1 Two in vivo models, in the rat, were used to investigate, in the presence of di erent substrates, the overall and net intestinal elimination of cipro¯oxacin: an open-intestinal perfusion model and an intestinal loop model respectively. 2 In the presence of quinidine, verapamil and cyclosporin (substrates of the P-glycoprotein (P-gp)), plasma AUCs of cipro¯oxacin were 1.5 ± 2 fold increased, while biliary clearance (1.5 ± 2 fold), intestinal overall and net clearances (2 ± 4 fold and 1.5 ± 8 fold respectively) decreased. The weak e ect obtained with cyclosporin as compared to verapamil and especially quinidine, suggests, for cipro¯oxacin, the existence of transport systems distinct from the P-gp, as the OCT1 transporter which could be inhibited by quinidine. 3 With cephalexin and azlocillin, two b-lactam antibiotics, plasma AUCs of cipro¯oxacin increased and biliary and intestinal overall clearances decreased in a similar fashion (1.3 ± 2 fold), suggesting the involvement of organic anion and/or cation transporters. 4 In the presence of structural analogues, the e ect was dependent on the compound administered: Spar¯oxacin had no e ect on intestinal clearance of cipro¯oxacin. In contrast, with pe¯oxacin, overall intestinal clearance of cipro¯oxacin was decreased and net intestinal clearance increased. 5 The speci®city of cipro¯oxacin intestinal transport appears to be di erent from P-gp as outlined by the lack of competition with spar¯oxacin, a P-gp substrate. Cipro¯oxacin intestinal elimination seems to be mediated by organic anion and/or cation transporters and a mechanism sensitive to quinidine and verapamil.

Mechanical and metabolic stimuli within contracting skeletal muscles reflexly increase sympathetic nervous system activity and blood pressure. That reflex, termed the exercise pressor reflex, is exaggerated in patients with peripheral artery disease (PAD) and in a rat PAD model with a chronically ligated femoral artery. The cyclooxygenase (COX) pathway contributes to the exaggerated pressor response during rhythmic skeletal muscle contractions in patients with PAD, but the specific mechanism(s) of the COX-mediated exaggeration are not known. In decerebrate, unanesthetized rats with a chronically ligated femoral artery (“ligated” rats), we hypothesized that hindlimb arterial injection of the COX inhibitor indomethacin would reduce the pressor response during 1-Hz dynamic hindlimb skeletal muscle stretch; a model of the activation of the mechanical component of the exercise pressor reflex (i.e., the mechanoreflex). In ligated rats ( n = 7), indomethacin reduced the pressor response during stretch (control: 30 ± 4; indomethacin: 12 ± 3 mmHg; P < 0.01), whereas there was no effect in rats with “freely perfused” femoral arteries ( n = 6, control: 18 ± 5; indomethacin: 17 ± 5 mmHg; P = 0.87). In ligated rats ( n = 4), systemic indomethacin injection had no effect on the pressor response during stretch. Femoral artery ligation had no effect on skeletal muscle COX protein expression or activity or concentration of the COX metabolite prostaglandin E2. Conversely, femoral artery ligation increased expression of the COX metabolite receptors endoperoxide 4 and thromboxane A2-R in dorsal root ganglia tissue. We conclude that, in ligated rats, the COX pathway sensitizes the peripheral endings of mechanoreflex afferents, which occurs principally as a result of increased expression of COX metabolite receptors. NEW & NOTEWORTHY We demonstrate that the mechanoreflex is sensitized by the cyclooxygenase (COX) pathway within hindlimb skeletal muscles in the rat chronic femoral artery ligation model of simulated peripheral artery disease (PAD). The mechanism of sensitization appears attributable to increased receptors for COX metabolites on sensory neurons and not increased concentration of COX metabolites. Our data may carry important clinical implications for patients with PAD who demonstrate exaggerated increases in blood pressure during exercise compared with healthy counterparts.

