Somatostatin and alpha 2-adrenergic agonists selectively inhibit vasopressin-induced cyclic AMP accumulation in MDCK cells

Emerging therapies for autosomal dominant polycystic kidney disease with a focus on cAMP signaling

Autosomal dominant polycystic kidney disease (ADPKD), with an estimated genetic prevalence between 1:400 and 1:1,000 individuals, is the third most common cause of end stage kidney disease after diabetes mellitus and hypertension. Over the last 3 decades there has been great progress in understanding its pathogenesis. This allows the stratification of therapeutic targets into four levels, gene mutation and polycystin disruption, proximal mechanisms directly caused by disruption of polycystin function, downstream regulatory and signaling pathways, and non-specific pathophysiologic processes shared by many other diseases. Dysfunction of the polycystins, encoded by the PKD genes, is closely associated with disruption of calcium and upregulation of cyclic AMP and protein kinase A (PKA) signaling, affecting most downstream regulatory, signaling, and pathophysiologic pathways altered in this disease. Interventions acting on G protein coupled receptors to inhibit of 3',5'-cyclic adenosine monophosphate (cAMP) production have been effective in preclinical trials and have led to the first approved treatment for ADPKD. However, completely blocking cAMP mediated PKA activation is not feasible and PKA activation independently from cAMP can also occur in ADPKD. Therefore, targeting the cAMP/PKA/CREB pathway beyond cAMP production makes sense. Redundancy of mechanisms, numerous positive and negative feedback loops, and possibly counteracting effects may limit the effectiveness of targeting downstream pathways. Nevertheless, interventions targeting important regulatory, signaling and pathophysiologic pathways downstream from cAMP/PKA activation may provide additive or synergistic value and build on a strategy that has already had success. The purpose of this manuscript is to review the role of cAMP and PKA signaling and their multiple downstream pathways as potential targets for emergent therapies for ADPKD.

VX-809 mitigates disease in a mouse model of autosomal dominant polycystic kidney disease bearing the R3277C human mutation

Autosomal dominant polycystic kidney disease (ADPKD) is associated with the formation of renal cysts. We have devised a therapeutic approach, based on reversing the cyst phenotype from secretion to absorption by using VX-809, a modulator of the cystic fibrosis transmembrane regulator trafficking and processing. Our goal is to test VX-809 in RC/RC mice bearing the R3277C human mutation to demonstrate its therapeutic potential. We found that by 5 months of age, RC/RC mice had large cysts and impaired renal function, but when treated with VX-809 between the ages of 3 and 5 months, or 6 and 8 months, the cyst area was reduced in both groups, suggesting that VX-809 had shrunk previously existing cysts. After 2 months of treatment, the cyst size was lower than that of untreated animals of the same age. Our co-localization studies confirmed that cystic fibrosis transmembrane conductance regulator (CFTR) is found predominately at the apical membrane in the untreated animals of each age group, consistent with its role in Cl^- secretion; after VX-809 treatment, the basolateral membrane co-localization of CFTR increased ~4-fold, accompanied by a decrease of ~2-3-fold in its apical co-localization, indicating that VX-809 alters the phenotype to favor fluid absorption. Sodium/hydrogen exchanger and epithelial sodium channel, found in normal kidneys at the apical membrane, were almost absent from the cysts. VX-809 restored both levels toward normal. HSP27 is highly expressed in RC/RC mice and lowered toward normal by VX-809. Our demonstration of cyst reduction, improved renal function, and generation of an absorptive phenotype all strongly support the therapeutic potential of VX-809 as a treatment for ADPKD. We show here in an animal model of slowly progressing cyst formation typical of human ADPKD that VX-809 reduces the growth of already established cysts. The magnitude of the effect in the RC/RC mouse model when compared to previous experiments using the same mouse model to evaluate tolvaptan indicates that CFTR modulators warrant further development as a treatment for ADPKD.

