane. Stimulus evoked changes in blood pressure and heart rate were recorded from the left carotid artery and cortical electroence-phalographic (EEG) activity was continuously monitored using subdermal needle electrodes. After i.t. strychnine (40 micrograms), repetitive brushing of the hair (hair deflection) evoked a progressive increase in mean arterial pressure and heart rate, an abrupt motor withdrawal response, and desynchronization of the EEG, equivalent to those elicited by the chemical nociceptive agent, mustard oil (without strychnine). Pretreatment with mexiletine (5-30 mg/kg i.v. 5 min before i.t. strychnine) dose-dependently inhibited the responses evoked by noxious hind paw pinch (no strychnine) and hair deflection (after i.t. strychnine) with equal potency (ED50's = 9.1-17 mg/kg). Below 30 mg/kg, this effect was achieved without a change in EEG synchrony (cortical activity reflecting the level of anesthesia) and without affecting motor efferent pathways. Strychnine allodynia was also significantly blocked by i.t. AP-7. The ED50's and 95% confidence intervals were 1.1 micrograms (0.7-1.8) for mean arterial pressure, 1.7 micrograms (0.5-6.0) for heart rate, and 0.4 microgram (0.07-2.0) for withdrawal duration. Cortical EEG synchrony was unchanged after i.t. AP-7 consistent with a spinal site of action. The data indicate that: (i) robust allodynia can be selectively induced with i.t. strychnine in animals whose somatosensory systems are otherwise normal; (ii) sub-anesthetic doses of i.v. mexiletine inhibit the abnormal responses to low-threshold (A-fiber) afferent input in the strychnine model of allodynia (i.e., in the absence of peripheral or central nerve injury) at doses which affect normal nociception; and (iii) in the presence of i.t. strychnine, low-threshold afferent input activates a spinal NMDA-receptor mediated process normally restricted to noxious afferent input. Systemic mexiletine may have an important spinal site of action in abnormal pain states.