Plasma Growth Hormone as a Prognostic Biomarker to Durvalumab and Tremelimumab in Patients with Advanced Hepatocellular Carcinoma

Introduction

In this study, we explored the potential of plasma growth hormone (GH) as a prognostic biomarker in patients with advanced HCC treated with durvalumab plus tremelimumab (D+T).

Methods

In this study, we included 16 patients with advanced HCC who received D+T at MD Anderson Cancer Center between 2022 and 2023 and had plasma GH measurements recorded before treatment. Plasma GH levels were measured from prospectively collected blood samples and were correlated with progression-free survival (PFS) and overall survival (OS). The cutoff for normal GH levels in women and men was defined as ≤3.7 μg/L and ≤0.9 μg/L, respectively. The Kaplan-Meier method was employed to compute the median OS and PFS, while the Log rank test was applied to compare the survival outcomes between the GH-high and GH-low groups.

Results

Sixteen patients were included in this analysis, two female and fourteen male, with a median age of 65.5 years. At the time of the analysis, the 6-month OS rate was 100% among GH-low patients (6 patients) and 30% among GH-high patients (10 patients). OS was significantly longer in GH-low patients (not evaluable) compared to GH-high patients (3.94 months) (p = 0.030). PFS was also significantly longer in GH-low patients (not evaluable) compared to the GH-high patients (1.87 months) (p = 0.036).

Conclusion

Plasma GH is a prognostic biomarker in patients with advanced HCC treated with D+T. Given the relatively small patient cohort size, this finding should be further validated in larger randomized clinical trials in advanced HCC patients.

The Gut Microbiome as a Biomarker and Therapeutic Target in Hepatocellular Carcinoma

The microbiome is pivotal in maintaining health and influencing disease by modulating essential inflammatory and immune responses. Hepatocellular carcinoma (HCC), ranking as the third most common cause of cancer-related fatalities globally, is influenced by the gut microbiome through bidirectional interactions between the gut and liver, as evidenced in both mouse models and human studies. Consequently, biomarkers based on gut microbiota represent promising non-invasive tools for the early detection of HCC. There is a growing body of evidence suggesting that the composition of the gut microbiota may play a role in the efficacy of immunotherapy in different types of cancer; thus, it could be used as a predictive biomarker. In this review, we will dissect the gut microbiome's role as a potential predictive and diagnostic marker in HCC and evaluate the latest progress in leveraging the gut microbiome as a novel therapeutic avenue for HCC patients, with a special emphasis on immunotherapy.

Clinical and Prognostic Biomarker Value of Blood-Circulating Inflammatory Cytokines in Hepatocellular Carcinoma

INTRODUCTION

Circulating inflammatory cytokines play critical roles in tumor-associated inflammation and immune responses. Recent data have suggested that several interleukins (ILs) mediate carcinogenesis in hepatocellular carcinoma (HCC). However, the predictive and prognostic value of circulating ILs is yet to be validated. Our study aimed to evaluate the association of the serum ILs with overall survival (OS) and clinicopathologic features in a large cohort of HCC patients.

METHODS

We prospectively collected data and serum samples from 767 HCC patients treated at the University of Texas MD Anderson Cancer Center between 2001 and 2014, with a median follow-up of 67.4 months (95% confidence interval [CI]: 52.5, 83.3). Biomarker association with OS was evaluated by the log-rank method.

RESULTS

The median OS in this cohort was 14.2 months (95% CI: 12, 16.1 months). Clinicopathologic features were more advanced, and OS was significantly inferior in patients with high circulating levels of IL1-R1, IL-6, IL-8, IL-10, IL-15, IL-16, and IL-18.

CONCLUSION

Our study shows that several serum IL levels are valid prognostic biomarker candidates and potential targets for therapy in HCC.

Predictive capacity of a miRNA panel in identifying teratoma in post-chemotherapy consolidation surgeries

Objectives

To investigate the utility of a novel serum miRNA biomarker panel to distinguish teratoma from nonmalignant necrotic/fibrotic tissues or nonviable tumours in patients with NSGCT undergoing post-chemotherapy consolidation surgery.

Patients and methods

We prospectively collected pre-surgical serum samples from 22 consecutive testicular NSGCT patients with residual NSGCT after chemotherapy undergoing post-chemotherapy consolidation surgery. We measured serum miRNA expression of four microRNAs (miRNA-375, miRNA-200a-3p, miRNA-200a-5p and miRNA-200b-3p) and compared with pathologic findings at time of surgery. Receiver operating characteristic (ROC) curves were performed to assess the ability of these miRNA to differentiate between teratoma and necrosis or viable malignancy.

