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M D Culler

Publications and source records attributed to M D Culler.

At least 55 records · Page 3Linked to original sources
PubMed1992

Immunohistochemical detection of proluteinizing hormone-releasing hormone peptides in neurons in the human hypothalamus.

To determine the presence of LHRH prohormone products in the human hypothalamus, antisera raised against LHRH and GnRH-associated peptide (GAP) were used to search for the presence of the corresponding antigens in the human adult and fetal hypothalamus by an immunohistochemical approach. The comparison of immunostaining on adjacent sections shows that all of the cells labeled with LHRH antiserum are also labeled with GAP antiserum and vice versa. Labeled cells are detectable during the 9th week of fetal life, this being the earliest time evaluated. At this time, the LHRH/GAP-positive cells frequently have a neuroblastic appearance. The first detectable fibers appear during the 11th week, and these were observed in the lamina terminalis cinerea and median eminence. In the adult brain, fibers and endings labeled with LHRH or GAP antiserum in the median eminence demonstrate the same topography and morphological characteristics, which are distinct from fibers labeled with other neuropeptide antisera. These results show that the LHRH precursor molecule is produced throughout life in the human hypothalamus, including the earliest stages of development of the peptidergic neurons. Moreover, the detection of LHRH- and GAP-positive fibers in the median eminence by the 11th week of fetal life suggests the possibility of an early role of LHRH and, possibly, other LHRH prohormone-derived peptides in the development of anterior pituitary function during the fetal period.

Adult↗
PubMed1991

Evidence that inhibin plays a major role in the regulation of follicle-stimulating hormone secretion in the fully adult male rhesus monkey (Macaca mulatta).

In the juvenile male rhesus monkey in which an adult-like pattern of endocrine activity in the pituitary-testicular axis is imposed by pulsatile stimulation with exogenous GnRH, administration of inhibin antiserum elicits a marked and selective hypersecretion of FSH. This finding suggests that in the monkey, testicular inhibin plays a major role in the postpubertal regulation of this gonadotropin. The purpose of the present study was to confirm this view more directly. To this end, 10 adult male rhesus monkeys were implanted with indwelling venous catheters and housed in specialized cages that permit continuous access to the venous circulation with minimal restraint and without tranquilization. Six of the males received a continuous infusion of an ovine antiserum to the alpha-subunit of human inhibin (iv bolus injection of 2.22 ml/kg BW, followed by a continuous infusion of serum at 0.62 ml/kg BW.24 h), and 4 animals received a similar infusion of control ovine immune serum. The duration of the infusion of the inhibin antiserum ranged from 2.5-7.5 days, and that for the control serum was 7.5 days. The FSH response to immunoneutralization of circulating inhibin was determined by measuring concentrations of this gonadotropin in sequential plasma samples collected between 1900-2300 h on the day before initiation of the anti-serum infusion and, depending on the duration of the infusion, on days 0.5, 1.5, 2.5, 4.5, and 6.5 of antiserum administration. In 5 of the 6 animals that received the inhibin antiserum, a progressive hypersecretion of FSH was observed during the initial 2.5 days of the infusion. This increase in circulating FSH concentration, which reached, by day 2.5 of treatment, a value 2- to 3-fold greater (P less than 0.05) than the pretreatment control level, was not associated with changes in either LH or testosterone levels. Continuation of the infusion of the inhibin antiserum beyond 2.5 days invariably resulted in a marked decline in LH and testosterone secretion, suggesting that the hypophysiotropic drive to the pituitary-testicular axis may have been compromised, presumably by a mechanism related to the infusion of heterologous serum. Infusion of the control immune serum for 2.5 days was not associated with an elevation of circulating FSH concentrations, and changes in circulating concentrations of plasma LH and testosterone were, as expected, unremarkable. Continuation of the infusion of control serum, like that of antiserum, generally resulted in a temporary but precipitous decline in LH and testosterone secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Pituitary adenylate cyclase-activating polypeptide (PACAP) potentiates the gonadotropin-releasing activity of luteinizing hormone-releasing hormone.