Somatostatin analog therapy effectiveness on the progression of polycystic kidney and liver disease: A systematic review and meta-analysis of randomized clinical trials

BACKGROUND

Uncertainty underlies the effectiveness of somatostatin analogues for slowing the progression of polycystic kidney or liver disease.

METHODS

Eligible studies included randomized controlled trials (RCTs) evaluating somatostatin analog as therapy for patients with polycystic kidney disease (PKD) or polycystic liver disease (PLD) compared to placebo or standard therapy. Two reviewers independently screened studies identified from databases (MEDLINE, EMBASE, Cochrane Database), clinical trial registries, and references from pertinent articles and clinical practice guidelines. Outcome measurements were changes in total liver volume (TLV), total kidney volume (TKV), and estimated glomerular filtration rate (eGFR).

RESULTS

Of 264 nonduplicate studies screened, 10 RCTs met the inclusion criteria. The body of evidence provided estimates warranting moderate confidence. Meta-analysis of 7 RCTs including a total of 652 patients showed that somatostatin analogs are associated with a lower %TLV growth rate compared to control (mean difference, -6.37%; 95% CI -7.90 to -4.84, p<0.00001), and with a lower %TKV growth rate compared to control (mean difference, -3.66%; 95% CI -5.35 to -1.97, p<0.0001). However, it was not associated with a difference in eGFR decline (mean difference, -0.96 mL/min./1.73m2; 95% CI -2.38 to 0.46, p = 0.19).

CONCLUSIONS

Current body of evidence suggests that somatostatin analogs therapy slows the increase rate of TLV and TKV in patients with PKD or PLD compared to control within a 3-year follow-up period. It does not seem to have an effect on the change in eGFR. Somatostatin analogs therapy can be a promising treatment for ADPKD or ADPLD, and we need to continue to research its effectiveness for ADPKD or ADPLD.

Modulation of polycystic kidney disease by G-protein coupled receptors and cyclic AMP signaling

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a systemic disorder associated with polycystic liver disease (PLD) and other extrarenal manifestations, the most common monogenic cause of end-stage kidney disease, and a major burden for public health. Many studies have shown that alterations in G-protein and cAMP signaling play a central role in its pathogenesis. As for many other diseases (35% of all approved drugs target G-protein coupled receptors (GPCRs) or proteins functioning upstream or downstream from GPCRs), treatments targeting GPCR have shown effectiveness in slowing the rate of progression of ADPKD. Tolvaptan, a vasopressin V2 receptor antagonist is the first drug approved by regulatory agencies to treat rapidly progressive ADPKD. Long-acting somatostatin analogs have also been effective in slowing the rates of growth of polycystic kidneys and liver. Although no treatment has so far been able to prevent the development or stop the progression of the disease, these encouraging advances point to G-protein and cAMP signaling as a promising avenue of investigation that may lead to more effective and safe treatments. This will require a better understanding of the relevant GPCRs, G-proteins, cAMP effectors, and of the enzymes and A-kinase anchoring proteins controlling the compartmentalization of cAMP signaling. The purpose of this review is to provide an overview of general GPCR signaling; the function of polycystin-1 (PC1) as a putative atypical adhesion GPCR (aGPCR); the roles of PC1, polycystin-2 (PC2) and the PC1-PC2 complex in the regulation of calcium and cAMP signaling; the cross-talk of calcium and cAMP signaling in PKD; and GPCRs, adenylyl cyclases, cyclic nucleotide phosphodiesterases, and protein kinase A as therapeutic targets in ADPKD.

Management of autosomal-dominant polycystic kidney disease-state-of-the-art

Autosomal-dominant polycystic kidney disease (ADPKD) is the most frequent genetic cause of end-stage renal disease in adults. Affected individuals and families face a significant medical and psychosocial burden due to both renal and extrarenal manifestations. Consequently, interventions that ameliorate the course of the disease and specifically slow down the loss of kidney function are of special interest. Major research efforts in both the clinical and pre-clinical setting in the last two decades resulted in a number of pivotal clinical trials aimed to ameliorate the disease. These studies have underlined the important role of specific supportive measures and provided the basis for first targeted pharmacological therapies. Very recently, the concept of repurposing drugs approved for other conditions for a use in ADPKD has gained increasing attention. Here, we review the current best-practice management of ADPKD patients with a focus on interventions that have reached clinical use to maintain kidney function and give an outlook on future trials and potential novel treatment strategies.

