Pituitary Mapping

Abstract

1662 PURPOSE: The purpose of this study was to examine the responses and adaptations of pituitary gland to produce immunoreactive growth hormone (iGH) in response to an acute resistance exercise stress before and after training in rats. METHODS: A 4-group block design: pre-training (i.e., pre-exercise group and post-exercise group) and post-training (pre-exercise group and post-exercise groups) was used. Twelvemonth old male Sprage-Dawley rats were randomly assigned to one of the 4 groups (n = 9/group). The acute exercise stress and the resistance training protocol consisted of climbing a 1-meter long ladder set at an 85o angle with a weight attached to a tail sleeve. The exercise session consisted of 10 individual repetitions of climbing with each repetition separated by a 2 min rest period. The training program was performed 3 days per week for 7 weeks. The mass lifted was gradually increased from 50 g to 535 g by the conclusion of the training program. Rats were kept on a 12: 12 h light dark cycle at 21o C and provided standard laboratory animal chow ad libitum. The Institutional Animal Care and Use Committee approved all procedures. Rats were euthanized by decapitation and immediately following death the pituitary was harvested and subsequently analyzed dividing the gland into eight distinct anatomical sections. Basal GH release was measured from sections placed in gyrotory incubation for three consecutive periods (20 min each). Tissues and cells were analyzed by light microscopy and flow cytometry. Immunoassay was used to detect iGH signals in both the peripheral blood and pituitary media with immunocytohistochemistry performed on pituitary slices to determine GH activity. RESULTS: Exercise significantly (P<0.05) increased GH concentrations and number of GH producing cells in the pituitary after exercise. With training the number of GH producing cells after exercise increased as well as [GH] in the blood and media when compared to pre-training values. No significant changes for iGH were observed pre-exercise. Surprisingly, no significant differences were observed among the different quadrants of the pituitary for the iGH signals. CONCLUSIONS: These data indicate that post-exercise increases in the concentrations of iGH with resistance exercise and training are due to an increased number of GH producing cells throughout the pituitary gland. A lack of changes at rest for iGH supports human observations of little or no changes in iGH with resistance training. How other molecular variants of the GH molecule or aggregates respond to resistance exercise and training and are anatomically located in the pituitary remains to be further characterized.