In order to determine if the newly discovered neuropeptide, pituitary adenylate cyclase activating polypeptide (PACAP), interacts with the known hypothalamic releasing factors to modulate pituitary hormone secretion, the effect of PACAP, either alone or in combination with either LHRH, TRH, CRF or GHRH, was examined in rat anterior pituitary cell cultures. While PACAP alone weakly stimulated LH and FSH release, PACAP and LHRH, in combination, interacted synergistically to stimulate gonadotropin secretion. No significant changes in the secretion of either TSH, ACTH, or GH were observed in response to PACAP, either alone or in combination with the other releasing factors. Addition of an LHRH antagonist demonstrated that the PACAP effect on gonadotropin release was neither mediated by the LHRH receptor nor the result of LHRH contamination of the PACAP preparation. Because of the sequence homology (68%) between the N-terminal 28 amino acids of PACAP and VIP, the addition of a VIP antagonist was used to demonstrate that the PACAP effect is not mediated through the VIP receptor. The observation that PACAP interacts synergistically with LHRH in stimulating gonadotropin release suggests intriguing possibilities for PACAP in regulating gonadotropin secretion and reproductive function.

Animals↗
PubMed1990

Destruction of testicular Leydig cells reveals a role of endogenous inhibin in regulating follicle-stimulating hormone secretion in the adult male rat.

It has previously been demonstrated that passive immunoneutralization of endogenous inhibin results in a dramatic elevation in follicle-stimulating hormone (FSH) secretion in the adult female rat but not in the adult male. The purpose of the present study was to investigate whether the effects of immunoneutralizing endogenous inhibin on FSH secretion in the adult male rat might be masked by the presence of additional, compensating, FSH-suppressing factors. This was determined by examining the individual and combined effects of removing the testicular influences provided by the Leydig cells using the selective toxicant, ethane dimethane sulfonate (EDS), and passive immunoneutralization of endogenous inhibin. Within 24 h of a single i.p. injection of EDS, plasma testosterone levels were lowered to near assay limits and by 3 days were undetectable. Plasma FSH levels were significantly elevated 3 and 7 days after EDS treatment, but not to the levels observed in rats castrated for similar periods of time. Castration of rats, treated 3 days earlier with EDS, resulted in a further significant increase in FSH secretion as compared with EDS-treated, sham-operated controls, indicating that the testes were providing an additional FSH-suppressing factor(s) other than those originating in the Leydig cells. Injection of anti-inhibin serum, into rats treated 3 or 7 days earlier with EDS, induced a further significant increase in FSH secretion that raised plasma FSH to a level comparable to that observed in male rats castrated for similar periods of time. Plasma LH secretion was also dramatically elevated by EDS treatment to levels that equaled or exceeded those observed in similarly timed castrates. Pituitary sensitivity, as tested by the injection of an exogenous challenge of luteinizing hormone-releasing hormone (LHRH), was significantly increased 3 or 7 days after either EDS treatment or castration in terms of LHRH-stimulated LH release, but not in terms of LHRH-stimulated FSH release. Immunoneutralization of endogenous inhibin induced no further observable changes in pituitary sensitivity to LHRH. These results demonstrate that in the absence of the Leydig cells a secondary role is revealed for endogenous inhibin in suppressing FSH secretion that, in combination with the Leydig cell influence(s), accounts for the postcastration increase in FSH. The need to remove the Leydig cell influence(s) to reveal an effect of endogenous inhibin on FSH secretion in the adult male rat may suggest that the inhibin effect is normally masked by the presence of the comparatively larger suppressive influence(s) derived from the Leydig cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Immunoneutralization of circulating inhibin in the hypophysiotropically clamped male rhesus monkey (Macaca mulatta) results in a selective hypersecretion of follicle-stimulating hormone.

