Sex hormones and triose metabolism

Abstract

In man there is a direct relationship between the consumption of sucrose and the concentration of blood triglycerides and high blood triglyceride levels are believed to be related to atherosclerosis and coronary heart disease (CHD). From about 35 years of age onwards the incidence of CHD in men is high relative to the incidence in premeho-pausal women. In men dietary fructose leads to higher fasting blood triglyceride levels than in premenopausal women but in this respect post-menopausal women resemble the men and they also have a high incidence of CHD. Hence it is possible that CHD is related to fructose intake and subsequent conversion to fats and that this whole process is under the control of sex hormones. The sex relationship between dietary fructose and the level of blood fats has also been observed in a number of animals other than man. The trioses, glyceraldehyde and glycerol, are on a metabolic pathway from fructose to triglycerides and hence the effect of sex hormones on the metabolism of these compounds has been investigated. The enzymes involved in the conversion of glyceraldehyde to L-glycerol-3-phosphate were compared in liver tissues from adult male and female rats and an attempt has been made to change the activities by castration and/or administration of exogenous sex hormones. NAD-dependent glycerol dehydrogenase was found to be equally active in both male and female rat livers Injection of testosterone, estrone or estradiol into animals of either sex did not affect the activity. Similar results were obtained with the NADP-dependent glycerol dehydrogenase. Glycerol kinase activity was observed to be 30~40% higher in male rat liver than in the female tissues. Injection of testosterone into male animals had little effect on the liver kinase but decreased activity was observed with the antiandrogens, estradiol-17[beta] and cyproterone. Castration of male animals lowered the kinase activity and testosterone injection was observed to restore activity. Hypophysectomy also lowered liver kinase activity in males but, in this case, the activity could not be restored by male hormone injection. In female rats neither testosterone not estradiol-17[beta] affected the liver glycerol kinase level. In vitro incubation of liver slices from rats of both sexes with testosterone resulted in increased kinase activity. Attempts were made to investigate the mode of action of testosterone in the in vitro system. The investigation suggests that glycerol kinase is under control of sex hormones and this, in part, may account for the sex differences observed in the conversion of fructose to triglycerides.