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S R Ojeda

Publications and source records attributed to S R Ojeda.

At least 109 records · Page 6Linked to original sources
PubMed1986

Vasoactive intestinal peptide induces the synthesis of the cholesterol side-chain cleavage enzyme complex in cultured rat ovarian granulosa cells.

Vasoactive intestinal peptide (VIP) has been identified in ovarian nerves and stimulates steroid secretion from immature ovaries. To gain insight into its mechanism of action, the effect of VIP on the synthesis of the cholesterol side-chain cleavage enzyme complex was studied in ovarian granulosa cells from immature estrogen-primed rats. The cells were cultured for 48 hr in serum-free medium; the proteins were labeled with [35S]methionine; and the synthesis of cytochrome P-450, iron-sulfur protein, and NADPH:iron-sulfur protein reductase was evaluated by electrophoretic analysis after immunoisolation with polyclonal antibodies directed against the bovine adrenal enzymes. VIP at concentrations ranging from 0.001 to 1 microM stimulated 3- to 5-fold the synthesis of cytochrome P-450 and iron-sulfur protein. Peptide NH2-terminal histidine, COOH-terminal isoleucine, which has greater than 50% sequence homology of VIP, stimulated the synthesis of both proteins at approximately 50% of VIP effectiveness. Secretin, another member of the glucagon-secretin family of peptides, which has only 30% sequence homology to VIP, was without effect. Similar results were observed with the NADPH:iron-sulfur protein reductase. VIP-induced synthesis of the cholesterol side-chain cleavage enzyme complex was accompanied by a dose-related increase in cAMP accumulation and progestin formation. It is concluded that VIP regulates the synthesis of the ovarian cholesterol side-chain cleavage enzyme complex, which catalyzes the rate-limiting reaction in progesterone biosynthesis, and that the VIP effect is at least partially mediated through cAMP. It is suggested that a stimulatory action of VIP on the synthesis of ovarian progesterone may contribute to regulating the functional development of the ovary.

Animals↗
PubMed1986

Neonatal release of gonadotropins is essential for development of ovarian follicle-stimulating hormone receptors.

In the rat, ovarian follicle-stimulating hormone (FSH) receptors increase markedly during the first two postnatal weeks, when serum gonadotropin levels are most elevated. This study was conducted to evaluate the hypothesis that these high gonadotropin levels, and in particular FSH, are involved in the acquisition of FSH receptors by the developing ovary. Gonadotropin release was suppressed by administration of several non-aromatizable androgens, among which dihydrotestosterone propionate (DHTP) was the most effective. In one series of experiments the steroids were administered from Days 5 to 11, and serum FSH and luteinizing hormone (LH) were measured on Day 12. Surprisingly, FSH receptor content was greater in rats with suppressed serum gonadotropins than in controls. The greatest increase in available receptors was observed in DHTP-treated rats in which serum FSH was reduced to 20% of control values and LH suppressed to undetectable values. DHTP failed to directly increase available FSH receptors in hypophysectomized immature rats. Magnesium chloride (MgCl2) treatment of ovarian membranes removed bound 125I-hFSH by 87% without affecting receptor viability. Exposure of control 12-day-old ovaries to MgCl2 increased available FSH receptors to a level similar to that of ovaries from DHTP-treated rats not exposed to MgCl2, suggesting that more receptors were available in DHTP-treated rats because serum FSH was suppressed. Earlier initation of DHTP treatment (postnatal Day 1) suppressed serum FSH and LH to undetectable values by Day 5 and decreased FSH receptor content below control values by Day 12. MgCl2 treatment only slightly increased available receptors in these DHTP-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗
PubMed1986

Prepubertal rat ovary: hormonal modulation of beta-adrenergic receptors and of progesterone response to adrenergic stimulation.

