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In Vitro Responses of Anterior Pituitary Glands from Normal, Castrated and Androgen-Treated Male Rats to LH-Releasing Factor (LRF) and High Potassium Medium

The University of Texas, Southwestern Medical School Dallas, Texas 75235

Abstract

In vitro incubation experiments were carried out with paired rat anterior pituitary halves for 6 hr at 37 C in Krebs-Ringer bicarbonate medium, and the effect of partially purified LRF and high potassium medium on release and synthesis of LH was studied. The release and total amount of LH in the system (medium plus glands) were measured by bioassay, and ¹⁴C-leucine incorporation into LH was examined after an immunochemical separation. Incorporation into protein was also determined. LRF or high potassium medium caused a good stimulation of LH release from the pituitaries of normal and castrated animals, but no significant effect on the release from glands of animals pretreated with testosterone propionate (TP) (1 mg im every other day for 2–3 weeks) in which the LH content had been reduced to to of that in normal glands. When LH content was kept at the normal level in castrates by properly adjusting the dose of TP, the glands responded normally to LRF. These facts suggest that the LH-releasing action of LRF and high potassium is dependent upon pituitary LH content. LRF failed to affect the total amount of LH in the incubation system and the incorporation of ¹⁴Cleucine into general protein or LH fractions from the pituitaries of normal, castrated or TP-treated animals. High potassium medium similarly failed to alter biosynthesis of LH. These results indicate that the predominant action of LRF is on release of LH, and that it may influence de novo biosynthesis of the hormone only as a secondary effect. (Endocrinology 87: 771, 1970)

Footnotes

¹ Present address: National Institute of Radiological Sciences, Chiba-shi, Japan.

² Please direct reprint requests to Dr. S. M. McCann, Dept. Physiol., Southwestern Medical School, Dallas, Texas 75235.

Received February 2, 1970.