Isoquinoline sulfonamides have recently been shown to exert novel inhibitory effects on mammalian protein kinases by competitively binding to the ATP substrate site (Hidaka, H., M. Inagaki, S. Kawamoto, and Y. Sasaki, 1984, Biochemistry, 23: 5036-5041). We synthesized a unique analog of the previously reported compounds, 145-isoquinolinesulfonyl) piperazine (C-I), in order to assess the role of protein kinases in modulating the agonist-stimulated oxidative burst of human polymorphonuclear leukocytes (PMN).Compound C-I, at micromolar concentration, markedly inhibited the release of superoxide anion from human PMN stimulated with phorbol myristate acetate or the synthetic diacylglycerol, 1-oleoyl-2-acetyl glycerol. These data are consonant with previously reported data which indicate that the calcium and phospholipid.4ependent protein kinase, protein kinase C, serves as the intracellular receptor for these agonists. In contrast, superoxide anion production stimulated by the complement anaphylatoxin peptide C5a or the synthetic chemotaxin formylmethionyl-leucyl-phenylalanine were not inhibited by C-I. These data suggest that parallel pathways exist for the agonist-stimulated respiratory burst of human neutrophils, only one of which utilizes the calcium and phospholipid-dependent protein kinase.

We tested the effects of the neutral metalloendopeptidase (NEP) inhibitor, thiorphan (0.17, 0.5, and 1.7 mg i.v), and the angiotensin-converting enzyme (ACE) inhibitor, captopril (0.5, 1.7, and 5.0 mg i.v.), on the bronchoconstrictor response to rapid intravenous infusions of substance P (0.1 to 30 nmol/kg) in anesthetized, mechanically ventilated guinea pigs. The decreases in pulmonary conductance and dynamic compliance caused by substance P were greater in animals treated with either thiorphan or captopril than in control animals. Thiorphan (0.5 mg) had no effect on airway responsiveness to intravenously administered methacholine, whereas captopril (1.7 mg) caused a small increase in methacholine responsiveness. Both drugs significantly increased the recovery of immunoreactive substance P in arterial plasma after exogenous administration of the peptide. We conclude that degradation of substance P by both NEP and ACE is important for determining the magnitude of the bronchoconstriction caused by intravenous administration of this neuropeptide. These data suggest that conditions associated with diminished peptidase activity could result in enhanced responses to stimuli which cause the release of endogenous substance P.

The responsiveness ofisolated guinea pig lung parenchymal strips to substance P was enhanced by at least 100-fold in the presence of the endopeptidase inhibitors phosphoramidon (1 gM) or thiorphan (1 &M), but not with the converting enzyme inhibitor, captopril, or an inhibitor of serum carboxypeptidase N (both 1 t&M). Responses of guinea pig tracheal rings to substance P were also markedly potentiated by phosphoramidon. The increase in tissue responsiveness by these inhibitors was relatively specific for substance P among several other spasmogenic peptides, including formyl-methionyl-leucyl-phenylalanine and the complement peptides C3a and C5a. The enhanced responses appear to result from a decrease in the rate of substance P degradation in the presence of neutral endopeptidase inhibitors. Specific binding of substance P to its receptor on bronchial membranes was increased by three to fourfold in tIhe presence of phqsphoramidon.These data demonstrate an enhanced potential for substance P to contract lung tissues when degradation by a neutral endopeptidase-like enzyme is blocked.

No abstract

We studied the contractile response elicited by platelet-activating factor (PAF) administered intra-arterially into the tracheal circulation of 34 dogs in vivo. A method that avoided tachyphylaxis encountered in prior investigations was developed for isometric measurement of multiple dose-response effects. PAF was a very potent contractile agent; active tension was elicited with 10(-11) mol ia PAF. To determine the mechanism by which contraction was induced, dose-response curves were generated in groups of five animals each treated with either 0.5 mg/kg (approximately 1.5 X 10(-5) mol) iv + 10(-3) mg/kg (3 X 10(-8) mol) ia atropine, 5 mg/kg iv indomethacin (INDO), or 7.5 mg/kg iv hexamethonium (HEX). After pretreatment with atropine, contraction still was elicited with 10(-11) mol ia PAF. However, maximal contraction was only 16.2 +/- 2.74 g/cm (vs. 35.7 +/- 5.74 g/cm for untreated controls; P less than 0.02). The dose at which maximal contraction was elicited after atropine was 10(-7) mol ia (vs. 1.9 X 10(-9) mol for controls; P less than 0.001). Pretreatment with INDO caused minimal attenuation, and HEX had no effect on the response elicited by ia PAF. We demonstrate a method for assessing the effects of PAF in central airways that avoids tachyphylaxis and permits dose-response studies in the same animal. We also demonstrate that PAF is an extremely potent mediator that elicits tracheal smooth muscle contraction at least in part by postganglionic activation of parasympathetic nerves. A direct contractile effect of PAF which is not related to secretion of products of the cyclooxygenase pathway is also suggested.