241

Fundam Clin Pharmacol(l992) 6,247-249 0 Elsevier, Paris

Rolipram inhibits PAF-induced airway microvascular leakage in guinea-pig: a comparison with milrinone and theophylline JL Ortiz 1, J Cortijo 1, JM Valles 1, J Bou 2, EJ Morcillo 1 I

Depariament de Farmacologia, Facultat de Uedicina i Odonfologia, Universitat de Valencia, Av Blasco I baiiez 15, 46010 ValPncia 2 Departamento de Farmacologia, LaboratoriosAlmirall SA,Barcelona, Spain

(Received 10 August 1992; accepted 24 August 1992)

Summary - The effects of 3 phosphodiesterase (PDE) inhibitors, rolipnun (PDE IV), milrinone (PDE 111) and theophylline (nonselective) on PAF (50 ng @-I; iv)-induced airway vascular leakage have been evaluated in guinea-pigs. Roliprarn (3-300 pg k g l ;iv) reduced the increase in permeability induced by PAF at a l l airway levels whereas rnilrinone (10-1000 pg kg-l ; iv) and theophylline (30 rng kg-1; iv) were without effects. The anti-leakage activity of roliprarn may be of therapeutic value in asthma rdipram I vascular permeability I guinea-pig airway

Asthma is increasingly recognized as an inflammatory disorder. Despite the relevance of airway plasma exudation in asthma, limited and controversial information is available concerning the influence of anti-asthma drugs on this process (Boschetto et al, 1989). The recent identification of multiple isoenzymes of cyclic nucleotide phosphodiesterase (PDE) and the availability of selective inhibitors have permitted the re-evaluation of the relationship between PDE inhibition and anti-asthma activity (Torphy and Undem, 1991). The purpose of this study was to compare the effects of three PDE inhibitors, rolipram (PDE IV), milrinone (PDE 111) and theophylline (nonselective), on platelet activating factor (PAF)-induced microvascular leakage in guinea-pig airways in vivo. Microvascular permeability was quantified by the extravasation of intravenously injected Evans blue dye (Boschetto ef af, 1989).

Tricoloured guinea-pigs weighing 0.4-0.5 kg were anasthetized with urethane (1.25 g kg-1, ip). At time 0, vehicle (saline or diluted dimethylsulfoxide, 1 ml kg-I), theophylline (30 mg kg-I), milrinone (10, 100 or lo00 pg kg-l) or rolipram (3, 30 or 300 pg kg-1) was injected intravenously followed, 9 min later by Evans blue dye (30 mg kg-1). After a further 1 min, PAF (50 mg kg-1) or vehicle (bovine serum albumin 0.25% in saline) was injected intravenously. Five min later, the experiment was terminated and the intravascular Evans blue removed. The lower part of the trachea, main bronchi and proximal and distal intrapulmonary airways were obtained. Evans blue was extracted by incubating tissues in 2 ml formamide at 37°C for 16 h and its concentration determined by light absorbance at 620 nm (Uvikon 940 spectrophotometer; Konuon). The mean arterial blood pressure was monitored and the responses to milri-

JLOrtiz ct al

248

Tracllca

loo

30

0

1

*

*

1,l B

1

T

&

A

loo

C

D E F

501il! 0

CHI

A

Pro xi m a I In t ra p u 1mon a ry airways 100

* L

*T

B

C

D E F

CHI

Distal i n t r a p u l m o n a r y airways loo

1

* -r

* I T

50

0 :\

B

Fig 1. Histograms showing PAF (50 ng kg-1, iv) induced microvascular leakage in guinea-pig airways. Responses to vehcle (A) or to PAF (B to I) (1 min after Evans blue dye administration) after vehicle (A, B). theophylline (30 mg k g l , iv (C)), robpram (3 (D), 30 (E) or 300 (F) P8 k-', iv). or milrinone (10 ( G ) ,100 (H) or 1000 Cr) pg k g ' , iv). Means (SEM shown by vertical bars) of 5-7 mimals are shown. * P c 0.05 from vehicle values (A); P < 0.05 from control PAF @).

