Significance of the adrenergic system in the regulation of vasopressin secretion in rat neurohypophyseal tissue cultures.

Unlabelled: The effects of adrenaline (A) and noradrenaline (NA) on vasopressin (VP) secretion were studied in 13-14-day cultures of isolated rat neurohypophyseal (NH) tissue. The VP contents of the supernatant media were determined by radioimmunoassay after a 1 or 2-h incubation. Significantly increased VP levels were detected in the tissue culture media following the administration of A (an alpha+beta(2)-receptor agonist), depending on the dose of A. The VP secretion elevation was totally blocked by the previous administration of phentolamine (an alpha(1)+alpha(2)-receptor antagonist) or corynanthine (an alpha(1)-receptor antagonist). Yohimbine (an alpha(2)-receptor antagonist) did not influence the VP secretion increase induced by A. After the administration of NA (a beta+alpha(1)-receptor agonist), a VP secretion elevation was again detected, but the degree of enhancement proved smaller than that of the VP secretion increase induced by A. Propranolol (a beta(1)+beta(2)-receptor antagonist) before NA administration prevented the VP secretion increase. Atenolol (a beta(1)-receptor antagonist) did not block the VP secretion elevation induced by NA. Corynanthine (an alpha(1)-receptor antagonist) treatment before NA administration reduced the NA-induced VP enhancement, because NA has an alpha(1)-receptor agonist character in addition to its main character (a beta-receptor agonist). Surprisingly, the administration of pindolol (a beta(1)+beta(2)-receptor antagonist) enhanced VP secretion. This contradictory effect can be explained in that pindolol not only acts as a blocker, but also exerts "intrinsic sympathomimetic action" and a strong adrenergic agonist effect. Pindolol before NA administration significantly increased the NA-induced VP elevation.
Conclusions: Mainly the alpha(1)- and beta(2)-adrenergic receptors are involved in the A- or NA-induced increase of VP secretion in isolated NH tissue cultures. The results indicate that VP release is influenced directly by the adrenergic system, and the adrenergic control of VP secretion from the NH tissue in rats can occur at the level of the posterior pituitary.