We have previously shown that, in the rat, ovarian beta-adrenergic receptor content varies during the time of puberty, with values first increasing and then decreasing abruptly on the afternoon of the first proestrus, i.e., at the time of the preovulatory surge of gonadotropins and prolactin (Prl). In the present study, experiments have been conducted to determine: 1) if hormones other than follicle stimulating hormone (FSH) that are known to be involved in regulating prepubertal ovarian function can mimic the facilitatory effect of FSH on progesterone (P) response of granulosa cells to beta-adrenergic stimulation; 2) if beta-adrenergic receptor content of granulosa cells is under hormonal regulation; and 3) whether the facilitatory effect of hormones on the P response to beta-adrenergic stimulation is due to an increased cyclic AMP response to receptor activation. A 48-h in vitro preexposure of granulosa cells from juvenile, 29-day-old ovaries to the pituitary hormones Prl, luteinizing hormone (LH), or FSH showed that only the latter was able to facilitate the subsequent P response to Zinterol, a beta2-adrenergic agonist. Follicle-stimulating hormone also increased basal P release. Of the two nonpituitary hormones examined, the luteinizing hormone-releasing hormone (LHRH) agonist D-(Ala6,Pro9)-LHRH-ethylamide (LHRH-A) failed to affect P responsiveness, whereas corticosterone enhanced both basal P release and P response to Zinterol. This effect was less pronounced than that of FSH. Luteinizing hormone, Prl and corticosterone decreased beta-adrenergic receptor content to different extents, with corticosterone being the most effective and LH the least (50% and 15% decrease, respectively); LHRH-A was ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1986

Activation of estradiol-positive feedback at puberty: estradiol sensitizes the LHRH-releasing system at two different biochemical steps.

Experiments were performed to examine whether estradiol (E2) can influence some of the intraneuronal mechanisms involved in luteinizing hormone-releasing hormone (LHRH) release during the onset of puberty in the female rat. The capacity of median eminence (ME) nerve terminals to secrete LHRH, as determined by both their basal release of LHRH and by their response to prostaglandin E2 (PGE2) in vitro, increased significantly during the juvenile-early peripubertal periods of development (postnatal days 22-34). Ovariectomy (OVX) on day 22 led to a striking reduction in LHRH response to PGE2 on day 34. E2 administered via s.c. Silastic capsules, at a dose that reproduces juvenile serum E2 levels, restored the response. Simulation of first proestrous serum E2 levels in late juvenile (28-day-old) female rats enhanced both the sensitivity and the responsiveness of LHRH-containing terminals to PGE2. Furthermore, E2 enhanced the sensitivity and the responsiveness of LHRH terminals to norepinephrine (NE). This effect appeared to be related to both the increased LHRH response to PGE2 and an enhanced sensitivity of the PGE2-synthesizing pathway to NE. This is because MEs from E2-treated rats showed a marked increase in PGE2 release in response to a NE concentration which was barely effective in untreated controls. It is suggested that one of the mechanisms by which E2 activates the first preovulatory discharge of LHRH release in the female rat is by facilitating the occurrence of two different but sequentially related biochemical events: the stimulation of PGE2 formation by NE and the enhancement of LHRH release by PGE2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

The development of afternoon minisurges of luteinizing hormone secretion in prepubertal female rats is ovary dependent.

