No abstract

The production of prostaglandin E2- (PGE2) like and thromboxane A2-(TXA2) like substances is increased after release of unilateral ureteral obstruction (UUO) for 3 days in the isolated perfused rabbit kidney. It has been postulated that this increase in TXA2 biosynthesis might contribute to the development of vasoconstriction in the obstructed kidney. In the present studies, the production of TXA2 and PGE2 in the kidney was further investigated in rats after UUO for 2-18 h. Radioimmunoassay was used to determine thromboxane B2 (TXB2), a chemically stable metabolite of TXA2, and PGE2 production during the incubation of renal slices in vitro. Unlike previous studies, an increase in TXB2 and PGE2 production was demonstrable in the obstructed kidney even in the absence of pharmacological stimulation by bradykinin or angiotensin II. The effect of UUO on prostaglandin production differed in the different anatomical parts of the kidney. In the papilla, production of both TXB2 and PGE2 was increased in the obstructed kidney. In the cortex, however, UUO had a stimulatory effect only on TXB2 production but not on PGE2 production. The increase in TXB2 and PGE2 production was demonstrable as early a 2 h (tested) after ureteral obstruction. Prolongation of ureteral obstruction for 18 h diminished the stimulatory effect of UUO on PGE2 production but not on TXB2 production.

DAB486IL-2 is a recombinant fusion toxin in which the native receptor binding domain of diphtheria toxin has been replaced with human interleukin-2 (IL-2). It selectively binds and intoxicates only cells that bear the high-affinity receptor for IL-2. In the first clinical trial of a genetically engineered ligand fusion-toxin, we have treated 18 patients with chemotherapy-resistant IL-2 receptor expressing hematologic malignancies with escalating doses of DAB486IL-2. The maximal tolerated dose of a daily intravenous bolus of DAB486IL-2 was 0.1 mg/kg per day for 10 doses, established by asymptomatic, reversible elevations of hepatic transaminases without changes in other tests of liver function. Other mild reversible side effects noted were rash, nausea, elevated creatinine, chest tightness, and fever. Pharmacokinetic analysis showed a monophasic clearance of 5.8 +/- 0.7 minutes with peak levels of 3,549 +/- 1,041 mg/mL at the 0.1 mg/kg dose. Approximately 50% of patients developed an antibody response to diphtheria toxin or DAB486IL-2. The presence of such antibodies did not preclude patients from experiencing an antitumor response as four of the six patients with antitumor effect had detectable antibody titers. Although this was a phase I trial designed to define the safety of DAB486IL-2, remissions were observed in three patients lasting from 5 to over 18 months. The ability to achieve significant tumor reductions in this group of heavily treated patients is encouraging and suggests additional trials are warranted in hematologic malignancies.

There is a considerable amount of interest in prostaglandin E2 (PGE2) metabolism in potassium depletion, but the findings remain inconclusive. Thromboxane A2 (TXA2) is another type of prostaglandin with a vasoconstrictive property and its biosynthesis in the kidney is altered under pathophysiological conditions. We investigated the production of both immunoassayable PGE2 and thromboxane B2 (TXB2), a chemically stable metabolite of TXA2, in the chronically K+-depleted rat kidney. During a 90-min in vitro incubation of papillary slices obtained from K+-depleted rats, TXB2 production was increased, but PGE2 biosynthesis was decreased and PGF2 alpha remained unaltered compared with control rats. In the cortex, TXB2 production was low, but it was greater in K+-depleted rats compared with control rats. Deletion of K+ from the incubation medium had no measurable effect on either TXB2 or PGE2 production in both K+-depleted and control rats. Formation of [14C]TXB2 from [14C]PGH2 by microsomes from renal papilla was greater in K+-depleted rats compared with control rats, suggesting that the increased TXB2 production in the K+-depleted rat kidney is probably due to an activation of TXA2 synthetase.

A B S T RA C T Ca2+ flux and protein phosphorylation have been implicated as playing an important role in the induction ofthe platelet release reaction. However, the interactions between Ca2+, protein phosphorylation, and the release reaction have been difficult to study because secretion in human platelets is independent of extracellular Ca2+. Thus, we studied rabbit platelets, which, unlike human platelets, require extracellular Ca2+ for serotonin release to occur. Thrombin, basophil platelet-activating factor (PAF), or ionophore A23187 treatment of intact 32PO43-_loaded rabbit platelets resulted in a 200-400% increase in phosphorylation of two peptides of Mr 41,000 and 20,000, designated as P7P and P9P, respectively. These peptides were similar in all respects to the peptides phosphorylated in thrombin-treated human platelets. When Ca2+ was replaced in the medium by EGTA, (a) thrombin-and PAF-induced rabbit platelet [3H]serotonin release was inhibited by 60-75%, whereas ionophore-induced release was blocked completely; (b) thrombin-, PAF-, or ionophore-induced P9P phosphorylation was inhibited by 60%; and (c) ionophore-induced P7P phosphorylation was decreased by 60%, whereas that caused by thrombin or PAF was decreased by only 20%. At 0.25-0.5 U/ml of thrombin, phosphorylation preceded [3H]serotonin release with the time for half-maximal release being 26.0±1.3 s SE (n = 3) and the time for half-maximal phosphorylation being 12.3±1.3 s SE (n = 3) for P7P and 3.7±0.17 s SE (n = 3) for P9P. P9P phosphorylation was significantly inhibited (P < 0.015) by removal of Ca2+ from the medium at a time point before any thrombin-or ionophore-induced serotonin release was detectable. Thus, our data suggest that Ca2+ flux precedes the onset of serotonin secretion and that the