Effect of Lanreotide on Kidney Function in Patients With Autosomal Dominant Polycystic Kidney Disease: The DIPAK 1 Randomized Clinical Trial

Importance

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by progressive cyst formation in both kidneys and loss of renal function, eventually leading to a need for kidney replacement therapy. There are limited therapeutic management options.

Objective

To examine the effect of the somatostatin analogue lanreotide on the rate of kidney function loss in patients with later-stage ADPKD.

Design, Setting, and Participants

An open-label randomized clinical trial with blinded end point assessment that included 309 patients with ADPKD from July 2012 to March 2015 at 4 nephrology outpatient clinics in the Netherlands. Eligible patients were 18 to 60 years of age and had an estimated glomerular filtration rate (eGFR) of 30 to 60 mL/min/1.73 m2. Follow-up of the 2.5-year trial ended in August 2017.

Interventions

Patients were randomized to receive either lanreotide (120 mg subcutaneously once every 4 weeks) in addition to standard care (n = 153) or standard care only (target blood pressure <140/90 mm Hg; n = 152).

Main Outcomes and Measures

Primary outcome was annual change in eGFR assessed as slope through eGFR values during the 2.5-year treatment phase. Secondary outcomes included change in eGFR before vs after treatment, incidence of worsening kidney function (start of dialysis or 30% decrease in eGFR), change in total kidney volume and change in quality of life (range: 1 [not bothered] to 5 [extremely bothered]).

Results

Among the 309 patients who were randomized (mean [SD] age, 48.4 [7.3] years; 53.4% women), 261 (85.6%) completed the trial. Annual rate of eGFR decline for the lanreotide vs the control group was -3.53 vs -3.46 mL/min/1.73 m2 per year (difference, -0.08 [95% CI, -0.71 to 0.56]; P = .81). There were no significant differences for incidence of worsening kidney function (hazard ratio, 0.87 [95% CI, 0.49 to 1.52]; P = .87), change in eGFR (-3.58 vs -3.45; difference, -0.13 mL/min/1.73 m2 per year [95% CI, -1.76 to 1.50]; P = .88), and change in quality of life (0.05 vs 0.07; difference, -0.03 units per year [95% CI, -0.13 to 0.08]; P = .67). The rate of growth in total kidney volume was lower in the lanreotide group than the control group (4.15% vs 5.56%; difference, -1.33% per year [95% CI, -2.41% to -0.24%]; P = .02). Adverse events in the lanreotide vs control group included injection site discomfort (32% vs 0.7%), injection site papule (5.9% vs 0%), loose stools (91% vs 6.6%), abdominal discomfort (79% vs 20%), and hepatic cyst infections (5.2% vs 0%).

Conclusions and Relevance

Among patients with later-stage autosomal dominant polycystic kidney disease, treatment with lanreotide compared with standard care did not slow the decline in kidney function over 2.5 years of follow-up. These findings do not support the use of lanreotide for treatment of later-stage autosomal dominant polycystic kidney disease.

Trial Registration

ClinicalTrials.gov Identifier: NCT01616927.

The expression of somatostatin receptor 2 decreases during cyst growth in mice with polycystic kidney disease

IMPACT STATEMENT

Somatostatin (SST) analogs have been shown to halt cyst growth and progression of autosomal dominant polycystic kidney disease by several clinical trials. However, two studies suggest that the effect of the SST analog octreotide on kidney growth during the first year of treatment is reduced in the subsequent follow-ups and the kidney enlargement resumes. This biphasic change in kidney growth during octreotide treatment may be partially explained by alterations in SSTR2 expression. Here, we found that SSTR2 is mainly expressed in distal tubules and collecting ducts in murine kidneys, and the expression of SSTR2 decreases during cyst growth in two PKD mouse models. Our data may thus provide possible explanations for the lack of efficacy in long-term treatment with SST analogs.

