Neurotransmitter feedback is not important in modulating the noradrenergic component of responses of rat vas deferens to twin pulse electrical field stimulation.
1. Drug effects on the full time-course of tension responses of the rat vas deferens to challenges of twin pulse field stimulation (TPFS) were examined. A microprocessor-controlled system was used to regulate stimulus delivery, on-line data collection and subsequent data analysis. 2. The second, noradrenergic phase of the response to the second stimulus of TPFS was missing when the interpulse interval was set at 3 s but was progressively restored as the interpulse interval was extended to 120 s. 3. With a 3 s interpulse interval, the missing second phase of the response to the second stimulus was not restored by the selective alpha 2-adrenoceptor antagonists yohimbine, imiloxan or idazoxan, indicative that alpha 2-adrenoceptor-mediated feedback inhibition of noradrenaline release is not the predominant mechanism modulating this response component. 4. Incubation with the P1-purinoceptor antagonist 8-phenyl-theophylline also failed to restore the missing noradrenergic component in the response to the second stimulus of TPFS. 5. Nevertheless, both responses to TPFS were impaired by the selective alpha 2-adrenoceptor agonist clonidine and by the P1-purinoceptor agonist 2-chloroadenosine, indicating the presence of functional presynaptic receptors of both types. These agonist-induced inhibitory effects were readily reversed by those antagonists which had failed to restore the missing noradrenergic component in the second response to TPFS.
Department of Pharmacology and Therapeutics, University of Wales College of Medicine, Health Park, Cardiff, UK.
N J
NJ
Mallard
R W
RW
Marshall
T L
TL
Spriggs
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D004347:Drug Interactions; D004558:Electric Stimulation; D005246:Feedback / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011983:Receptors, Purinergic / Q000502:physiology; D014649:Vas Deferens / Q000187:drug effects / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011942:Receptors, Adrenergic, alpha; D011983:Receptors, Purinergic; D009638:Norepinephrine