Sympathetic Β‐receptors and the Guinea‐pig Vas Deferens

1 The effects of adrenoceptor agonists and other agonists on the contractile responses of the prostatic and epididymal portions of the rat isolated vas deferens to single pulse field stimulation were investigated. 2 a-Adrenoceptor agonists produced prejunctional c2-mediated inhibition and post-junctional cxl-mediated potentiation of the nerve-induced responses. Guanabenz and xylazine produced mainly inhibitory effects, xylazine being 10 times less potent. Clonidine and oxymetazoline produced inhibition with similar potency to guanabenz but at higher concentrations excitatory effects were present, particularly in the epididymal portion. Phenylephrine produced only potentiation of the nerveinduced response in both portions. Potentiation of nerve-induced responses was a more sensitive and quantitative index of excitation than was direct contraction of the tissue. 3 Isoprenaline and salbutamol both gave fl2-mediated inhibition of the nerve-induced responses in both portions of tissue. At least part of the effect was post-junctional since phenylephrine contractions were inhibited. Isoprenaline also produced a post-junctional ocx-mediated excitation. 4 Noradrenaline produced effects qualitatively similar to those of the other ax-adrenoceptor agonists, inhibition and excitation predominating in the prostatic and epididymal ends respectively. 5 Morphine produced inhibition in the mouse but not in the rat vas deferens. In rat vas, however, enkephalin analogues produced pre-junctional inhibition of responses in both portions which could be partly reversed by naloxone; restoration of the adrenergic component was more complete. Rat anococcygeus showed no equivalent effect. 6 Adenosine 5'-triphosphate (ATP) inhibited nerve-induced responses in each portion with a greater effect on the prostatic portion.

Section: Discussionsupporting

confidence: 80%

The Distribution of Adrenoceptors and Other Drug Receptors Between the Two Ends of the Rat Vas Deferens as Revealed by Selective Agonists and Antagonists

Macdonald

McGrath

1980

“…It seemed likely that isoprenaline was acting on /8-adrenoceptors to produce the inhibition of the contractions in response to acetylcholine, and that the augmentation could be due to the weak a-adrenoceptor stimulating property of isoprenaline (Bickerton, 1963;Large, 1965;Sutter, 1965;Gay, Rand & Wilson, 1967;Flacke, Osgood & Bendixen, 1967;Coupar, 1970;Day & Dixon, 1971;Eyre, 1971). In accordance with this, it was found that propranolol (1-7 piM) completely prevented the inhibitory action of isoprenaline (Fig.…”

Section: Effect Of Isoprenaline On Responses To Acetylcholinesupporting

confidence: 62%

“…These curves were reminiscent of the ones obtained by Large (1965) on the guinea-pig vas deferens-hypogastric nerve preparation, which he described as 'inverted parabolic curves'.…”

Section: Effect Of Isoprenaline On Responses To Acetylcholinementioning

confidence: 68%

The presence of β‐adrenoceptors in the guinea‐pig seminal vesicle

Spedding

Weetman

1972

Summary . The preparation of longitudinal smooth muscle strips from guinea‐pig seminal vesicles is described. . Isoprenaline and salbutamol inhibited contractions produced by parasympathomimetic agents. . The inhibitory action of isoprenaline was blocked by low concentrations of propranolol and butoxamine. It was concluded that β2‐adrenoceptors were present in the tissue. . The inhibitory action of isoprenaline was not apparent when adrenaline, noradrenaline, hypogastric nerve or transmural stimulation were used to contract the tissue.

“…A similar relationship exists in the guinea-pig vas deferens. Here, the ineffectiveness of isoprenaline, at high concentrations, is due to its weak agonist effects on excitatory postsynaptic a-adrenoceptors which counter the inhibitory effects of f-adrenoceptor stimulation (Large, 1965;Spedding & Weetman, 1972). In the present experiments, the ability of high concentrations of isoprenaline to cause a phentolamine-susceptible contraction indicates that isoprenaline also activates postsynaptic a-adrenoceptors in the rat vas deferens.…”

Section: Discussionmentioning

confidence: 55%

Effects of Metoclopramide and Isoprenaline in the Rat Vas Deferens; Interactions With Α‐adrenoceptors

Spedding

1980

3 From these results it is concluded that metoclopramide (2.8 to 280 pM) is a presynaptic a-adrenoceptor antagonist in the rat vas deferens.4 Following,-adrenoceptor blockade with (±)-propranolol (3.3 gM), (--isoprenaline (0.47 to 14 gM) inhibited responses to field stimulation but not to phenylephrine. These propranolol-resistant effects of isoprenaline were antagonized by metoclopramide (2.8 to 280 pM) and by phentolamine (0