Comparison of Induced Corpora Lutea from Prepuberal Gilts and Spontaneous Corpora Lutea from Mature Gilts: Hydroxysteroid Dehydrogenase Activity

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Abstract
The activity of hydroxysteroid dehydrogenases was histochemically quantified in corpora lutea (CL) from prepuberal gilts induced to ovulate and mature gilts. Prepuberal (P) gilts, 120 to 130 d of age were induced to ovulate with 1,500 IU pregnant mare serum gonadotropin (PMSG) followed 72 h later by 500 IU human chorionic gonadotropin (hCG). Three P gilts and three mature (M) gilts each were ovariectomized on d 10, 14, 18, 22 and 26 (d 0 = day of hCG for P gilts and onset of estrus for M gilts). Gilts ovariectomized on d 14, 18, 22 and 26 were hysterectomized on d 6 to ensure luteal maintenance. At the time of ovariectomy, CL were frozen in liquid nitrogen and then stored at −80 C until analysis. Cryostat sections (12 µm) were histochemically analyzed for Δ5 −3β-hydroxysteroid dehydrogenase (3β OHSD), 17α-hydroxysteroid dehydrogenase (17α OHSD) and 20α-hydroxysteroid dehydrogenase (20α OHSD). The intensity of staining (greater enzyme activity resulted in darker staining) was quantified using a Zeiss SF microscope integrated with a Zonax photometer, which measured the percentage of light transmitted through a given area (22,500 µm2) of the tissue section. Data were subjected to analysis of variance using the general linear models procedure of Statistical Analysis System (SAS). The 3β OHSD activity did not change over days, but the mean activity (throughout all days) in the P gilts (32.6 ± 1.8) tended (P<.08) to be elevated above that of M gilts (27.9 ± 1.7). The 17α OHSD activity was similar for P and M gilts but 17α OHSD activity was different (P<.05) between days (d 10, 5.3 ± .9; d 14, 9.2 ± .9;d 18, 7.1 ± .8; d 22, 5.7 ± .9 and d 26, 5.5 ± 1.0). The 20α OHSD activity was greater (P<.05) in P gilts (6.7 ± .5) than in M gilts (5.1 ± .5); there was also an effect (P<.01) of day (d 10, 3.9 ± .8; d 14, 10.7 ± .9; d 18, 5.6 ± .8; d 22, 6.5 ± .8 and d 26, 3.4 ± .9). The results indicate that the progesterone metabolic pathway may be different in the induced CL from P gilts and the spontaneous CL from M gilts. These differences may contribute to abnormal function of the induced CL and subsequent inability of the P gilt to maintain pregnancy. Copyright © 1987. American Society of Animal Science . Copyright 1987 by American Society of Animal Science