We have recently disclosed sustained episodes of LH release (minisurges) during the afternoons of the juvenile-peripubertal transition period in the female rat. To determine if these LH minisurges are gonad independent, i.e. develop in the absence of the ovaries, animals were ovariectomized when neonates, and the mode of LH release was examined using a 5-min blood-sampling regimen at one of three ages corresponding to the juvenile, peripubertal, or adult phase of development. In no instance was a minisurge of LH secretion detected. We were concerned, however, that LH minisurges may have been obscured by the exceedingly high level of LH secretion in these long term ovariectomized rats and, therefore, decided to pursue the study employing a short term (48-h) ovariectomy paradigm. Late juvenile rats which had been ovariectomized for 48 h exhibited conspicuous LH pulses, but, again, LH minisurges were not detected, further suggesting that these sustained secretory episodes do not occur in the absence of the ovaries. Next, plasma estradiol (E2) levels were differentially raised in 48-h ovariectomized juvenile rats via sc implantation of Silastic capsules containing the steroid (dissolved in corn oil at various concentrations), and plasma LH was measured at 1-h intervals. The highest E2 concentration elicited a midafternoon LH increase of preovulatory magnitude in all cases, whereas the lowest E2 concentrations consistently suppressed plasma LH. However, intermediate E2 concentrations (producing plasma E2 levels 20-30% greater than those found in intact controls) elicited, in several instances, an increase in LH release of intermediate magnitude. To clarify the nature of these LH responses, we examined, using a 5-min blood-sampling regimen, the afternoon pulsatile pattern of LH release after treatment with appropriate doses of E2. As expected from the results of the infrequent blood-sampling paradigm, the highest E2 dose induced proestrus-like surges of LH secretion, while the lowest dose suppressed pulsatile LH release. Moreover, an intermediate E2 dose which raised plasma E2 levels just above those of intact animals, was again able to cause suppression of LH pulses, a proestrus-like surges of LH secretion, while the lowest dose suppressed pulsatile LH release. Moreover, an intermediate E2 dose which raised plasma E2 levels just above those of intact animals, was again able to cause suppression of LH pulses, a proestrus-like increase in LH output, or, more importantly, a minisurge of LH secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

The immature rat ovary is innervated by vasoactive intestinal peptide (VIP)-containing fibers and responds to VIP with steroid secretion.

The nature and role of the peptidergic innervation of the ovary were examined by determining the location and function of vasoactive intestinal peptide (VIP)-containing nerve fibers in the immature rat ovary. Immunohistofluorescence analysis of prepubertal ovaries using a specific VIP antibody revealed sparse delicate VIP-immunoreactive fibers localized around veins and arterioles, in the interstitial tissue, and associated with the thecal layers of developing follicles. Radioimmunoassayable VIP content was found to be approximately 100 pg/ovary (3 nM). The VIP immunoreactivity coeluted with authentic VIP when subjected to Sephadex G-25 chromatography. VIP enhanced in vitro progesterone release from infantile (12 days old), juvenile (30 days old), and peripubertal ovaries and estradiol release during the two latter developmental periods. The maximal estradiol response to VIP occurred during the early and first proestrous phases of puberty. No response was observed during estrus or first diestrus. The progesterone response to VIP increased moderately between day 12 and first proestrus, and then strikingly at estrus and first diestrus. The stimulatory effect of VIP on ovarian steroid production was dose related, as determined in ovaries from PMSG-treated immature rats (ED50 = 215, 44, and 51 nM for estradiol, androgen, and progesterone, respectively). The specificity of the VIP effect was tested using five other gastrointestinal peptides (porcine peptide histidine isoleucine, gastric inhibitory polypeptide, secretin, motilin, and glucagon). Only peptide histidine isoleucine, which has the greatest sequence homology with VIP, enhanced ovarian steroid production at 50% of VIP effectiveness. VIPergic nerves thus appear to be involved in the developmental regulation of ovarian steroidogenesis.

Androgens↗
PubMed1986

Substance P- and vasoactive intestinal peptide-containing fibers reach the ovary by independent routes.

The immature rat ovary is innervated by both substance P (SP)- and vasoactive intestinal peptide (VIP)-containing nerve fibers. To determine the origin of these fibers, juvenile rats were sham operated or subjected to transection of the abdominal vagus nerves, superior ovarian nerves, or ovarian plexus nerves or to concomitant transection of the vagal and superior ovarian nerves. Specific immunofluorescent staining of ovarian sections for SP and VIP revealed that VIP innervation to the ovary occurs only via the superior ovarian nerves, whereas ovarian SP innervation is exclusively via the plexus nerves. Thus, specific SP and VIP nerves reach the gland via anatomically different routes. The results indicate that autonomic regulation of ovarian function may be exerted via independent peptidergic neural pathways.

Animals↗
PubMed1986

Development and amplification of mid-afternoon surges of prolactin secretion in ovariectomized immature rats.

