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Biomedical subjects

P C Kothary

Publications and source records attributed to P C Kothary.

8 recordsLinked to original sources
PubMed1992

Identification and partial characterization of a somatostatin-14 binding protein on rat liver plasma membranes.

Binding of somatostatin-14 to rat liver plasma membranes was characterized with 125-labeled[tyr11] somatostatin-14. Binding at 24 degrees C reached a plateau at 50 min and was reversible by synthetic somatostatin-14. Scatchard analysis revealed a single class of binding sites (affinity constant = 2.4 +/- 0.2 nmol/L, binding capacity = 148 +/- 0.02 fmol/mg protein). Specificity for somatostatin-14 was demonstrated by the inhibition of 125I-[tyr11]somatostatin-14 binding by biologically active somatostatin analogs but not by a biologically inactive somatostatin analog or unrelated peptides. The radioiodinated binding site complex could be cross-linked with disuccinimidyl suberate. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel autoradiography revealed a 70,000-Da band. Dithiothreitol, a reducing reagent, did not alter the mobility of the band, and the band could be abolished in the presence of 10 mumol/L synthetic somatostatin-14. Covalently cross-linked, iodinated binding protein complexes could be solubilized by the nonreducing detergents Zwittergent 3-12 and 3-([3-cholamidopropyl] diethylammonio)-1-propanesulfonic acid (CHAPS). Solubilized complex bound to wheat-germ agglutinin-agarose columns and was eluted by N,N',N"-triacetylchitotriose. Binding to wheat-germ agglutinin agarose columns was lost after pretreatment with endo-beta-N-acetylglucosaminidase F. Binding studies with liver plasma membranes, 125I-labeled[tyrosine11]somatostatin-14 and guanine nucleotides showed inhibition of binding in the presence of guanine nucleotides. These results indicate that the purified rat liver plasma membranes contain a specific binding protein for somatostatin-14, the binding protein appears to be glycosylated and somatostatin-14 binding to rat liver plasma membranes may be regulated by G proteins.

Adenosine Diphosphate↗
PubMed1992

Inhibition of DNA synthesis by somatostatin in rat hepatocytes stimulated by hepatocyte growth factor or epidermal growth factor.

The antiproliferative effects of somatostatin on hepatocytes stimulated by hepatocyte growth factor (HGF) or epidermal growth factor (EGF) were investigated using primary cultures of adult rat hepatocytes. Somatostatin inhibits HGF-induced (at a dose of 10 ng/mL) or EGF-induced (at a dose of 100 ng/mL) 3H-thymidine incorporation into hepatocytes in a dose-dependent manner (10(-10) to 10(-8) M). This inhibition was confirmed by autoradiography. The effect of somatostatin was nontoxic as judged by preserved albumin synthesis, a marker for differentiated hepatocyte function. In the presence or absence of somatostatin, neither HGF nor EGF significantly altered intracellular cyclic adenosine monophosphate (cAMP). We conclude that somatostatin is a potent inhibitor of HGF- or EGF-induced deoxyribonucleic acid synthesis in adult rat hepatocytes. The mechanism of this inhibition appears to be independent of cAMP. The significance of somatostatin in liver regeneration has yet to be assessed.

Animals↗
PubMed1992

Transforming growth factor-alpha (TGF-alpha) improves hepatic DNA synthesis after hepatectomy in cirrhotic rats.

Impaired liver regeneration in cirrhosis complicates the surgical treatment of liver tumors which arise in this setting. We developed a rat model to investigate the regenerative response of cirrhotic liver after hepatectomy and studied the effect of exogenous transforming growth factor-alpha (TGF-alpha), a potent liver mitogen. Micronodular cirrhosis was established by the simultaneous administration of CCl4 and phenobarbital. Hepatic DNA synthesis ([3H]thymidine incorporation into DNA) 24 hr after partial hepatectomy in cirrhotic rats was 15.6 +/- 3.4 cpm/micrograms DNA (means +/- SEM), which was significantly lower than in normal rats (37.3 +/- 3.4 cpm/micrograms DNA, P less than 0.05). Exogenous TGF-alpha (30 nmol/kg, sc every 12 hr) significantly improved [3H]thymidine incorporation (35.6 +/- 8.2 cpm/micrograms DNA, P less than 0.05). An autoradiographic nuclear labeling index also confirmed increased DNA synthesis (6.7% vs 13.4%). TGF-alpha had no effect on normal regenerating liver (42.5 +/- 8.8 cpm/micrograms DNA, NS). Although the significance of TGF-alpha-enhanced liver regeneration in cirrhosis has yet to be assessed, this model may be useful for the study of mechanisms which control hepatic proliferation.

Animals↗
PubMed1991

The liver plays an important role in the regulation of somatostatin-14 in the rat.

Since little is known about the in vivo disposition of circulating somatostatin-14 (SRIF-14), we examined hepatic processing of SRIF-14 in the rat. Three minutes after the intraportal injection of iodine 125 (125I)-labeled SRIF-14, 16.0 +/- 2.0% of the injected dose is localized to the liver. In the presence of unlabeled SRIF-14, hepatic uptake can be decreased by 68%. Five minutes after the intraportal injection of 125I-SRIF-14, 9.5 +/- 1.4% of the tracer is localized to the liver, more than any other organ tested. Serial collections of bile reveal peak radioactivity at between 10 and 20 minutes. Simultaneous administration of unlabeled SRIF-14 decreases biliary radioactivity by 40%. HPLC analysis of radioactive bile reveals a chromatographic profile similar to that of intact SRIF and is 73% immunoprecipitable by an anti-SRIF antibody. Pretreatment with chloroquine, a lysosomal enzyme inhibitor, does not significantly decrease biliary radioactivity. We conclude that the data are consistent with saturable hepatic uptake and predominantly nonlysosomal transcellular transport.

