Biomedical subjects

K Yasuda

Publications and source records attributed to K Yasuda.

At least 739 records · Page 41Linked to original sources

PubMed1993

Reduced response to metoclopramide and anomalous rising response to upright posture of plasma aldosterone concentration in Japanese patients with aldosterone-producing adenoma.

We examined the changes in plasma aldosterone concentration (PAC) during 3 kinds of postural stimulation tests and a metoclopramide test in 20 Japanese patients with surgically proven aldosterone-producing adenoma. In the 2-h upright test (n = 16), PAC increased (P < 0.01) in 14 of 16 patients, with a mean percent change of 135 +/- 42% (+/- SD) of the supine levels without any significant change in plasma cortisol. In the furosemide-upright test (n = 17), PAC increased (P < 0.01) in 15 of 17 patients by 131 +/- 27%, with a significant increase in cortisol. However, in the furosemide upright test after dexamethasone pretreatment, which suppressed plasma cortisol during the test, PAC also increased (P < 0.01) in all 9 patients examined by 158 +/- 36%. Angiotensin-II infusion failed to increase PAC in all 4 patients examined whose PAC increased with postural stimulation tests. Injection of 10 mg metoclopramide (n = 13) induced a significant, but less marked, increase (P < 0.01) in PAC to 157 +/- 59% of basal levels, which was lower than those in previously reported series in Western countries. These results suggest that 1) there is a difference in PAC responsiveness to postural stimulation tests and to metoclopramide injection between Japanese and Western patients; and 2) the difference in the metoclopramide-induced aldosterone response implies a relative reduction of tonic dopaminergic inhibition of aldosterone secretion in our Japanese patients with aldosterone-producing adenoma.

Adrenal Cortex↗

PubMed1993

Photodynamic DNA strand breaking activities of acridine compounds.

Induction of single strand breaks in DNA was assessed by the conversion of supercoiled closed circular plasmid DNA into the open circular form. Euflavine produced single-strand breaks following irradiation but not in the control maintained in the dark. The single strand breaking activity of photoactivated euflavine was found to be dose-dependent. The effective dose conversion 50% (ED50) of the closed circular DNA to the open circular form was 0.53 microM. A comparison of 8 acridine compounds revealed that the ED50 of diaminoacridines such as euflavine, proflavine and acridine yellow or the 3,6-dimethylamino-derivative (acridine orange) was less than 1 microM while the ED50 values of the other acridines were greater than 80 microM. Euflavine was markedly inhibited by singlet oxygen scavengers such as NaN3, histidine, alpha-tocopherol or beta-carotene and partly inhibited by superoxide dismutase, mannitol or catalase. These results suggest that enflavine induces single strand breaks in DNA mainly by a type II photodynamic mechanism. Photodynamic single strand breaking activities appeared related to their mutagenic activities on yeast. This experimental system described here is useful for the quantitative assessment of the single strand breaking activities of various photosensitizers in vitro and for the determination of active oxygen species involved in those processes.

Acriflavine↗

PubMed1993

Construction of a physiologically based pharmacokinetic model to describe the hepatobiliary excretion process of ligands: quantitative estimation of intracellular diffusion.

A physiologically based pharmacokinetic model was established to describe the hepatobiliary excretion process for ligands which are excreted into the bile without metabolic conversion. In this model, the following processes were taken into consideration: influx and efflux across the liver sinusoidal membrane, intracellular diffusion, and excretion across the canalicular membrane into the bile. The partial differential equation by which these processes were described was solved to obtain the Laplace transformed solution for the biliary excretion rate of ligands, based on the plasma concentration profiles as an input function. The time profiles for the biliary excretion rate of dibromosulfophthalein (DBSP; 6.80 mg/kg b.w.) or cefodizime (15.0 mg/kg b.w.) after i.v. bolus administration to rats were fitted to the solution using a nonlinear least-squares program based on a fast inverse Laplace transform (MULTI-FILT [Y. Yano et al., Chem. Pharm. Bull., 37, 1035 (1989)] to determine the permeability-surface area product across the plasma membrane as well as the apparent intracellular diffusion coefficient. DBSP and cefodizime were used as model compounds since these two ligands possess different binding characteristics for cytosol protein(s). Although both ligands are present predominantly in the cytosol, DBSP binds to intracellular protein(s) (such as ligandin) to a great extent whereas the protein binding of cefodizime is not so extensive. The fitted lines were superimposed on the experimental results.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile↗

PubMed1993

Blood gas analysis in dogs with pulmonary heartworm disease.