Results

Twenty-two patients with NSGCT were split into two groups based on pathology at time of post-chemotherapy consolidation surgery (teratoma group vs. necrosis/fibrosis/viable tumour group, i.e., NFVT). Patients with teratoma were older at diagnosis compared with those patients with NFVT (median age 28.7 vs. 23.9). Patients with NFVT were more likely to have embryonal carcinoma in their primary tumour (81.8% vs. 27.3%; p = 0.01). The majority of patients in both groups were stage III (63.6% vs. 72.7%). In this analysis, none of the miRNAs had good sensitivity or specificity to predict teratoma. There was no significant association between the expression levels of the miRNAs and the presence of teratoma. There was no statistically significant correlation between any of the miRNAs and teratoma size.

Conclusion

This novel miRNA panel (miRNA-375, miRNA-200a-3p, miRNA-200a-5p and miRNA-200b-3p) did not distinguish teratoma from nonmalignant necrotic/fibrotic tissues or nonviable tumours in patients with NSGCT undergoing post-chemotherapy consolidation surgery.

Neuronal CD200 Signaling Is Protective in the Acute Phase of Ischemic Stroke

BACKGROUND AND PURPOSE

CD200 (cluster of differentiation 200), a highly glycosylated protein primarily expressed on neurons in the central nervous system, binds with its receptor CD200R to form an endogenous inhibitory signal against immune responses. However, little is known about the effect of neuronal CD200 signaling in cerebral ischemia. The aim of this study was to investigate how neuronal CD200 signaling impacts poststroke inflammation and the ischemic injury.

METHODS

CD200 tma1^lf/fl:Thy1CreER mice were treated with tamoxifen to induce conditional gene knockout (ICKO) of neuronal CD200. The mice were subjected to a 60-minute transient middle cerebral artery occlusion. Stroke outcomes, apoptotic cell death, immune cell infiltration, microglia activation, and other inflammatory profiles were evaluated at 3 and 7 days after stroke.

RESULTS

Infarct volumes were significantly larger, and behavioral deficits more severe in ICKO versus control mice at 3 days after middle cerebral artery occlusion. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay also revealed a significant increase in apoptotic neuronal death in CD200 ICKO mice. An enhancement in lymphocytic infiltration and microglial proinflammatory responses were revealed by flow cytometry at 3 and 7 days after stroke in ICKO mice, accompanied by an increased microglial phagocytosis activity. Plasma proinflammatory cytokine (TNFα [tumor necrosis factor alpha] and IL [interleukin]-1β) levels significantly increased at 3 days, and IL-1β/IL-6 levels increased at 7 days in ICKO versus control animals. ICKO led to significantly lower baseline level of CD200 both in brain and plasma.

CONCLUSIONS

Neuronal CD200 inhibits proinflammatory responses and is protective against stroke injury.

Pulmonary cavitation in patients with thyroid cancer receiving antiangiogenic agents

Background

Thyroid malignancies are among the most common endocrine cancers worldwide. Owing to the angiogenic nature of these malignancies, tyrosine kinase inhibitors (TKIs) are an attractive potential treatment. However, TKIs have been associated with an increased risk of tumor cavitation, in turn linked to poor outcomes, in patients with malignancies in the lungs, where thyroid cancer commonly metastasizes.

Method

We performe d a retrospective cohort study of patients with thyroid cancer and evidence of metastatic disease to the lung that were treated with multi-targeted antiangiogenic TKIs. The primary objective of this study was to determine the incidence of pulmonary cavitation. The secondary objective was to evaluate the effect of pulmonary cavitation on survival.

Results

Of the 83 patients with pulmonary nodules, 10 developed cavitation during treatment. Of these 83 patients, two patients had to stop the treatment due to pneumothorax. Additionally, cavitation did not demonstrate any significant effect on survival.

Conclusion

In patients with thyroid cancer and evidence of metastatic disease to the chest, the use of multi-targeted TKIs led to cavitations that were not uncommon but clinical consequences were marginal. Treatment was stopped only in two patients that developed pneumothorax, however the small sample is a strong limitation of our study.

