Studies on the Microheterogeneity of Follicle-Stimulating Hormone Present within the Anterior Pituitary Gland of Ovariectomized Hamsters*

Abstract

The administration of 17β-estradiol (E₂) to ovariectomized hamsters at 0900 h (day 1) induced a proestrous-like gonadotropin surge the following day (day 2). Immediately before serum LH and FSH levels reached maximal concentrations on day 2, the concentration of FSH within the anterior pituitary gland (AP) remained unchanged. However, an increase was observed in the amount of AP FSH that failed to attach to the lectin, Concanavalin A (Con A), compared to that species that did interact with Con A. When the various forms of FSH present within the AP of ovariectomized animals before or after E₂ injection were separated by polyacrylamide gel isoelectric focusing six species of immunologically active FSH were observed (pI values of 5.8, 5.7, 5.4, 5.1, 4.7, and 4.0). Five of these six species were consistently present in pituitary extracts collected 0, 24, and 28 h postinjection of E₂. The sixth species (pI 4.0) was observed in increasing amounts with time after E₂ treatment. The ability of each species of immunologically active FSH to bind to Con A was tested by two different methods, and similar results were obtained. Four of the six species were able to bind to the lectin, whereas two species (the third and the sixth (pI values 5.4 and 4.0, respectively) did not interact with Con A. Treatment of pituitary extracts with neuraminidase (an enzyme that cleaves sialic acid residues) before polyacrylamide gel isoelectric focusing decreased the number of observed FSH peaks. The above results demonstrate the existence of multiple species of immunologically active FSH within the hamster AP. Four of the six species bind to the lectin, Con A. Two did not interact with the lectin, increased in content after E₂ treatment, and may represent the releasable form of AP FSH.