Developmental changes in the response of rat isolated duodenum to nicotine

Purinergic signalling and development of the autonomic nervous system

Most early studies of the role of nucleotides in development have evidenced their crucial importance as carriers of energy in all organisms. However, an increasing number of studies are now available to suggest that purines and pyrimidines, acting as extracellular ligands specifically on receptors of the plasma membrane, may play a pivotal role throughout pre- and postnatal development in a wide variety of organisms including amphibians, birds, and mammals. Purinergic receptor expression and functions have been studied in the development of many organs, including the autonomic nervous system (ANS). Nucleotide receptors can induce a multiplicity of cellular signalling pathways via crosstalk with bioactive molecules acting on growth factors and neurotransmitter receptors which are fundamental for the development of a mature and functional ANS. Purines and pyrimidines may influence all the stages of neuronal development, including neural cell proliferation, migration, differentiation and phenotype determination of differentiated cells. Indeed, the normal development of the ANS is disturbed by dysfunction of purinergic signalling in animal models. To establish the primitive and fundamental nature of purinergic neurotransmission in the ontogeny of the ANS, in this review the roles of purines and pyrimidines as signalling molecules during embryological and postnatal development are considered.

The birth and postnatal development of purinergic signalling

The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.

Postnatal development of P2 receptors in the murine gastrointestinal tract

The actions of purine and pyrimidine compounds on isolated segments of the mouse intestine were investigated during postnatal development. The localization of P2Y(1), P2Y(2), P2Y(4), P2X(1,) P2X(2) and P2X(3) receptors were examined immunohistochemically, and levels of expression of P2Y(1), P2X(1) and P2X(2) were studied by Western immunoblot. From day 12 onwards, the order of potency for relaxation of longitudinal muscle of all regions was 2-MeSADP>or=alpha,beta-meATP>or=ATP=UTP=adenosine, suggesting P2Y(1) receptors. This was supported by the sensitivity of responses to 2-MeSADP to the selective antagonist MRS 2179 and P2Y(1) receptor immunoreactivity on longitudinal muscle and a subpopulation of myenteric neurons. A further alpha,beta-meATP-sensitive P2Y receptor subtype was also indicated. ATP and UTP were equipotent suggesting a P2Y(2) and/or P2Y(4) receptor. Adenosine relaxed the longitudinal muscle in all regions via P1 receptors. The efficacy of all agonists to induce relaxation of raised tone preparations increased with age, being comparable to adult by day 20, the weaning age. During postnatal development the contractile response of the ileum and colon was via P2Y(1) receptors, while the relaxant response mediated by P2Y(1) receptors gradually appeared along the mouse gastrointestinal tract, being detectable in the stomach from day 3 and in the duodenum from day 6. In the ileum and colon relaxant responses to 2-MeSADP were not detected until days 8 and 12, respectively. 2-MeSADP induced contractions on basal tone preparations from day 3, but decreased significantly at day 12 and disappeared by day 20. At day 8, contractions of colonic longitudinal muscle to ATP showed no desensitisation suggesting the involvement of P2X(2) receptors. Immunoreactivity to P2X(2) receptors only was observed on the longitudinal muscle of the colon and ileum from day 1 and on a subpopulation of myenteric neurons from day 3. These data suggest that P2Y(1) receptors undergo postnatal developmental changes in the mouse gut, with a shift from contraction to relaxation. Such changes occur 1 week before weaning and may contribute to the changes that take place in the gut when the food composition changes from maternal milk to solid food.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

Postnatal development of purinoceptors in rat visceral smooth muscle preparations

1. Adenosine and ATP have well-established functions as neuromodulator and neurotransmitter, respectively, in smooth muscle preparations, and purinergic control may be an early form of autonomic control in both evolution and ontogenesis. 2. This review describes the postnatal development of responses mediated by the various receptors for adenosine and for nucleotides in the rat duodenum, colon, urinary bladder and vas deferens and considers the implications that this development may have for the importance of purinergic control in neonates and adults.

