Sumiko Homma

AVP inhibits LPS- and IL-1β-stimulated NO and cGMP via V1 receptor in cultured rat mesangial cells

The present study examined how arginine vasopressin (AVP) affects nitric oxide (NO) metabolism in cultured rat glomerular mesangial cells (GMC). GMC were incubated with test agents and nitrite, and intracellular cGMP content, inducible nitric oxide synthase (iNOS) mRNA, and iNOS protein were analyzed by the Griess method, enzyme immunoassay, and Northern and Western blotting, respectively. AVP inhibited lipopolysaccharide (LPS)- and interleukin-1β (IL-1β)-induced nitrite production in a dose- and time-dependent manner, with concomitant changes in cGMP content, iNOS mRNA, and iNOS protein. This inhibition by AVP was reversed by V1- but not by oxytocin-receptor antagonist. Inhibition by AVP was also reproduced on LPS and interferon-γ (IFN-γ). Protein kinase C (PKC) inhibitors reversed AVP inhibition, whereas PKC activator inhibited nitrite production. Although dexamethasone and pyrrolidinedithiocarbamate (PDTC), inhibitors of nuclear factor-κB, inhibited nitrite production, further inhibition by AVP was not observed. AVP did not show further inhibition of nitrite production with actinomycin D, an inhibitor of transcription, or cycloheximide, an inhibitor of protein synthesis. In conclusion, AVP inhibits LPS- and IL-1β-induced NO production through a V1 receptor. The inhibitory action of AVP involves both the activation of PKC and the transcription of iNOS mRNA in cultured rat GMC.

Application of Plasma Perfusion in Hepatic Failure

To evaluate the efficacy of plasma perfusion as a liver-assistance system, 17 patients with hepatic failure were treated with a total 37 sessions of plasma perfusion and 43 sessions of plasma exchange. For plasma perfusion, Plasma-flo AP-08-H was used as a plasma separator, and the separated plasma was passed through an adsorber, Bespore UPC-III (Jap.Med.Suppl., Hiroshima) or BR 350 (Asahi Med. Co., Tokyo). The mean treated plasma volume was 5.0 liters. The mean proportion of bilirubin removed by routine plasma exchange was 29% with a mean of plasma exchange volume of 2.1 L. In the plasma perfusion with Bespore and BR, the removal rates were 37% and 42%, respectively. The plasma ammonia level decreased by 16% (from 121 to 97 mumol/L) with plasma exchange. Likewise, plasma perfusion decreased the plasma ammonia level from 75 to 56 mumol/L with an average decrement rate of 23%. The capacity for removal of amino acids was analyzed in terms of the change in the Fisher score ([Val+Leu+Ileu]/[Tyr+Phe]). The Fisher score was improved by plasma perfusion from 1.8 to 2.4. Thus, we concluded that in terms of removal of bilirubin, ammonia and amino acids, plasma perfusion was as efficient a therapy as plasma exchange. However, further clinical evaluation will be required before this procedure can be applied for the treatment of hepatic failure.

Endothelin‐1 affects AVP‐stimulated cAMP but not ANP‐induced cGMP productions in cultured rat IMCD cells

Summary: The present study was undertaken to explore a potential interaction of endothelin‐1 (ET‐1) on vasopressin (AVP)‐dependent cyclic 3′,5′‐adenosine monophosphate (cAMP) and atrial natriuretic peptide (ANP)‐dependent cyclic 3′,5′‐guanosine monophosphate (cGMP) metabolisms in primary cultured rat inner medullary collecting duct (IMCD) cells. Endothelin‐1 did not affect ANP‐stimulated cGMP accumulation in the presence or absence of 3‐isobutyl‐1‐methylxanthine (IBMX). Levels of 10−10 to 10−7 mol/LET‐1 showed a dose‐dependent inhibition of the AVP‐dependent cAMP accumulation in the presence of IBMX and 10−7 mol/LET‐1 inhibited the cAMP generation by 34 ± 5.3% (n= 5, n= 20, P<0.01). Endothelin‐1 did not affect the cAMP generation either by 100 ng/mL cholera toxin or by 10−4 mol/L forskolin. Endothelin‐1 failed to inhibit the cAMP generation in the presence of 100 ng/mL pertussis toxin (PTX). the inhibitory effect of ET‐1 was reversed by 10−8 mol/L staurosporin (SSP), a protein kinase C (PKC) inhibitor. Furthermore, this inhibitory effect of ET‐1 was mimicked by 10−8 mol/L phorbol 12‐myristate 13‐acetate (PMA), an activator of PKC. A dose of 5 × 10−6 mol/L indomethacin did not affect this inhibitory effect of ET‐1. From these results, we suggest that the effect of ET‐1 on cyclic nucleotides metabolism seem to be selective. Endothelin‐1 did not affect the cGMP generation by ANP, whereas it inhibited cAMP production by AVP via PTX and SSP sensitive pathway in cultured rat IMCD cells.