Involvement of P₁‐purinoreceptors in the relaxing effect of adenosine in rat duodenum

Abstract

1. In isolated segments of rat duodenum, adenosine (50 microM-2 mM) caused a very rapid and short-lasting relaxation that was associated with a marked decrease in the amplitude of spontaneous contractions. 2. Theophylline (0.1-0.8 mM) and 8-phenyltheophylline (1-10 microM) antagonized, in a concentration-dependent manner, the effects of 0.3 mM adenosine on smooth muscle tension and spontaneous activity. 3. The concentration-response curves for adenosine (50 microM-2 mM) were progressively shifted to the right by increasing concentrations of theophylline and of 8-phenyltheophylline, with no change in the maximum effect. 4. 8-Phenyltheophylline (5 microM) did not affect relaxations induced by noradrenaline (0.5 microM) and by isoprenaline (5 nM). 5. These results indicate that the effects exerted by adenosine on rat duodenum are mediated by P1-purinoreceptors.

A2A and A3 receptors mediate the adenosine‐induced relaxation in spontaneously active possum duodenum in vitro

“…Our findings were somewhat unexpected, however they support previous studies in rabbit and rat duodenum where exogenous adenosine also induced a relaxation (Small & Weston, 1979; Gaion et al ., 1988; Mule et al ., 1989). Our data extends the more recent studies in the rat duodenum, which identified A 1 R and predicted A 2B R to be present (Nicholls et al ., 1992,1996).…”

“…There are several reports of adenosine causing relaxation in the duodenum, however, the magnitude of the response appears to differ between species and the preparations studied. In the rabbit, adenosine causes a decrease in the contraction amplitude of spontaneous contractions (Small & Weston, 1979), whereas in the rat a rapid and short‐lasting decrease in basal tension occurs followed by a marked decrease in the contraction amplitude (Gaion et al ., 1988). Furthermore, studies using an isometric/isovolumic preparation of rat duodenum found that exogenous adenosine caused a fall in pressure and tension (Mule et al ., 1989; Serio et al ., 1990).…”

The ontogeny of purinoceptors in rat urinary bladder and duodenum

“…In the adult rat bladder ATP and AMP-PCP caused contraction, the potency order being AMP-PCP > ATP, which indicates an effect mediated by P2x-purinoceptors. Adenosine was inhibitory on both the rat duodenum and rat urinary bladder, and it has been demonstrated that its effects in both tissues are mediated by Pl-purinoceptors (Dahlen & Hedqvist, 1980;Gaion et al, 1988).…”

“…The rat urinary bladder was chosen as a model to study the development of P2x-purinoceptors, as in this tissue ATP causes contraction (Brown et al, 1979), and for the study of P2y-purinoceptors the rat duodenum was used as ATP relaxes this tissue (Manzini et al, 1985). Adenosine is inhibitory in both tissues (Dahlen & Hedqvist, 1980;Gaion et al, 1988), so the development of P1-purinoceptors could be followed in each. In addition, ATP has been proposed as a nonadrenergic, non-cholinergic neurotransmitter in both the rat bladder and the rat duodenum (Burnstock et al, 1970;1972a).…”

Central and Peripheral Actions of Adenosine and Its Analogues on Intestinal Myoelectric Activity and Propulsion in Rats

“…The presence of adenosine receptors has also been demonstrated in myenteric nerve endings (71, and A1 and A2 receptors coexist on intestinal smooth muscle cells (8). These receptors are involved in the relaxing effects of adenosine on isolated intestinal strips (9) through either a modulation of neurotransmission (10) or a direct action on smooth muscle cells (8).…”