Plasma sex steroid-binding protein in mature heifers: effects of reproductive status, nutritional level, and porcine growth hormone, and estradiol-17 beta treatments

Biology of Reproduction
V Lermite, M Terqui

Abstract

In heifers, the specific 5 alpha-dihydrotestosterone (5 alpha-DHT) binding to sex steroid-binding protein (SBP) was 53 nM in midluteal phase and was 20% lower (p less than 0.05) in early luteal phase. In ovariectomized heifers on a high (H) or a low (L) energy diet, SBP bound testosterone with high specificity and estradiol-17 beta (E2) with a lower specificity; the affinity constant with 5 alpha-DHT was similar in the two groups independent of diet (Ka = 1.0 and 1.3 x 10(9) x M-1 for H and L heifers, respectively). Electrophoretic mobility of SBP was not affected by undernutrition. The specific 5 alpha-DHT binding to SBP in anestrous heifers compared to heifers in early luteal phase was 17% lower 18 days after cessation of ovarian activity (p less than 0.05) and 35% lower after 78 days of anestrus (p less than 0.001). Specific 5 alpha-DHT binding to SBP was 33% lower (p less than 0.001) in L heifers than in H heifers (40 nM). Porcine growth hormone (pGH) and E2 injections increased specific 5 alpha-DHT binding to SBP in both H and L heifers, but the effect depended on diet. Simultaneous injections of pGH and E2 increased specific binding in H heifers (p less than 0.02), whereas it had no effect in L heifers. We conclude that S...Continue Reading

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