Ovine Allantoic Fluid Contains High Concentrations of Activin A: Partial Dissociation of Immunoactivity and Bioactivity¹

^d Institute of Reproduction and Development, ^e Department of Physiology, Monash University, ^f Prince Henry's Institute for Medical Research, Monash Medical Centre, Clayton, Victoria 3168, Australia ^g School of Biological and Molecular Sciences, Oxford Brookes University, Oxford, United Kingdom

In a preliminary study, allantoic fluid collected from pregnant sheep across gestational ages of 20–124 days contained significantly higher levels of activin bioactivity (189 ± 74 ng/ml, mean ± SE) than did amniotic fluid (3.2 ± 0.6 ng/ml). Using a combination of chromatography steps, we isolated from 5 L of allantoic fluid approximately 612 µg of immunoactive activin, which eluted over 10 fractions from a C8 reversed-phase column. When these fractions were assayed in a rat pituitary cell culture bioassay, in a specific RIA, and in an activin A two-site ELISA, the RIA activity was skewed to the less hydrophobic side of the activin profile, while the bioactivity was skewed to the more hydrophobic forms. The activity measured in the two-site ELISA more closely matched the mass of activin as determined by laser densitometry. Amino-terminal sequencing of fractions containing either peak immunoactivity or bioactivity showed each to be identical to activin A. This was confirmed by internal sequences from a fraction that eluted in the area of overlapping immunoactivity and bioactivity. A peptide containing at least 18 amino acids at its amino terminus, which were identical to the conserved region of the acute-phase protein serum amyloid A, was identified in the most immunoactive activin fractions.

¹ This research was supported by a grant from the NH&;, Australia.

² Correspondence: D.M. de Kretser, Institute of Reproduction and Development, Level 3, Block E, Monash Medical Centre, 246 Clayton Road, Clayton, Victoria 3168, Australia. FAX: 61 3 9550–3584; david.de.kretser{at}med.monash.edu.au

³ Current address: Department of Physiology, University of New England, Armidale, NSW 2351, Australia.

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