Graduate Thesis Or Dissertation
 

In vitro hormonal and metabolic control of bovine mammary glucose 6-phosphate dehydrogenase activity

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  • Two studies were conducted to determine the in vitro metabolic and hormonal effects on glucose 6-phosphate dehydrogenase activity (G6PD) in bovine mammary explants. Study I was conducted to determine the effects of palmitoyl CoA (5 and 25 uM), acetate (1 and 10 mM), spermidine (0.4 mM) and putrescine (0.4 mM) on bovine mammary G6PD activity in vitro and whether these effects were dependent upon stage of lactation. Treatment of early lactation explants with 5 uM palmitoyl CoA or 1 mM acetate significantly reduced (P < .05) G6PD activity compared with 25 μM palmitoyl CoA or 10 mM acetate and was significantly less (P < .01) than control values. Addition of acetate in combination with 5 uM palmitoyl CoA significantly reversed G6PD inhibition (P < .05 for 1 mM and P < .01 for 10 mM). Addition of either 1 or 10 mM acetate in combination with 25 uM palmitoyl CoA failed to reverse G6PD inhibition. Spermidine (0.4 mM) significantly reversed (P < .05) palmitoyl CoA-induced inhibition at 5 μM, but not at 25 μM palmitoyl CoA. Spermidine also reversed G6PD inhibition by acetate after 120 min of incubation. Putrescine (0.4 mM) significantly decreased (P < .05) G6PD activity compared to explants treated with spermidine alone. Control values for G6PD activity were significantly higher (P < .01) in early lactation than midlactation explants. No statistical difference was found between any treatments in explants from mid-lactation cows. It is concluded that palmitoyl CoA and acetate will inhibit G6PD activity in early lactation, but not mid-lactation explants; and addition of spermidine will reverse this inhibition. Study II was conducted to determine the in vitro effect of estradiol on early lactation (32-56 d postpartum) bovine mammary G6PD activity. Mammary explants were incubated with 0, 10, 50, 100 or 500 ng /ml estradiol for 12, 24, 36, 40, 48, 60 or 72 h. From split plot analysis of variance it is concluded that there were no significant differences (P > .1) in enzyme activity due to level of estradiol, animal, or treat x time interaction. Variation in ene activity due to the time of incubation were significant (P < .05). It is concluded that estradiol did not stimulate bovine mammary G6PD in vitro.
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