The purpose of this experiment was to examine directly whether inhibin is involved in the testicular regulation of FSH secretion in the male rhesus monkey. To this end, the pituitary-testicular axis in eight juvenile monkeys was prematurely activated by a chronic iv infusion of GnRH (0.1 microgram/min for 3 min every 3 h). After a minimum of 5 weeks of pulsatile GnRH stimulation, four animals received a brief (30-min) iv infusion of an ovine antiserum to inhibin alpha-subunit (approximately 10 ml/kg BW), and four monkeys received a comparable volume of a control ovine immune serum. The pulsatile GnRH infusion continued without interruption throughout the entire experiment. The FSH response to passive immunization against inhibin was determined by measuring concentrations of this gonadotropin in sequential plasma samples collected immediately before a GnRH infusion and for 3 h thereafter (an inter-GnRH pulse interval) on days 0.5, 1, 2, 4, 8, and 16 after injection of the immune serum. Administration of the antiserum to inhibin alpha-subunit resulted, within 2 days, in a 2- to 3-fold increase in the mean concentration and pulse amplitude of plasma FSH. The hypersecretion of FSH induced by administration of the antiserum to inhibin alpha-subunit was maintained until day 4, and then mean concentrations and mean pulse amplitudes of plasma FSH declined, reaching preantibody control levels by day 16. The time course of the antiserum-induced hypersecretion of FSH was closely correlated to changes in circulating inhibin-binding activity. Most importantly, the hypersecretion of FSH observed during the first 2 days after immunoneutralization of circulating inhibin was indistinguishable from that elicited during the initial 2 days after subsequent bilateral orchidectomy and concomitant testosterone (T) replacement. Administration of a control immune serum did not influence circulating FSH concentrations, and neither the antiserum to inhibin alpha-subunit nor the control immune serum induced changes in pituitary LH secretion and testicular T release. Since the exogenous drive to the pituitary-testicular axis of the animals was clamped in a mode that produced a pattern of pulsatile LH and T secretion comparable to that observed in adult monkeys, the present findings provide evidence for the view that inhibin plays a major role in the testicular regulation of FSH secretion during adulthood by exerting a selective inhibition on the secretion of this gonadotropin directly at the level of the anterior pituitary gland.

Animals↗
PubMed1990

Role of Leydig cells and endogenous inhibin in regulating pulsatile gonadotropin secretion in the adult male rat.

The purpose of the present study was to determine the parameters of pulsatile gonadotropin secretion in the adult male rat that are regulated by the suppressive feedback influences provided by factors originating in the Leydig cells or by endogenous inhibin, or both. This was achieved by examining the changes in the secretion parameters of FSH and LH that result from selectively destroying the Leydig cells using the toxicant ethane dimethane sulfonate (EDS) or passively immunoneutralizing endogenous inhibin using high-titer anti alpha-inhibin subunit serum, or both. Both FSH and LH were secreted in a pulsatile manner in intact male rats as determined using two different pulse-detection methods. Destruction of the Leydig cells with EDS 6 days before sampling significantly increased basal FSH secretion without affecting pulsatile FSH secretion. Injection of anti-inhibin serum into intact (vehicle treated) males 18 h before sampling produced no observable alteration in any parameter of FSH secretion. Either administration of anti-inhibin serum or castration of rats previously treated with EDS induced further significant, selective increases in the basal parameters of FSH secretion, raising mean FSH to levels comparable to those observed in 6-day castrate rats. When examined individually, however, the parameters of mean trough and peak FSH level and mean pulse amplitude remained significantly higher in the 6-day castrate males. In sharp contrast to the selective effects on basal FSH, destruction of the Leydig cells with EDS dramatically elevated all parameters of LH secretion to levels comparable to those observed in similarly timed castrate rats. Neither immunoneutralization of endogenous inhibin nor castration of EDS-treated rats 18 h before sampling caused any further alteration in any parameter of LH secretion. The results from these studies demonstrate that the Leydig cell provides all of the suppressive influence of the testes on LH secretion and a major portion of the suppressive influence over FSH secretion. This influence is exerted through a suppression of all parameters of LH secretion, but through a selective suppression of basal FSH secretion parameters. Collectively, the results suggest that the Leydig cell-derived influences suppress those parameters of gonadotropin secretion that are mediated by LHRH, acting, at least in part, through a suppression of pituitary sensitivity to LHRH. In the absence of the Leydig cells, endogenous inhibin can be demonstrated to also suppress basal FSH secretion in the adult male rat.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Isolation of a novel 38 residue-hypothalamic polypeptide which stimulates adenylate cyclase in pituitary cells.

