A single intrauterine infusion of sustained recombinant ovine interferon-tau extends corpus luteum lifespan in cyclic ewes

Delivery carriers were developed to permit sustained release of recombinant ovine tau-interferon (roIFN-tau) to increase corpus luteum (CL) lifespan in cyclic ewes following a single intrauterine administration on Day 10 post estrus. A single infusion with 1.7 mg roIFN-tau covalently bound to carboxymethyl biogel agarose (carbodiimide coupling) significantly increased the interestrus interval (P < 0.01) in treated (n = 4) versus control animals (n = 6), whereas liposomally encapsulated roIFN-tau administered to experimental ewes (n = 8) versus control ewes (n = 6) was less effective (P < 0.05). RoIFN-tau covalently bound to trisacryl (glutaraldehyde coupling) was also effective in cyclic ewes (n = 6), but covalent binding to Eupergit C through oxirane bonds yielded ineffective preparations. Ewes that were given 1.7 mg soluble roIFN-tau (n = 8) displayed slight extension of the CL lifespan compared with ewes that were given 1.7 mg soluble BSA (n = 6), but this extension lacked significance in the Mann-Whitney U-test (P > 0.05). These results are consistent with previous data from experiments performed with daily intrauterine infusion of soluble, native or recombinant oIFN-tau. In addition, because CL maintenance requires only a single administration, these methods are efficient and simple to use since they avoid animal catheterization and allow for reduced injection frequency. Moreover, they may permit the use of smaller amounts of IFN. It is concluded that the use of oIFN-tau sustained in some delivery systems may allow for the development of an experimental sheep pseudopregnancy model.