Steroid-like hormones

Another important hormone derived from cholesterol is vitamin D. This steroid-like hormone is involved in regulating calcium and phosphorus metabolism. The complete synthesis of vitamin D requires ultraviolet light to convert 7-dehydrocholesterol to previtamin Dj. The reaction scheme is shown in Figure 34-3. The active hormone 1,25-dihydroxycholecalciferol (calcitriol)... 

Steroids like cholesterol 335, cholic acid 336, or the sex hormone testosterone 337 play an important role in almost all living organisms. Therefore they are the... 

Although one would like to see the precision of these methods improved, it should be realized that most diagnostic problems in this field involve elevations in steroid levels in plasma or urine of the order of 2- to 10-fold and often of several hundredfold. By many criteria these levels of precision vary from not quite, to reasonably, adequate (W3). Despite the lack of quality control the satisfactory precision achieved by most modern methods for individual steroids is indicated by more recent studies in which they have been used for measurements of steroids providing rather sharp discrimination of normals from diseased patients. There is also reasonable concordance between normal values achieved by different workers for many steroid sex hormones and their metabolites. Also, in these studies the better GLC and double-isotope LLC methods are in general agreement (E2, T5). 

Adrenal and gonadal steroid hormones have long been known to regulate many important brain functions (Fuxe et al., 1981 McEwen, 1991). In addition, circulating steroids like progesterone, 11-deoxycorticosterone, and testosterone can be converted to neuroactive steroids within the brain (Mellon and Griffin,... 

Since the level of cholesterol was highest in the vegetative apices before their transition to flowering (Table 1), and cholesterol levels actually decreased during floral differentiation, it is also possible that cholesterol is in some way associated with the process of floral initiation. For instance, there is some evidence in the literature that the flower-inducing hormone may be an isopentenoid or steroid-like compound Various steroids occur in plants, and cholesterol has been shown to be a key intermediate in their biosynthesis Ojll. Thus, it is possible that cholesterol was being used to make steroids, which may be involved in floral induction. 

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