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Figure 1.
Intense somatostatin receptor type 1 immunoreactivity (A) and somatostatin receptor type 2 immunoreactivity(B) in the epithelial and vascular endothelial cells of choroid plexus villi(diaminobenzidine, original magnification ×400).

Intense somatostatin receptor type 1 immunoreactivity (A) and somatostatin receptor type 2 immunoreactivity(B) in the epithelial and vascular endothelial cells of choroid plexus villi(diaminobenzidine, original magnification ×400).

Figure 2.
Strong somatostatin receptor type 1 immunoreactivity (A) and somatostatin receptor type 2 immunoreactivity (B) on arachnoid cells, connective tissue, and dural layer cells in arachnoid granulations. Note red blood cells within the superior sagittal sinus (A)(diaminobenzidine, original magnification ×200 [A] and ×400 [B]).

Strong somatostatin receptor type 1 immunoreactivity (A) and somatostatin receptor type 2 immunoreactivity (B) on arachnoid cells, connective tissue, and dural layer cells in arachnoid granulations. Note red blood cells within the superior sagittal sinus (A)(diaminobenzidine, original magnification ×200 [A] and ×400 [B]).

1.
Speake  TWhitwell  CKajita  HMajid  ABrown  PD Mechanisms of CSF secretion by the choroid plexus. Microsc Res Tech. 2001;5249- 59Article
2.
Chodobski  ASzmydynger-Chodobska  J Choroid plexus: target for polypeptides and site of their synthesis. Microsc Res Tech. 2001;5265- 82Article
3.
Patel  YC Somatostatin and its receptor family. Front Neuroendocrinol. 1999;20157- 198Article
4.
Reisine  TBell  GI Molecular properties of somatostatin receptors. Neuroscience. 1995;67777- 790Article
5.
Vora  JPOwens  DRRyder  RAtiea  JLuzio  SHayes  TM Effect of somatostatin on renal function. Br Med J (Clin Res Ed). 1986;2921701- 1702Article
6.
Bausher  LPHorio  B Regulation of cyclic AMP production in adult human ciliary processes. Exp Eye Res. 1995;6043- 48Article
7.
Tulassay  TTulassay  ZRascher  WSzucs  LSeyberth  HWNagy  I Effect of somatostatin on kidney function and vasoactive hormone systems in healthy subjects. Klin Wochenschr. 1991;69486- 490Article
8.
Wax  MBBarret  DA Regulation of adenylyl cyclase in rabbit iris ciliary body. Curr Eye Res. 1993;12507- 520Article
9.
Xia  SLFain  GLFarahbaksh  NA Synergistic rise in Ca2+ produced by somatostatin and acetylcholine in ciliary body epithelial cells. Exp Eye Res. 1997;64627- 635Article
10.
Balster  DAO'Dorisio  MSSummers  MATurman  MA Segmental expression of somatostatin receptor subtypes sst(1) and sst(2) in tubules and glomeruli of human kidney. Am J Physiol Renal Physiol. 2001;280F457- F465
11.
Antaraki  APiadites  GVergados  JAndreou  AChlouverakis  C Octreotide in benign intracranial hypertension [letter]. Lancet. 1993;3421170Article
12.
Albers  ARO'Dorisio  MSBalster  DA  et al.  Somatostatin receptor gene expression in neuroblastoma. Regul Pept. 2000;8861- 73Article
13.
Klisovic  DDO'Dorisio  MSKatz  SE  et al.  Somatostatin receptor gene expression in human ocular tissues: RT-PCR and immunohistochemical study. Invest Ophthalmol Vis Sci. 2001;422193- 2201
14.
Thoss  VSPiwko  CProbst  AHoyer  D Autoradiographic analysis of somatostatin SRIF1 and SRIF2 receptors in the human brain and pituitary. Naunyn Schmiedebergs Arch Pharmacol. 1997;355168- 176Article
15.
Brazeau  PVale  WBurgus  R  et al.  Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone. Science. 1973;17977- 79Article
16.
Otten  BJRoettvel  JJCruysberg  JRM Pseudotumor cerebri following treatment with growth hormone [abstract]. Horm Res. 1992;3716Article