Routine Microbiologic Studies of Pleural Fluid Specimens in Cancer Patients

BACKGROUND

Patients who have pleural effusions typically undergo thoracentesis with examination of pleural fluid in their initial assessment. However, limited data are available on the diagnostic yield of pleural fluid bacterial cultures and fungal and acid-fast bacilli (AFB) smear and cultures in patients with cancer.

METHODS

We performed a retrospective cohort study of consecutive patients who had new onset pleural effusions and underwent an initial thoracentesis. The primary outcome was diagnostic yield of pleural fluid bacterial cultures and fungal and AFB smear and cultures.

RESULTS

Of 1637 patients, 1547 (94%) had evidence of active malignancy and 1359 (83%) had evidence of metastatic disease. Of the 1637 patients, 542 (33%) had high clinical suspicion of pneumonia within 14 days prior to thoracentesis. Only 14 patients (1.1%) had positive pleural fluid bacterial cultures, and only 6 of these positive cultures met the criteria for true pleural space infection.

CONCLUSIONS

The incidence of positive results from pleural fluid bacterial, fungal, and AFB in cancer populations is very low. Unless there is a suspicion for infection, microbiological analysis should be ordered selectively.

Abstract TP109: Microglial IRF5/4 Regulatory Axis: A Novel Therapeutic Target for Ischemic Stroke

Introduction: The Inflammatory response is a fundamental pathophysiological procedure in stroke, and the activation of microglia characterized by either M1 (pro-inflammatory) or M2 (anti-inflammatory) state is crucial in initiating, sustaining and resolving the post-stroke inflammation. IRF5/4 are key determinants in macrophage polarization. Our previous study has also shown IRF5/4 signaling corresponds to microglial M1/M2 activation in the early/late phases of ischemic stroke respectively. In the present study, we tested our hypothesis that manipulation of IRF5/4 regulatory axis impacts on post-stroke inflammation and stroke outcomes.

Methods: Microglia specific IRF5/4 conditional knockout (CKO) and lenti-IRF5/4 treated C57BL6 (for IRF5/4 overexpression) mice were subjected to a 60-minute middle cerebral artery occlusion (MCAO). Stroke outcomes including infarct size and behavior deficits were evaluated at 3d and 10d of MCAO. Microglial activation and peripheral immune cell infiltration were determined by flow cytometry (FC). IRF5/4 colocalization with microglia was examined with IHC, and multiplex was performed to measure cytokine levels in both the brain and blood samples.

Results: At both time points, IRF4 CKO mice exhibited increased infarct lesions and worse behavior outcomes, and this effect was reversed in IRF4 overexpressed mice. In contrast, IRF5 CKO mice had reduced infarct lesions and improved behavior deficits; whereas IRF5 over expression in microglia worsened stroke outcomes. FC results revealed that microglia exhibited M1 phenotype in IRF4 CKO and IRF5 over-expressed mice that concomitantly had pro-inflammatory profile demonstrated by cytokine data; however, IRF5 CKO and IRF4 over-expressed mice had M2 dominant microglia and anti-inflammatory responses. IHC showed IRF5 expression was upregulated in IRF4 CKO and IRF5 over-expressed mice, and IRF4 expression was augmented in IRF5 CKO and IRF4 over-expressed mice.

Conclusion: IRF5/4 regulatory axis regulates the microglial M1/M2 activation and impacts on stroke outcomes. Manipulation of IRF5/4 regulatory axis represents a novel therapeutic strategy for ischemic stroke.

Isolated islets in diabetes research

This review highlights some recent developments and diversified applications of islets in diabetes research as they are rapidly emerging as a model system in biomedical and biotechnological research. Isolated islets have formed an effective in vitro model in antidiabetic drug development programme, screening of potential hypoglycaemic agents and for investigating their mechanisms of action. Yet another application of isolated islets could be to understand the mechanisms of beta cell death in vitro and to identify the sites of intervention for possible cytoprotection. Advances in immunoisolation and immunomodulation protocols have made xeno-transplantation feasible without immunosuppression thus increasing the availability of islets. Research in the areas of pancreatic and non pancreatic stem cells has given new hope to diabetic subjects to renew their islet cell mass for the possible cure of diabetes. Investigations of the factors leading to differentiation of pancreatic stem/progenitor cells would be of interest as they are likely to induce pancreatic regeneration in diabetics. Similarly search for the beta cell protective agents has a great future in preservation of residual beta cell mass left after diabetogenic insults. We have detailed various applications of islets in diabetes research in context of their current status, progress and future challenges and long term prospects for a cure.

