Expression of functional ciliary neurotrophic factor receptors in immortalized gonadotrophin-releasing hormone-secreting neurones.

Ciliary neurotrophic factor (CNTF), a cytokine of the interleukin-6 superfamily, is known to exert pleiotropic actions, including regulation of food intake and permissive effects on reproduction, by facilitating the release of gonadotrophin-releasing hormone (GnRH) and gonadotrophins. CNTF activates membrane receptors (CNTF-Rs) composed of one ligand-specific binding subunit, defined CNTFR alpha, and two signal transducing subunits, termed leukaemia inhibitory factor receptor (LIFR) and gp130. However, it is not clear whether the effects of CNTF on GnRH release result from either a direct or an indirect action on GnRH-secreting hypothalamic neurones, or from a combination of these events. The hypothesis of a direct effect of CNTF was thus tested using the GT1-7 GnRH-secreting cell line. CNTF-R expression and CNTF-induced modulation of the Janus kinase (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway and of GnRH release were evaluated. GT1-7 cells were found to express CNTFR alpha, LIFR and gp130 genes, as shown by reverse transcription-polymerase chain reaction analysis, and the corresponding proteins, analysed by immunofluorescence and western blot. CNTFR alpha, LIFR and gp130 immunoreactive bands had an approximate size of 50, 190 and 130 kDa, respectively. Treatment of GT1-7 cells with 10(-12) M CNTF for 15-60 min resulted in a marked and transient increase of STAT3 phosphorylation via activation of JAK2. A 30-min exposure of GT1-7 cells to different CNTF concentrations increased the accumulation of GnRH into the culture medium, with a maximal effect at 10(-11) M. In conclusion, the present results provide new information about the regulation of the reproductive axis by CNTF, and suggest that it might operate at the hypothalamic level by directly influencing the activity of GnRH-secreting neurones, in addition to the possible indirect effects via interneurones proposed by previous studies.

Involvement of postnatal gonads in the maturation of dopaminergic regulation of prolactin secretion in male rats.

Permanent effects of postnatal gonads on dopamine (DA)-mediated regulation of PRL secretion were examined in adult male rats of the Wistar-Imamichi strain. Rats were bilaterally orchidectomized at varying postnatal days, i.e. 8 h after birth [neonatal castration (NC)] or at 1, 2, 3, 4, or 6 weeks of age, and subjected to experiments at the age of about 10 weeks. Ten-week-old intact adults were also examined. All groups were injected ip with saline or sulpiride (1 mg/kg BW), and blood samples were collected by rapid decapitation 20 min later. Anterior pituitaries (AP) thus obtained were subjected to determination of PRL content. The circulating level of testosterone was similar among all castrated groups. Rats castrated on or after 3 weeks of age showed a significantly smaller PRL response to sulpiride than intact adults. In turn, sulpiride-induced PRL release in rats castrated on or before 2 weeks of age was similar to that in intact adults. However, the AP PRL content of saline control was uniformly lower in castrated males than in intact adults regardless of age at castration (P less than 0.01). The value in males castrated at 1 week was 2.0-fold higher than that in NC males, but a decreasing trend was observed in groups castrated at 2 or 3 weeks. That such a stimulation of AP PRL content by the neonatal testis is not mediated by an action of estradiol converted from testosterone has been suggested by the failure of daily neonatal tamoxifen (estrogen antagonist) treatment of intact males, before castration at 1 week, to decrease AP PRL content during adulthood. Sulpiride-induced reduction of the AP PRL content was significant only in males castrated at 6 weeks and intact adults. Characteristics of AP DA receptors labeled by [3H]spiperone were not different between males castrated at 6 weeks and intact adults. However, a heterogeneity was observed between NC males and a set of males castrated at 6 weeks and intact adults. The Kd was significantly (P less than 0.05) greater in NC males (mean +/- SE, 1.19 +/- 0.22 nM) than in males castrated at 6 weeks (0.52 +/- 0.08 nM), and the number of binding sites was significantly (P less than 0.05) larger in NC males (20.4 +/- 1.6 fmol/pituitary) than in both males castrated at 6 weeks and intact adults (12.6 +/- 2.0 and 13.1 +/- 1.9 fmol/pituitary, respectively).(ABSTRACT TRUNCATED AT 400 WORDS)

Involvement of postnatal gonads in the maturation of dopaminergic regulation of prolactin secretion in female rats.