Many Genes-One Disease? Genetics of Nephronophthisis (NPHP) and NPHP-Associated Disorders

Nephronophthisis (NPHP) is a renal ciliopathy and an autosomal recessive cause of cystic kidney disease, renal fibrosis, and end-stage renal failure, affecting children and young adults. Molecular genetic studies have identified more than 20 genes underlying this disorder, whose protein products are all related to cilia, centrosome, or mitotic spindle function. In around 15% of cases, there are additional features of a ciliopathy syndrome, including retinal defects, liver fibrosis, skeletal abnormalities, and brain developmental disorders. Alongside, gene identification has arisen molecular mechanistic insights into the disease pathogenesis. The genetic causes of NPHP are discussed in terms of how they help us to define treatable disease pathways including the cyclic adenosine monophosphate pathway, the mTOR pathway, Hedgehog signaling pathways, and DNA damage response pathways. While the underlying pathology of the many types of NPHP remains similar, the defined disease mechanisms are diverse, and a personalized medicine approach for therapy in NPHP patients is likely to be required.

Novel therapeutic approaches to autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited disorder characterized by the progressive growth of renal cysts that, over time, destroy the architecture of the renal parenchyma and typically lead to kidney failure by the sixth decade of life. ADPKD is common and represents a leading cause of renal failure worldwide. Currently, there are no Food and Drug Administration-approved treatments for the disease, and the existing standard of care is primarily supportive in nature. However, significant advances in the understanding of the molecular biology of the disease have inspired investigation into potential new therapies. Several drugs designed to slow or arrest the progression of ADPKD have shown promise in preclinical models and clinical trials, including vasopressin receptor antagonists and somatostatin analogs. This article examines the literature underlying the rationale for molecular therapies for ADPKD and reviews the existing clinical evidence for their indication for human patients with the disease.

Tolvaptan plus pasireotide shows enhanced efficacy in a PKD1 model

Autosomal dominant polycystic kidney disease (ADPKD) is a leading cause of ESRD. A central defect associated with ADPKD pathology is elevated levels of 3', 5'-cyclic AMP (cAMP). Compounds such as tolvaptan and pasireotide, which indirectly reduce adenylyl cyclase 6 (AC6) activity, have hence proven effective in slowing cyst progression. Here, we tested the efficacy of these compounds individually and in combination in a hypomorphic PKD1 model, Pkd1(R3277C/R3277C) (Pkd1(RC/RC)), in a 5-month preclinical trial. Initially, the Pkd1(RC/RC) model was inbred into the C57BL/6 background, minimizing disease variability, and the pathogenic effect of elevating cAMP was confirmed by treatment with the AC6 stimulant desmopressin. Treatment with tolvaptan or pasireotide alone markedly reduced cyst progression and in combination showed a clear additive effect. Furthermore, combination treatment significantly reduced cystic and fibrotic volume and decreased cAMP to wild-type levels. We also showed that Pkd1(RC/RC) mice experience hepatic hypertrophy that can be corrected by pasireotide. The observed additive effect reinforces the central role of AC6 and cAMP in ADPKD pathogenesis and highlights the likely benefit of combination therapy for patients with ADPKD.

Safety study of somatostatin analogue octreotide for autosomal dominant polycystic kidney disease in Japan

BACKGROUND

The total kidney volume (TKV) and total liver volume (TLV) increase and renal function decreases progressively in patients with autosomal dominant polycystic kidney disease (ADPKD). Somatostatin analogues, such as octreotide, reduce these increases in TKV and TLV. The aim of this study was to examine the safety of the short-term administration of octreotide long-acting release (octreotide-LAR) in a small number of cases.