17.
Malozowski  STanner  LAWysowski  DKFleming  GA Growth hormone, insulin-like growth factor I, and benign intracranial hypertension. N Engl J Med. 1993;329665- 666Article
18.
Lordereau-Richard  IRoger  MChaussain  JL Transient bilateral papilloedema in a 10-year-old boy treated with recombinant insulin-like growth factor I for growth hormone receptor deficiency. Acta Paediatr Suppl. 1994;399152Article
19.
Guevara-Aguirre  JVasconez  OMartinez  V  et al.  A randomized, double blind, placebo-controlled trial on safety and efficacy of recombinant human insulin-like growth factor-I in children with growth hormone receptor deficiency. J Clin Endocrinol Metab. 1995;801393- 1398
20.
Malozowski  STanner  LAWysowski  DKFleming  GAStadel  BV Benign intracranial hypertension in children with growth hormone deficiency treated with growth hormone. J Pediatr. 1995;126996- 999Article
21.
Price  DAClayton  PELoyd  IC Benign intracranial hypertension induced by growth hormone treatment. Lancet. 1995;345458- 459Article
22.
Wingenfeld  PSchmidt  BHoppe  B  et al.  Acute glaucoma and intracranial hypertension in a child on long-term peritoneal dialysis treated with growth hormone. Pediatr Nephrol. 1995;9742- 745Article
23.
Francois  ICasteels  ISilberstein  JCasaer  Pde Zegher  F Empty sella, growth hormone deficiency and pseudotumour cerebri: effect of initiation, withdrawal and resumption of growth hormone therapy. Eur J Pediatr. 1997;15669- 70Article
24.
Koller  EAStadel  BVMalozowski  SN Papilledema in 15 renally compromised patients treated with growth hormone. Pediatr Nephrol. 1997;11451- 454Article
25.
Azcona  CPreece  MARose  SJ  et al.  Growth response to rhIGF-I 80 µg/kg twice daily in children with growth hormone insensitivity syndrome: relationship to severity of clinical phenotype. Clin Endocrinol (Oxf). 1999;51787- 792Article
26.
Rogers  AHRogers  GLBremer  DLMcGregor  ML Pseudotumor cerebri in children receiving recombinant human growth hormone. Ophthalmology. 1999;1061186- 1190Article
27.
Lai  ZNEmtner  MRoos  PNyberg  F Characterization of putative growth hormone receptors in human choroid plexus. Brain Res. 1991;546222- 226Article
28.
De Keyser  JWilczak  NDe Backer  JPHerroelen  LVaquelin  G Insulin-like growth factor-I receptors in human brain and pituitary gland: an autoradiographic study. Synapse. 1994;17196- 202Article
29.
Frystyk  JVestbo  ESkjaerbaek  CMogensen  CEOrskov  H Free insulin-like growth factors in human obesity. Metabolism. 1995;44 (10) suppl 437- 44Article
30.
Frystyk  JSkjaerbaek  CVestbo  EFisker  SOrskov  H Circulating levels of free insulin-like growth factors in obese subjests: the impact of type 2 diabetes. Diabetes Metab Res Rev. 1999;15314- 322Article
31.
Nam  SYMarcus  C Growth hormone and adipocyte function in obesity. Horm Res. 2000;53suppl 187- 97Article
32.
Klisovic  DDSall  JWO'Dorisio  MSKatz  SE Somatostatin and octreotide inhibit IGF-1 mediated IGF-1Rb phosphorylation in human retinal pigment epithelium. Invest Ophthalmol Vis Sci. 2001;42244
Laboratory Sciences
November 2002

Expression of Somatostatin Receptors 1 and 2 in Human Choroid Plexus and Arachnoid GranulationsImplications for Idiopathic Intracranial Hypertension

Author Affiliations

From the William H. Havener Eye Center (Drs Katz, Klisovic, and Lubow) and the Arthur James Cancer Hospital (Dr Katz), The Ohio State University, Columbus; and Departments of Pediatrics (Dr O'Dorisio) and Pathology (Dr Lynch) and Holden Comprehensive Cancer Center (Dr O'Dorisio), The University of Iowa, Iowa City.