Blood gases were analyzed in dogs with pulmonary heartworm (HW) disease. The arterial oxygen tension (PaO2) in dogs with mild signs of dirofilariasis (mildly affected group, n = 48, 85.7 +/- 8.2 mmHg) and in dogs with signs of right heart failure (severely affected group, n = 13, 76.4 +/- 11.6 mmHg) was lower (p < 0.01) than in dogs without HW infection (HW-free group, n = 19, 91.5 +/- 7.3 mmHg). Only 2 dogs in the severely affected group had a PaO2 less than 60 mmHg. The arterial carbon dioxide tension (PaCO2, p < 0.01) and mixed venous O2 (p < 0.01) and CO2 (p < 0.01) tensions were lower, and alveolar-arterial oxygen difference (AaDO2, p < 0.01) was greater in the severely affected group than in the HW-free and mildly affected groups. Arterial pH and bicarbonate (HCO3-) concentrations were lower (p < 0.01) in both affected groups than in the HW-free groups. The anion gap level was not different among the 3 groups. Serum lactic acid level in the severely affected group was higher (p < 0.01) than in the HW-free and mildly affected groups. However, a slightly higher serum lactic acid concentration was found only in 2 dogs of the severely affected group (3.84 mmol/l and 3.82 mmol/l). The PaO2 (r = -0.62) and AaDO2 (r = 0.66) correlated significantly (p < 0.01) with mean pulmonary arterial pressure. One week after HW removal, blood gases, pH and HCO3- concentration remained unchanged in the mildly affected group. In the severely affected group, blood gas values were the same, but pH and HCO3- concentration improved slightly.

Alanine Transaminase↗

PubMed1993

Effects of reserpine treatment on pituitary-adrenocortical axis in patients with Cushing's disease.

Effects of reserpine treatment, not associated with pituitary irradiation, on the pituitary-adrenocortical axis in a total of 37 untreated patients with Cushing's disease were evaluated. With short-term treatment (2 mg daily for 2 weeks, n = 36), basal excretion of urinary 17-OHCS significantly decreased from 11.2 +/- 5.2 mg/day/m2 (body surface area) (mean +/- SD) to 9.6 +/- 4.4 mg/day/m2 (P < 0.01), and metyrapone-induced incremental responses of urinary 17-OHCS decreased from 58.4 +/- 41.4 mg/3 days/m2 to 45.9 +/- 29.8 mg/3 days/m2 (P < 0.05). Long-term treatment (1.7 +/- 0.3 mg/day for a mean of 15.8 +/- 19.9 weeks) induced a marked reduction in plasma cortisol, and 24-h urinary 17-OHCS and/or free cortisol in 4 of 8 patients examined. Long-term reserpine administration caused normal suppression of plasma cortisol (or 11-OHCS) in 3 of 9 patients with 1 mg, and in all of 5 patients with an 8 mg overnight dexamethasone suppression test. Plasma ACTH response to CRH was evidently decreased in one patient evaluated one month after the initiation of reserpine. The circadian rhythm of plasma cortisol was normal in one patient when the basal glucocorticoid level became normal with reserpine treatment. The present findings suggest that reserpine itself contributes in a causal fashion to the effectiveness of our regimen, reserpine and pituitary irradiation, for some Cushing's disease patients in whom it is effective.

17-Hydroxycorticosteroids↗

PubMed1993

Low plasma 19-hydroxyandrostenedione levels in patients with aldosterone-producing adenoma.

