Robert L. Griffin

Bronchopulmonary and cardiovascular effects of prostaglandin D2 in the dog

The effects of intravenously administered prostaglandin D2 (PGD2) on bronchopulmonary and cardiovascular functions were examined in the dog. PGD2 (0.03-1.0 microng/kg) was shown to be more active than PGF2alpha, a known bronchoconstrictor, in decreasing dynamic lung compliance, tidal volume, and expiratory airflow rate, as well as in elevating lung resistance. PGD2 demonstrated a potency approximately 4-6 times that of PGF2alpha on pulmonary mechanics. Atropine sulfate infusions reduced significantly the resistance and compliance responses to PGF2alpha, but only the resistance responses to PGD2, thereby suggesting that part of the bronchoconstrictor activities of these agents involved a cholinergic component. In another series of anesthetized dogs, PGD2 (0.1-10.0 microng/kg) increased pulmonary arterial pressure (comparable to PGF2alpha) and heart rate (greater than PGF2alpha, but less than PGE2), while concomitantly decreasing systemic arterial pressure in a dose-related manner (1/10 that of PGE2). Qualitatively similar alterations in cardiovascular parameters were obtained for PGD2 in conscious dogs. Therefore, potent biologic activity of PGD2 has been shown in the dog. No physiologic or pathologic role for PGD2 has yet been demonstrated, but nonetheless, since it is a naturally occurring PG derived from arachidonic acid, further studies are warranted.

Bronchodilator effects of prostacyclin (PGI2) in dogs and guinea pigs

prostacyclin (PGI2), a recently discovered unstable product in the biosynthetic conversion of prostaglandin endoperoxides, was examined for bronchopulmonary actions. in anesthetized dogs, PGI2 given i.v. (0.3-30.0 microgram/kg) and by aerosol (0.002-0.2%) inhibited significantly PGF2 alpha-induced increases in pulmonary resistance and decreases in dynamic lung compliance in a dose-related fashion. Intrinsically, PGI2 affected resting bronchopulmonary and cardiac functions minimally, but decreased peripheral and pulmonary vascular pressures. PGI2 (0.1-10 mg/kg, i.p.) afforded protection against histamine-induced asphyxial collapse in normal guinea pigs and ovalbumin-induced anaphylaxis in sensitized animals. Cumulative concentrations of PGI2 (1.0 x 10(-9)--3.0 x 10(-4) M) relaxed contractions of the isolated guine pig trachea produced by carbachol. These bronchodilator and hemodynamic effects could not be ascribed to the stable metabolic product of PGI2, because 6-keto-PGF1 alpha was inactive or markedly less active than PGI2 in these test systems. The results of this investigation suggest that PGI2 possesses considerable bronchodilator and vasodilator activity in experimental animal systems.

Pulmonary Ferritin: Differential Effects of Hyperoxic Lung Injury on Subunit mRNA Levels

Ferritin is an iron storage protein that is regulated at the transcriptional and transcriptional levels, resulting in a complex mixture of tissue- and condition-specific isoforms. The protein shell of ferritin is composed of 24 subunits of two types (heavy or light), which are encoded by two distinct and independently regulated genes. In the present studies, the isoform profile for lung ferritin differed from other tissues (liver, spleen, and heart) as determined by isoelectric focusing (IEF) and polyacrylamide gel electrophoresis (PAGE). Lung ferritin was composed of equal amounts of heavy and light subunits. Differences in isoform profiles were the result of tissue-specific differential expression of the ferritin subunit genes as demonstrated by Northern blot analyses. Like heart ferritin, lung ferritin exhibited a low iron content that did not increase extensively in response to iron challenge, which contrasts with ferritins isolated from liver or spleen. When animals were exposed to hyperoxic conditions (95% oxygen for up to 60 h), ferritin heavy subunit mRNA levels did not markedly change at any of the investigated time points. In contrast, ferritin light subunit mRNA increased severalfold in response to hyperoxic exposure. Investigation of the cytoplasmic distribution of ferritin mRNA showed that a substantial portion was associated with the ribonucleoprotein (RNP) fraction of the cytosol, suggesting that a pool of untranslated ferritin mRNA exists in the lung. Upon hyperoxic insult, all ferritin light subunit mRNA pools (RNP, monosomal, polysomal) were elevated, although a specific shift from RNP to polysomal pools was not evident. Therefore, the increase in translatable ferritin mRNA in response to hyperoxia resulted from transcriptional rather than specific translational activation. The observed pattern of light chain-specific transcriptional induction of ferritin is consistent with the hypothesis that hyperoxic lung injury is at least partially iron mediated.

