Arginine Vasopressin as an Intragonadal Hormone in Brattleboro Rats: Presence of a Testicular Vasopressin-Like Peptide and Functional Vasopressin Receptors*

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Abstract
We have previously demonstrated the presence of an arginine vasopressin (AVP)-like peptide and AVP receptors in rat testis. We have also shown a direct inhibitory effect of AVP on androgen biosynthesis by cultured testicular cells. This study examined the presence of testicular AVP-like peptides and AVP receptors in homozygous (di/di) Brattleboro rats, a genetic mutant known to be deficient in hypothalamic, pituitary, and circulating AVP. The supernatant of homogenized 0.1 N acetic acid-extracted testis from adult homozygous Brattleboro rats was chromatographed on a Sephadex G-25 column. The elution profile of AVP immunoreactivity, as measured by a specific RIA, showed three distinct peaks. The first peak eluted close to the column void volume, a second peak eluted at the column total volume, while a third peak coeluted with synthetic AVP. The third peak of immunoreactive material (375 pg/g tissue) behaved similarly to authentic AVP on octadecylsilica adsorption chromatography, showed a competition curve parallel to that of AVP in the RIA, and comigrated with AVP on Sephadex G-25 and reverse phase TLC. The first, but not the second, immunoreactive peak contained enzyme activity that degraded labeled AVP in a time-dependent manner. Additional studies investigated the presence of AVP receptors in testes from Brattleboro rats. Saturable and specific [3H]AVP-binding sites were present in an enriched testicular interstitial cell preparation from these animals. Scatchard analysis indicated a Kd of 5.6 .times. 10-10 M and a binding capacity of 9.7 fmol AVP bound/106 cells. These receptors were of the vasopressor (V1) subtype, as indicated by the potencies of selective AVP analogs for composition of [3H]AVP binding. The functionality of these receptors was shown by AVP inhibition of gonadotropin-induced androgen biosynthesis in cultured testicular cells derived from Bratleboro rats. Thus, testes from Brattleboro rats contain a high amount of an AVP-like peptide even though these animals lack hypothalamic, pituitary, and circulating AVP. Also, an AVP-degrading enzyme and AVP receptors with a Kd and binding capacity similar to those of Sprague-Dawley rats are present in the testes of Brattleboro rats. These findings add further support to the hypothesis that locally produced AVP acts as an intratesticular modulator of androgen biosynthesis.