Arch Ophthalmol. 2002;120(11):1540-1543. doi:10.1001/archopht.120.11.1540
Abstract

Objective  To investigate the localization of somatostatin receptor types 1 and 2 in human choroid plexus (CP) and arachnoid granulations (AGs) by immunohistochemistry.

Methods  A prospective study was performed in an institutional setting. Immunohistochemistry was performed on 15 samples of CP and 12 samples of AGs from 15 patients who died with no signs or symptoms of intracranial disease (age range, 52-81 years). The CP samples were dissected from the lateral ventricles and AG samples were dissected from the superior sagittal sinus.

Results  We demonstrated the presence of both somatostatin receptor types 1 and 2 in all samples of normal human CP and AGs.

Conclusions  Analogous to their demonstration and to their function in kidney and ocular tissues, these receptors may be involved in the processes of cerebrospinal fluid production and absorption, and may play a role in the increased intracranial pressure of idiopathic intracranial hypertension.

Clinical Relevance  Somatostatin analogues have been used to treat idiopathic intracranial hypertension, a disorder of cerebrospinal fluid homeostasis. Data are scarce regarding the cell-specific distribution of somatostatin receptors in normal human CP and AGs, the sites of cerebrospinal fluid production and egress.

THE PRODUCTION and absorption of cerebrospinal fluid (CSF) are complex and poorly understood phenomena.1 The choroid plexus (CP) is known to be the site of CSF production in various mammalian species, including humans. Recent work has demonstrated synthesis of numerous peptides and their receptors in CP.2 Peptide molecules and their receptors involved in the process of CSF absorption, which takes place in the arachnoid granulations (AGs), are largely unknown.

Somatostatin (SST) is a ubiquitously distributed neuropeptide with antisecretory and antiproliferative properties.3 Its biological activity is mediated by 5 distinct membrane-bound SST receptors (SSTR1-5).4 These receptors have been discovered on diverse human and animal tissues involved in the production and absorption of extracellular fluid.510 Octreotide acetate, a long-acting SSTR2-specific analogue, has been used as an adjunctive treatment for idiopathic intracranial hypertension (IIH) without understanding of its mechanism or site of action.11

The purpose of this study was to investigate the localization of SSTR1 and SSTR2 in human CP and AGs by immunohistochemistry. These findings are discussed in the context of abnormalities associated with IIH, a disorder of CSF homeostasis.

METHODS

Fifteen samples of CP and 12 samples of AGs were obtained at autopsy from 15 patients who died with no signs of intracranial disease (age range, 52-81 years). Samples of CP were dissected from lateral ventricles, and AG samples were dissected from superior sagittal sinus. Tissue samples were obtained and processed in accordance with tissue procurement protocols from The University of Iowa, Iowa City. Specimens were fixed in 4% buffered formalin, embedded in paraffin, and serially cut on a microtome at 4 µm. Tissue sections were placed on charged slides, deparaffinized in xylene, and rehydrated. The slides were placed into preheated 10% sodium citrate (Antigen Retrieval Solution; Biogenics, Napa, Calif), microwaved for 10 minutes, and left in a sealed container for 15 minutes, then washed in phosphate-buffered saline 3 times. Afterward, the slides were washed in OptiMax Wash Buffer (Biogenics) and incubated in Power Block (Biogenics) for 10 minutes. Expression of SSTR1 and SSTR2 was studied by immunohistochemistry. Newly developed antibodies raised against N-terminal 57–amino acids of SSTR1 and N-terminal 45–amino acids of SSTR2 were used.12 Preparation of rabbit polyclonal SSTR1 antibody (Ab) and SSTR2 Ab as well as specificity testing were previously described.12,13 The slides were incubated overnight at 4°C with primary SSTR1 Ab and SSTR2 Ab (1:1000 and 1:2000 dilution in 3% bovine serum albumin in phosphate-buffered saline, respectively). Sections were washed with phosphate-buffered saline 3 times and incubated for 1 hour at room temperature with peroxidase-labeled polyclonal anti–rabbit Ab (DAKO A/S, Glostrup, Denmark). Immunohistochemical binding was visualized by incubating the tissue sections with diaminobenzidine chromogen for up to 15 minutes. The slides were then washed, counterstained, and coverslipped. Antigen competition was performed by preabsorbing SSTR1 Ab and SSTR2 Ab with corresponding truncated SSTR1 and SSTR2 proteins that were used as antigens in antigen preparation (for 3 hours at room temperature; final concentration of peptide was 50 mg/mL). Concentrations of preabsorbed Abs used for immunohistochemistry were corrected to account for dilution with blocking peptide.