Papillary carcinoma in a giant thyroglossal duct cyst

Thyroglossal duct cysts (TGDCs) are common, however, a malignancy occurring in a TGDC is rare. The presence on an underlying malignancy is clinically occult but may be detected on preoperative imaging studies. We describe the CT findings of a papillary carcinoma occurring in a TGDC.

Actinobacillus actinomycetemcomitans immunosuppressive protein is a member of the family of cytolethal distending toxins capable of causing a G2 arrest in human T cells

We have previously shown that Actinobacillus actinomycetecomitans produces an immunosuppressive factor (ISF) capable of impairing human lymphocyte function by perturbing cell cycle progression. We now report that ISF is the product of the cdtB gene, one of three genes encoding the family of cytolethal distending toxins (Cdt). The ISF polypeptide exhibits >/=95% identity with Hemophilus ducreyi CdtB protein and </=60% homology with Escherichia coli or Campylobacter jejuni CdtB. Pretreatment of PHA-activated lymphocytes with 5-25 ng ISF results in G2 arrest of CD4+ and CD8+ T cells. Similarly, treatment of HeLa cells results in G2 arrest and cell elongation and distension. However, lymphocytes are at least 5 times more sensitive to ISF than HeLa cells and do not undergo the elongation and distension that characterizes interactions of Cdts with cell lines. ISF-treated lymphocytes express normal cyclin A and B1 levels, but contain reduced levels of cell cycle-dependent kinase-1 (Cdk1). Additionally, the majority of Cdk1 is in the hyperphosphorylated, inactive, form. In contrast, PHA-induced G2 cells contain elevated levels of the hypophosphorylated, active Cdk1. Failure of ISF-treated cells to dephosphorylate Cdk1 is not associated with decreased availability of Cdc25. These studies suggest that the CdtB protein alone is capable of inducing G2 arrest in lymphocytes and cell cycle arrest, elongation, and distension of HeLa cells. Our studies also suggest that lymphocytes may be primary targets for A. actinomycetemcomitans CdtB (ISF) and possibly for other Cdt family members as well. Thus, Cdts may function to impair host immunity and contribute to the pathogenesis of disease associated with Cdt-producing organisms.

Inhibition of poly(ADP-ribose) polymerase rescues human T lymphocytes from methylmercury-induced apoptosis

The objective of this investigation was to determine the role of poly(ADP-ribose) polymerase (PARP) in methylmercuric chloride (MeHgCl)-induced T-cell apoptosis. Following exposure of human T-cells to 2.5 microM MeHgCl, we observed PARP activation within 45 min. Maximal activation was observed at 90 min after MeHgCl treatment; thereafter, PARP activity declined. The loss in enzyme activity was coincidental with the cleavage of 116-kDa intact PARP protein to an 85-kDa fragment. To address the relationship between PARP activation and induction of apoptosis, we first examined the redox status of T cells treated with MeHgCl. We found that exposure of T cells to low concentrations of this toxicant resulted in decreased levels of reduced pyridine nucleotides and an increase in the relative amounts of oxidized flavoproteins. Thus, the possibility exists that activation of PARP leads to NAD+ depletion and thereby alters mitochondrial redox status. To determine if PARP activation is indeed part of the proapoptotic (destructive) response or a component of the antiapoptotic (protective) response, we employed two inhibitors: 3-aminobenzamide and nicotinamide. Pretreatment of T cells with these inhibitors protected cells from MeHgCl-induced apoptosis; this was seen as a reduction in the uptake of Hoechst 33258 and DNA fragmentation. Moreover, these inhibitors blocked MeHgCl-induced oxidative stress as evidenced by a reduction in reactive oxygen species (ROS) generation. These agents, however, failed to block MeHgCl-dependent decline in mitochondrial transmembrane potential (delta psi m). We conclude that PARP activation leads to proapoptotic events that contribute to MeHgCl-induced cell death.

