engleski

Application of growth hormone releasing factor (GHRF) on the synthesis of growth hormone (GH) at the female sheep anterior pituitary (AP)

The pituitary gland as the main gland of the neuroendocrine system plays a key role in the maintenance of homeostasis. There are at least three levels of feedback control in the hypothalamus and the pituitary gland at the neuroendocrine level: long, short and ultrashort feedback systems. Releasing factors are released from the end of the axons of the neurosecretory cells into the blood supply to the AP to regulate hormone production. GH produced and stored in the AP stimulates protein synthesis and carbohydrate metabolism. GH controls the rate at which tissues can mobilise nutrients from the blood. GH directly inhibits the deposition and stimulate cell division, protein synthesis and bone growth. The objeczive of this study was to find out influence of age on the possible stimulation of GH synthesis in AP with GHRF after in vitro treatment. Despite the similarity of bovine and ovine GH, the administration of exogenous bovine GH to lambs has produced disappointing results. We present preliminary results on the effective dose of GHRF on the neuroendocrine regulation of GH synthesis. The AP (18 and 38 days old lambs) have been removed immediatelly after sacrificing, washed in saline to remove a traces of blood, put into ice and transfered to the laboratory for the futher experiments. AP have been devided and a half of each has been after slicing incubated as a control with only BEM with Earles salt and to another half has been added 10 microgram of GHRF. In vitro incubation of AP slices (cca 20 mg) was performed in 95 percent + 5 percent (air + CO 2) for 3 hours at 37 C. After the incubation tissue slices were separated and submitted for histochemical (Burck, 1969), electron microscopy (Johannessen, 1978, Zechner-Krpan, 1998) or immunochemical examinations (Farmilo, 1989, Naish, 1989) for the determination of GH producing cells. With the PAGE produced GH in the AP has been determined. In the control AP (18 days), GH cells show typical ultrastructural features. There are elongated or ovoid, with circular dense granules. The granules show a regular disposition and have usual size and structures. These cells have large, rounded nuclei with finely granular chromatin and prominent nucleoli. The rough endoplasmatic reticulum is well developed. In the GHRF treated AP somatotropic cells are different than cells in the control group. These cells contain numerous rounded dense granules, different size. Treatment of anterior pituitary tissue by GHRF in vitro has shown that: - bovine GHRF is active on the sheep pituitary, - GH producing cells present in the AP are mature on the 18th day of age (Figure 1), but probably hypothalamus synthesis of GHRF is lacking. AP from 38 days old lambs are already producing significant ammounts of GH but still able to increase production (Figure 2), - AP from 18 days old lamb is more sensitive on the influence of GHRF than those from 38 days old, - stimulation of 18 days old lambs by GHRF could increase meat and milk production, - stimulation of hypothalamus to produce GHRF at the early stage of life should be one from the future research goals.

growth hormone releasing factor (GHRF); growth hormone (GH); anterior pituitary; sheep

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