Sex-related differences in the activity of liver mitochondrial alpha-glycerophosphate dehydrogenase in the rat.
The rat liver mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) is an enzyme that markedly responds to thyroid hormone administration. Its activity is considered a good index of thyroid status in peripheral tissues. In this study alpha-GPD activity and the binding characteristics of nuclear T3 receptors (maximal binding capacity, MBC, and affinity constant, Ka) were compared in male and female rats. Basal alpha-GPD activity in adult females was significantly higher than in the age-matched males. The same difference was observed in immature animals. The cyclic physiological variations in the ovarian steroid hormones during the estrous cycle did not significantly affect alpha-GPD activity, MBC or Ka. Orchiectomy or replacement doses of testosterone administered to orchiectomized rats, had no effect on alpha-GPD activity compared to sham-operated normal males. In females, neither oophorectomy nor testosterone injection to oophorectomized animals induced changes in the enzyme activity. Liver nuclear T3-content, MBC and Ka revealed no systematic differences in both sexes. The T3-induced alpha-GPD activity after a single large dose of T3 designed to fully saturate the nuclear sites for a 24 h period, was significantly higher in female compared to male rats. The kinetics of alpha-GPD showed an identical Km in both sexes, while Vmax was significantly higher in the females. The data suggest that the factors leading to the different activity of alpha-GPD in both sexes, although unknown, may be not related to the sex-hormone differences.
Coleoni
A H
AH
Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
Cherubini
O
O
D000818:Animals; D004971:Estrus; D005260:Female; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000201:enzymology*; D009919:Orchiectomy; D010052:Ovariectomy; D051381:Rats; D011919:Rats, Inbred Strains; D011988:Receptors, Thyroid Hormone / Q000032:analysis; D012727:Sex Characteristics; D012737:Sex Factors; D013739:Testosterone / Q000008:administration & dosage; D014284:Triiodothyronine / Q000378:metabolism
D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D013739:Testosterone; D005993:Glycerolphosphate Dehydrogenase