The present study was performed to clarify changes in plasma levels of 19-hydroxyandrostenedione (19-OH-AD), an amplifier of aldosterone and a possible hypertensinogenic steroid, during several tests for the renin-angiotensin system in 20 patients with aldosterone-producing adenoma (APA) and to determine whether 19-OH-AD participates in the etiology of the hypertension in this disorder. Basal plasma 19-OH-AD levels in patients with APA were significantly lower than those in 50 normal subjects, and correlated positively with basal plasma cortisol levels (r = 0.45, P < 0.05). Plasma 19-OH-AD levels were not changed significantly by 2-h standing during which plasma renin activity (PRA) remained suppressed. With 40 mg iv furosemide plus 2-h standing during which PRA remained suppressed, plasma 19-OH-AD levels increased significantly with a concomitant significant increase in plasma cortisol. With dexamethasone pretreatment, however, such positive responses of plasma 19-OH-AD and cortisol disappeared. After the removal of the APA with the adjacent adrenal tissue, PRA and plasma aldosterone concentrations became normal or low-normal, but plasma 19-OH-AD and cortisol did not change as compared with the preoperative levels. There were no significant correlations between basal plasma 19-OH-AD levels and mean blood pressure either before or after the adrenal operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗

PubMed1993

Aldosterone binding to mineralocorticoid receptors of mononuclear leukocytes in diabetic subjects.

We present the characteristic features of mineralocorticoid receptor regulation in human mononuclear leukocytes in patients with diabetes mellitus. Eighteen diabetic patients (3M and 15F, aged from 28 to 77 years with a mean of 53 +/- 14 (mean +/- SD) years) and 7 normal subjects (6M and 1F, aged from 29 to 59 years with a mean of 41 +/- 13 years) were studied. The mean plasma aldosterone concentration in the diabetic patients was significantly lower than that in the normal subjects (137 +/- 62 vs 189 +/- 36 pmol/l, p < 0.05). Seven of the 18 diabetic patients were hypoaldosteronemic. These 7 patients, however, showed normokalemia, except one with mild hyperpotassemia. The number of binding sites of [3H]aldosterone to mineralocorticoid receptor in the diabetic patients was significantly higher than that in the normal subjects (853 +/- 281 vs 488 +/- 109 sites/cell, p < 0.05), but there was no significant difference in Kd of [3H]aldosterone binding to mineralocorticoid receptor between the diabetic patients and normal subjects (1.34 +/- 0.37 vs 0.99 +/- 0.61 nmol/l). In the diabetic patients, a significant negative correlation was observed (r = 0.70, p < 0.01) between plasma aldosterone concentration and the binding sites, but not between plasma aldosterone concentration and Kd. In the total subjects, including normal subjects and diabetic patients, a significant negative correlation was also found between plasma aldosterone concentration and binding sites (r = 0.72, p < 0.001). These results suggest that increased binding sites of mineralocorticoid receptor may help to prevent diabetic patients from being hyperkalemic.

Adult↗

PubMed1993

Tetany due to hypomagnesemia induced by cisplatin and doxorubicin treatment for synovial sarcoma.

Hypocalcemic crisis developed in a patient with monophasic synovial sarcoma after amputation of the right leg, followed by long-term treatment with cisplatin and doxorubicin. Laboratory data revealed severe hypomagnesemia and hypocalcemia. High normal intact parathyroid hormone (PTH), elevated mid-region PTH and undetectable osteocalcin levels had already been found before the appearance of obvious symptoms concomitantly associated with moderate hypomagnesemia and hypocalcemia. Further, both PTH levels measured by two different methods gradually decreased until the initiation of magnesium supplementation. The magnesium supplement immediately relieved the tetany, and induced striking increases in both intact and mid-region PTH levels transiently and continuous elevations of osteocalcin levels. These results suggest that magnesium depletion has dual effects on PTH secretion, from stimulation to inhibition, as hypomagnesemia progresses. Both relative hypoparathyroidism and refractoriness of bone to PTH were thought to be responsible for hypocalcemia due to hypomagnesemia.

Adolescent↗

PubMed1993

Clinical significance of the galvanic body sway test in cerebellopontine angle tumors.