The exercise pressor reflex is a feedback autonomic and cardiovascular control mechanism evoked by mechanical and metabolic signals within contracting skeletal muscles. The mechanically sensitive component of the reflex (the mechanoreflex) is exaggerated in peripheral artery disease (PAD) patients and in a rat model of simulated PAD in which a femoral artery is chronically ligated. Products of cyclooxygenase enzyme activity have been shown to chronically sensitize the mechanoreflex in PAD but the identity of the muscle afferent receptors that mediate the sensitization is unclear. We hypothesized that injection of the endoperoxide 4 receptor (EP4-R) antagonist L161982 or the thromboxane A2 receptor (TxA2-R) antagonist daltroban into the arterial supply of the hindlimb would reduce the pressor response to repetitive, dynamic hindlimb skeletal muscle stretch (a model of isolated mechanoreflex activation) in rats with a femoral artery that was ligated ~72 hours before the experiment but not in rats with freely perfused femoral arteries. We found that EP4-R blockade had no effect on the pressor response (peak Δ mean arterial pressure) to stretch in "freely perfused" (n=6, pre: 14±2, post: 15±2 mmHg, p=0.97) or "ligated" (n=8, pre: 29±4, post: 29±6 mmHg, p=0.98) rats. In contrast, TxA2-R blockade had no effect on the pressor response to stretch in freely perfused rats (n=6, pre: 16±3, post: 17±4 mmHg, p=0.99) but significantly reduced the response in ligated rats (n=11, pre: 29±4, post: 17±5 mmHg, p<0.01). We conclude that TxA2-Rs contribute to chronic mechanoreflex sensitization in the chronic femoral artery ligated rat model of simulated PAD.

Passive limb movement and limb muscle stretch in humans and animals are common experimental strategies used to investigate activation of the muscle mechanoreflex independent of contraction-induced metabolite production. Cyclooxygenase (COX) metabolites, however, are produced by skeletal muscle stretch in vitro and have been found to impact various models of mechanoreflex activation. Whether COX metabolites influence the decerebrate rat triceps surae muscle stretch mechanoreflex model remains unknown. We examined the effect of rat triceps surae muscle stretch on the interstitial concentration of the COX metabolite prostaglandin E2 (PGE2). Interstitial PGE2 concentration was increased above baseline values by 4 min of both static (38% increase, P = 0.01) and dynamic (56% increase, P < 0.01) triceps surae muscle stretch ( n = 10). The 4-min protocol was required to collect enough microdialysis fluid for PGE2 detection. The finding that skeletal muscle stretch in vivo was capable of producing COX metabolites prompted the hypothesis that intra-arterial administration of the COX inhibitor indomethacin (1 mg/kg) would reduce the pressor and cardioaccelerator responses evoked during 30 s (the duration most commonly used in the rat mechanoreflex model) of static and dynamic rat triceps surae muscle stretch. We found that indomethacin had no effect ( P > 0.05, n = 9) on the pressor or cardioaccelerator response during 30 s of either static or dynamic stretch. We conclude that, despite the possibility of increased COX metabolite concentration, COX metabolites do not activate or sensitize thin-fiber muscle afferents stimulated during 30 s of static or dynamic hindlimb skeletal muscle stretch in healthy rats.

Mechanical signals within contracting skeletal muscles contribute to the generation of the exercise pressor reflex; an important autonomic and cardiovascular control mechanism. In decerebrate rats, the mechanically activated channel inhibitor GsMTx4 was found to reduce the pressor response during static hindlimb muscle stretch; a maneuver used to investigate specifically the mechanical component of the exercise pressor reflex (i.e., the mechanoreflex). However, the effect was found only during the initial phase of the stretch when muscle length was changing and not during the later phase of stretch when muscle length was relatively constant. We tested the hypothesis that in decerebrate, unanesthetized rats, GsMTx4 would reduce the pressor response throughout the duration of a 30 sec, 1 Hz dynamic hindlimb muscle stretch protocol that produced repetitive changes in muscle length. We found that the injection of 10 μg of GsMTx4 into the arterial supply of a hindlimb reduced the peak pressor response (control: 15 ± 4, GsMTx4: 5 ± 2 mmHg, P < 0.05, n = 8) and the pressor response at multiple time points throughout the duration of the stretch. GsMTx4 had no effect on the pressor response to the hindlimb arterial injection of lactic acid which indicates the lack of local off‐target effects. Combined with the recent finding that GsMTx4 reduced the pressor response only initially during static stretch in decerebrate rats, the present findings suggest that GsMTx4‐sensitive channels respond primarily to mechanical signals associated with changes in muscle length. The findings add to our currently limited understanding of the channels that contribute to the activation of the mechanoreflex.