Dopamine induces contraction in the proximal, but relaxation in the distal rat isolated small intestine.
In the gut, dopamine is released by enteric neurons and modulates motility of small intestine smooth muscle cells. Here, we systematically analyzed the dopamine-induced effects on the longitudinal smooth muscle of different sections of the rat isolated small intestine. We found that exogenous dopamine had biphasic effects and could lead to both an early contraction and a late relaxation, depending on the region of small intestine. Thus, dopamine-induced early contractions were commonly observed in the duodenum, but less frequently in the jejunum, and rarely in the ileum. The amplitudes of these early contractions showed a striking regional dependence (duodenum>jejunum>ileum) and were significantly blocked by SCH23390 and raclopride. Conversely, dopamine-induced late relaxations were regularly obtained in the ileum and in the jejunum, but less frequently in the duodenum. Interestingly, the amplitudes of these relaxations showed an inverse regional dependence (ileum>jejunum>duodenum), and were insensitive to dopamine receptor antagonists. Rather, they were significantly inhibited by propranolol and prazosin. We conclude that dopamine exerts differential effects on smooth muscle motility in different regions within the rat small intestine. In proximal parts, dopamine predominantly causes D(1) and D(2) dopamine receptor-dependent contraction, whereas it leads to alpha and beta adrenoceptor-dependent relaxation in more distal parts.
Kirschstein
Timo
T
Institute of Physiology, University of Rostock, Gertrudenstrasse 9, 18057 Rostock, Germany. timo.kirschstein@uni-rostock.de
Dammann
Fabian
F
Klostermann
Jenny
J
Rehberg
Mirko
M
Tokay
Tursonjan
T
Schubert
Rudolf
R
Köhling
Rüdiger
R
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects / Q000502:physiology*; D007082:Ileum / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007583:Jejunum / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D020891:Raclopride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D001552:Benzazepines; D018492:Dopamine Antagonists; C534628:SCH 23390; D020891:Raclopride; D011433:Propranolol; D004298:Dopamine; D011224:Prazosin