Since 1984, we have been modifying a new method of recording fine body sway elicited by low current stimuli of less than 0.4 mA, and of quantitatively evaluating the responses by Fourier transform. In order to easily and early detect acoustic tumors, we have applied a test battery consisting ABR, caloric test and galvanic body sway test (GBST) to 31 cases with acoustic neurinoma, to 5 cases with other CPA-tumors, and to 24 cases suspected of having CPA tumors. Of 27 cases with acoustic neurinoma on whom the GBST was performed, 25 cases (92.6%) shows abnormal responses. On the other hand, the ABR was abnormal in all cases, except for one case in the early stage of an ear tumor. However, the ABR was positive in 12 cases out of 24 with suspected findings without tumor, but the GBST was positive in only 3 cases out of 17 tested. Moreover, 26 cases (83.9%) with acoustic tumors showed abnormal CP in their first caloric tests. Comparing these observations with the results of image diagnosis, we conclude that the GBST is as useful for detecting small acoustic neurinomas as the ABR and the carloric test. Therefore, we have routinely used a test battery consisting ABR, caloric test and GBST for evaluation of acoustic neurinomas. However, we could not differentiate between acoustic neurinoma and CPA-tumor by using the three-test battery.

Auditory Threshold↗

PubMed1993

The central projections of the monkey tooth pulp afferent neurons.

Transganglionic transport of horseradish peroxidase conjugated to wheatgerm agglutinin (HRP:WGA) entrapped in hypoallergenic polyacrylamide gel was used to study the patterns of termination of primary afferents that innervate the upper and lower tooth pulps within the trigeminal sensory nuclear complex (TSNC) of the monkey. HRP:WGA injections were also made into the lower incisors and molars, in order to examine the topographic arrangement of pulpal afferent projections. HRP-labeled pulpal afferents innervating lower and upper teeth projected ipsilaterally to the rostral subnucleus dorsalis (Vpd) and caudal subnucleus ventralis (Vpv) of the nucleus principalis (Vp); the rostrodorsomedial (Vo.r) and dorsomedial (Vo.dm) subdivisions of the nucleus oralis (Vo); the dorsomedial subdivision of the nucleus interpolaris (Vi); and laminae I-II and/or V of the nucleus caudalis (Vc) at its rostralmost level. The HRP-labeled terminals from upper and lower pulpal afferents formed a rostrocaudal column from the midlevel of Vp to the rostral tip of Vc. The label in Vp and Vo was considerably dense, but the column of terminals was interrupted at the Vpd-Vpv transition. The label in Vi and Vc was much less dense compared to that in the rostral nuclei, and the column of terminals was interrupted frequently. The representation of the upper and lower teeth in TSNC was organized in a somatotopic fashion that varied from one subdivision to the next, though their terminal zones overlapped within Vpd. The upper and lower teeth were represented in Vpv, Vo.r, Vo.dm, Vi, and Vc in a ventrodorsal, dorsoventral, lateromedial, lateromedial, and lateromedial sequence, respectively. Topographic arrangement was also noticed for the projections of pulpal afferents from the lower incisors and molars: The representations of the lower incisors and molars in Vpv, Vo.r, Vo.dm, Vi, and Vc were organized in a lateromedial, dorsoventral, ventrodorsal, ventrodorsal, and lateromedial sequence, respectively. The present results indicating sparse projections from pulpal afferents in the monkey's Vc are in good correspondence with a clinical report that trigeminal tractotomy just rostral to the obex has no significant effect on dental pain perception in patients. Furthermore, the present study indicates that projection patterns of pulpal afferents--which include the termination sites, the density of terminations between nuclei, and topographic arrangement--differ among animal species.

Afferent Pathways↗

PubMed1993

Effects of the current used on determining a critical temperature by electrical resistivity measurements in dental alloys.

The electrical resistivity measurement to determine a critical temperature (Tc) in a stoichiometric CuAu alloy is discussed on the dependence of the current used. The temperature was measured on two ways: With the thermocouple connected to the specimen by spot-welding, and with them separated. In the latter case, the greater the current, the lower the apparent Tc because of the generation of Joule heat. To obtain a more precise Tc, the current should be as small as possible or the thermocouple should be located as close as possible to the specimen. It is highly desirable for the thermocouple and the specimen to be welded together, if the effects of some contamination can be ignored in measuring system.

Copper↗

PubMed1993

Splice variant of the somatostatin receptor 2 subtype, somatostatin receptor 2B, couples to adenylyl cyclase.

