Comparison of the effects of crude and highly purified bovine inhibin (Mr 32 000) on plasma concentrations of FSH and LH in chronically ovariectomized prepubertal heifers

Abstract

Chronically ovariectomized prepubertal heifers were used for a comparison of the effects of highly purified bovine inhibin (Mr 32,000) and steroid-free bovine follicular fluid (bFF) on the secretion of FSH and LH. In view of the limited availability of highly purified inhibin, an initial study was undertaken to establish the optimal method for administration of bFF inhibin activity. In comparison with the FSH response to a single large i.v. bolus injection of bFF (50 ml; 3250 mg protein), a far more effective suppression of plasma FSH concentrations was achieved when considerably less bFF (6.3 ml; 410 mg protein) was administered gradually over an extended time-period (2 days) either as a continuous i.v. infusion or as a series of 2-hourly i.v. injections. Following a single i.v. bolus injection of bFF, immunoreactive inhibin was cleared rapidly from the circulation (half-life 51 +/- 8 (S.E.M.) min, n = 5), presumably accounting for its limited ability to suppress FSH secretion when administered in this manner. In a second experiment, treatment of ovariectomized heifers (three per group) with highly purified Mr 32,000 bovine inhibin at a dose rate of 15 micrograms/2 h for 2 days significantly (P less than 0.05) suppressed plasma FSH concentrations, which reached their minimum values (40% suppression) during day 2 of treatment. At a lower dose rate (5 micrograms/2 h), inhibin did not significantly affect plasma FSH levels. Administration of bFF was also associated with a dose-dependent suppression of FSH secretion. For each of three dose rates tested (three heifers per group), plasma FSH concentrations were maximally suppressed during day 2 of treatment (65 mg/2 h, 86% suppression, P less than 0.001; 21.7 mg/2 h, 66% suppression, P less than 0.001; 7.2 mg/2 h, 15% suppression, P greater than 0.05). Neither highly purified inhibin nor bFF significantly affected mean plasma LH concentrations, LH pulse frequency or LH pulse amplitude. Thus we have shown for the first time that highly purified Mr 32,000 bovine inhibin does possess in-vivo biological activity in cattle, promoting a selective suppression of plasma FSH concentrations qualitatively similar to that evoked by steroid-free bFF.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bovine follicular fluid and partially purified bovine inhibin on FSH and LH release by bovine pituitary cells in culture

“…These results agree with the results obtained when either highly purified bovine or porcine inhibin was tested in rat pituitary cell culture (Robertson et al, 1985;Ling et al, 1987;Miyamoto et al, 1987) or injected in ovariectomized heifers (Ireland et al, 1983;Beard et al, 1990 (Nakamura et al, 1990; Kogawa et al, 1991;Shimonaka et al, 1991 Therefore, the purification of bovine inhibin with H256 as ligand may also copurify follistatin and activin,, and these bound proteins appear as a multiplicity of bands in the 25-35-kDa region. These results underline the potential problems of purifying inhibin by immunoaffinity chromatography from biological fluid.…”

“…Inhibin has been identified as one of the proteins responsible for suppression of spontaneous FSH release (Ying, 1988;Ling et al, 1990;Knight, 1991). In cattle, it has been shown that injection of either BFF or purified inhibin reduces endogenous FSH concentration in the systemic circulation of intact (Miller et al, 1979;Quirk and Fortune, 1986;Lussier and Carruthers, 1989) hemiovariectomized Lussier et al, 1988) and ovariectomized cows (Ireland et al, 1983;Beard et al, 1990 the mixture at a ratio of 0.1 ml/ml of gel. The affinity gel column was equilibrated with 50 mM Tris-HCI, pH 7.5.…”

Effects of androgens, progesterone and their antagonists on the developmental competence of in vitro matured bovine oocytes

“…Concentrations of total ir-α-inhibin were measured using the competitive radioimmunoassay reported by Knight et al (1989) and Beard et al (1990). Purified bovine 32 kDa inhibin A was used as the standard and the sensitivity of the assay was approximately 1 ng ml -1…”

Active Immunization against Inhibin Improves Superovulatory Response to Exogenous FSH in Cattle

“…Additionally, it has been established that inhibin is responsible for the regulation of FSH secretion in cattle. Injection of steroid-free bovine follicular fluid [11] or highly purified bovine inhibin [12] has the ability to suppress FSH secretion in ovariectomized and cyclic heifers. Previous studies showed that the number of follicles 2 mm in diameter or larger was increased, by neutralization of endogenous inhibin u s i n g a c t i v e [ 1 3 -1 5 ] a n d p a s s i v e [ 1 6 -1 9 ] immunization, through a rise in the basal level of endogenous FSH.…”