Activity of three-beta-hydroxysteroid dehydrogenase in granulosa cells treated in vitro with luteinizing hormone, follicle-stimulating hormone, prolactin, or a combination.

Three-beta-hydroxysteroid dehydrogenase (3beta-HSD) is a key enzyme in the pathway that produces progesterone. Hy-Line hens (W36, W98, and Brown) were subjected to mild heat stress [36 degrees C for 24 h (acute heat stress, AHS) or 2 wk (chronic heat stress, CHS)] or maintained at 22 degrees C (thermoneutral, TN). Granulosa cells (GC) from the 3 largest follicles were isolated, dispersed, and incubated with luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), a combination, or no hormone (control), and then with pregnenolone nitro blue tetrazolium to determine 3beta-HSD activity. Treatment by LH (TN, P = 0.04; AHS, CHS, P < 0.0001) and by LH+FSH (TN, AHS, CHS, P < 0.0001) resulted in increased enzyme activity compared with the respective controls. In TN and CHS, LH+FSH increased the activity to a greater extent than LH alone (TN, P = 0.02; CHS, P = 0.0004); in AHS the increase was not significant (P = 0.29). Treatment with FSH, PRL, or LH+PRL decreased (TN, AHS) or had no effect (CHS) on 3beta-HSD activity. In TN and AHS cells, FSH and PRL reduced enzyme activity (P = 0.006 and 0.0580, respectively). When LH was added to PRL, suppression by PRL was mitigated somewhat. When LH and FSH were added to PRL, 3beta-HSD activity in AHS and CHS cells actually increased compared with the respective controls (P = 0.052 and 0.003) but remained below the activity of cells incubated with LH+FSH or LH alone. This suggests that gonadotropic actions of LH and LH+FSH are countered by the antigonadotropic action of PRL and, conversely, that PRL reduces the stimulatory action of LH and FSH. Strain differences in GC response to hormones were observed primarily in the CHS-treated birds; generally, W98 was highest; Browns showed the weakest response, and W36 was intermediate. In earlier studies, HS reduced circulating LH and GC progesterone and 3beta-HSD activity in vitro and increased circulating PRL. The results suggest a mechanism by which reduced activity of 3beta-HSD and progesterone by GC during HS might be explained, particularly with the differences in strains observed.