The diverse biological actions of somatostatin (SRIF) are mediated by a family of receptors, of which five have been cloned and characterized. One of the SRIF receptor subtypes, SSTR2, has been shown to exist in two forms. SSTR2A and SSTR2B are 369 and 346 amino acids in size, respectively, and differ in length and amino acid sequence in their intracellularly located carboxyl termini. SSTR2A and SSTR2B are generated by alternative splicing of SSTR2 mRNA. We previously characterized mouse SSTR2A and showed that it could be distinguished from other cloned SRIF receptor subtypes by its high affinity for MK-678 and its lack of coupling to adenylyl cyclase. To determine whether the properties of mouse SSTR2A and SSTR2B differ, we have expressed both in COS-7 cells and characterized their ligand-binding properties and ability to couple to adenylyl cyclase. The two receptors exhibited similar affinities for a number of SSTR2-selective agonists such as MK-678. Pretreatment with SRIF of COS-7 cells expressing each receptor reduced high affinity agonist binding to both SSTR2A and SSTR2B, indicating that both receptors can be regulated. Furthermore, agonist binding to both receptors was reduced by GTP analogs and Na+, indicating that they both associate with G proteins. As shown previously, SSTR2A could not mediate SRIF inhibition of forskolin-stimulated cAMP formation. In contrast, SSTR2B was coupled to adenylyl cyclase and was able to mediate SRIF inhibition of forskolin-stimulated cAMP formation. Thus, SSTR2A and SSTR2B differ in their ability to couple to adenylyl cyclase. Because SSTR2A and SSTR2B differ only in the length and amino acid sequence of their carboxyl termini, these findings imply that the carboxyl-terminal 15 residues of SSTR2B may be involved in coupling this receptor to adenylyl cyclase.

Adenylyl Cyclases↗

PubMed1993

Low friction total knee arthroplasty with the alumina ceramic condylar prosthesis.

This paper evaluates the failure and wear properties of the alumina ceramic posterior cruciate condylar total knee prosthesis, and reports the preliminary clinical results of this prosthesis. Thirteen sets of the alumina ceramic prostheses were used for destruction and wear tests. The average ultimate load in the static destruction tests showed 2.63 x 10(4) Newtons in the femoral component, and 1.28 x 10(4) Newtons in the tibial component. The average ultimate energy in the impact destruction tests showed 22.1 Joules in the femoral components, and 20.3 Joules in the tibial components. The wear test demonstrated that the average depth of wear was 0.04 mm in the alumina ceramic prostheses, and 0.20 mm in the Vitallium prostheses. Observation of the UHMWPE wear surface with a scanning electron microscope indicated many deep scratches and a scooped concave lesion in the Vitallium prostheses; there were few deep scratches in the alumina ceramic prostheses. Thirty patients underwent 32 total knee arthroplasties using the alumina ceramic posterior cruciate condylar prosthesis between 1988 and 1990. The results were evaluated as excellent for 59%, good for 28%, fair for 10%, and poor for 3%. Critical roentgenographic review demonstrated no cases of loosening or sinking after arthroplasties using the alumina ceramic prosthesis. Radiolucent lines were observed only in 4 knees (12%) cases. All were observed around the tibial components, but were less than 1 mm in thickness. The frequency of the radiolucent lines is less than that observed in the Vitallium prosthesis at the same followup period. The alumina ceramic posterior cruciate condylar prosthesis may have sufficient durability and excellent wear properties for low friction total knee arthroplasty.

Aluminum Oxide↗

PubMed1993

[Localization of salazopyrin in colonic mucosa patients with ulcerative colitis].

In this study SASP metabolite levels were measured in colonic mucosal specimens and plasma samples from 31 patients with ulcerative colitis (UC) under treatment with the drug. Colonic tissue specimens were obtained by endoscopically guided biopsy and plasma was isolated from peripheral blood. Measurements were performed by HPLC according to the procedure of Fischer et al. The levels of 5-ASA and SP in either of colonic tissue or plasma were significantly lower than those of Ac-5-ASA and Ac-SP, respectively. The tissue level of 5-ASA had a significant correlation to the dosage of 5-ASA. The tissue levels of 5-ASA and Ac-5-ASA were low in an active stage of UC than during a remission period and the difference observed with respect to the latter metabolite was significant. These findings suggest that acetylation of 5-ASA is inhibited in the colonic mucosa in an active stage of the disease.