Permanent effects of postnatal gonads on dopamine (DA)-mediated regulation of PRL secretion were examined in adult female rats of the Wistar-Imamichi strain. Experiments were uniformly done at the age of about 10 weeks. First, rats were bilaterally ovariectomized on varying postnatal days, i.e. 24 h after birth [neonatal castration (NC)] or at 1, 2, 3, 4, or 6 weeks of age. Intact diestrous females were also examined. All groups were injected ip with saline or sulpiride (1 mg/kg BW), and blood samples were collected by rapid decapitation 20 min later. Also, in saline control groups, the anterior pituitary (AP) PRL content was determined. In NC females, significant PRL release was not observed by either sulpiride or saline. However, stimulation of PRL release by sulpiride was observed consistently in rats ovariectomized on or after 1 week of age. Although there was not a complete correlation between the plasma PRL level attained after sulpiride treatment and the AP PRL content, the general trend was that the AP PRL content was increased as the postnatal age of the ovariectomy was delayed. Values in intact adult females exceeded those in all of the castrated groups in both parameters. Second, daily sc injection for 7 days with estradiol benzoate (E2; 2.5 micrograms/kg BW) and/or progesterone (P; 5 mg/kg BW) was given after NC to determine which ovarian secretion(s) is involved in the aforementioned findings. Sulpiride stimulated PRL release in NC females that had been treated neonatally (postnatal days 3-9) with either E2 or P. This effect was accompanied by an increase in the AP PRL content. An enhancement of both parameters was also observed when the same dose of E2 or P was given in the fourth week (postnatal days 22-28). However, neither parameter was further augmented by concurrent administration of E2 and P at either postnatal time. Characteristics of AP DA receptors were subsequently analyzed in some of the foregoing groups using [3H]spiperone. The number of binding sites, when expressed as femtomoles per pituitary, did not differ among all groups examined. However, a significant difference in the dissociation constant (Kd) was observed between NC females and females castrated at 6 weeks of age. The Kd in NC females was not altered by subsequent neonatal treatment with E2 and/or P. Nonetheless, the E2 effect on Kd was dependent on when E2 was given after NC.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of postnatal gonadal function in the determination of thyrotropin (TSH) releasing hormone-induced TSH response in adult male and female rats.

Permanent effects of postnatal gonadal function on the hypothalamo-pituitary-thyroid axis were examined in male and female rats of the Wistar-Imamichi strain. Animals were used at the age of about 10 weeks. Neonatally castrated (NC) males showed a significantly higher plasma TSH response to TRH (10 micrograms/kg BW, ip) than males castrated at 1, 2, 3, 4, or 6 weeks of age. The TSH response in intact males was similar to that seen in NC males. Neonatal androgenization of NC males with 100 micrograms/rat of testosterone propionate decreased the TSH response in the group. The anterior pituitary (AP) TSH content was similar among all male groups. The number of AP TRH receptors was significantly higher in both NC males and intact males than in both NC + neonatal androgenization males and 6-week-castrated males. In female rats, TRH-induced TSH response, AP TSH content, and AP TRH receptor number were all unaffected by the age of castration, whereas intact females significantly exceeded 6-week-castrated females in these three variables. The circulating levels of T3 and T4 and hypothalamic TRH content were similar in all groups in each sex. These results indicate biphasic effects of postnatal testosterone on the TSH response to TRH, that is, a permanent inhibition in early postnatal days and a transient stimulation in adult age. The effects occurred not via changes in AP TSH content but via changes in AP TRH receptor number. In females, however, postnatal gonads did not exert any permanent effects on the TRH-TSH system.

Stimulation by peptide histidine methionine (PHM) of adrenocorticotropin secretion in patients with Cushing's disease: a comparison with the effect of vasoactive intestinal peptide (VIP) and a study on the effect of combined administration of corticotropin-releasing hormone with PHM or VIP.

The effect of peptide histidine methionine (PHM) on ACTH and cortisol secretion was examined in 12 female patients with Cushing's disease and 8 normal women. For comparison, we examined in both groups the effects of vasoactive intestinal peptide (VIP), human (h) CRH plus PHM, and hCRH plus VIP. Each peptide was given as an i.v. bolus in a dose of 100 micrograms, and plasma levels of ACTH and cortisol were measured before and at intervals up to 120 min after the injection. In all normal subjects, hCRH induced significant rises in ACTH (> 50% above the basal) and cortisol (> 20% above the basal), but PHM and VIP were without effect. In this group, hormonal responses after hCRH plus PHM and hCRH plus VIP were statistically indistinguishable from those after hCRH alone. Of the patients with Cushing's disease, 9 (75%) were responsive to hCRH, 5 (42%) were to VIP, and 3 (25%) were to PHM, showing significant increases in both ACTH and cortisol. All the 3 PHM responders were also responsive to VIP, and all the 5 VIP responders were also responsive to hCRH. Interestingly, the responders to VIP and PHM had higher ACTH and cortisol responses to hCRH compared with the nonresponders. In addition, in the patients with Cushing's disease the coadministration of hCRH with PHM or VIP produced additive increases in both ACTH and cortisol. These results suggest that PHM may be another hypothalamic hormone capable of paradoxically stimulating ACTH secretion in at least some patients with Cushing's disease. Although the ACTH-releasing action of PHM appears less potent than those of hCRH and VIP, the possibility was suggested that a certain common mechanism may operate in inducing the ACTH response to these 3 peptides.

