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|Title:||Hormone Stimulable Adenylyl Cyclase Activity in Ovarian Granulosa Cells of the Domestic Hen (Gallus Domesticus)|
|Author(s):||Calvo, Francisco Omar|
|Department / Program:||Physiology and Biophysics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Biology, Animal Physiology|
|Abstract:||The hormone stimulable AC of chicken granulosa cells was characterized and was found to be similar to that of mammalian reproductive tissues under the conditions tested. A principal difference, however, is the stability of the enzyme. Gonadotropin dose response studies suggest that there is an increase in affinity as indicated by the apparent Km, as well as responsiveness of the LH stimulable AC as the follicles mature. In contrast, FSH did not stimulate the AC system appreciably except in F(,3)Gr at very high gonadotropin concentrations. The lack of response argues for the existence of an FSH-AC system which develops earlier during follicular maturation and is waning by the time a follicle enters the hierarchy. This phenomenon is analogous to that found in mammals.
The Gr-AC activity of the F(,1), F(,2), F(,3), and POF throughout the follicular cycle was also investigated. An increase in the LH stimulable AC activity 12 h before ovulation with a drop in activity 4 h before ovulation of the F(,1) was observed. However, the increase in sensitivity was markedly different among the 3 preovulatory follicles. There is an increase in the LH stimulability of the Gr as the follicles mature. The enhancement of activity may be related to an increase in the availability of LH receptors and the AC coupling to the LH receptor as the follicles approach ovulation. The Gr-AC system of all 3 preovulatory follicles was still responsive to LH after the endogenous LH surge. These results are in agreement with those of mammals which have shown that the AC system of follicular tissue is still responsive to gonadotropins when physiological levels of the hormones are used. The POFGr LH stimulable AC activity differed in that 2 h after the ovulation of this follicle, the cAMP synthesizing ability was enhanced (3.3 fold over basal). Thereafter, the POFGr-AC system was unresponsive to LH for the length of the follicular cycle. This was the only instance in which long term desensitization was observed even though the POFGr continue to secrete significant amounts of P(,4).
Studies designed to determine if there was a desensitization of the Gr-AC system to an exogenous physiological dose of oLH revealed that refractoriness did not occur in the Gr of the F(,1), F(,2), and F(,3). Instead, an increase in the LH stimulability as well as a different pattern of response was observed. This difference in response may be the result of a protective mechanism which prevents the less mature follicles from ovulating prematurely. The mechanism of action responsible for this effect is not known.
From these experiments a salient feature emerges, that is the increase in the Gr LH stimulable AC activity as the follicles progress through the hierarchy. The increase in AC system activity probably represents an increase in the availability or the number of LH receptors with a decrease in FSH receptors as the follicles mature. Studies of the kinetics and developmental changes in the Gr gonadotropin receptor population of the different follicles should help to answer this question. This study will be especially interesting because the steroidogenic activity and profile of the theca are distinctly different from that of the Gr cells.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
|Date Available in IDEALS:||2014-12-14|
This item appears in the following Collection(s)
Dissertations and Theses - Molecular and Integrative Physiology
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois