Adenylyl Cyclase Activities in Ovarian Tissues. III. Regulation of Responsiveness to LH, FSH, and PGEX in the Prepubertal, Cycling, Pregnant, and Pseudopregnant Rat

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Abstract
In the ovaries of prepubertal rats, responsiveness of adenylyl cyclase (AC) to LH, FSH, and PGE, is acquired at day 10, coinciding with the appearance of the ability to produce steroids in response to gonadotrophins. The activity and responsiveness of AC on day 11 were similar to those at puberty on day 40 and relatively stable in between. In the follicles of the cycle, the responsiveness of AC to LH and FSH was poor (ca 2-fold stimulation) on metestrus and diestrus, and became high (ca 10-fold stimulation) between 1000 h of diestrus and 1000 h of proestrus. Thereafter, the system slowly became desensitized to LH and FSH, being unresponsive by the morning of estrus. Nembutal injected at 1230 h and again at 1500 h on proestrus blocked ovulation and prevented the decline in LH- and FSH-stimulated AC activity. In the CL of the cycle, the AC was unresponsive to LH on day 1 (estrus), became responsive by the morning of day 2 (metestrus), and maintained responsiveness throughout that day. Thereafter, the responsiveness and basal AC activity declined rapidly. In the CL of pregnancy, LH-stimulated AC was indistinguishable from that of the CL of the cycle during days 1 and 2, then increased steadily until day 9, showing a transient decrease on days 10 and 11, followed by a sharp rise to maximal activity on days 15 and 16. Thereafter, activity declined as parturition approached. In the CL of pseudopregnancy (PSP), LH-stimulated AC was very similar to that of the CL of pregnancy during the first 11 days. Thereafter, it decreased coincident with the termination of PSP. Injections of PRL (100 µg, SC twice daily, from metestrus through estrus, and from proestrus through proestrus) or estradiol-17² (20 µg, SC at 1230 h on metestrus) resulted in “rescue” of the CL-AC system, which remained at metestrus levels when measured on the days of expected proestrus or estrus. Injections of pregnant mare serum gonadotrophin into prepubertal rats at day 26 (3 IU, iv), induced by day 28 a highly responsive AC system in follicles, with activities equivalent to those found in Graafian follicles on proestrus. By day 29, synchronous ovulation had occurred with a concomitant loss of LH-stimulated AC such as seen in the 1-day-old CL of mature rats. Our results suggest that the LH-sensitive AC may be indicative of the final development of ovulability of the follicles, and that it may correlate with the functional capacity of CL during various reproductive stages of the rat. (Endocrinology99: 198, 1976)