A novel neuropeptide which stimulates adenylate cyclase in rat anterior pituitary cell cultures was isolated from ovine hypothalamic tissues. Its amino acid sequence was revealed as: His-Ser-Asp-Gly-Ile-Phe-Thr-Asp-Ser-Tyr-Ser-Arg-Tyr-Arg-Lys-Gln- Met-Ala- Val-Lys-Lys-Tyr-Leu-Ala-Ala-Val-Leu-Gly-Lys-Arg-Tyr-Lys-Gln-Arg-Val-Lys-Asn-Lys - NH2. The N-terminal sequence shows 68% homology with vasoactive intestinal polypeptide (VIP) but its adenylate cyclase stimulating activity was at least 1000 times greater than that of VIP. It increased release of growth hormone (GH), prolactin (PRL), corticotropin (ACTH) and luteinizing hormone (LH) from superfused rat pituitary cells at as small a dose as 10(-10)M (GH, PRL, ACTH) or 10(-9)M (LH). Whether these hypophysiotropic effects are the primary actions of the peptide or what physiological action in the pituitary is linked with the stimulation of adenylate cyclase by this peptide remains to be determined.

Adenylyl Cyclases↗
PubMed1989

Immunocytochemical localization of the gonadotropin-releasing hormone-associated peptide portion of the LHRH precursor in the hypothalamus and extrahypothalamic regions of the rat central nervous system.

The gonadotropin-releasing hormone-associated peptide (GAP) of the LHRH precursor and the decapeptide LHRH were localized in the rat brain by immunocytochemistry in 12- to 18-day-old animals, by use of thick Vibratome sections and nickel intensification of the diaminobenzidine-reaction product. Our results indicate that the GAP portion of the LHRH precursor is present in the same population of neurons that contain LHRH in the rat brain. An important difference observed was that the GAP antiserum, in contrast to LHRH antisera, stained several perikarya in the medial basal hypothalamus. GAP-immunoreactive perikarya were observed in the following regions: the olfactory bulb and tubercle, diagonal band of Broca, medial septum, medial preoptic and suprachiasmatic areas, anterior and lateral hypothalamus, and several regions of the hippocampus. In addition to the preoptico-terminal and the septo-preoptico-infundibular pathways, we also observed GAP-immunopositive processes in several major tracts and areas of the brain, including the amygdala, stria terminals, stria medullaris thalami, fasciculus retroflexus, stria longitudinalis medialis, periventricular plexus, periaqueductal gray of the mesencephalon and extra-cerebral regions, such as the nervus terminalis and its associated ganglion. These results confirm the specificity of previous immunocytochemical results obtained with antisera to LHRH. The presence of GAP immunoreactivity in nerve terminals of the rat brain indicates that GAP or a GAP-like peptide is located in the proper site to serve as a hypophysiotropic substance and/or as a neurotransmitter or neuromodulator.

Animals↗
PubMed1989

Passive immunoneutralization: a method for studying the regulation of basal and pulsatile hormone secretion.

The combination of passive immunoneutralization of an endogenous factor with frequent sampling techniques to delineate the pattern of secretion represents a powerful tool for dissecting the contribution of that factor to normal and/or abnormal pituitary function. Passive immunoneutralization offers all of the advantages of other known means of abolishing endogenous factors. It has the specificity and the selectivity of antagonists while retaining the potential for replacement of biological activity that is possible with organ removal or selective brain cuts or lesions. The only major drawback to this approach is the potential difficulty in obtaining the appropriate reagents. The inherent flexibility of the model, however, increases the probability of obtaining useful data with those reagents that are available. At present, the number of studies using immunoneutralization is relatively small, but the knowledge gained from these studies has been substantial. As the number of immunoneutralization and replacement studies increases in the future, the usefulness of this powerful approach will be extended to its full potential.

Animals↗
PubMed1989

Endogenous inhibin suppresses only basal follicle-stimulating hormone secretion but suppresses all parameters of pulsatile luteinizing hormone secretion in the diestrous female rat.

