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ABSTRACT
In the mouse, follicular formation and development is largely postnatal. Changes in ovarian steroidogenesis during early postnatal life are likely, therefore, to reflect changes in follicular activity during early folliculogenesis. In this study, basal progesterone and androstenedione production and responsiveness to gonadotrophins, dibutyryl cyclic AMP (dbcAMP) and 22R-hydroxycholesterol have been measured following short-term in-vitro incubations of ovaries from mice aged 1, 3, 5, 7, 10 or 15 days. On the day of birth (day 1), basal and gonadotrophin-stimulated progesterone and androstenedione production were undectectable although a response to dbcAMP and a low level of cholesterol side-chain cleavage (CSCC) activity (measured using 22R-hydroxycholesterol) were present. On day 3 progesterone and androstenedione production were undetectable under all conditions. On day 5 only a low level of CSCC activity was detectable but on day 7 there was an increase in ovarian steroid production. Basal progesterone and androstenedione were detectable and LH, but not FSH, increased the production of both steroids. These changes were associated with a marked increase of more than 80-fold in CSCC activity. Basal steroid output increased from days 7 to 15 and LH continued to stimulate progesterone accumulation although no effect on androstenedione was seen. Addition of FSH had no effect on steroidogenesis on day 10 but significantly increased progesterone production on day 15. Ovaries from the mice used in these studies contained primordial follicles and stromal tissue on day 1. By day 5 primary and secondary follicles were present and the major increase in steroid production between days 5 and 7 was associated with an increase in secondary follicles and increased differentiation of the thecal tissue. These results show that there is a major increase in ovarian steroidogenesis at day 7 in the mouse and suggest that during folliculogenesis significant gonadotrophin-sensitive steroidogenesis may first be seen in the thecal tissue of the secondary follicle.
Journal of Endocrinology (1991) 130, 101–106
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ABSTRACT
It has been proposed that changes in steroidogenesis which occur during early development of the corpus luteum may be due to increased availability of lipoproteins. Bovine follicular fluid, however, contains significant amounts of high-density lipoprotein (HDL), and granulosa cells are exposed to this lipoprotein before ovulation. To determine whether bovine granulosa cells can utilize HDL the effects of this lipoprotein on freshly isolated, non-luteinized granulosa cells and on granulosa cells undergoing luteinization in serum-free culture were examined. Cells were isolated from non-atretic, antral follicles and cultured for 12 h in 10% (v/v) lipoprotein-deficient serum to allow cell attachment. After this time cells were cultured in serum-free medium. During culture the cells underwent functional luteinization as assessed by an increase in basal progesterone output (9·6-fold in 7 days) which was associated with a marked increase in activity of cholesterol side-chain cleavage and loss of aromatase activity. Dibutyryl cyclic AMP (dbcAMP) increased basal production of progesterone about twofold but HDL alone had no effect. Addition of HDL plus dbcAMP, in contrast, caused a very marked stimulation (up to ten times) of basal steroidogenesis. This trophic effect of HDL and dbcAMP lasted at least 2 weeks. Activity of cholesterol side-chain cleavage was stimulated (threefold over basal) by dbcAMP during culture but HDL was without effect, alone or with dbcAMP.
Addition of HDL (in the presence or absence of dbcAMP) to freshly isolated granulosa cells had no significant stimulatory effect on progesterone production over 12 h in six experiments, and in two of these experiments a significant inhibitory effect was seen. Incubation with 22R-hydroxycholesterol, in contrast, caused a marked stimulation of progesterone production, indicating that the steroidogenic capacity of the cells was not already saturated. Results presented here suggest that bovine granulosa cells are able to utilize HDL for steroidogenesis only after luteinization. The massive secretion of progesterone by luteinized granulosa cells which occurs in the presence of HDL suggests that this lipoprotein is very important in the development and maintenance of luteal cell function in cattle.
Journal of Endocrinology (1990) 124, 255–260
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ABSTRACT
Neuropeptide Y (NPY) is the most powerful appetite stimulant known, and chronic administration leads to obesity. The hypothalamic content of NPY varies with nutritional status, suggesting that it is of physiological importance. We measured NPY in specific hypothalamic nuclei and NPY mRNA in the hypothalamus by Northern blotting in rats made obese by feeding a highly palatable diet compared with controls fed standard chow. In animals fed the palatable diet, NPY concentrations were increased in the paraventricular nucleus (mean ± s.e.m.; 19·5 ± 2·3 vs 11·1 ± 1·1 fmol/μg protein, P < 0·02), the arcuate nucleus (20·4 ± 3·3 vs 9·3 ± 0·6 fmol/μg protein, P < 0·01), the medial preoptic area (9·1 ± 0·9 vs 5·9 ± 0·7 fmol/μg protein, P < 0·02) and the anterior hypothalamus (2·7 ± 0·2 vs 2·0 ± 0·1 fmol/μg, P < 0·02). Hypothalamic NPY mRNA measured by Northern blot analysis was, however, unchanged. These results suggest that the increase in NPY was due to decreased release rather than increased NPYergic activity. The findings are in accord with the neuroendocrine disturbance and increased thermogenesis observed in this model of obesity.
Journal of Endocrinology (1992) 132, 299–304