Relaxant effect of aspirin-like drugs on isolated guinea pig tracheal chain

Effect of aspirin on vasodilation to bradykinin and substance P in patients with heart failure treated with ACE inhibitor

AIMS

We wanted to examine some of the mechanisms by which aspirin might be responsible for counteraction of the effects of ACE inhibitors. Aspirin has been reported to counteract the effects of ACE inhibitors in patients with heart failure. Despite this, there is little evidence on what the mediator of such an effect might be, although there is some evidence to implicate bradykinin and, perhaps, substance P.

METHODS

Twelve patients with congestive heart failure treated with an ACE inhibitor were studied on two occasions, after abstaining from aspirin for 14 days, and after 14 days of aspirin 150 mg once daily. Forearm blood flow was measured by venous occlusion plethysmography during intrabrachial infusions of bradykinin and substance P, before and after intrabrachial aspirin.

RESULTS

Bradykinin caused profound vasodilation (peak 390%, 95% confidence intervals (CI) 300, 480%; P < 0.01), substance P slightly less (peak 222%, 95% CI 162, 283%; P < 0.01). Intra-brachial aspirin had no effect on its own. The response to bradykinin was unchanged by intrabrachial aspirin (peak 404%, 95% CI 304, 504%) or oral aspirin (peak 320%, 95% CI 209, 431%; P = 0.2). The response to substance P was unchanged by intrabrachial aspirin (peak 226%, 95% CI 171, 281%) or oral aspirin (peak 220%, 95% CI 142, 297%; P = 0.86).

CONCLUSIONS

Aspirin has no effect on the vasodilator response to bradykinin and substance P in patients with heart failure treated with an ACE inhibitor. Neither bradykinin nor substance P is likely to contribute to the reported interaction between aspirin and ACE inhibitors.

Mechanisms of intrinsic tone in bullfrog lung: relaxant effects of indomethacin, ouabain and potassium

Bullfrog hemilungs showed minimal relaxation (9 +/- 2% of the maximal relaxant effect of theophylline, Imax) after a 16 h incubation in 10(-5) M indomethacin, indicating that prostaglandin synthesis plays little or no role in the high intrinsic tone characteristic of this preparation. A higher concentration of indomethacin (10(-4) M) produced greater relaxation (23 +/- 3% of Imax), but also markedly potentiated isoprenaline-induced relaxation. The interaction with isoprenaline was similar to that previously found for papaverine, a phosphodiesterase inhibitor. Ouabain (10(-5) and 10(-4) M) produced an initial contraction followed by marked relaxation (50% of Imax), indicating that a ouabain-sensitive mechanism is of major importance in the maintenance of intrinsic tone. Ouabain-treated hemilungs showed reversal (relaxation) of the normal contractile response to 26 mM potassium and marked impairment of the contractile response to calcium in calcium-depleted preparations. These effects suggest that ouabain-induced relaxation reflects a drug action on calcium movements. The marked relaxation (30 to 40% of Imax) produced by 26 mM potassium in ouabain-treated hemilungs is of particular interest in that it indicates a mechanism of potassium-induced relaxation distinct from stimulation of sodium-potassium ATPase.

Some properties of calcium-induced contraction in the isolated human and guinea-pig tracheal smooth muscle

We studied the effects of the cyclooxygenase inhibitors, indomethacin and aspirin, the leukotriene antagonist, FPL 55712 and the Ca antagonist, verapamil on basal tone and Ca-induced contractions in the human and guinea-pig tracheal muscle. Indomethacin and aspirin usually increased spontaneous tone or Ca-induced contractions in human strips, while consistently decreased tension development in the guinea-pig muscle. FPL 55712 strongly reduced contractions in the human, whereas it had a very weak effect on the guinea-pig muscle. Verapamil had a small inhibitory effect in the human trachea, either at 5.9 or 40 mM K, but markedly suppressed Ca-induced contractions of guinea-pig trachea in 40 mM K and had little effect on contractions in 5.9 mM K in this tissue. It is concluded that active tone in the two different tracheal muscles were controlled by different processes; that different arachidonate by-products may exert an effect on basal tone in the two different muscles; and that different plasma membrane Ca channels may be operative under basal conditions in the different muscles.

Effect of meseclazone and other non-steroidal anti-inflammatory drugs on isolated tracheal chain tone

Meseclazone, 5-CSA and several representative NSAIDs caused concentration-dependent relaxation of the tracheal ring preparation and are listed in order of descending potency: isoproterenol greater than naproxen greater than ibuprofen greater than diflunisal greater than tolmetin approximately equal to fenoprofen approximately equal to indomethacin greater than phenylbutazone greater than meseclazone greater than 5-CSA greater than aspirin. This relaxation may be related to inhibition of prostaglandin synthetase, but relative potencies of NSAIDs in this test do not necessarily correspond to their potency in inhibiting PG synthethase in other tissue. Thus other factors may play a role.