Novel steroid‐based inhibitors of lung inflammation

It is now well-recognized that eosinophil products contribute to the mucosal damage which is a prominent feature of bronchial asthma. Eosinophils migrate to the bronchial epithelium following allergen inhalation in sensitive subjects, and increases in eosinophil numbers are associated with late-phase broncho-conslrictions [I]. The eosinophils capacity to generate lipid mediators [2.3] and the presence of cytotoxic. highly-charged, arginine-rich proteins in the eosinophil granules implicate this cell further as a contributor to mucosal inflammation. An attractive goal in the search for novel anti-asthma drugs would be to discover and develop compounds which inhibit eosinophil activation and/or prevent the influx of eosinophils into the airways. Steroids arc probably the most efficacious drugs currently available for the treatment of asthma, and improvements in symptoms in patients treated with steroids have been associated with a parallel reduction in blood eosinophil counts [4]. Corticosteroids have also been shown to abrogate the development of late-phase asthmatic reactions with a parallel reduction in eosinophil activity as measured by serum eosinophil cationic protein (ECP) levels [5]. Inhaled glucocorticoids which demonstrate few side-effects are increasingly being used worldwide as a prophylactic treatment for the disease. Novel inhaled glucocorticoids which have been designed to break down rapidly after reaching the systemic circulation are currently being developed and are even less likely to suppress the hypothalamo-pituitary adrenal axis. In this paper we have reviewed some of the novel. steroid-based molecules currently in clinical development for treating asthma. In addition we emphasize the change in direction the pharmaceutical industry has taken towards the use of inflammation-based animal models for the screening of novel compounds, and we also describe the activity of some novel, non-glucocorticoid. 21 -aminosteroids which may prove useful in the treatment of asthma.

The effects of nifedipine and verapamil on antigen-induced bronchoconstriction in dogs

The effects of calcium channel blockers, nifedipine and verapamil (i.v. and aerosol), were investigated in beagle dogs natively allergic to Ascaris suum antigen. Control exposures to an aerosol of Ascaris antigen provoked significant bronchopulmonary changes, i.e., increases in pulmonary resistance (RL) and decreases in dynamic lung compliance (CDYN). Pretreatment with either nifedipine or verapamil (200 micrograms/kg, i.v.) provided significant inhibition in the RL responses to Ascaris antigen (P less than 0.015) while neither agent significantly affected CDYN changes. When administered as an aerosol, verapamil (1.0%; 10 breaths) significantly inhibited both the RL and CDYN responses to Ascaris antigen (P less than 0.05), whereas a similar concentration of nifedipine was without effect. Resting basal levels of RL and CDYN were unaffected by either the i.v. route or by aerosols of either nifedipine or verapamil. These results suggest that calcium channel blockers may have beneficial effects against allergen-provoked bronchoconstriction; however, differences appear to exist in the choice of agent, route of administration and site of action.

Potent bronchoconstrictor effects of aerosolized prostaglandin D2 in dogs

Previously, we demonstrated that prostaglandin D2 (PGD2), a natural product of the endoperoxide PGH2, evoked bronchoconstriction when given I.V. to dogs (PROSTAGLANDINS 13:255-269, 1977). The present investigation in anesthetized dogs demonstrated that aerosols of PGD2 (0.001-0.1%) produced concentration-dependent increases in pulmonary resistance (RL) and decreases in dynamic lung compliance(CDYN) which were short-lived and equipotent to PGF2 alpha. These alterations in pulmonary mechanics were partially, yet significantly, inhibited by atropine, thereby suggesting that at least a portion of the bronchoconstriction may be cholinergically mediated. Concomitant cardiovascular depressant effects of both PGD2 and PFG2 alpha aerosols were much less and more variable than their bronchopulmonary effects. These results demonstrate a potent bronchoconstrictor effect of aerosolized PGD2 in dogs. PGD2 warrants further attention as a possible mediator of the bronchospasm seen in acute, reversible airways obstruction.

