The Presence of Two Species of Follicle-Stimulating Hormone within Hamster Anterior Pituitary Glands as Disclosed by Concanavalin A Chromatography*

Abstract

Anterior pituitary gland (AP) homogenates and serum samples were obtained from hamsters at hourly intervals between 1100–1700 h during proestrus. The presence of two species of immunologically active FSH in AP homogenates was revealed by an affinity adsorption technique that employs the lectin, Concanavalin A (Con A). One species did not bind to the lectin (Con A-unbound), whereas the other form (Con A-bound) did attach to the Con A and was eluted with a glucopyranoside solution. The relative ratios of both species of FSH within AP homogenates were determined throughout the afternoon of proestrus. Immediately before the proestrous FSH surge (1100–1400 h), the total AP concentration of FSH remained elevated and unchanged; however, the relative ratio of Con A-unbound to Con A-bound forms of AP FSH increased dramatically. As serum concentrations of FSH rose during proestrous afternoon (between 1500–1700 h), both the AP FSH concentration and the ratio of Con A-unbound to Con A-bound FSH declined. Serum FSH collected from animals during the proestrous surge did not bind to Con A. The depletion of the total AP FSH concentration, the rise in serum FSH levels, and the diminution in the ratio of Con A-unbound to Con A-bound FSH observed at 1500 h on proestrus could be prevented by phenobarbital injection. These inhibitory effects of phenobarbital were reversed by LHRH administration. Both species of hamster AP FSH displaced labeled FSH from a FSH antibody in a similar fashion, which was parallel to a dose-response curve generated with the NIAMDD-Rat FSHRP-1 standard. Both species also displaced ¹²⁵I-labeled FSH from FSH receptors present upon isolated hamster granulosa cells. These findings demonstrate that the ratio of Con A-unbound to Con A-bound FSH within AP extracts was greatest immediately before the proestrous FSH surge. This ratio within the AP declined during the spontaneous or LHRH-induced FSH rise. FSH within serum samples collected during the proestrous surge existed in the Con A-unbound form. The Con A-unbound species present within the AP may represent the releasable form of this hormone.