The immature female rat shows a mid-afternoon surge of prolactin secretion which reaches a maximum on the day of first pro-oestrus. The present experiments were undertaken to elucidate the mechanisms which underly the development of this prolactin discharge. Detailed plasma prolactin profiles were obtained from short-term (48 h) ovariectomized rats at 23, 28 or 37 days of age. In the two older groups, but not the youngest, a mid-afternoon surge of prolactin secretion occurred in spite of the absence of the ovaries. To exclude the possibility that such an apparent ovarian-independent discharge of prolactin was due to an oestradiol effect which persisted for 2 days following ovariectomy, another study was conducted using long-term ovariectomized animals. Plasma profiles were obtained from neonatally ovariectomized rats at ages equivalent to juvenile (26-28 days), peripubertal (38-41 days) or adult (46-49 days) phases of development. A mid-afternoon surge of prolactin secretion was observed in the majority of animals (eight out of twelve) irrespective of the interval after ovariectomy; this finding further indicates that in the female rat there is a centrally originated mid-afternoon episode of prolactin secretion which is expressed during juvenile development even in the absence of the ovaries. The relatively small magnitude of these ovarian-independent prolactin discharges (c.f. the preovulatory prolactin surge) suggested that in the intact animal they are amplified by ovarian secretions. To test this hypothesis, oestradiol-containing silicone elastomer capsules were implanted s.c. into juvenile rats, immediately after ovariectomy, and plasma prolactin profiles examined 2 days later (28 days of age).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Presence of luteinizing hormone releasing hormone (LHRH) in milk.

Evidence is presented a luteinizing hormone-releasing hormone (LHRH)-like substance exists in milk of the rat and that this substance is transferred to the offspring during suckling. This milk "LHRH" generates an inhibition curve parallel to authentic LHRH in the LHRH radioimmunoassay (RIA) and coelutes, to a significant extent, with LHRH upon Sephadex G-25 chromatography. An increase in LHRH-like immunoreactivity (LHRH-LI) can be detected in both the stomach and plasma of infantile rats during suckling. Available ovarian LHRH receptors increase in the pups after separation of the mother and return to basal values following suckling. This change is prevented by i. v. administration of an LHRH antiserum. Milk LHRH stimulates gonadotropin release in vitro and inhibits both gonadotropin-induced steroid secretion from granulosa cells in culture and the binding of LHRH to ovarian membranes.

Animals↗
PubMed1985

Evidence for the existence of substance P in the prepubertal rat ovary. I. Biochemical and physiologic studies.

The presence of substance P (SP) in the immature rat ovary was determined by radioimmunoassay (RIA) of acidic extracts. The extracts produced an inhibition-displacement curve of 125I-SP binding parallel to that generated by authentic SP in the SP RIA. Initial chromatographic characterization of ovarian SP in Sephadex G-25 revealed the presence of a molecular form that coeluted with authentic SP and a more abundant component that eluted earlier, suggesting the presence of a heavier peptide, immunologically similar to SP. Nevertheless, further characterization of these two seemingly different components by reversed-phase high-performance liquid chromatography (HPLC) demonstrated that both of them had a retention time similar to that of authentic SP. The ovarian concentration of SP-like immunoreactivity (SP-LI) varied in relation to the onset of puberty, with values increasing significantly between the late juvenile phase and the day of first proestrus. Substance P seems to be devoid of steroidogenic capacity since SP itself and its stable analog [pGlu5,MePhe8,Sar9]-SP5-11 (SP-A) failed to stimulate steroid secretion from either granulosa cells in culture or ovarian fragments in short-term incubation. Substance P also failed to stimulate prostaglandin E2 release from whole ovaries and to modify the steroidal response of cultured granulosa cells to follicle-stimulating hormone and to the beta 2-adrenergic agonist Zinterol. Production of SP-LI from granulosa cells in culture could not be detected under either basal or gonadotropin-stimulated conditions. These observations and the distribution of the peptide within the ovary presented in the companion paper (Dees et al., this issue) strongly suggest that SP is not directly involved in regulating steroidogenesis. Instead, SP may be a component of the so-called sensory innervation of the ovary, and among other undisclosed functions it may contribute to the regulation of ovarian blood flow.