Modulation of chondrocyte proliferation by ascorbic acid and BMP-2

Chondrocytes show an unusual ability to thrive under serum-free conditions as long as insulin, thyroxine, and cysteine are present. Studies with sternal chondrocytes from chick embryos indicate that thymidine incorporation in chondrocytes cultured under serum-free conditions is 30-50% of that seen with fetal bovine serum (FBS). In contrast, skin fibroblast proliferation in serum-free culture is <5% of that seen with serum. Addition of 30-50 microM ascorbic acid to serum-free medium stimulates chondrocyte proliferation 4-5x, resulting in levels of thymidine incorporation higher than that seen with 10% serum. Three to five hours of ascorbate exposure is sufficient to stimulate proliferation, with maximal stimulation seen after 12-15 h. Bromo-deoxyuridine (BrdU) labelling indicated that approximately 25% of chondrocytes transit S phase during a 4-h period (16-20 h after ascorbate). Once maximal stimulation is reached, the proliferation rate remains fairly constant over at least 40 h. Ascorbate therefore increases the steady-state level of chondrocytes in the cycle. Because the stimulation of chondrocyte proliferation was greater than the net increase in cell numbers, we examined the level of apoptosis. Nuclear morphology, terminal uridine nucleotide end-labelling (TUNEL) assay, and 7-AAD/Hoechst dye FACS analyses all indicated that approximately 15% of the ascorbate-treated chondrocytes were undergoing apoptosis, while only 5% of the control chondrocytes were apoptotic. When prehypertrophic chondrocytes from the cephalic region of embryonic sternae were stimulated to undergo hypertrophy with rhBMP-2 + ascorbate, levels of apoptosis were similar to that seen with ascorbate alone. In contrast, treatment of caudal chondrocytes with BMP plus ascorbate does not induce hypertrophy, and the proportion of apoptotic cells was less than that seen with ascorbate alone. These results imply that in chondrocytes the transition to hypertrophy is associated with a decreased number of proliferating cells and a relatively high level of apoptosis.

Mercuric compounds inhibit human monocyte function by inducing apoptosis: evidence for formation of reactive oxygen species, development of mitochondrial membrane permeability transition and loss of reductive reserve

The focus of this investigation was to examine the effects of low concentrations of organic mercuric compounds on human monocyte function and to relate these effects to apoptosis. Following exposure of monocytes to 0-5 microM MeHgCl, phagocytic function and capacity to generate a respiratory burst, following PMA activation, were determined. We found that the mercury-treated cells exhibited reduced phagocytic activity. Exposure to the same mercury concentration range, also caused a marked increase in cell death. To ascertain if monocyte death was due to apoptosis, a number of flow cytometric studies were performed. Mercury-treated cells exhibited increased Hoechst 33258 fluorescence, while maintaining their ability to exclude the vital dye 7-aminoactinomycin D. Furthermore, monocytes exhibited changes in light scatter patterns that were consistent with apoptosis; these included decreased forward light scatter and increased side scatter. The percentage of cells undergoing apoptosis was dependent upon the mercury content of the medium, regardless of whether the metal was present as methyl, ethyl or phenyl mercury. Mercury-treated cells also exhibited changes in lipid organization within the plasma membrane as evidenced by increased uptake of the fluorescent probe, merocyanine 540, and by elevated annexin V binding to phosphatidylserine. Using the fluorescent probes DiOC6(3) and rhodamine 123 we noted that within 1 h of exposure to mercury, monocytes exhibited a decrease in mitochondrial transmembrane potential (psi m). Since a decreased psi m is associated with altered mitochondrial function, the hypothesis that mercury potentiated reactive oxygen species (ROS) generation and that these species promoted apoptosis was tested. We noted that treated cells generated ROS, as evidenced by oxidation of hydroethidine and the generation of the fluorescent product, ethidium. Finally, since ROS would also lower monocyte reductive reserve, we also measured GSH levels in mercury-treated cells. Chemical measurement of GSH indicated that there was thiol depletion. We suggest that the low thiol reserve predisposes cells to ROS damage and at the same time activates death-signaling pathways.

Induction of apoptosis in human T-cells by organomercuric compounds: a flow cytometric analysis

