“…In vivo experiments have usually reported an inhibitory action of aor fi-agonists on protein secretion (Pfeffer & Hinton, 1956;Rudick, Gonda, Rosenberg, Chapman, Dreiling & Janowitz, 1973) or no effect at all (Roze, De la Tour, Chariot, Souchard, Vaille, Dupont, Jean & Wepierre, 1976;Furuta, Hashimoto & Washizaki, 1978;Demol & Sarles, 1980). In the case of inhibitory actions, it has been difficult to distinguish direct effects (due to activation ofreceptors located on the cell membrane) from indirect ones (due to vasoconstriction or an increase in vascular pressure) (Elisha, Hutson & Scratcherd, 1984). Moreover, during in vivo experiments, oc-agonists might act at both peripheral and central sites (Chariot, Roze, De la Tour, Souchard & Vaille, 1983).…”