Adult↗

PubMed1993

Cloned somatostatin receptors: identification of subtype-selective peptides and demonstration of high affinity binding of linear peptides.

The recent molecular cloning of the genes encoding three somatostatin (SRIF) receptor subtypes has allowed for the individual expression of these receptors in mammalian cells and characterization of their respective pharmacological profiles. In the present study, we have investigated the affinities of a battery of SRIF analogues to bind to SRIF receptor subtypes SSTR1 (cloned somatostatin complex), SSTR2, and SSTR3, as well as their abilities to inhibit the release of growth hormone from anterior pituitary cells in vitro. We labeled SSTR1 and SSTR3 receptors expressed in Chinese hamster ovary and COS-1 cells, respectively, with the metabolically stable SRIF analogue 125I-CGP 23996. SSTR2 receptors expressed in Chinese hamster ovary cells were labeled with the SSTR2-specific radioligand 125I-MK-678. Inhibition studies were performed using SRIF analogues of differing structures, including hexapeptide analogues similar to MK-678, octapeptide analogues similar to SMS 201-995, pentapeptide analogues similar to c[Ahep-Phe-D-Trp-Lys-Thr(Bzl)] (SA), and linear SRIF analogues. SSTR1 bound SRIF and SRIF-28 with high affinity and the peptide SA and its structural analogues with low affinity. The hexapeptides did not interact with SSTR1 at concentrations as high as 1 microM, and only a few of the octapeptides or linear peptides bound, with very low affinities. In contrast, 125I-MK-678 binding to SSTR2 was potently inhibited by the hexapeptides, octapeptides, and some of the linear compounds, whereas SA and its analogues did not bind to SSTR2. The potencies of the various SRIF agonists to inhibit growth hormone release in vitro was highly correlated with their potencies to inhibit radioligand binding to SSTR2, but not to SSTR1 or SSTR3. SSTR3 bound analogues of each class but with moderate to low affinities, with the exception of several linear peptides and one of the octapeptides. We report for the first time the binding affinities of linear analogues of SRIF, some of which display subnanomolar affinities and are highly selective for SRIF receptor subtypes. Most importantly, these studies identify several peptide analogues that are highly potent, specific, and selective for individual subtypes of SRIF receptors. Such information, coupled with the knowledge of the distribution of these receptor subtypes in normal and pathological tissues, will be critical for more specific experimental and therapeutic interventions.

Amino Acid Sequence↗

PubMed1993

Mutation of an aspartate at residue 89 in somatostatin receptor subtype 2 prevents Na+ regulation of agonist binding but does not alter receptor-G protein association.

Sodium ions have been shown to reduce the binding of agonists to a number of G protein-linked receptors. They are believed to do so by interacting with aspartate residues in the second membrane-spanning region of these receptors to cause G protein uncoupling, resulting in a diminished affinity of the receptors for agonists. To investigate Na+ regulation of agonist binding to somatostatin receptors, Na+ was tested for its effect on the binding of agonists to cloned somatostatin receptor type 1 (SSTR1) and somatostatin receptor type 2 (SSTR2) stably expressed in Chinese hamster ovary cells. Na+ reduced agonist binding to SSTR2 but not to SSTR1. Because high affinity agonist binding to SSTR1 does not depend on G protein coupling but agonist binding to SSTR2 is reduced by guanosine-5'-(beta, gamma-imido)triphosphate and pertussis toxin treatment, the selective Na+ effect on SSTR2 is consistent with previous findings with other receptors showing that Na+ uncouples receptors from G proteins, thereby reducing the affinity of the receptors for agonists. Conversion of Asp89 to Asn89 in SSTR2 resulted in a mutant receptor whose affinity for agonists was not altered by Na+, indicating that Asp89 is involved in mediating the effects of Na+ on agonist binding to SSTR2. However, the affinities of the mutant and wild-type receptors for somatostatin were the same, and both guanosine-5'-O-(gamma-thio)triphosphate and pertussis toxin treatment reduced agonist binding to the mutant and wild-type receptors. These findings differ from the results of similar mutagenesis studies on other G protein-linked receptors, in that the mutant and wild-type SSTR2 forms associate with G proteins in similar ways. These results indicate that Asp89 acts in a novel manner to regulate agonist binding and G protein interaction with SSTR2.