The purpose of these studies was to ascertain which parameters of pulsatile gonadotropin secretion are regulated by endogenous inhibin in the intact diestrous female rat. This was determined by examining the changes in the secretion parameters of FSH and LH that resulted from immunoneutralizing endogenous inhibin in diestrous I female rats. Passive immunoneutralization of endogenous inhibin was achieved using specific, high titer ovine antiserum generated against the alpha-subunit of the recently described inhibin molecule. The optimal times after inhibin immunoneutralization to observe the changes in FSH secretion were determined in initial experiments. Pulsatile secretion of both FSH and LH was observable in the diestrous female. Two hours after inhibin immunoneutralization, the mean trough level, mean peak level, and overall mean level of FSH began to increase. The maximal increase and plateau of these parameters were observed 5 h after antiserum injection. During the period of increase, mean FSH pulse amplitude was also increased, but returned to the level observed in control (normal sheep serum-injected) animals when the parameters of trough, peak, and overall mean FSH reached their plateau levels. FSH pulse frequency was not changed at any time. These results indicate that endogenous inhibin affects only the basal parameters of FSH secretion without affecting pulsatile FSH secretion. The transient increase in FSH pulse amplitude resulted from FSH pulses being superimposed on the increasing basal FSH secretion. In contrast, immunoneutralization of endogenous inhibin rapidly increased all parameters (i.e. pulse amplitude and frequency, mean trough and peak levels, and mean plasma levels) of LH secretion. In addition, pituitary sensitivity to an exogenous LHRH challenge was increased in inhibin-immunoneutralized females in terms of stimulated LH secretion. As a result of the already increased rate of basal secretion, the actual quantity of FSH released in response to the LHRH challenge was greatly increased in the inhibin-immunoneutralized rats compared with the normal sheep serum-injected controls; however, the increase in the rate of FSH secretion stimulated by the LHRH challenge was the same in both groups. The observations from these studies collectively demonstrate that inhibin acts endogenously to suppress those parameters of gonadotropin secretion that are regulated by LHRH.

Animals↗
PubMed1988

Differential secretion of proLHRH fragments in response to [K+], prostaglandin E2 and C kinase activation.

ProLHRH contains the luteinizing hormone-releasing hormone (LHRH) decapeptide and a 56 amino acid peptide designated gonadotropin-releasing hormone-associated peptide (GAP). We studied the effects of various known secretagogues of LHRH on the in vitro release of proLHRH fragments from the median eminence (ME) and subsequently characterized these immunoreactive products according to molecular weight (MW). GAP- and LHRH-like immunoreactive (LI) materials were secreted simultaneously into the media under basal conditions. Prostaglandin E2 stimulated release of both peptides by approximately 2-fold. Both phorbol ester and [K+] stimulated release of GAP-LI by 4-fold and LHRH-LI by 9-fold over baseline levels. When materials from [K+]-stimulated media were separated according to MW by high performance size-exclusion chromatography, a single peak eluted at 1300 MW in the same position as synthetic LHRH. Two GAP-LI peaks were observed. One eluted in the void volume, while the predominant peak co-eluted with synthetic rat GAP1-56 at approximately 6500 MW. These results indicate that GAP and LHRH are co-secreted, that they are released as intact peptides, and that activation of different intracellular pathways may cause their differential secretion. These results emphasize the importance of using both in vitro and chromatographic methodologies to evaluate the changes which may occur in LHRH prohormone processing and secretion.

Animals↗
PubMed1988

Adenosine receptor-dependent modulation of inhibin secretion in cultured immature rat Sertoli cells.

Inhibitory (A1) adenosine receptors that attenuate adenylate cyclase activity are present in cultured Sertoli cells. To investigate the possible effect of activating these receptors on the secretion of inhibin by the Sertoli cell, immature rat Sertoli cells were incubated for 24 h with follicle-stimulating hormone (FSH) in the absence or presence of the non-metabolizable, adenosine agonist phenyl-isopropyl-adenosine (PIA), and the accumulation of alpha-inhibin immunoreactivity was measured in the medium. Although devoid of effects when added alone, PIA inhibited the FSH-dependent secretion of alpha-inhibin in a concentration-dependent manner (ED50 = 1-1.5 nM). PIA treatment of the Sertoli cells also rendered the cells less sensitive to FSH in terms of alpha-inhibin secretion. The concentration-response curve to FSH was shifted to the right when cells were incubated in the presence of 100-1000 nM PIA. In contrast, dibutyryl cAMP stimulation of alpha-inhibin accumulation was unaffected by treatment with PIA, indicating that the site of PIA action is at the level of cAMP synthesis. These data provide experimental evidence of adenosine modulation of inhibin secretion by the Sertoli cell and suggest that adenosine may act as a local modulator within the pituitary-testicular axis.

Animals↗
PubMed1988

Passive immunoneutralization of endogenous inhibin: sex-related differences in the role of inhibin during development.

The purpose of these studies was to ascertain the extent to which endogenous inhibin regulates follicle-stimulating hormone (FSH) secretion at different intervals during development in the male and female rat. This was determined by examining the changes in plasma FSH that resulted from immunoneutralizing endogenous inhibin in male and female rats at different ages during development and into adulthood. Passive immunoneutralization of endogenous inhibin was achieved using specific, high titer ovine antiserum, generated against the alpha-subunit of the recently described inhibin molecule. Optimal antiserum volumes and time after injection required to observe maximal changes in FSH secretion were determined in initial experiments. No clear effect of immunoneutralizing endogenous inhibin could be demonstrated on FSH secretion in female rats until 20 days of age, after the completion of the endogenous rise in FSH which occurs between days 5 and 20. Thereafter, injection of the anti-alpha-inhibin serum (anti-alpha IN) produced a progressively marked increase in plasma FSH as the age of the females increased. In male rats, injection of the anti-alpha IN serum caused an increase in FSH secretion as early as 5 days of age, although the response was more delayed at this age than at later times. The ability of the anti-alpha IN serum to increase plasma FSH was observed through 20 days of age. At 30 days of age, during the peak of the endogenous rise in plasma FSH, injection of the anti-alpha IN serum failed to further increase the already elevated levels of plasma FSH. As the endogenously high levels of FSH gradually decreased, the ability of anti-alpha IN serum to increase FSH secretion returned (40 days of age) but was diminished by 50 days of age and was completely lost by 60 days of age. The results of the present study indicate that inhibin plays an increasingly important role as a regulator of FSH secretion in the female from at least 20 days of age into adulthood. In the male, however, the role of inhibin in regulating FSH secretion, which is clearly present during early postnatal development, is apparently lost at the time of puberty.

Age Factors↗
PubMed1988

The Pro-LHRH system of the rat brain. Effects of changes in the endocrine background.

The gonadotropin-releasing hormone-associated peptide (GAP) and luteinizing hormone-releasing hormone (LHRH) portions of the LHRH precursor were localized by immunocytochemistry in prepubertal female rats, in adult female rats at different stages of the estrous cycle, and in ovariectomized rats. Our results indicate that GAP is present in the same population of neurons as LHRH in the rat brain. These results confirm the specificity of previous immunocytochemical studies which used antisera to LHRH alone. The endocrine status of the animal was demonstrated to affect the immunocytochemical appearance of the GAP system. The number of GAP immunopositive cells and terminals is highest during diestrus II and lowest on the day of estrus, suggesting either a role in and/or a dependence upon the endocrine changes associated with the estrous cycle. Ovariectomy results in a gradual decrease in GAP immunoreactivity in the median eminence. This observation, in concert with other recent studies, suggests that ovarian factors may be acting to maintain the LHRH system and that ovariectomy may result in decreased synthesis and/or processing of the LHRH system and that ovariectomy may result in decreased synthesis and/or processing of the LHRH precursor.

Animals↗
PubMed1988

Orchidectomy induces temporal and regional changes in the processing of the luteinizing hormone-releasing hormone prohormone in the rat brain.

The structures of the complementary DNA (cDNA) that encode the rat and human hypothalamic LHRH prohormones were recently determined and the corresponding amino acid sequences deduced. In addition to the LHRH decapeptide, the prohormone contains a 56-amino acid peptide sequence which has been designated gonadotropin-releasing hormone associated peptide (GAP). In the present study we examined the effect of orchidectomy on LHRH prohormone processing in three brain regions known to contain the various elements of the LHRH neuronal system; the preoptic-anterior hypothalamic area, the hypothalamus (HYP), and the median eminence. Both LHRH-like and GAP-like immunoreactivities (LHRH-LI and GAP-LI) were quantitated in these regions in intact male rats and male rats orchidectomized for 1, 2, 3, 5, 7, 14, or 40 days. In addition, the LHRH and GAP immunoreactivities were localized and the effects of orchidectomy examined using immunocytochemical techniques. One day after orchidectomy, a small decrease in GAP-LI and an increase in LHRH-LI were evident in extracts of the preopticanterior hypothalamic area which resulted in a significant decrease in the GAP/LHRH molar ratio. A similar selective decrease in GAP-LI and in the GAP/LHRH molar ratio was also observed in extracts of the HYP, but not until 2 days after orchidectomy. The GAP/LHRH ratio in both regions gradually returned to that of the intact controls. In both the HYP and median eminence, GAP-LI and LHRH-LI gradually declined in parallel through 14 days after orchidectomy. The gradual loss of immunoreactivity in these regions was evident by both RIA quantification and immunocytochemistry. These observations suggest that 1) production and processing of both LHRH and its prohormone are affected by testicular factors, 2) that divergent enzyme and/or transport systems, regulating LHRH and GAP processing, may exist at the level of the perikarya, and 3) long term orchidectomy results in decreased biosynthesis of the prohormone and/or in parallel increases in LHRH and GAP degradation or transport.