(-)Nicotine inhibits the activations of phospholipases A2 and D by amyloid beta peptide

It has been established that amyloid beta peptide (AbetaP) activates phospholipase A2, phospholipase C and phospholipase D of LA-N-2 cells and other cell types. Nicotine in addition to being a cholinergic agonist, may be neuroprotective. We have investigated the ability of (-)nicotine to blunt the phospholipase activations by AbetaP in LA-N-2 cells. (-)Nicotine inhibits the AbetaP activation of phospholipase A2, with an IC50 of 76 microM and of phospholipase D with an IC50 of 252 microM. (-)Nicotine did not blunt the AbetaP activation of phospholipase C. These inhibitions of AbetaP activations were not observed with (+)nicotine or cotinine. The (-)nicotine inhibition of AbetaP activation of these two phospholipases was unaffected by hexamethonium and D-tubocurarine. There was no inhibition of the phospholipase A2 activity present in homogenates of LA-N-2 cells. Exposure of LA-N-2 cells to (-)nicotine for 2 h resulted in the blockade of phospholipase A2 activation by kainate and AbetaP but did not affect the ability of quisqualate and AbetaP to activate phospholipase D. These data suggest that if the nicotine inhibition of AbetaP activations is receptor occupancy mediated then it is by an atypical receptor type.

Involvement of vasoactive intestinal polypeptide in nicotine-induced relaxation of the rat gastric fundus

1. Nicotine-induced relaxation and release of vasoactive intestinal polypeptide (VIP)- and peptide histidine isoleucine (PHI)-like immunoreactivity (LI) were measured in longitudinal muscle strips from the rat gastric fundus. 2. Under non-cholinergic conditions (0.3 microM atropine), nicotine (3-300 microM) produced concentration-dependent relaxations of the 5-hydroxytryptamine (3 microM)-precontracted strips. Under non-adrenergic non-cholinergic (NANC) conditions (0.3 microM atropine + 1 microM phentolamine + 1 microM nadolol), relaxations induced by sub-maximal nicotine concentrations (10 and 30 microM) were significantly smaller, while that produced by the highest concentration used (300 microM) was similar to that seen under non-cholinergic conditions. 3. Re-exposure to the same nicotine concentration 1 h later induced smaller relaxations, indicating desensitization. The reductions seen in the second responses were proportional to the concentration used. 4. Under non-cholinergic conditions, the relaxant response to 30 microM nicotine was abolished by hexamethonium (100 microM) and significantly reduced by tetrodotoxin (TTX, 3 microM). The TTX-resistant component was not observed under NANC conditions. 5. NANC relaxation induced by 30 microM nicotine was significantly reduced by a specific anti-VIP serum (approximately 35% less than that seen with normal rabbit serum). 6. Nicotine (30-300 microM) caused significant, concentration-dependent increases in the outflow of VIP- and PHI-LI from the strips; these effects were also diminished with re-exposure. The increases in both types of immunoreactivity evoked by nicotine (300 microM) were abolished by hexamethonium (300 microM), TTX (3 microM) and a calcium-free medium. 7. These findings indicate that VIP and possibly PHI are involved in NANC relaxation of the rat gastric fundus induced by nicotine.

Development of cholinergic and inhibitory non-adrenergic non-cholinergic responses in the rat gastric funds

1. Cholinergic contractions and inhibitory non-adrenergic non-cholinergic (NANC) relaxations were studied in longitudinal muscle strips of the gastric funds of 2, 4 and 8 week old rats. 2. Contractions induced by electrical stimulation of the cholinergic neurones and by administration of acetylcholine decreased during development. The potentiating effect of physostigmine was similar in the 3 age groups. 3. Short train stimulation in NANC conditions induced fast relaxations, which were more pronounced in 4 and 8 week than in 2 week old rats. These relaxations were almost completely inhibited by NG-nitro-L-arginine methyl ester (L-NAME) in the 3 age groups. The nitric oxide-induced relaxations did not change during development. 4. Sustained electrical stimulation in NANC conditions induced an initial relaxation, which was almost totally blocked by L-NAME, followed by an almost complete recovery of tone at lower frequencies of stimulation. At higher frequencies of stimulation, the recovery of tone was incomplete or absent. This sustained relaxation was only partially reduced by L-NAME and almost abolished by L-NAME plus alpha-chymotrypsin. The initial relaxations increased during development, while the sustained relaxations remained similar during this period. Vasoactive intestinal polypeptide-induced relaxations were also similar in the 3 age groups. 5. These results show that the sensitivity of the gastric fundus to acetylcholine decreases from 2 weeks to 8 weeks postnatally, while the importance of the nitrergic innervation increases during this period.