Animals↗

PubMed1993

Characterization of cloned somatostatin receptors SSTR4 and SSTR5.

The recent molecular cloning of the genes and cDNAs encoding multiple somatostatin (SRIF) receptor subtypes has allowed for the individual expression of these receptors in mammalian cells and characterization of their respective pharmacological profiles. Previously, we fully described and compared the pharmacological properties of the first three SRIF receptor subtypes, SRIF receptor type (SSTR)1, SSTR2, and SSTR3. In the present study, we have investigated the properties of the newly cloned SRIF receptor subtypes SSTR4 and SSTR5 with regard to pharmacological profiles, the regulation of high affinity agonist binding to these receptors by stable GTP analogues, Na+, or prior exposure to agonists, and the inhibition of forskolin-stimulated cAMP accumulation mediated by these receptors. We labeled SSTR4 and SSTR5 expressed in Chinese hamster ovary (CHO-K1) and COS-1 cells, respectively, with the metabolically stable SRIF analogue 125I-CGP 23996. Radioligand binding competition studies were performed using SRIF analogues of differing structures, including hexapeptide analogues similar to MK-678, octapeptide analogues similar to SMS 201-995, pentapeptide analogues similar to c[Ahep-Phe-D-Trp-Lys-Thr(Bzl)], and linear SRIF analogues. SSTR4 bound compounds in all structural classes with high to moderate affinities, and several compounds were identified that are > 100-fold selective for SSTR4, compared with the other cloned SRIF receptors, including the linear SRIF analogue BIM-23052 and the CGP 23996-like SRIF analogue L-362,855. In contrast, SSTR5 bound very few SRIF analogues with high affinity. Both receptors could be regulated by prior exposure to agonist. In addition, agonist binding to SSTR4 was reduced by stable GTP analogues, Na+, and pertussis toxin, but agonist binding to SSTR5 was not affected by these treatments. SSTR4 is efficiently coupled to the inhibition of adenylyl cyclase activity, whereas SSTR5 appears not to couple to this cellular effector system. Such differences between the cloned SRIF receptors provide useful strategies for identifying regions of these receptor subtypes that may be involved in ligand-binding specificities and G protein and cellular effector system coupling. The identification of subtype-selective SRIF analogues may lead to more specific therapeutic interventions.

Amino Acid Sequence↗

PubMed1993

Comparison of mutations of ras oncogene in human pancreatic exocrine and endocrine tumors.

BACKGROUND: Ras oncogene mutations have been found in many human cancers; however, pancreatic endocrine tumors have rarely been studied. The purpose of this study was to analyze ras mutations in pancreatic endocrine tumors and to compare these results with the incidence of ras mutations in pancreatic exocrine cancers studied in our laboratory. METHODS: Ras oncogene mutations were studied in 33 foregut endocrine tumors (pancreatic 31, duodenal submucosa 2). Eleven were insulinomas, 12 gastrinomas, 2 glucagonomas, and 11 others were nonfunctioning islet cell carcinomas. Thirteen were benign and 20 were malignant. These were compared with 65 pancreatic exocrine cancers. Tumors were microdissected from paraffin-embedded sections. DNA was extracted and amplified by polymerase chain reaction. Mutations were detected by a oligonucleotide hybridization method with sequence-specific phosphorus 32-radiolabeled probes. RESULTS: No ras mutations were identified among the 33 pancreatic endocrine tumors. In contrast, 51 of 65 (78.5%) pancreatic exocrine cancers exhibited a ras mutation. Fifty were K-ras mutations and one unusual tumor exhibited a N-61 ras mutation. CONCLUSIONS: Ras oncogene mutations do not play a role in the tumorigenesis of pancreatic endocrine tumors.

Adenoma, Islet Cell↗