METHODS

Four ADPKD patients with an estimated glomerular filtration rate (eGFR) > 45 mL/min/1.73 m(2), TKV > 1,000 mL, and TLV > 3,000 mL were enrolled. Two 20-mg octreotide-LAR intramuscular injections were repeated every 4 weeks for 24 weeks. Laboratory and clinical assessments were repeated every 4 weeks, and TKV and TLV were measured by magnetic resonance imaging before and after the study.

RESULTS

In the laboratory tests, there was no abnormal variable except for a significant decrease of alanine aminotransferase. The means of TKV and TLV decreased from 2,007 to 1,903 mL and from 9,197 to 8,866 mL, respectively, but the changes were not significant. eGFR did not change significantly. Adverse events involved loose stools in two patients, as well as injection site granuloma and abdominal pain in one patient each, which resolved spontaneously.

CONCLUSION

Octreotide-LAR may be safe and effective for preventing TKV and TLV increases (UMIN000009214).

Strategies targeting cAMP signaling in the treatment of polycystic kidney disease

Polycystic kidney disease (PKD) is a leading cause of ESRD worldwide. In PKD, excessive cell proliferation and fluid secretion, pathogenic interactions of mutated epithelial cells with an abnormal extracellular matrix and alternatively activated interstitial macrophages, and the disruption of mechanisms controlling tubular diameter contribute to cyst formation. Studies with animal models suggest that several diverse pathophysiologic mechanisms, including dysregulation of intracellular calcium levels and cAMP signaling, mediate these cystogenic mechanisms. This article reviews the evidence implicating calcium and cAMP as central players in a network of signaling pathways underlying the pathogenesis of PKD and considers the therapeutic relevance of treatment strategies targeting cAMP signaling.

Randomized clinical trial of long-acting somatostatin for autosomal dominant polycystic kidney and liver disease

There are no proven, effective therapies for polycystic kidney disease (PKD) or polycystic liver disease (PLD). We enrolled 42 patients with severe PLD resulting from autosomal dominant PKD (ADPKD) or autosomal dominant PLD (ADPLD) in a randomized, double-blind, placebo-controlled trial of octreotide, a long-acting somatostatin analogue. We randomly assigned 42 patients in a 2:1 ratio to octreotide LAR depot (up to 40 mg every 28+/-5 days) or placebo for 1 year. The primary end point was percent change in liver volume from baseline to 1 year, measured by MRI. Secondary end points were changes in total kidney volume, GFR, quality of life, safety, vital signs, and clinical laboratory tests. Thirty-four patients had ADPKD, and eight had ADPLD. Liver volume decreased by 4.95%+/-6.77% in the octreotide group but remained practically unchanged (+0.92%+/-8.33%) in the placebo group (P=0.048). Among patients with ADPKD, total kidney volume remained practically unchanged (+0.25%+/-7.53%) in the octreotide group but increased by 8.61%+/-10.07% in the placebo group (P=0.045). Changes in GFR were similar in both groups. Octreotide was well tolerated; treated individuals reported an improved perception of bodily pain and physical activity. In summary, octreotide slowed the progressive increase in liver volume and total kidney volume, improved health perception among patients with PLD, and had an acceptable side effect profile.

Safety and efficacy of long-acting somatostatin treatment in autosomal-dominant polycystic kidney disease

BACKGROUND

The fluid filling renal cysts in human polycystic kidneys is secreted chiefly by the tubular epithelium lining the cysts via secondary chloride transport. Inhibiting this process by somatostatin therapy should induce shrinking of renal cysts.

METHODS

In this randomized, cross-over, placebo-controlled trial we compared the risk/benefit profile of 6-month treatment with long-acting somatostatin (octreotide-LAR, 40 mg intramuscularly every 28 days) or placebo in autosomal-dominant polycystic kidney disease (ADPKD) patients with mild-to-moderate renal insufficiency and no evidence of other kidney disease. Volumes of kidney structures were evaluated by a two-slice computed tomography (CT) scanner; while glomerular filtration rate (GFR) was estimated by iohexol plasma clearance.