Animals↗
PubMed1985

Evidence for the existence of substance P in the prepubertal rat ovary. II. Immunocytochemical localization.

Nerve fibers containing substance P (SP) were localized in ovaries from juvenile and peripubertal rats by immunofluorescence. These fibers were closely associated with the theca externa of antral follicles, as well as being in the interstitial tissue and within the tunica adventitia of small blood vessels, mostly arterioles. Consistently, the greatest amount of SP immunoreactivity was observed surrounding the ovarian vasculature. Substance P was not detected in cells or within the corpora lutea (CL). Additionally, the peripubertal animals seemed to have a greater concentration of ovarian SP than the juvenile animals. Possible functional roles for this peptide in the ovary are discussed.

Animals↗
PubMed1985

Estradiol-induced LH release in juvenile female rats: nembutal blocks both the decline and the exposure of nonavailable pituitary LHRH receptor sites.

We have previously shown that, as seen in the adult rat, pituitary LHRH receptor content declines during the hours encompassing the first preovulatory LH surge. This decrease in receptor number was prevented, however, when pituitary membranes were treated with MgCl2 to dissociate endogenously bound ligand(s). The present study investigates: whether the first proestrous reduction in available LHRH receptors can be reversed by subjecting the pituitary membranes to a less drastic, dilution-washing procedure previously reported to be highly effective in dissociating bound LHRH, and whether Nembutal blockade of the proestrous decline in LHRH receptors also prevents the dissociation-induced exposure of additional LHRH binding sites. A premature LH surge was induced by exposing juvenile female rats to proestrous-type levels of plasma estradiol (E2) via Silastic capsules. A decline in available LHRH receptors was found around the time of this steroid-induced LH surge. A marked increase in receptor number was, however, observed upon dilution-washing of the membranes. The increase in receptor number was not accompanied by any changes in receptor affinity (ka). Nembutal administration blocked both the LH surge and the decline in available LHRH receptors. Moreover, dilution-washing of pituitary membranes from Nembutal-treated rats failed to uncover additional LHRH binding sites. The results suggest that a significant portion of the proestrous decline in pituitary LHRH receptors is due to a reduced availability of the receptor to binding. Whether such a phenomenon is due to true occupancy by endogenous ligand(s) or to binding-dependent localization of the receptor within the cell membrane is unclear.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Prostaglandin E2-induced luteinizing hormone-releasing hormone release involves mobilization of intracellular Ca+2.

The present in vitro experiments were performed to examine the involvement of Ca+2 in the mechanism by which prostaglandin E2 (PGE2) induces LHRH release from the median eminence (ME) of the hypothalamus. Stepwise decreases in the Ca+2 concentration of the incubation medium reduced the LHRH response to PGE2. Nevertheless, neither complete omission of Ca+2 (residual Ca+2 concentration, 3.5 microM) nor chelation of residual Ca+2 with EGTA prevented the stimulatory effect of the PG, suggesting that a significant portion of the PGE2 effect on LHRH release is independent of extracellular Ca+2. Blockade of Ca+2 influx with verapamil, a Ca+2 entry blocker, demonstrated that this component of the PGE2 effect is completely independent of inward Ca+2 movement. Depletion of intraterminal Ca+2 stores by exposure of the MEs to the Ca+2 ionophore A23187 in medium without Ca+2 containing EGTA almost completely obliterated the subsequent LHRH response to PGE2, indicating that normal intraterminal Ca+2 levels are important for the PGE2 effect to occur. Preloading the ME terminals with 45Ca+2 and subsequent stimulation with PGE2 demonstrated that even in the absence of extracellular Ca+2, PGE2 stimulates Ca+2 efflux from the terminals, and this Ca+2 movement occurs temporarily associated with LHRH release. Depolarization of ME terminals with 56 mM K+ in the presence of normal Ca+2 concentration resulted in massive efflux of 45Ca+2 and a greater LHRH response than that produced by PGE2, suggesting that the effect of PGE2 is not the consequence of a nonspecific general depolarization of ME nerve terminals. Thus, although a full LHRH response to (exogenous) PGE2 necessitates normal extraterminal Ca+2 concentrations, the results indicate that translocation of Ca+2 from intracellular stores is an event involved in the mechanism by which PGE2 releases LHRH.

