Avian Luteinizing Hormone-Releasing Factor*

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Abstract
Avian luteinizing hormone-releasing factor (LRF) was partially purified and characterized. Extracts of chicken hypothalami were purified by ultrafiltration and chromatography on Sephadex G-25 and CM Sephadex C-2S. Columns were monitored by optical density (254 mμ) measurement and vasopressor assay. LRF activity was evaluated by the ability of fractions to elicit release of LH from rat adenohypophyses in vitro. Incubations were conducted in the balanced incomplete block design, and released LH was assayed by radioimmunoassay. Although separation was incomplete, the LRF activity consistently emerged from Sephadex after arginine vasotocin (AVT). For further purification the LRF fraction was applied to a column ( 1 × 7 cm) of CM-Sephadex and eluted in 2 ml fractions with a gradient of ammonium acetate. LRF (tubes 11-20) emerged immediately after the bulk of the optically dense material. The LRF fraction (CM-2) was devoid of vasopressor activity, and all other fractions contained no LRF activity. Synthetic AVT emerged from identical columns at tubes 36-46. Fraction CM-2 was tested for ability to elicit dose-related release of LH. Three dose levels at three-fold increments released 2.02, 3.31, 4.39 \ig LH per hemipituitary respectively. The responses elicited by increasing doses of CM-2 and ultrafiltered extracts of rat hypothalamus were compared. Dose response curves to both preparations were linear and did not deviate significantly from parallelism. These data demonstrate the existence of an avian LRF which is not AVT, which behaves on Sephadex similarly to mammalian LRF, and which elicits a release of LH from the rat adenohypophysis proportional to the logarithm of the dose. Thus avian and mammalian LRF may be similar. (Endocrinology89: 1454, 1971)

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