Animals↗
PubMed1991

Inhibitory effects of somatostatin on rat hepatocyte proliferation are mediated by cyclic AMP.

Somatostatin (SS-14) is known as an antigrowth factor for a variety of cell types, including gastrointestinal mucosa, exocrine pancreas, lymphocytes, and some tumors. We have recently identified and biochemically characterized SS-14-binding protein on rat liver plasma membranes (S. E. Raper, P. C. Kothary, and J. DelValle, Gastroenterology 96: A408, 1989; P. C. Kothary et al., Digestion 46 (Suppl 1): 58, 1990). We hypothesized that SS-14 may affect liver growth as well and investigated cellular mechanisms of this phenomenon focusing on the second messenger cAMP. Freshly isolated rat hepatocytes were plated on tissue culture dishes coated with Matrigel (laminin, heparan sulfate, and type IV collagen). The medium was not supplemented with serum or hormones. Either dibutyryl-cAMP (1 mM) or isobutylmethylxanthine (IBMX, 0.1 mM) was added in the presence or absence of SS-14 (10 nM). DNA synthesis was estimated by the rate of [3H]thymidine incorporation into DNA and by the labeling index (an autoradiographic measurement of the number of labeled nuclei). SS-14 significantly inhibited both [3H]thymidine incorporation and labeling index of rat hepatocytes stimulated by dibutyryl-cAMP or IBMX. SS-14 also inhibited intracellular cAMP accumulation stimulated by IBMX. We conclude that SS-14 exerts at least part of its antiproliferative effects via the adenylate cyclase system. Further study using other signal transduction systems may yield more information about mechanisms of hepatocyte growth.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Somatostatin-14 blocks the hepatotrophic effects of insulin in the rat.

UNLABELLED: We hypothesized that somatostatin-14 (SS-14) might inhibit insulin-stimulated hepatic growth. Rat hepatocytes were isolated by a two-step collagenase perfusion technique and cultured on Matrigel. Differentiated hepatocyte function was documented by albumin synthesis. Hepatocytes were incubated with insulin in the presence or absence of SS-14. Hepatocyte proliferation was assessed by tritiated thymidine ([3H]thy) incorporation into DNA. [3H]thy incorporation was increased by 230% in the presence of insulin and was essentially abolished by the addition of SS-14. Insulin-stimulated cyclic-AMP accumulation was also decreased from 190 to 108% of control levels (P less than 0.05) by the addition of SS-14. Pretreatment with pertussis toxin, which inactivates the inhibitory G-protein, Gi, blocked the effect of SS-14. CONCLUSIONS: (i) In the rat, SS-14 effectively blocks insulin-stimulated [3H]thy incorporation into DNA, possibly by blocking intracellular cAMP accumulation. (ii) Pertussis toxin blocks the growth inhibitory effects of SS-14, suggesting that inhibitory G proteins are involved in the mechanism of SS-14 action. Somatostatin may be useful in studying the role of second messengers in cell growth.

Cell Division↗
PubMed1986

Evaluation of NH2-terminus gastrins in gastrinoma syndrome.

Forty-six patients with the gastrinoma syndrome were divided into 2 categories: 1) benign sporadic gastrinoma (n = 30), and 2) gastrinoma with metastases to liver (n = 16). Thirteen of the 46 patients had multiple endocrine neoplasia type I syndrome. Serum gastrin levels in patients fasted overnight were determined by RIA using antisera directed toward the NH2- and COOH-terminals of heptadecapeptide gastrin (G17) and the NH2-terminus of the triacontatetrapeptide (G34). These results were compared with findings in 50 normal subjects. In the normal subjects, the mean COOH-terminal gastrin-17 level was higher [65 +/- 8 (+/- SEM) pg/ml] than the NH2-terminal gastrin-17 level (11 +/- 0.2 pg/ml) and lower than the NH2-terminal gastrin-34 level (134 +/- 20 pg/ml). The levels of NH2-terminal gastrin-17 were higher in patients with metastatic disease than in those with benign gastrinoma, whereas the COOH-terminal gastrin-17 and the NH2-terminal gastrin-34 levels were similarly high in both groups. The mean ratio of NH2-terminal gastrin-17 to COOH-terminal gastrin-17 was less than 1 in normal subjects (0.22 +/- 0.02) and benign gastrinoma patients (0.2 +/- 0.04), and it was 2.2 +/- 0.41 in the patients with metastatic gastrinoma. An NH2 to COOH gastrin-17 ratio greater than 1 was found in 13 of 16 patients with metastatic gastrinoma, but in none of the patients with benign gastrinoma or normal subjects. Similar results were found in multiple endocrine neoplasia type I patients with benign and metastatic disease. A high NH2 to COOH gastrin-17 ratio is suggestive of metastatic gastrinoma. In 4 patients with metastatic gastrinoma, the NH2 to COOH gastrin-17 ratio fell in parallel with the response to chemotherapy.

Chromatography, Gel↗