抄録
The chemical structure of growth hormone-releasing hormone (GH-RH) is not disclosed yet because of some difficult problems on purification. One of the most troublesome problems is the lack of sensitive and specific in vivo-assay method for GH-RH. Therefore, this study was attempted to search for 1) a more sensitive assay method using rats, and 2) a new reference standard as GH-RH instead of crude hypothalamic extracts (SME).
Adult male or female rats weighing 180-250 g were used in all experiments. Hypothalamic lesion was placed in some rats, which medial hypothalami were completely destructed by using a modified Halász-Pupp knife. Urethane or sodium pentobarbital was used as anesthetics. Reserpine or/and Estrogen + Progesteron was given subcutaneously prior to experiments in an attempt to increase the sensitivity of an assay method. Samples in physiological saline were administered intracarotedly once or twice, or were given intravenously through the jugular vein. Blood samples were taken at the various times from the jugular vien, or were collected from trunk by decapitation. Plasma GH, LH and prolactin were determined by the double antibody radioimmunoassay.
The following results were obtained;
1) Urethane anesthesia was able to lower plasma rat GH levels to 0 ng/ml for over 4 hours, and was suitable for GH-RH assay, whereas pentobarbital anesthesia gave the opposite results.
2) Reserpine pretreatment was advisable to increase the sensitivity of GH-RH assay. Using reserpene + urethane-rats, the minimum effective dose of GH-RH was 3 rat SME when injected intracarotedly.
3) The pretreatment of Estrogen + Progesterone or repeated administration of SME gave no benefit of GH-RH assay.
4) Prostaglandin E1 was able to stimulate the release of OH and prolactin in the hypothalamic lesioned rats as well as intact rats. This means that Prostaglandin E1 can act directly on the pituitary gland. This strong stimulator of GH release could be useful as a reference standard for GH-RH on establishing the more sensitive GH-RH assay system.
5) Similar results with 2) and 3) were obtained by using PGE 1 instead of SME. the maximum concentration of plasma GH and prolactin reached 5 minutes after PGE1 injection. Therefore, it should be tried to collect blood samples 5 minutes after sample injection in GH-RH assay.
Thus, the present investigation has shown a newly-established, improved in vivo assay system for GH-RH.