Although several lines of investigation demonstrate that many heavy metals are cytotoxic to host defense cells, the mechanism of killing is poorly understood. The major focus of this investigation was to determine if organic mercuric compounds kill human lymphocytes by inducing the cells to undergo apoptosis and to evaluate possible flow cytometric systems for assessing cell death. T-cells were exposed to 0.6-5 microM MeHgCl, EtHgCl, or PhHgCl for up to 24 hr and then analyzed by flow cytometry. Mercury-treated cells exhibited increased Hoechst 33258 and 33342 fluorescence while maintaining their ability to exclude the vital stain 7-AAD. Furthermore, T-cells exposed to mercury exhibited changes in light scatter patterns that included decreased forward light scatter and increased side scatter. The light scatter and fluorescent changes were consistent with changes that cells display during apoptosis. To further evaluate cell death and to distinguish between apoptosis and necrosis, merocyanine 540 staining and annexin V binding to the plasma membrane as well as DNA fragmentation were assessed. Mercury-treated cells exhibited increased merocyanine 540 fluorescence and annexin V binding along with changes in nuclear morphology consistent with the notion of apoptosis. Conventional agarose gel electrophoresis failed to demonstrate low-molecular-weight DNA bands; however, when probed by flow cytometry using both nick translation and a modified TUNEL assay, patterns consistent with nuclear fragmentation were evident. We noted that the percentage of T-cells undergoing apoptosis was dependent upon the amount of serum present in the medium; as serum concentrations were increased from 0 to 10%, cell death declined. Apoptosis (33%) was observed within 1 hr of exposure to MeHgCl; maximum cell death (67%) occurred after 24 hr exposure. Induction of apoptosis was dependent on the mercury concentration and independent of the hydrophobicity of the mercury ligand. Finally, we assessed mercury-dependent apoptosis in activated T-cells. When treated with mitogen, mercury failed to induce apoptosis in these cells. Indeed, there was no evidence of either apoptosis nor necrosis in these populations. It was concluded that the activation process prevented development of a metabolic state that was required for induction of apoptogenic genes.

Fusobacterium nucleatum inhibits human T-cell activation by arresting cells in the mid-G1 phase of the cell cycle

Fusobacterium nucleatum has been implicated in the pathogenesis of several diseases, including urinary tract infections, bacteremia, pericarditis, otitis media, and disorders of the oral cavity such as pulpal infections, alveolar bone abscesses, and periodontal disease. We have previously demonstrated that sonic extracts of F. nucleatum FDC 364 were capable of inhibiting human T-cell responses to mitogens and antigens. In this study, we have further characterized this immunosuppressive protein (FIP) and initiated experiments to determine its mode of action. The purified FIP has an apparent molecular mass of 90 to 100 kDa; sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that the FIP is actually composed of two subunits with molecular masses of 48 and 44 kDa. Purified FIP retained its biological activity and was capable of inhibiting mitogen-induced proliferation of human T cells. Inhibition was dose dependent, and the FIP exhibited a specific activity approximately 250-fold greater than that of the crude extract. Cell cycle analysis indicates that FIP-treated cells were prevented from exiting the G0/G1 phase of the cell cycle. However, FIP did not alter the expression of activation markers (CD69, CD25, and CD71) or interleukin-2 secretion. The latter observations suggest that the T cells did indeed become activated and had entered the G1 phase of the cell cycle. Analysis of the expression of cyclins indicates that the phase of the cell cycle that is FIP sensitive resides somewhere beyond the restriction point of cyclin D2 (early to mid-G1) but prior to that of cyclins D3 and E (mid- to late G1). Finally, analysis of the expression of the proliferating cell nuclear antigen indicates that this is the earliest detectable defect in T cells exposed to FIP. We propose that if a block in the G1 phase of the cell cycle occurs in vivo in lymphocytes, it may result in a state of local and/or systemic immunosuppression. These suppressive effects could alter the nature and consequences of host-parasite interactions, thereby enhancing the pathogenicity of F. nucleatum itself or that of some other opportunistic organisms.

Testing the "redirection hypothesis" of prostaglandin metabolism in the kidney

Furosemide increases the synthesis of two major renal eicosanoids, prostacyclin (PGI2) and thromboxane A2 (TXA2), by stimulating the release of arachidonic acid which in turn is metabolized to PGG2/PGH2, then to PGI2 and TXA2. PGI2 may mediate, in part, the early increment in plasma renin activity (PRA) after furosemide. We hypothesized that thromboxane synthetase inhibition should direct prostaglandin endoperoxide metabolism toward PGI2, thereby enhancing the effects of furosemide on renin release. Furosemide (2.0 mg . kg-1 i.v.) was injected into Sprague-Dawley rats pretreated either with vehicle or with U-63,557A (a thromboxane synthetase inhibitor, 2 mg/kg-1 followed by 2 mg/kg-1 X hr-1). Urinary 6ketoPGF1 alpha and thromboxane B2 (TXB2), reflecting renal synthesis of PGI2 and TXA2, as well as PRA and serum TXB2, were measured. Serum TXB2 was reduced by 96% after U-63,557A. U-63,557A did not affect the basal PRA. Furosemide increased PRA in both vehicle and U63,557A treated rats. However, the PRA-increment at 10, 20 and 40 min following furosemide administration was greater in U-63,557A-treated rats than in vehicle-treated rats and urine 6ketoPGF1 alpha excretion rates were increased. These effects of thromboxane synthesis inhibition are consistent with a redirection of renal PG synthesis toward PGI2 and further suggest that such redirection can be physiologically relevant.