In vitro characterization of tripitramine, a polymethylene tetraamine displaying high selectivity and affinity for muscarinic M2 receptors

1. The antimuscarinic effects of tripitramine were investigated in vitro in isolated driven left (force) and spontaneously beating right (force and rate) atria as well as in the ileum of guinea-pig and rat and in the trachea and lung strip of guinea-pig and compared with the effects of methoctramine. 2. Tripitramine was a potent competitive antagonist of muscarinic M2 receptors in right and left atria. The pA2 values ranged from 9.14 to 9.85. However, in the guinea-pig and rat left atria but not in guinea-pig right atria, tripitramine at lower concentrations (3-10 nM) produced a less than proportional displacement to the right of agonist-induced responses owing to the presence of a possible saturable removal process. 3. Tripitramine was about three orders of magnitude less potent in ileal and tracheal than in atrial preparations (pA2 values ranging from 6.34 to 6.81) which makes it more potent and more selective than methoctramine. 4. Another intriguing finding was the observation that the pA2 value of 7.91 observed for tripitramine in guinea-pig lung does not correlate with that found at both muscarinic M2 and M3 receptor subtypes, which clearly indicates that the contraction of guinea-pig lung strip is not mediated by these muscarinic receptor subtypes. 5. A combination of tripitramine with atropine resulted in addition of the dose-ratios for left atria as required for two antagonists interacting competitively with the same receptor site, whereas the same combination gave a supra-additive antagonism on guinea-pig ileum which suggests that tripitramine interacts with a second interdependent site. 6. Tripitramine was more specific than methoctramine since, in addition to muscarinic receptors, it inhibited only frog rectus abdominis muscular (pIC50 value of 6.14) and rat duodenum neuronal (pIC50 value of 4.87) nicotinic receptors among receptor systems investigated, namely alpha 1-, alpha 2-, and beta 1-adrenoceptors, H1- and H2-histamine receptors, and muscular and neuronal nicotinic receptors.

Developmental changes in response to endothelins and receptor subtypes of isolated rat duodenum

The response of isolated duodenum to endothelin-1, -3 and IRL 1620 (Suc-[Glu9,Ala11,15]endothelin-1 (8-21)), a selective endothelin ETB receptor agonist, was studied in both neonatal (1-week-old) and adult rats by recording mechanical activity isotonically. Endothelin-1, -3 and IRL 1620 (1-100 nM) elicited sustained contraction of neonatal duodenum, in a concentration-dependent manner, with a potency order of endothelin-1 = endothelin-3 > IRL 1620. The response to endothelin-1 and -3 (10-1000 nM) of adult duodenum was biphasic, i.e., transient relaxation followed by contraction, with a potency order of endothelin-1 > endothelin-3. The contractile response to endothelin-1 of adult but not neonatal duodenum was significantly antagonized by pretreatment with FR139317 (1 microM), an endothelin ETA receptor antagonist. An endothelin ETB receptor antagonist, RES-701-1 (3 microM), weakly antagonized the IRL 1620-induced contraction of neonatal duodenum. However, RES-701-1 (10 microM) did not affect the response to endothelin-1 of either adult or neonatal duodenum. These results indicate that the duodenal response to endothelins changes from a sustained contraction in neonates to a biphasic response in adults. The contractile response to endothelins of neonatal duodenum is suggested to be mediated through endothelin ETB receptors or possibly RES-701-1-resistant ETB receptor subtypes and contraction of adult duodenum through endothelin ETA receptors. The mechanism of the endothelin-induced response of duodenum was also studied.