EFFECTS OF ACUTE ADMINISTRATION OF GROWTH HORMONE-RELEASING HORMONE (GHRH) AND OXYTOCIN ON SOMATOTROPH CELLS IN SHEEP - MORPHOMETRIC STUDY AND GROWTH-HORMONE (GH) SECRETION

In this work, the combined use of the morphometric study of somatotroph cells and plasma GH levels provided new data for the interpretation of the role played by OT and GHRH on GH cells. GHRH 1-29 (15 mu g/kg), oxytocin (2.5 IU animal) or 1 ml saline solution were administered to male lambs. The GH plasma concentration was measured by RIA and for the morphometric study the cellular area, nuclear area and volume density of the somatotroph cells were measured in 1 mu m semi-thin sections immunolabeled with avidin-biotin technique (ABC), The area under the GH response curve for 3 hours after injection was similar in both saline and OT-treated animals (24.8 +/- 9.1 and 31.4 +/- 14.7 mu g/ml, respectively) and much lower than that observed in GHRH-treated animals (445.5 +/- 126.7 mu g/ml). The cell area of somatotrophs was smaller in the GHRH-treated lambs and larger in the CT-treated lambs than in the control lambs (71.47 +/- 1.56, 91.42 +/- 1.72 and 83.1 +/- 1.74 mu m(2), respectively). A similar change was observed in the nuclear area; it decreased in the GHRH-treated lambs (21.61 +/- 0.52 mu m(2)) and increased in the OT-treated lambs (25.45 +/- 0.68 mu m(2)) with respect to the control group (23.75 +/- 0.44 mu m(2)). No significant differences were found in volume density, These results show a decrease in the size and an increase in the number of somatotrophs in the GHRH-treated lambs; while in oxytocin-treated lambs there is an opposite effect, an increase in the size of the cells and a decrease in the number of cells staining with anti-GH ovine with aspect to control lambs. This study provides information on the mechanism regulating the secretion of GH by GHRH and oxytocin in sheep.