Thromboxane B2--comparative bronchoactivity in experimental systems.

Abstract Thromboxane B2 (TxB2), a major product of prostaglandin endoperoxide metabolism, was examined quantitatively for bronchoactivity in the intact, anesthetized dog and on the isolated guinea pig trachea. In the dog, TxB2 (0.1 − 30.0 μg/kg i.v.) produced dose-related decreases in airflow rate, tidal volume and dynamic lung compliance, while simultaneously increasing pulmonary airway resistance. These pulmonary changes were qualitatively similar to those observed for PGF2α, yet were only 0.07-0.11 times as effective. Aerosolized TxB2 (0.001 − 0.1%) also produced smaller alterations in pulmonary mechanics than did aerosols of PGF2α. All respiratory changes returned to pre-drug levels within 5–10 min. In the isolated tracheal preparation, TxB2 (106-104 M) contracted the strips to a lesser degree than acetylcholine, histamine, PGF2α, or two PG cyclic ether endoperoxide analogs. TxB2 appears to be a naturally occurring bronchoactive metabolite (albeit weak) in the bioconversion of arachidonic acid. Since it is produced in substantial amounts in the lungs comparable to the prostaglandins, TxB2 or its more active immediate precursor, TxB2, may be involved in regulating bronchomotor tone in the healthy state and/or bronchospasm in the pathological state.

The effect of lodoxamide ethyl[diethyl N,N′-(2-chloro-5-cyano-m-phenylene)dioxamate] on in vivo anaphylactic reactions

Orally administered lodoxamide ethyl (U-42,718) inhibited anaphylactic reactions in a dose-related manner in the following test animals: (1) In the rat PCA reaction, excellent activity (75% inhibition at 0.1 mg/kg) was seen with a duration of activity of 30 min, (2) In the ascaris-sensitive primate (45% inhibition at 1.0 mg/kg) in lung parameters related to increased resistance and decreased compliance which persisted for up to 3 h, and (3) 50 mg/kg protected guinea pigs, sensitized to egg albumin, from lung function changes. Activity in these animal systems indicates that this orally active drug may hold promise in clinical asthma.

Effect of the 21-aminosteroid, U-74389F, on hyperoxic lung injury in rats

Hyperoxia (>95% oxygen) in rats caused an increase in lung weight and an accumulation of fluid in the thorax. The mean lung wet weight of air-breathing controls at 60 h was 1.2±0.01 g, and that of vehicle-treated, oxygen-exposed animals was 2.45±0.05 g. Treatment with the 21-aminosteroid U-74389F, 3, 10, and 30 mg/kg twice daily throughout oxygen exposure, produced 8, 42, and 18% inhibition of the oxygen-induced increase in lung weight, respectively. However, U-74389F did not inhibit the hyperoxia-induced accumulation of neutrophils in bronchoalveolar lavage fluid.No pleural fluid could be aspirated from the thorax of air-breathing controls. The volume of pleural fluid in oxygen-exposed, vehicle-treated animals and animals treated with 3, 10, and 30 mg/kg U-74389F b.i.d. was 6.5±0.9, 2.6±0.6, 0.8±0.3, and 1.3±0.5 ml, respectively.U-74389F or its biologs are of potential value for the treatment of lung diseases in which oxidant damage has been implicated.

Chasing the elusive animal model of late-phase bronchoconstriction: Studies in dogs, guinea pigs and rats

SummaryAntigen inhalation in sensitized dogs, guinea pigs and rats resulted in a marked, late-phase, eosinophil-rich, influx of inflammatory cells into the bronchial lumen. Attempts to demonstrate an associated late-phase bronchoconstriction were disappointing. We were unable to demonstrate a late-phase bronchoconstriction in either rats or dogs, even when dogs were pretreated with metyrapone to reduce blood cortisol levels. In ovalbumin-sensitized guinea pigs, challenged with low doses of ovalbumin, we observed an immediate bronchoconstriction, a late-phase bronchopulmonary eosinophilia but no late-phase bronchoconstriction. However, inhalation of very high doses of antigen in mepyramine-treated sensitized guinea pigs did induce a moderate late-phase bronchoconstriction.