Effects of oestradiol, phenobarbitone and luteinizing hormone releasing hormone upon the isoelectric profile of pituitary follicle-stimulating hormone in ovariectomized hamsters

Abstract

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 inhibin-containing 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 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.

Are circulating gonadotropin isoforms naturally occurring biased agonists? Basic and therapeutic implications

“…4. There are data supporting the notion that the degree of glycosylation of gonadotropins is regulated by gonadal steroids [4,60,68,69]. Furthermore, in menopausal women a higher predominance of more acidic FSH isoforms (more bioactive) has been demonstrated as compared with women of reproductive age [70,71].…”

“…A full discussion of the role of glycosylation is out of scope of this review but it is important to describe, in general, the importance of posttranslational processing on the function of these hormones; particularly since the glycosylation pattern has a profound effect on the biology of the gonadotropins. Tight regulation of glycosylation of gonadotropins suggests an important physiological role for the presence of glycosylated variants of LH, hCG and FSH [4][5][6][7][8][9]. However, the understanding how this modification conveys specific attributes to the function of the hormones is not without controversy.…”

Dynamic Change in Charge Heterogeneity of Pituitary FSH throughout the Estrous Cycle in Female Rats.

“…Microheterogeneity of FSH has been demonstrated in the rat (Foulds and Robertson, 1983;Blum et al, 1985), hamster (UlloaAguirre and Chappel, 1982), monkey (Chappel et al, 1984) and man (Zaidi et al, 1981). Furthermore, it has been shown that the charge heterogeneity of FSH changes according to the sex, age and endocrine status (Robertson et al, 1982;Cameron and Chappel, 1985;Galle et al, 1983).…”

The Fertile Window and Biomarkers: A Review and Analysis of Normal Ovulation Cycles

“…FSH levels increase during the follicular phase and are higher in the preovulatory period, with a typical surge at the middle of the cycle. During a woman's reproductive years, when plasma estradiol concentration is greater, the FSH molecule is less glycosylated and has a shorter half-life, but more receptor affinity (8,9). At the start of the menstrual cycle, a folliclestimulating hormone induces cellular differentiation and proliferation in the preovulatory follicle.…”