Effects of galanin on the secretion and proliferative activity of the immature and regenerating adrenal glands of rats

The effects of galanin and the galanin-receptor antagonist (galanin-A) [D-T hr(6), D-Trp(8,9),15-ol]-galanin(1-15) on the immature and regenerating rat adrenal glands have been investigated in vivo. Adult female rats with adre nal regeneration and their offpring (20-day-old) were given three subcutane ous injections (28,16, and 4 h before being killed) of 2 nmol/100 g galanin and/or galanin-A, and 0.1 mg/100 g vincristin 3 h before being killed. Pla sma corticosterone concentration was measured by radioimmunoassay, and the mitotic index (parts per thousand of metaphase-arrested cells) was evaluate d. In immature rats, galanin increased plasma corticosterone concentration, without affecting mitotic index; the secretagogue effect was reversed by g alanin-A, which alone was ineffective. In rats with regenerating adrenal, g alanin-A increased both blood level of corticosterone and mitotic index; ga lanin was ineffective, but blocked the effects of galanin-A. These findings allowed us to draw the following conclusions: 1) galanin exerts a moderate glucocorticoid secretagogue action on immature rat adrenals, but endogenou s galanin does not play a major physiological role in the functional contro l of the gland; and 2) endogenous galanin exerts a maximal tonic inhibitory control on both glucocorticoid secretion and proliferative activity of reg enerating rat adrenals, whose physiological relevance remains to be investi gated. (C) 2000 Elsevier Science Inc. All rights reserved.