Monographs on endocrinology最新文献

With respect to the ovarian status and the estrous cycle as expressed by the vaginal cytology, it was emphasized that there is only a rough correspondence between the vaginal stages and the days of the cycle. The 4-day cycle tends to be the most frequent, with the 5-day cycle a normal variant. Spontaneous persistent vaginal estrus (SPE), an acyclic state occurring in older adult rats, reflects the presence in the ovaries of large vesicular follicles failing to luteinize and, hence, the absence of corpora lutea once the condition becomes well established. Pseudocyclic fluctuations in the vaginal smear during SPE resemble those in ovariectomized rats treated chronically with estrogen. The age of onset of SPE varies among different rat strains, appearing as early as 5 or 6 months in the DA and CD strains, but rarely before 12 months in the O-M strain. O-M/DA hybrids were intermediate. In the DA strain there was also a marked influence of length of daily illumination on the occurrence of SPE: exposure to 10 hours or less of light per day restored cycling to rats that had already shown SPE while exposed to longer days. An hereditary influence of age was also apparent in the rapidity with which continuous illumination induced persistent estrus (LLPE). Young DA females rapidly entered LLPE within 10 days, while young O-M females remained cyclic for 5 weeks. Hybrids again were intermediate. At middle age. O-M rats became as responsive as young rats of the DA strain. Like SPE in DA rats. LLPE was reversible, for estrous cycles returned after daily exposure to light was reduced. The special sensitivity of DA rats to lighting may have been a trait acquired from outcrossing with wild gray rats in years past. Normal cycling could be restored in SPE rats by daily injection of progesterone at low dosage. The same effect followed isolated treatments with progesterone upon return of proestrus/estrus after interruption of SPE. This was the first demonstration of positive feed-back of progesterone, the first sign of its biphasic action, and an indication that progesterone facilitates the action of estrogen in promoting ovulation. When progesterone treatment was delayed after proestrus/estrus there was progressively lower effectiveness during the next 10 days. Indirect support of regular ovulatory cycles resulted from treating DA SPE rats with prolactin (PRL) daily at low doses, provided that an initial set of corpora lutea was first induced by other means.(ABSTRACT TRUNCATED AT 400 WORDS)

Although a considerable amount of work has been carried out in the last ten years in developing methods for the separation of steroids by HPLC, it is still not widespread for the reasons discussed above. There is however no doubt that further developments in HPLC technology, in increasing sensitivity and/or specificity of detection systems, perhaps with microbore columns, may lead to an increase in the use of this powerful analytical procedure as an additional separation method to improve specificity of assay. Solution of the problem of simple interfacing of HPLC systems with mass spectrometers (discussed in another chapter by Games) should further increase the application of HPLC. HPLC is of particular value in providing a means of separating unstable compounds prior to assay by relatively nonspecific quantitation methods. Most steroids do not fall into this category, but the steroid vitamin D and its metabolites do and HPLC has proved in this area to be invaluable (see chapter by Jones & DeLuca). There are a multiplicity of different HPLC systems for the separation of steroids, varying in column type (and manufacturer), solvent composition and method of elution, temperature of elution, etc., and only a few attempts have been made to rationalise these data. It would therefore seem that a fruitful area of future study would be the investigation of computerised systems for the selection and optimisation of HPLC systems for particular steroid separations.