Animals↗
PubMed1985

In vitro simulation of prepubertal changes in pulsatile luteinizing hormone release enhances progesterone and 17 beta-estradiol secretion from immature rat ovaries.

We have previously demonstrated changes in the episodic pattern of LH secretion in female rats as they approach first ovulation. In the present study, ovaries were taken from peripubertal rats and perifused in vitro with a medium containing FSH and LH. The concentration of FSH in the medium was kept constantly low, whereas the concentration of LH was modulated, simulating as closely as possible the various episodic secretory profiles previously observed in vivo. Medium from the perifusion chambers was collected every 10 min for 5 h and assayed for progesterone (P) and 17 beta-estradiol (E2). Exposure of the ovaries to low amplitude LH pulses (20 ng/ml; comparable to those found in the plasma of peripubertal rats during the morning) did not elicit a significant steroidogenic response. On the other hand, exposure to large amplitude LH pulses (80 ng/ml; as seen during the afternoon) led to a marked increase in the output of both P and E2. Similarly, increased steroid secretion occurred when ovaries were exposed to a 2-h minisurge of LH (160 ng/ml) or to a minisurge preceded by three large amplitude pulses (as seen in some animals during the afternoons of the peripubertal period). Continuous exposure to LH at concentrations similar to either the large amplitude pulses or the LH minisurge increased P and E2 release. However, the increase was not significantly larger than that produced by the discontinuous LH perifusion patterns, even though the total amount of LH reaching the ovaries during the 5-h perifusion period was considerably greater. The results show that episodic LH secretion is functionally much more efficient at eliciting release of P and E2 from immature ovaries than is continuous LH secretion. Furthermore, they strongly suggest that changes in the LH secretory pulse patterns, as seen in vivo close to the time of puberty, are fundamental for the activation of ovarian steroidogenesis that leads to the first preovulatory surge of gonadotropins.

Animals↗
PubMed1985

The juvenile-peripubertal transition period in the female rat: establishment of a diurnal pattern of pulsatile luteinizing hormone secretion.

Previous descriptions of pulsatile LH release in immature female rats have been mostly inaccurate because of infrequent blood sampling, discontinuous and unbalanced blood replacement procedures, and possibly because of the use of a heterologous RIA. The present study was undertaken to circumvent these problems and to characterize more precisely the changes in episodic LH secretion previously observed during the juvenile-peripubertal transitional period (27-38 days of age). Changes in LH levels were measured in plasma samples obtained every 5 min from unrestrained conscious animals using a recently developed technique that permitted continuous withdrawal of blood for 4-5 h and simultaneous replacement with an artificial blood mixture. In virtually all of the rats, LH release was pulsatile. In both the juvenile (27-29 days old) and peripubertal (30-38 days old) animals, mean plasma LH levels and LH pulse amplitude were low in the mornings. A similar pattern of LH secretion was found in the afternoon during the juvenile period. In contrast, most of the peripubertal animals exhibited an afternoon increase in LH pulse amplitude. A change in pulse frequency was not detected at this time, but a 1.8-fold increase in mean LH levels suggests that large amplitude pulses may be accompanied by low amplitude, high frequency pulses not revealed by the 5-min sampling paradigm. Some of the peripubertal rats (5 of 12) had plasma LH profiles in which the large amplitude pulses were accompanied by a midafternoon minisurge of secretion which lasted for up to 2 h and reached peak levels of 174 +/- 19 ng/ml; the LH surge at first proestrus was greater than 1000 ng/ml. The results demonstrate the prepubertal development of an afternoon increase in LH pulse amplitude and the appearance of a more prolonged and larger secretory episode of LH secretion (minisurge). Disclosure of a concomitant increase in pulse frequency may necessitate blood sampling at more frequent intervals. It is suggested that the changes in the mode of LH release described here may enhance peripubertal ovarian steroidogenesis and provide an appropriate stimulus for initiating the final stages of ovarian development.