RESULTS

In all 15 CP samples, intense membrane and cytoplasmic SSTR1 and SSTR2 immunoreactivity (ir) was detected on all epithelial cells and vascular endothelial cells in capillaries within individual villi (Figure 1). Equally strong SSTR1-ir and SSTR2-ir was observed in arachnoid cells, connective tissue, and dural layer cells in all AG samples(Figure 2). No immunostaining was observed on slides where primary Ab was omitted or in the presence of competing antigen (data not shown). There was no apparent difference in the intensity of immunoreactivity for either receptor subtype in CP or AGs in regard to patient age (within the age range noted).

COMMENT

The SSTR1-ir and SSTR2-ir were observed in all human CP and AG samples. Strong SSTR1-ir and SSTR2-ir in CP are consistent with the previously published results by Thoss and colleagues.14 They detected binding of radioactively labeled (labeled with iodine 125 [125I]) SST analogues, ie, [125I]Tyr3-octreotide (binds SSTR2 and SSTR5), [125I]CGP 23996 (binds SSTR1 and/or SSTR4), and [125I]LTT-SRIF-28 (binds all types of SSTRs) in human CP. The SST analogues used in that study bind more than 1 receptor subtype. Those results were suggestive of but not conclusive for the presence of any specific SSTRs on CP. Distribution of SSTRs was not studied previously on AGs in humans or any primate species.

The exact function of SST and its receptors in CSF homeostasis in humans is unknown at present; however, the abundance of SSTRs on CP and AGs implies their involvement in the processes of CSF production and absorption. The CSF dynamics might be affected locally at the level of CP and AGs through SSTRs or systemically by modulating the levels or activity of circulating hormones(growth hormone, insulinlike growth factor [IGF] 1, insulin, leptin, etc). In addition, SSTR1 and SSTR2 might modulate blood flow in CP capillaries and filtration in CP epithelium.

The SST axis has a role in ion transport, extracellular fluid production, and absorption in different mammalian and human tissues.3 Recent work has demonstrated SST effects in kidney and in the eye. Intravenous injection of SST modulates glomerular filtration rate, renal plasma flow, urine volume, and water clearance in normal human kidney.5,7 The recent work of Balster and colleagues10 demonstrated SSTR1 and SSTR2 gene expression as well as orderly segmental distribution of SSTR1-ir and SSTR2-ir along the glomerular and tubular system in normal human kidney tissue.10 Such data offer us a reasonable theoretical model for a similar role of the SST axis in CSF dynamics.

In the rabbit eye, SST inhibits aqueous production by stimulating adenylyl cyclase activity and release of intracellular calcium in nonpigmented epithelium of ciliary processes.6,8,9 Using reverse transcription polymerase chain reaction, Klisovic and colleagues13 recently detected gene expression for SSTR1, SSTR2, and SSTR4 in ciliary body in normal human eyes. In addition, SSTR1-ir and SSTR2-ir were detected on nonpigmented epithelium of ciliary processes, in marginal capillaries in ciliary processes, and on endothelial cells in trabecular meshwork. These data again suggest an analogous role for SST in aqueous dynamics of the eye, as well as the CSF.

The best studied activity of SST and its analogues in humans is the inhibition of the release of growth hormone from pituitary, which in turn results in the reduction of circulating levels of IGF-1.15 This is of special interest, because it is now apparent that a side effect of recombinant IGF-1 treatment in children with growth hormone receptor deficiency is a transient increase in intracranial pressure.1626 The increased intracranial pressure resolves with complete cessation of IGF-1 treatment or reduction of IGF-1 dose by 50%.25 In this regard, it is important to recognize that CP epithelium has one of the highest densities of IGF-1 receptors in the human brain.27,28 These data suggest a role for high plasma IGF-1 levels in the pathogenesis of increased intracranial pressure in children.