Animals↗
PubMed1988

Processing of the luteinizing hormone-releasing hormone precursor in the preoptic area and hypothalamus of the rat.

The LHRH precursor is known to contain the decapeptide and a 56 amino acid peptide termed gonadotropin-releasing hormone-associated peptide (GAP). The purpose of our study was to characterize the proLHRH and its processed products from the cell body and fiber region and from the nerve terminal region of LHRH neurons. The median eminence (ME) and a tissue block containing the preoptic area and hypothalamus (POH) were dissected separately. Tissues were homogenized and peptides were separated according to mol wt. Three different LHRH antisera bound to one immunoreactive (IR) substance which eluted at approximately 1200 mol wt. Subsequently, this material coeluted with synthetic LHRH on a reversed-phase column as a single peak. There was approximately 1.6-fold more LHRH-like IR in the ME than in the POH. The four different GAP antisera recognized multiple mol wt forms of GAP-like IR at approximately 16,000 to 14,000, 8,200, 6,500, 3,500, and 2,800 mol wt. There were more of the high mol wt materials and less of the 6500 and lower mol wt materials in the POH than in the ME. The most abundant species in both regions was the 6500 mol wt form. This IR substance coeluted with synthetic rat GAP1-56 on a reversed-phase column as a single peak. These experiments demonstrate 1) that multiple IR forms of the LHRH prohormone exist in the POH of the rat and 2) that nerve terminals of the LHRH neurons contain LHRH, GAP1-56, and some lower mol wt GAP-like substances. These results provide the first information concerning the processing scheme for the LHRH prohormone in the rat brain.

Amino Acid Sequence↗
PubMed1987

The ovarian renin-angiotensin system: renin-like activity and angiotensin II/III immunoreactivity in gonadotropin-stimulated and unstimulated human follicular fluid.

Renin-like activity and angiotensin II/III immunoreactivity in follicular fluids from 34 women stimulated with human menopausal gonadotropin and human chorionic gonadotropin (56.8 +/- 6.5 ng angiotensin I per milliliter per hour and 187 +/- 21 pg/ml [mean +/- SEM], respectively) were much higher (p less than 0.001) than in follicular fluids from 12 unstimulated preovulatory women (1.41 +/- 0.37 ng angiotensin I per milliliter per hour and 58.5 +/- 13.7 pg/ml) and in simultaneously drawn plasma (4.47 +/- 0.73 ng angiotensin I per milliliter per hour and 31.8 +/- 11.6 pg/ml, respectively; p less than 0.001). Plasma renin-like activity and angiotensin II/III immunoreactivity in stimulated cycles did not differ from unstimulated cycles. Follicular fluid angiotensin II/III immunoreactivity correlated significantly with follicular fluid renin-like activity in stimulated (r = 0.72; p less than 0.01) and in unstimulated samples (r = 0.86; p less than 0.01). Significant correlation was found also between follicular fluid renin-like activity and estradiol. A sharp preovulatory rise of renin-like activity and angiotensin II/III immunoreactivity was noted in unstimulated follicular fluid samples collected on cycle days 13 and 14 compared to days 9 through 12 (p less than 0.01). The findings that follicular fluid renin-like activity and angiotensin II/III immunoreactivity are correlated, and that gonadotropins have a stimulatory effect on follicular fluid concentrations support our concept of a physiologic intrinsic ovarian renin-angiotensin system.

Angiotensin II↗