RESULTS

One patient on somatostatin and one on placebo were prematurely withdrawn because of nonsymptomatic, reversible colelithiasis and asthenia, respectively. In the remaining 12 patients somatostatin was well tolerated. Kidney volume increased by 71 +/- 107 mL (P < 0.05) on somatostatin and by 162 +/- 114 mL (P < 0.01) on placebo. The percent increase was significantly lower on somatostatin (2.2 +/- 3.7% vs. 5.9 +/- 5.4%) (P < 0.05). Cystic volume tended to increase less on somatostatin than on placebo (3.0 +/- 6.5% vs. 5.6 +/- 5.8%). The "parenchymal" volume nonsignificantly increased by 2.5 +/- 8.4% on placebo and slightly decreased by 4.4 +/- 8.9% on somatostatin. The GFR did not change significantly during both treatment periods.

CONCLUSION

In ADPKD patients, 6-month somatostatin therapy is safe and may slow renal volume expansion. This may reflect an inhibited growth in particular of smallest cysts beyond the detection threshold of CT scan evaluation. Whether this effect may prove renoprotective in the long term should be tested in additional trials of longer duration.

Modulation of cyclic AMP production by strial marginal cells from gerbil in culture

To further investigate the role of marginal cells (MCs) in the secretion of endolymph and because of the limitations encountered in investigating these cells in vivo, we used primary cultures of MCs derived from explants of gerbil stria vascularis and investigated modulation of the adenylate cyclase-cyclic AMP system. After 10 days on type I collagen coated plastic dishes, a confluent monolayer of epithelial-like cells was obtained which exhibited the morphologic and immunohistochemical features of the native marginal cells. The cyclic AMP (cAMP) content was determined at 37 degrees C, after 5 min of incubation with various agents, in the presence of a specific inhibitor of type III cAMP-dependent phosphodiesterase, RO 20-1724. The adenylate cyclase-cAMP system was associated with beta 2-adrenergic receptors. The cAMP content was increased by isoproterenol (23-fold), a beta-agonist, but not by octopamine, an alpha-agonist, and the affinity for ICI 118.551, a specific beta 2-antagonist, was greater than for CGP 20712A, a specific beta 1-antagonist (Kd: 0.03 x 10(-6) M and 15 x 10(-6) M respectively). The cAMP content was maximally increased by prostaglandin E2 > beta 2-adrenergic agonist >> vasopressine type 2 receptor agonist (26-, 23-, and 3-fold the basal cAMP content, respectively). The present study demonstrates that cultured marginal cells retain some of their in vivo properties including a modulated enzymatic cAMP system. This culture model should allow further in-depth investigation of the function of marginal cells.

Secretory diarrhea in villous adenoma of rectum: effect of treatment with somatostatin and indomethacin

The effects of treatment with the synthetic long-acting somatostatin analogue SMS-201-995 were studied in a patient with a fluid and electrolyte secreting villous adenoma of the rectum. The effects of SMS-201-995 on rectal fluid volume and electrolyte loss, and local and general prostanoid production were compared with those of treatment with indomethacin. During treatment with the somatostatin analogue iso-osmolar rectal fluid production increased about 25%; the quantity of prostaglandin E2 in the rectal fluid rose almost 20-fold. Prostaglandin F2 alpha, 6-keto-prostaglandin F1 alpha and 13,14-dihydro-15-keto-prostaglandin F2 alpha output showed similar, though less impressive increments during somatostatin treatment. The somatostatin analogue did not affect urinary prostanoid excretion except for levels of 2,3-dinor-thromboxane B2, which doubled. With indomethacin treatment diurnal rectal fluid production dropped by about 50% and all prostanoids measured in urine and rectal fluid decreased below control values. It appears that the somatostatin analogue SMS-201-995 has a marked stimulatory effect on the in vivo prostanoid production by the villous adenoma. Perhaps this stimulation is not confined to the tumor only, but also affects thromboxane synthesis.