The IGF-1 axis also has a significant role in the pathogenesis of obesity. Obese patients often have numerous hormonal abnormalities, including glucose intolerance, insulin resistance, hyperinsulinemia, low plasma levels of growth hormone, and high levels of free IGF-1 due to overproduction of IGF-1 by adipocytes.2931 Idiopathic intracranial hypertension is a disease that predominantly affects obese women of childbearing age. Octreotide treatment in such patients might decrease levels of circulating IGF-1 but could also counteract its biological activity at the level of CP epithelium. In human retinal pigment epithelial cells (SSTR1 and SSTR2 positive), SST and octreotide inhibit biological effects of IGF-1 by inhibition of autophosphorylation of IGF-1 receptors, thereby inhibiting the IGF-1 signaling cascade.32

In conclusion, we demonstrated the presence of SSTR1 and SSTR2 in normal human CP and AGs. Analogous to their demonstration and to their function in kidney and ocular tissues, these receptors may be involved in the processes of CSF production and absorption in humans and may play a role in the increased intracranial pressure in IIH.

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Article Information

Submitted for publication December 28, 2001; final revision received June 10, 2002; accepted June 13, 2002.

This study was supported in part by the Ohio Lions Eye Research Foundation, the Bremer Fund, the Robert and Miriam Mikesell Research Fund, and the Jacob and Florence Moses Fund (the Columbus Foundation), Columbus, Ohio, and grant ROI CA 64177 from the National Institutes of Health, Bethesda, Md.

We thank Florinda Jaynes for her superb technical assistance.

Corresponding author and reprints: Steven E. Katz, MD, William H. Havener Eye Center, 5717 University Hospitals Clinic, 456 W 10th Ave, Columbus, OH 43210 (e-mail: katz.16@osu.edu).

