Anterior pituitary glands were collected from immature and mature (intact and castrated) male hamsters. The various species of FSH present within these glands were separated by Concanavalin A (Con A) chromatography and polyacrylamide gel isoelectric focusing (PAG-IEF) and measured by a specific FSH radioimmunoassay (RIA) as well as a radioreceptor assay (RRA). Two distinct forms of FSH (Con A unbound and bound) were separated by Con A chromatography and detected by both RIA and RRA. These two populations of FSH were present within anterior pituitary glands of all three animal models tested. Castration before collection of anterior pituitary glands reduced the ratio of Con A unbound: bound immunoreactive FSH. When measured by RRA this reduction was not observed. When homogenates of anterior pituitary glands obtained from mature animals were separated by PAG-IEF, six distinct species of FSH were observed by RIA with isoelectric points (pI) of 6·0, 5·7, 5·3, 5·0, 4·7 and 4·2–3·8. Homogenates of anterior pituitary glands obtained from immature male hamsters did not contain one of these species of FSH (pI value, 4·7). The relative contribution of some of the species of FSH to the total amount of detectable FSH differed depending upon the endocrine status of the animal. The species with pI value of 4·2–3·8 did not show any receptor-binding activity in any of the three models studied. The overall ratio of the activity of FSH measured by RRA compared with RIA was highest in anterior pituitary glands from intact mature and immature hamsters and lowest in anterior pituitary glands obtained from castrated animals. The RRA: RIA ratio for each species of FSH in all models tested declined as the isoelectric point of that species decreased. Thus, these results demonstrated the presence of multiple species of FSH within the anterior pituitary glands of immature and mature male hamsters. The relative proportions and receptor-binding activities of these species differed according to the isoelectric point and the pattern of hormone secretion at the time of collection of pituitary glands. Gonadal and other endocrine factors may influence not only the relative amount of each species of FSH but also the receptor-binding capacity of the FSH species synthesized by the anterior pituitary gland.

Anterior pituitary glands were removed from ovariectomized hamsters after specific endocrine treatments. The presence and relative proportions of the multiple species of FSH present within them were assessed by radioimmunoassay after separation by chromatofocusing. This technique is superior to polyacrylamide gel-isoelectric focusing, as it can accommodate a greater sample volume and has increased resolution. Endocrine conditions which decreased hypothalamic LH releasing hormone (LHRH) release or the sensitivity of the pituitary gland to that neurohormone (phenobarbitone treatment or short-term oestradiol exposure) caused an increase in the relative proportions of the more acidic forms (isoelectric points (pI) 5·1–3·8) of pituitary FSH and a concomitant reduction in the more basic (pI values 6·0–5·3) forms of FSH. During times of increased pituitary LHRH exposure (immediately before the oestradiol-induced gonadotrophin surge or after injection of synthetic LHRH) an increase was observed in the relative proportion of the more basic forms of pituitary FSH. Treatment of ovariectomized hamsters with an inhibincontaining preparation reduced serum FSH concentrations as well as the relative proportion of the more basic forms of pituitary FSH. We have previously shown that the more basic forms of FSH exhibit more biological activity in an in-vitro test system. The present studies suggest that the existing hormonal milieu, in particular LHRH and oestradiol, influences the types of FSH produced and (presumably) secreted. Thus, through hormonal interactions, the pituitary gland regulates not only the absolute amount but also the potency of the FSH signal to the ovaries.