Antidiuretic hormone stimulation of adenylate cyclase in semicircular canal epithelium

Basal adenosine 3',5'-cyclic monophosphate (cAMP) content and the modulation of its production were studied in the frog's semicircular canal epithelium. This epithelium secretes endolymph, a K(+)-rich, positively polarized fluid. The basal cAMP content measured by microradioimmunoassay was 244 +/- 14.2 fmol/structure per 5 min (n = 30). This content was increased about 8 times by 10(-5) M forskolin. Vasotocin, the frog antidiuretic hormone, increased the cAMP production by factors of 1.3 and 3.3 at concentrations of 10(-8) M and 10(-7) M, respectively. This stimulatory effect of vasotocin was blunted by the addition of alpha 2-adrenergic agonists, such as 10(-8) M-10(-5) M norepinephrine, in the presence of 10(-5) M propranolol, or 10(-5) M clonidine. Prostaglandin E2 at a concentration of 10(-8) M, which did not affect the cAMP production, did not modify the response to vasotocin. Glucagon (10(-6) M), calcitonin (10(-6) M), and parathyroid hormone (10 units/ml) did not affect the cAMP content. Prostaglandin E2 (10(-7) M) and the beta-adrenergic agonist isoproterenol (10(-6) M) stimulated the cAMP production by a factor of 1.6. These results indicate that the frog semicircular canal is a target of both vasotocin and catecholamines and that catecholamines through alpha 2-receptors modulate vasotocin-induced cAMP generation. Further, this interaction might be of physiological relevance in the modulation of ion transport in this structure.

Astrocytes from forebrain, cerebellum, and spinal cord differ in their responses to vasoactive intestinal peptide

Astrocytes from cortex, cerebellum, and spinal cord responded to isoproterenol and vasoactive intestinal peptide (VIP) with increases in intracellular cyclic AMP levels. The response to VIP was as great as that to isoproterenol in cortical astrocytes (180-fold and 185-fold, respectively), and the effect of VIP in combination with isoproterenol was partially additive. Spinal cord astrocytes also responded to VIP and isoproterenol with equal potency (seven- to ninefold and eight- to 13-fold, respectively), but the level of response was much smaller than in cortex. Spinal cord astrocytes were synergistic in their response to VIP and isoproterenol. The response to VIP was lowest in cerebellar astrocytes (only threefold), and no additivity was observed when VIP was added together with isoproterenol. A small response to alpha-melanocyte stimulating hormone (alpha-MSH) was also observed in cortex and cerebellum, but not in spinal cord. Somatostatin inhibited the response to isoproterenol in cortex and cerebellum, but had no effect in spinal cord. The results from the above study show that astrocytes obtained from these three regions of the rat CNS express quite different responses to VIP and alpha-MSH and further point to possible astrocyte heterogeneity.

Somatostatin infusion inhibits the stimulatory effect of testosterone on endosteal bone formation in the mouse

To investigate whether the effects of testosterone (T) on endosteal bone metabolism may be mediated by growth hormone (GH), intact male mice were infused for ten days with T (5 or 15 mg/kg/d) alone, or combined either with native somatostatin (SRIF) (220 micrograms/kg/d) or with the long-acting somatostatin analog SMS 201-995. Testosterone infusion induced a dose-dependent increase in histomorphometric parameters of bone formation, causing a 25% increase in osteoblastic and osteoid surface and 10% to 12% stimulation of the matrix and mineral appositional rates. Stimulation of bone formation rate was associated with a 2- to 3-fold increase in the incidence of serum GH peaks of high amplitude. SRIF (220 micrograms/kg/d) and SMS at low dose (4.32 micrograms/kg/d) decreased parameters of bone formation by 20% to 25%. At a higher dosage (13 micrograms/kg/d), which mildly decreased serum glucose and longitudinal bone growth, SMS further reduced bone formation rate. Infusion of SRIF with T (5 mg/kg/d) blunted the stimulatory effect of T. Similarly, infusion of a high dose of SMS (13 micrograms/kg/d), together with T (15 mg/kg/d), abolished the effect of T (15 mg/kg/d) without altering serum glucose or mineral levels. The effect of SRIF on testosterone-induced (5 mg/kg/d) bone formation was associated with inhibition of T-induced high-amplitude GH peaks. The results indicate that T stimulates the osteoblastic bone formation in association with increased GH secretion, whereas SRIF and the analog SMS produce inhibitory effects.

