Characterization of postsynaptic α‐adrenoceptors in the arteries supplying the oviduct

Abstract

1 In vitro experiments were designed to characterize postjunctional a-adrenoceptor subtypes in ring segments (1 mm length; outer diameter 300-500pm) from arteries supplying the oviduct of the heifer. 2 Noradrenaline, adrenaline and phenylephrine evoked concentration-dependent contractile responses. The pD2 values were 5.67, 5.89 and 5.93, respectively. Medetomidine, clonidine and B-HT 920 (2-amino-6-allyl-5,6,7,8-tetra-hydro-4H-(thiazo)-4,5-d-azepine) were ineffective.3 The a-adrenoceptor selective antagonists, prazosin (1 nM-0.1 pM) and rauwolscine

Effect of the vascular endothelium on noradrenaline‐induced contractions in non‐pregnant and pregnant guinea‐pig uterine arteries

“…This conclusion is consistent with the concept that in nonpregnant and pregnant guinea-pig uterine arteries with intact endothelium m-adrenoceptors are mainly of the ml subtype (Fallgren & Edvinsson, 1986;Fallgren et al, 1988). Further evidence for this hypothesis is the observation that the obtained KA values for noradrenaline are in the range reported for KA in other vascular beds in which predominance of mi-adrenoceptors exists (Oriowo et al, 1989;Isla & Dyer 1990;Costa et al, 1992).…”

“…Besides, affinity estimates for noradrenaline itself also did not differ between the tissues studied, regardless of pregnancy status or endothelial condition. The -log KB values for prazosin obtained in our study (8.78-9.07) are higher than pA2 values reported for non-pregnant and pregnant guinea-pig uterine arteries with intact endothelium (7.52-7.97, Fallgren & Edvinsson, 1986;Fallgren et al, 1988), but similar to pA2 values reported for pregnant ovine uterine artery (9.1, Isla & Dyer, 1990) and for arteries supplying the heifers oviduct (9.38, Costa et al, 1992). Nevertheless, the affinities of prazosin for antagonizing the contraction induced by noradrenaline is within the range reported for aladrenoceptor blockade (Agrawal et al, 1984;Skarby & Larsson, 1987), which suggests the presence of contractionmediating ml-adrenoceptors in the preparations studied.…”

Endothelium‐dependent relaxation to acetylcholine in bovine oviductal arteries: mediation by nitric oxide and changes in apamin‐sensitive K+ conductance

“…Isometric wall tension was recorded on a Grass model 79D polygraph. Artery rings were stretched in a stepwise fashion to the optimal point of their length-tension relationship (1.75 mN mm-') as determined in previous studies (Costa et al, 1992 forth over the parallel stainless steel legs inside the organ baths. The absence of endothelium was confirmed pharmacologically by loss of relaxant response to ACh (10 AM).…”

“…However, little is known about the mechanisms underlying blood flow regulation in the oviduct. The existence of a dense adrenergic innervation (Black, 1974) and the presence of a-adrenoceptors in the vasculature of the oviduct (Costa et al, 1992) provide a contractile mechanism through which reactivity of oviductal vessels can be regulated by the sympathetic nervous system. In the uterine artery, from which the arterial supply of the oviduct is derived, several reports have shown that acetylcholine (ACh) elicits vasodilatation through the activation of muscarinic receptors (Jovanovic et al, 1994a), which in turn, release endothelium relaxing factors, mainly nitric oxide (NO) (Tare et al, 1990;Jovanovic et al, 1994b).…”

Endothelial modulation of resting and stimulated vascular tone in the pig capsular testicular artery

“…Some rings were previously treated for 30 min with indomethacin (10 −6 M). Heifer oviductal arteries with or without endothelium, were also mounted as above [3] to test whether the method of endothelium removal affected the K + curve in another type of vessel.…”