The effect of opioids on the electrical resistance of sheep's pleura and pericardium

The effect of morphine on the transmesothelial resistance (RTM) of sheep’s visceral and parietal pleura and parietal pericardium was studied using the Ussing chamber technique. The basal values were found to be 19,41 ± 0.31 Ω×cm2, 19,57 ± 0.32 Ω×cm2 and 21 ± 0.61 Ω×cm2, respectively. Immediately after the addition of morphine (10-9M) both apically and basolaterally on the parietal pleura and the parietal pericardium, these values were significantly increased (P<0.05). The addition of morphine (10-9M) on the visceral pleura caused a statistically significant increase of the RTM, only when added basolaterally. Addition of the nonselective opioid receptor blocker, naloxone (10-5M), suppressed this effect at all sites. The addition of loperamide (10-9Μ) as a μ opioid receptor agonist, on the same sites as morphine, caused a statistically significant increase of the RTM only when was added basolaterally on the visceral pleura. The addition of loperamide (10-6Μ) as a voltage dependent Ca2+ channels – L type blocker, suppressed the morphine effect on the basal surface of all three tissues. The addition of ouabain (10-3Μ), individually or combinationally with morphine, caused an additive increase of the RTM at all sites where morphine was effective. In conclusion, our results show that morphine has a rapid effect on the three tissues, with differences regarding to the surface and the duration of the effect. The rapid effect is mediated by the stimulation of the μ opioid receptors at all sites. The effect of morphine on the basal surface of both the pleurae and the parietal pericardium appears to be mediated by the voltage dependent Ca2+ channels – L type. The stimulation of μ opioid receptors never appears to be related with the Na+/K+ ATPase. The differences regarding the sites of activity between morphine and loperamide, probably signify the existence of multiple subtypes of μ opioid receptors. Contrary to the other sites, the effect of morphine on the basal surface of both the visceral pleura and the parietal pericardium was prolonged. This difference is probably related with same differences regarding the number or the distribution of the μ opioid receptors subtypes.Μελετήθηκε η επίδραση της μορφίνης στη διαμεσοθηλιακή αντίσταση (RTM) του τοιχωματικού και περισπλάχνιου υπεζωκότα και του τοιχωματικού περικαρδίου προβάτου, χρησιμοποιώντας την τεχνική Ussing Chamber. Η τιμές αναφοράς της RTM για τους παραπάνω ιστούς ήταν 19,57 ± 0.32 Ω×cm2, 19,41 ± 0.31 Ω×cm2 και 21 ± 0.61 Ω×cm2, αντίστοιχα. Ταχέως μετά την εφαρμογή μορφίνης (10-9M) στην κορυφαία και βασική επιφάνεια του τοιχωματικού υπεζωκότα και του τοιχωματικού περικαρδίου, αυτές οι τιμές αυξήθηκαν στατιστικά σημαντικά (P