Effect of cyclooxygenase and thromboxane synthetase inhibition on furosemide-stimulated plasma renin activity

We studied the effects of a specific thromboxane (TX) synthetase inhibitor (U-63,557A) and a cyclooxygenase inhibitor on furosemide-induced renin release. Furosemide (2.0 mg X kg-1) was injected into Sprague-Dawley rats pretreated with indomethacin (10 mg X kg-1, i.v.), U-63,557A (1.0-32.0 mg X kg-1, i.v.), or vehicle (Na2CO3 0.03 M). Plasma renin activity was measured in blood samples collected 0, 10, 20, and 40 min after the injection of furosemide. Blood was also collected after the administration of vehicle, indomethacin, or U-63,557A for serum TXB2, a measure of platelet TXA2 synthesis. The results demonstrated that plasma renin activity rose with time following furosemide in the various groups of rats; indomethacin suppressed the furosemide-induced increments in plasma renin activity, while U-63,557A at doses of 4-8 mg X kg-1 augmented it. At doses below 4 mg X kg-1 or above 8 mg X kg-1, U-63,557A did not augment renin secretion. Indomethacin and U-63,557A reduced serum thromboxane by 81 and 90%, respectively. Thus, these experiments suggest that thromboxane synthetase inhibition, within a narrow dosage range, potentiates furosemide-induced renin release while cyclooxygenase inhibition suppresses it.

Clonidine fails to reduce pressor responsiveness of conscious spontaneously hypertensive rats to vasopressin

Pressor responses and heart rate responses to intravenous injections (3.5-50.0 pmol/kg) of arginine vasopressin (AVP) were recorded in saline- and clonidine-treated spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Clonidine (20 micrograms/kg, i.v.) caused a marked fall of arterial pressure in SHR but not in WKY rats so that, 20 min after the injection of the alpha 2-adrenoceptor agonist, arterial pressure was similar in the two strains of rats. The curve expressing the relationship between the dose of AVP and the increase of arterial pressure for saline-treated SHR was positioned to the left of that for saline-treated WKY rats. This enhanced pressor responsiveness of SHR to AVP may have been related to impaired reflex activity since heart rate fell much less in SHR than in WKY rats for a given elevation in pressure. Pressure responses to AVP were augmented by clonidine in both SHR and WKY rats so that, similar to saline-treated rats, pressor responsiveness to the peptide was still greater in SHR. Heart rate responses to AVP were not altered significantly by clonidine. The results indicate that clonidine fails to enhance reflex activity and reduce pressor responsiveness of SHR to AVP. The increased pressor responsiveness of both SHR and WKY rats to AVP following clonidine was an unexpected finding and may be related to a peripheral interaction between alpha-adrenergic agonists and AVP.

Reflexes fail to reduce pressor activity of vasopressin in spontaneous hypertension

Pressor responses and heart rate responses were recorded in spontaneously hypertensive rats (SHR) and in Wistar-Kyoto (WKY) rats during intravenous infusions of arginine vasopressin and phenylephrine under two experimental situations, first when cardiovascular reflexes were impaired by pretreatment with a ganglionic blocking agent (pentolinium) and second, when reflexes remained intact. In rats with ganglia blocked, pressor responses of SHR to vasopressin or to phenylephrine were similar to those of WKY rats. In rats with intact reflexes, pressor responses of SHR to phenylephrine were also similar to those of WKY rats but, in contrast, pressor responses of SHR to vasopressin were enhanced. Heart rate fell much more for any given elevation of blood pressure in WKY rats than in SHR during infusions of vasopressin and phenylephrine, and the bradycardia associated with these pressor agents was largely abolished by pentolinium. The results are consistent with the hypothesis that baroreflexes buffer the pressor activity of vasopressin in the normotensive WKY rat and that an impairment of baroreflex activity in SHR contributes to the enhanced pressor activity of vasopressin in these rats.