Benzyl alcohol increases membrane fluidity and modulates cyclic AMP synthesis in intact renal epithelial cells

To evaluate a possible modulation by membrane fluidity of hormonal, cAMP-mediated effects on renal epithelial cells, we studied the effect of the neutral local anesthetic, benzyl alcohol, on membrane fluidity and on basal and stimulated intracellular cAMP content in intact MDCK cells. Benzyl alcohol induced a dose-dependent decrease of lipid order which was measured by steady-state fluorescence anisotropy using trimethylammonium-diphenylhexatriene and propionyl-diphenylhexatriene as fluorescent probes. Benzyl alcohol induced a 2-fold increase in basal cAMP content, likely as a consequence of increased prostaglandin synthesis since this effect was abolished by indomethacin. The effect of benzyl alcohol on stimulated cAMP synthesis depended on the nature of the ligand: 10 mM benzyl alcohol increased significantly the stimulatory effect of prostaglandin E2, glucagon and forskolin but not of vasopressin. At higher concentrations (40 mM), benzyl alcohol did not affect significantly the glucagon-stimulated cAMP content, while it inhibited significantly the prostaglandin E2-, forskolin- and vasopressin-stimulated cAMP synthesis. The 40 mM benzyl alcohol-induced inhibition was reversed by 1 mM Mn2+, which is known to block the inhibitory GTP-binding protein Ni. These results suggest that: (i) the various components of the adenylate cyclase-cAMP system and their coupling are affected differently by changes in membrane fluidity, which might reflect differences in their lipid environment, (ii) changes in membrane fluidity can modulate responses of renal tubular cells to hormones, and thus tubular functions.

Protein kinase C activators and bradykinin selectively inhibit vasopressin-stimulated cAMP synthesis in MDCK cells

To evaluate a possible modulation by protein kinase C of hormonal, cAMP-mediated effects on renal epithelial cells, we studied the effect of protein kinase C activators and of bradykinin on intracellular cAMP accumulation in MDCK cells. A 15-min pretreatment of cells with phorbol 12-myristate 13-acetate or 1-oleoyl-2-acetylglycerol induced a dose-dependent inhibition of vasopressin-stimulated cAMP synthesis, but not of basal or glucagon-, prostaglandin E2-, and forskolin-stimulated cAMP generation. 4 alpha-Phorbol 12,13-didecanoate, inactive on protein kinase C, did not affect cAMP accumulation. Bradykinin (0.1-10 microM) also inhibited the stimulatory effect of vasopressin on cAMP synthesis in a concentration-dependent manner, but affected neither basal cAMP content, nor its stimulation by glucagon, prostaglandin E2 and forskolin. The effect of activators of protein kinase C and of bradykinin occurred while renal prostaglandin synthesis was blocked with indomethacin. The inhibitory effect of protein kinase C activators and bradykinin on cAMP generation was reversed by the protein kinase C inhibitor H7, was enhanced by monensin, one effect of which is to block the recycling of membrane receptors, and persisted when the GTP-binding protein N1 was blocked with 1 mM Mn2+. Our data suggest that: protein kinase C can modulate the tubular effects of vasopressin by inhibiting cAMP generation; this effect is not mediated by renal prostaglandins, and might result from a direct action on the vasopressin receptor, or on its coupling with Ns; the modulation by bradykinin of vasopressin effects are likely to be exerted, at least partly, through activation of protein kinase C.