Nature of adrenoceptor sites in bovine teat muscles

Abstract

The motility of smooth muscles excised from the wall of bovine teats was studied "in vitro". These muscle preparations often show spontaneous rhythmic contractions. Administration of isoprenaline results in relaxation and decreased spontaneous motility, these effects being blocked by propranolol. Noradrenaline elicits contraction and stimulates rhythmical activity, these effects being inhibited by dibenamine. The effect of adrenaline is variable as it induces contraction or inhibition or biphasic responses. Dibenamine blocked contractions, whereas propranolol inhibited relaxations. It appears that alpha and beta adrenoceptors are present in teat muscles. Stimulation of the former elicits activation, whereas stimulation of the latter results in inhibition. These "in vitro" results are largely in agreement with "in vivo" responses described previously.

Catecholamines, oxytocin and milk removal in dairy cows

“…The y?-adrenoceptor agonist isoproterenol tended to improve milk removal and particularly enhanced time to peak flow, as reported by Bernabe & Peeters (1980), Hamann (1981) and Bernabe & Ricordel (1985a, 6) who also used isoproterenol or clenbuterol. Peeters et al (1977) and Bernabe & Peeters (1980) demonstrated relaxation of the smooth muscles of the teats as well as decreased spontaneous motility in response to isoproterenol. Thus, /?-adrenoceptor agonists seem to enhance milk flow rates by permitting greater opening of the teat canal.…”

“…However, marked inhibitory effects on milk let-down of locally released noradrenalin or of other amines can be expected under conditions of emotional stress. Alpha-and /?-adrenergic receptors are located on arterial and teat (sphincter) smooth muscle cells (Peeters & De Bruycker, 1975;Peeters et al 1977;Bernabe & Peeters, 1980;Vandeputte-Van Messom et al 1984a).…”

“…Alpha-adrenoceptor agonists stimulate contraction, whereas /?-adrenoceptor agonists and a-adrenergic blocking agents cause relaxation of these muscles (Peeters & De Bruycker, 1975;Peeters et al 1977;Bernabe & Peeters, 1980). The effects of adrenalin and noradrenalin are inhibited by a-adrenergic blocking agents, at least in cattle (Bernabe & Peeters, 1980;Vandeputte-Van Messom et al 1982, 1984a.…”

Relationship between numbers of α2- and β2-adrenoceptors on blood cells of bulls and milkability of their daughters

“…Bovine teats contain longitudinal smooth muscles in the wall of the teat cistern and circular muscles around the teat canal. From pharmacological studies on living cows and isolated teat muscle preparations, evidence has been provided for the presence of both a-and /^-adrenoceptors in these muscles (Peeters et al 1977;Bernabe & Peeters, 1980). Administration of a-agonists induces contraction, whereas administration of /?-agonists results in relaxation (Bernabe & Peeters, 1980;Vandeputte-Van Messom et al 1984).…”

Modifications des conditions d'extraction du lait sous l'effet d'un β-mimétique (Isoprénaline) administré par voie intrajugulaire pendant la traite mécanique de la vache

“…Les trayons de vaches en lactation se contractent spontanément peu avant la traite (Peeters et al, 1948 ;Sambraus, 1971) et les essais pharmacologiques conduits chez ce type d'animal soit in vitro (Peeters et al, 1977) En outre, les vaches, dont la citerne est abondamment remplie de lait, pré-sentent fréquemment des écoulements intermittents de lait consécutifs à des relâ-chements musculaires des trayons (Bernabé et Peeters, 1980 (Dhondt et al, 1973 Smith, 1964 ;Notsuki et Goto, 1967 ;Ovesen, 1972 ;Balthazar et Scott, 1978) ; -du contrôle physiologique des muscles pariétaux et sphinctériens qui s'exerce vraisemblablement par l'intermédiaire du système nerveux sympathique (Peeters et al, 1949 ;Lefcourt, 1982) comme semble le prouver l'augmentation significative du débit de traite après anesthésie soit des trayons (de Buhr, 1958et Barczynski, 1960, soit du nerf inguinal (Emerson, 1929) de la vache ou après dénervation de la glande mammaire de brebis (Labussière, Martinet et Denamur, 1969 …”