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Circulating Half-Lives of Follicle-Stimulating Hormone and Luteinizing Hormone in Pituitary Extracts and Isoform Fractions of Ovariectomized and Intact Ewes^*

Prince Henry's Institute of Medical Research (D.M.R., I.C.) South Melbourne, 3205, Victoria
Department of Anatomy (L.M.F.), Monash University Clayton, 3168, Victoria
Department of Agriculture and Rural Affairs (R.C.F.) Werribee, 3030, Victoria
Department of Neurosurgery (J.T.C.), St. Vincent's Hospital Fitzroy, 3065, Victoria, Australia

Address all correspondence and requests for reprints to: Dr. D. M. Robertson, Prince Henry's Institute of Medical Research, Box 118, South Melbourne, 3205, Victoria, Australia.

Abstract

Previous studies have shown that the circulating half-life (t) of serum FSH in ewes after hypophysectomy (HPX) increased 10-fold after ovariectomy (OVEX). The basis for this difference was examined in this study by determining the circulating half-life of serum FSH and LH in HPX ewes after administration of pituitary extracts and gonadotropin isoform fractions. High-speed supernatants of pituitaries from gonadal- intact and OVEX ewes were fractionated by electrofocusing in sucrose gradients and based on the pi distribution of FSH and LH divided into four pools, pH 4.3-4.8, 4.8-5.55, 5.8-6.7, and 6.7-10. These extracts were administered by iv bolus injection to HPX gonadal-intact ewes and blood samples collected between 15-1000 min later. The clearance pattern for both serum FSH and LH was heterogenous, indicative of a major rapid and a minor slow dissociating component. A significant (P < 0.05) difference in circulating half-lives (rapid component) was observed between pituitary extracts from intact and OVEX ewes for FSH (tvi = 32.8 ± 8.6 min us. 89.9 ± 32.3 min) but not LH (31,3 ± 9.2 min us. 39.3 ± 6.1 min, respectively), whereas no significant difference was observed between the corresponding FSH or LH isoform preparations.

To establish if the difference in circulating half-lives obtained after HPX and bolus iv injection was due to mode of delivery, an extract of pituitaries from OVEX ewes was infused for 12 h into HPX sheep and the t values determined after cessation of treatment and compared to those after a bolus injection. The clearance of both FSH and LH from plasma after infusion was significantly prolonged than after a bolus injection.

It is concluded that the difference in circulating half-lives of FSH between pituitary extracts from intact and OVEX ewes after bolus administration is due to a difference in pituitary FSH composition. However, the prolonged clearance with infusion compared to bolus administration suggests that extrapituitary factors are also responsible. (Endocrinology 129: 1805–1813, 1991)

Footnotes

^* This work was funded by the National Health and Medical Research Council of Australia.

Received January 4, 1991.

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