References
1.
Speake  TWhitwell  CKajita  HMajid  ABrown  PD Mechanisms of CSF secretion by the choroid plexus. Microsc Res Tech. 2001;5249- 59Article
2.
Chodobski  ASzmydynger-Chodobska  J Choroid plexus: target for polypeptides and site of their synthesis. Microsc Res Tech. 2001;5265- 82Article
3.
Patel  YC Somatostatin and its receptor family. Front Neuroendocrinol. 1999;20157- 198Article
4.
Reisine  TBell  GI Molecular properties of somatostatin receptors. Neuroscience. 1995;67777- 790Article
5.
Vora  JPOwens  DRRyder  RAtiea  JLuzio  SHayes  TM Effect of somatostatin on renal function. Br Med J (Clin Res Ed). 1986;2921701- 1702Article
6.
Bausher  LPHorio  B Regulation of cyclic AMP production in adult human ciliary processes. Exp Eye Res. 1995;6043- 48Article
7.
Tulassay  TTulassay  ZRascher  WSzucs  LSeyberth  HWNagy  I Effect of somatostatin on kidney function and vasoactive hormone systems in healthy subjects. Klin Wochenschr. 1991;69486- 490Article
8.
Wax  MBBarret  DA Regulation of adenylyl cyclase in rabbit iris ciliary body. Curr Eye Res. 1993;12507- 520Article
9.
Xia  SLFain  GLFarahbaksh  NA Synergistic rise in Ca2+ produced by somatostatin and acetylcholine in ciliary body epithelial cells. Exp Eye Res. 1997;64627- 635Article
10.
Balster  DAO'Dorisio  MSSummers  MATurman  MA Segmental expression of somatostatin receptor subtypes sst(1) and sst(2) in tubules and glomeruli of human kidney. Am J Physiol Renal Physiol. 2001;280F457- F465
11.
Antaraki  APiadites  GVergados  JAndreou  AChlouverakis  C Octreotide in benign intracranial hypertension [letter]. Lancet. 1993;3421170Article
12.
Albers  ARO'Dorisio  MSBalster  DA  et al.  Somatostatin receptor gene expression in neuroblastoma. Regul Pept. 2000;8861- 73Article
13.
Klisovic  DDO'Dorisio  MSKatz  SE  et al.  Somatostatin receptor gene expression in human ocular tissues: RT-PCR and immunohistochemical study. Invest Ophthalmol Vis Sci. 2001;422193- 2201
14.
Thoss  VSPiwko  CProbst  AHoyer  D Autoradiographic analysis of somatostatin SRIF1 and SRIF2 receptors in the human brain and pituitary. Naunyn Schmiedebergs Arch Pharmacol. 1997;355168- 176Article
15.
Brazeau  PVale  WBurgus  R  et al.  Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone. Science. 1973;17977- 79Article
16.
Otten  BJRoettvel  JJCruysberg  JRM Pseudotumor cerebri following treatment with growth hormone [abstract]. Horm Res. 1992;3716Article
17.
Malozowski  STanner  LAWysowski  DKFleming  GA Growth hormone, insulin-like growth factor I, and benign intracranial hypertension. N Engl J Med. 1993;329665- 666Article
18.
Lordereau-Richard  IRoger  MChaussain  JL Transient bilateral papilloedema in a 10-year-old boy treated with recombinant insulin-like growth factor I for growth hormone receptor deficiency. Acta Paediatr Suppl. 1994;399152Article
19.
Guevara-Aguirre  JVasconez  OMartinez  V  et al.  A randomized, double blind, placebo-controlled trial on safety and efficacy of recombinant human insulin-like growth factor-I in children with growth hormone receptor deficiency. J Clin Endocrinol Metab. 1995;801393- 1398
20.
Malozowski  STanner  LAWysowski  DKFleming  GAStadel  BV Benign intracranial hypertension in children with growth hormone deficiency treated with growth hormone. J Pediatr. 1995;126996- 999Article
21.
Price  DAClayton  PELoyd  IC Benign intracranial hypertension induced by growth hormone treatment. Lancet. 1995;345458- 459Article
22.
Wingenfeld  PSchmidt  BHoppe  B  et al.  Acute glaucoma and intracranial hypertension in a child on long-term peritoneal dialysis treated with growth hormone. Pediatr Nephrol. 1995;9742- 745Article
23.
Francois  ICasteels  ISilberstein  JCasaer  Pde Zegher  F Empty sella, growth hormone deficiency and pseudotumour cerebri: effect of initiation, withdrawal and resumption of growth hormone therapy. Eur J Pediatr. 1997;15669- 70Article
24.
Koller  EAStadel  BVMalozowski  SN Papilledema in 15 renally compromised patients treated with growth hormone. Pediatr Nephrol. 1997;11451- 454Article
25.
Azcona  CPreece  MARose  SJ  et al.  Growth response to rhIGF-I 80 µg/kg twice daily in children with growth hormone insensitivity syndrome: relationship to severity of clinical phenotype. Clin Endocrinol (Oxf). 1999;51787- 792Article
26.
Rogers  AHRogers  GLBremer  DLMcGregor  ML Pseudotumor cerebri in children receiving recombinant human growth hormone. Ophthalmology. 1999;1061186- 1190Article
27.
Lai  ZNEmtner  MRoos  PNyberg  F Characterization of putative growth hormone receptors in human choroid plexus. Brain Res. 1991;546222- 226Article
28.
De Keyser  JWilczak  NDe Backer  JPHerroelen  LVaquelin  G Insulin-like growth factor-I receptors in human brain and pituitary gland: an autoradiographic study. Synapse. 1994;17196- 202Article
29.
Frystyk  JVestbo  ESkjaerbaek  CMogensen  CEOrskov  H Free insulin-like growth factors in human obesity. Metabolism. 1995;44 (10) suppl 437- 44Article
30.
Frystyk  JSkjaerbaek  CVestbo  EFisker  SOrskov  H Circulating levels of free insulin-like growth factors in obese subjests: the impact of type 2 diabetes. Diabetes Metab Res Rev. 1999;15314- 322Article
31.
Nam  SYMarcus  C Growth hormone and adipocyte function in obesity. Horm Res. 2000;53suppl 187- 97Article
32.
Klisovic  DDSall  JWO'Dorisio  MSKatz  SE Somatostatin and octreotide inhibit IGF-1 mediated IGF-1Rb phosphorylation in human retinal pigment epithelium. Invest Ophthalmol Vis Sci. 2001;42244
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