EVALUATION OF CIRCULATING GALANIN LEVELS AFTER EXERCISE-INDUCED PITUITARY-HORMONE SECRETION IN MAN

The neuropeptide galanin (GAL) is widely distributed in the central an d peripheral nervous systems, anterior pituitary, and adrenal medulla. GAL is colocalized with corticotropin (ACTH) in the human pituitary a nd with epinephrine (E) and norepinephrine (NE) in chromaffin cells of the adrenal medulla. The function of GAL in peripheral tissues is not known, although the presence of the peptide in corticotrophs and the adrenal gland suggest that it participates in stress responses. In the present study, we investigated whether GAL is cosecreted with ACTH du ring activation of corticotrophs by an acute physical exercise test. C irculating levels of GAL and pituitary hormones were measured in healt hy exercise-tested and control male subjects. Blood samples were colle cted during basal conditions, maximal power output (MPO), and the reco very period. Control subjects were sampled during the resting conditio n. The pituitary response to exercise was characterized by a significa nt increase in ACTH plasma levels (peak value 13.28 +/- 2.19 v 6.68 +/ - 1.01 pmol/L, P < .05) and growth hormone (GH) serum levels (peak val ue, 14.53 +/- 5.59 v 0.29 +/- 0.1 mu g/L, P < .02), with the peak in h ormone levels detected 15 minutes after the end of exercise. No change in circulating prolactin (PRL) levels was detected. An expected signi ficant increase in plasma levels of both E (peak value, 1,574.41 +/- 4 03.31 v 267.44 +/- 60.03 pmol/L, P < .01) and NE (peak value, 7,275.25 +/- 955.80 v 961.51 +/- 168.40 pmol/L, P < .01) was also observed. Pl asma GAL levels were not affected by the acute exercise test, with the levels being comparable to baseline during the exercise test and the recovery phase. At any sample time, GAL values were comparable between exercise-tested and control subjects. These data show that despite th e colocalization of GAL and ACTH within the same pituitary cells, the two peptides are not coreleased in response to stress resulting from a cute physical exercise. Furthermore, pituitary GAL seems not to be inv olved in the stimulation of GH secretion in exercise tested subjects. The results also indicate that GAL is not coreleased with E or NE in r esponse to the exercise-induced stress condition. Copyright (C) 1997 b y W.B. Saunders Company.