Renotropic Activity in Ovine Luteinizing Hormone Isoform(s)*

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Abstract
Renotropic activity was previously demonstrated in an ovine LH prepartion. This preparation was further purified with a series of chromatographic steps, and the fractions were assayed for renotropic activity in vivo by their ability to stimulate [3H]thymidine incorporation into renal DNA of castrated hypophysectomized male rats. A purified preparation could be dissociated acid treatment into two major constituent subunits, designated .alpha. and .beta., each of which was composed of three microhetreogeneous components (subunits .alpha.1-3 and .beta.1-3) by reverse phase HPLC. Peptide mapping, including amino acid analyses and partial sequencing of the purified peptides, showed that 1) subunits .alpha.3 and .beta.3 possess the full length of the polypeptide chains, with the same amino acid sequences as those of the corresponding LH subunits .alpha. and .beta., respectively; and 2) subunits .alpha.1 and .alpha.2 are complexes of three polypeptides which are missing several N-terminal residues from subunit .alpha.3. Conversely, subunits .beta.1 and .beta.2 lack the C-terminal two residues and one residue, respectively, of subunit .beta.3. Renotropic activity was not detected in any of the dissociated subunits alone, but association of .alpha.1-3 with .beta.1-3 reconstituted the hormonal activity with different potencies. In particular, combination of subunits .alpha.3 and .beta.3 (.alpha.3 .cntdot. .beta.3) yielded a potent rentoropic activity with weak gonadotropic activity. The carbohydrate composition of the purified preparation exhibiting renotropic activity differed from that of a reference oLH preparation, which possessed greater gonadotropic activity but was devoid of renotropic activity. Furthermore, renotropic activity was decreased after removal of sialic acid by treatment with neuraminidase. Thus, the oligosaccharide moieties as well as the amino acid sequences of the subunits may play an important role in the expression of rentoropic activity in vivo, these effects over and above those arising from differential metabolic clearance. We conclude that pituitary renotropin represents a novel activity of a LH- isoform(s) and that the posttranslational (or the artificial, i.e. during preparation) modification of the constituent LH subunits may be responsible for modulation of renotropic activity as well as the intrinsic gonadotropic activity.