Aging↗
PubMed1985

Stimulation of cyclic adenosine 3',5'-monophosphate production enhances hypothalamic luteinizing hormone-releasing hormone release without increasing prostaglandin E2 synthesis: studies in prepubertal female rats.

A role for cAMP in the process of LHRH release was suggested several years ago, but only recently has the validity of this notion come under close scrutiny. In the present experiments we have used three probes, which stimulate adenylate cyclase activity via different mechanisms, to determine whether an increase in endogenous cAMP results in LHRH release from the hypothalamus of prepubertal female rats. Median eminences from juvenile, 28-day-old animals were incubated in vitro with either forskolin (F), cholera toxin (CT), or pertussis toxin (PT). All three substances enhanced LHRH release. The estimated ED50 values were 28.7 microM and 20.0 ng/ml, for F and PT, respectively. The effect of CT appeared biphasic and thus no ED50 could be calculated. None of these agents increased the release of prostaglandin E2 (PGE2), an obligatory component in the process of norepinephrine-induced LHRH secretion. Doses of PGE2 and F, which were maximally effective in stimulating LHRH release when administered separately, did not produce any further response when administered concomitantly, thus suggesting that PGE2 and F act along a common pathway. Blockade of phosphodiesterase activity with 1-methyl-3-isobutylxanthine increased LHRH secretion without enhancing PGE2 release, implying that cAMP metabolism was elevated in the median eminence nerve terminals in vitro. Addition of 1-methyl-3-isobutylxanthine augmented the LHRH response to CT and PT, but it did not increase further the already marked LHRH response to PGE2 or F. The results indicate that both an increase in adenylate cyclase activity and a decrease in phosphodiesterase activity lead to LHRH release from the median eminence. They also suggest that, upon proper (neurotransmitter?) stimulation, cAMP production increases subsequent to the activation in PGE2 synthesis, which itself causes LHRH release. Furthermore, the capacity of PT to induce LHRH release suggests the involvement of an inhibitory guanine nucleotide-binding regulatory protein in transducing inhibitory inputs impinging on LHRH-secreting neurons.

1-Methyl-3-isobutylxanthine↗
PubMed1985

Physiological peripubertal activation of the ovary is not reproduced by pregnant mare serum gonadotropin (PMSG) administration.

During the days preceding the first ovulation the ovary of the rat exhibits a remarkable increase in estradiol (E2) and progesterone (P) release in response to gonadotropins. No such increase is observed in the case of androgens (A, testosterone + dihydrotestosterone). The present experiments were undertaken to examine the possibility of reproducing these developmental events by stimulating the ovary with a gonadotropin that has substantial FSH-like activity. In vivo administration of pregnant mare serum gonadotropin (PMSG) to juvenile 29-day-old rats greatly increased the in vitro E2 and A response to human chorionic gonadotropin (hCG) measured 2 days later in the morning. The magnitude of the A response was significantly larger than that of ovaries from juvenile animals or rats in first proestrus. The E2 response was much greater than that of juvenile ovaries but similar to that of ovaries from late proestrous rats. In contrast, the P response to hCG was not enhanced by PMSG. In fact the response was similar to that of juvenile ovaries and markedly less than that of first proestrous rats. This decreased P response was not due to a greater conversion of P to its less active metabolite 20 alpha-hydroxy-4-pregnen-3-one (20 alpha-OH-P). The results suggest that PMSG enhances the E2 and A response of immature ovaries to hCG at the expense of that of P. Treatment of immature rats with PMSG may represent a useful model to study E2 release from preovulatory ovaries, but it cannot be used to reproduce in its entirety the developmental changes in steroidal response to gonadotropins associated with normal puberty.

Animals↗