*

none (10-1OOO pg kg-1, iv) or rolipram (3-300 pg kg-l, iv) recorded. Data are expressed as mean f SEM. Statistical analysis of the results was performed by the Mann-Whitney U-test. PAF increased microvascular permeability

(fig 1). Theophylline (30 mg kg-1) failed to decrease the effect of PAF thus confirming other studies (Boschetto el al, 1989). However, Raeburn and Karlsson (1992), using a different technique, found that theophylline (200 pg, intratracheal) reduced

Rolipram on airway vascular leakage

PAF-induced extravasation in bronchi and not in trachea. Milrinone did not have any significant effect on PAF-induced vascular leakage. In contrast, rolipram reduced the increase in microvascular permeability induced by PAF at all airway levels. At 300 pg kg-l, rolipram completely blocked the effect of PAF in all tissues studied except trachea (fig l). Milrinone produced transient decreases of arterial blood pressure except for the highest dose tested which resulted in sustained hypotension (46 k 5% inhibition of control values; n = 6). Rolipram produced small and transient decreases of arterial blood pressure (datanot shown). A recent communication by Raebum and Karlsson (1992) shows that rolipram (200 pg, intratracheal) inhibits PAF (4 nM, intratrachea1)-induced microvascular leakage in guinea-pig airways whereas the PDE I11 inhibitor siguazodan was without effect. These results are in good agreement with those reported in the present study. The effect of PAF producing plasma exudation in the guineapig airways is considered a direct effect (Boschetto et al, 1989), although the participation of inflammatory mediators cannot be excluded. In contrast to PDE I11 inhibitors, selective inhibitors of PDE IV reduce the release of mediators from inflammatory cells (Dent et al, 1991; Torphy and Undem, 1991) and may also act to decrease airway eosinophilia and inflammation. Both PDE 111 and PDE IV inhibitors are vasodilators although their effects on tracheal mucosal blood flow have not yet been determined. The anti-leakage effect of rolipram is probably unrelated to vasodilatation since selective inhibitors of PDE IV do not have marked vasodilator potential (Heaship et al, 1991) and vasodilatation would augment rather than diminish microvascular permeability. The antiexudative effects of rolipram were obtained with doses in the range of those required in vivo for inhibition of histamine-induced bronchoconstriction (Harris el al, 1989; Heaslip et al, 1991).

249

In conclusion, our results show that rolipram, a selective inhibitor of PDE IV, inhibits PAF-induced airway microvascular leakage in the guineapig whereas PDE 111 inhibitors, such as milrinone (this study) or siguazodan (Raebum and Karlsson, 1992), do not. This effect may have potential therapeutic value in the management of asthma. Acknowledgments This work was supported in part by grants FAR90-0680 and FAR91-0875 from CICYT (Ministerio de Industria y Energia; Spain). The authors thank Mr P Santamariafor valuable technical assistance.

References Boschetto P. Roberts NM, Rogers DF, Barnes PJ (1989) Effect of antiasthma drugs on microvascular leakage in guinea-pig airways. A m Rev Respir Dis 139, 416421 Giembycz MA, Dent G (1992) Prospects for selective nucleotide phosphodiesterase inhibitors in the treatment of bronchial asthma. Clin Exp Allergy 22, 337-344 Harris AL, Connell MJ, Ferguson EW, Wallace AM, Gordon RJ, Pagani ED, Silver PJ (1989) Role of low Km cyclic AMP phosphodiesterase inhibition in tracheal relaxation and bronchodilation in the guineapig. J Pharmacol Exp Ther 25 1, 199-206 Heaslip RJ, Buckley SK. Sickels BD, Grimes D (1991) Bronchial vs cardiovascular activities of selective phosphodiesterase inhibitors in the anesthetized betablocked dog. J Pharmacol Exp Ther 257,741-747 Raeburn D, Karlsson JA (1992) Comparison of t h e effects of isoenzyme-selective phosphodiesterase inhibitors and theophylline on PAF-induced plasma leak in the guinea-pig airways in vivo. Am Rev Respir Dis 145, A612 Torphy TJ, Undem BJ (1Wl) Phosphodiesterase inhhibitors: new opportunities for the treatment of asthma. Thorax 46.512-523