Paradoxical response of growth hormone to peptide histidine methionine in acromegaly: comparison with the effects of thyrotropin-releasing hormone and vasoactive intestinal peptide.

We examined whether peptide histidine methionine (PHM) induces a paradoxical rise in plasma GH in patients with acromegaly. PHM (100 micrograms) was given as an iv bolus to eight patients with active acromegaly, and plasma GH levels were measured before and at intervals up to 120 min after the injection. For comparison, the effects of TRH (500 micrograms) and vasoactive intestinal peptide (VIP, 100 micrograms), peptides known to paradoxically stimulate GH secretion in acromegalics, were assessed in all of the patients. A paradoxical rise (greater than 50% above the basal) in plasma GH was observed in five patients after both TRH and VIP administrations, although TRH responders were not always VIP responders, nor did VIP responders always respond to TRH. In two patients, the GH response to PHM fulfilled the criteria of a paradoxical increase. Both of these patients were also TRH and VIP responders. These results suggest that PHM may be another hypothalamic hormone capable of paradoxically stimulating GH secretion in at least some acromegalics, although PHM appears to be a less potent stimulator of GH release than TRH and VIP. The pathophysiological significance of this phenomenon is yet to be determined.

Food conversion is transiently affected during 4-week chronic administration of melanocortin agonist and antagonist in rats.

The central melanocortin system is involved in the regulation of food intake and body weight. In this study, we investigated the effect of a 4-week intracerebroventricular infusion of the melanocortin receptor agonist MT-II and the selective melanocortin-4 receptor antagonist HS024 on food intake and body weight homeostasis. The MT-II-treated rats ate less and lost considerably more weight than the control rats during the first week of treatment. During the second and third week, they gained weight and, by the end of the treatment period, the weight gain was similar to that of the control rats. The HS024 treatment caused hyperphagia and development of obesity during the entire period. Extensive accumulations of fat and a sixfold increase in leptin levels were observed in the HS024-treated rats, as compared with controls, after the 4-week period. Food conversion ratio, defined as body weight increase relative to weight of ingested food, was clearly increased in the HS024-treated rats, while it was lowered in the MT-II-treated rats compared with controls. The effect on food conversion ratio was transient, being greatest for both experimental groups during the first week and it was then attenuated to reach the level of controls at the end of the study. The results suggest that long-term injection of exogenous melanocortin receptor active substances may have an important transient effect on food conversion.

A case of cyclical Cushing's disease associated with corticosteroid-binding globulin deficiency: a rare pitfall in the diagnosis of Cushing's disease.

We experienced an extremely unusual combination of Cushing's disease and corticosteroid-binding globulin (CBG) deficiency that has been reported in only one similar case to date. A 53-year-old woman presented at a medical clinic with clinical Cushing's disease. However, her plasma levels of adrenocorticotropin (ACTH) and cortisol were in the normal range. Six months later, during a second visit, a high urinary excretion of 17-hydroxycorticosteroids was found, but plasma ACTH and cortisol levels were normal again. Further investigation revealed a decreased CBG concentration. Free plasma cortisol levels were clearly elevated. Furthermore, the Cushing's disease of our patient was complicated by periodic secretion of ACTH and cortisol, with high or normal outputs of corticosteroids occurring alternately every 1-3 days, which explained the occasionally normal plasma ACTH and cortisol levels. A combination of a decreased serum CBG concentration and periodic secretion of ACTH can be an important pitfall in the diagnosis of Cushing's disease.

Effects of Neonatal Exposure to Estradiol on Prolactin Secretion and Activity of the Tubero-lnfundibular Dopamine System in Young Adulthood: Comparison with Neonatal Prolactin Deficiency*.

Abstract Previous results from this laboratory indicate that female rats who consume milk deficient in prolactin (PRL) during the neonatal period subsequently display hyperprolactinemia, associated with decreased activity in the tubero-infundibular dopamine (DA) system and decreased lactotrope responsiveness to DA receptor stimulation. The present studies tested whether these neuroendocrine consequences of neonatal PRL deficiency can be mimicked by exposure of neonatal rats to estradiol. Female rats were injected sc with 1 mUg estradiol benzoate or oil vehicle on postpartum Days one to 3, while in other experiments, females were made neonatally deficient in PRL through treatment of their mothers with the DA agonist bromocriptine, a treatment that reduces the levels of PRL in milk. Females treated neonatally with estradiol benzoate, as well as offspring of the bromocriptine-treated mothers, displayed hyperprolactinemia as young adults, as compared to their respective vehicle-matched controls, and in both cases, this was abolished by ovariectomy, indicating dependence upon ovarian secretions. As reported previously in neonatal PRL-deficient females, neonatal estradiol benzoate-treated animals also exhibited reduced steady state levels and decreased turnover rates of DA in the median eminence when 35 days of age. DA levels and turnover rates in this region were still significantly reduced on postpartum Day 60. The DA agonist bromocriptine suppressed PRL release to a similar extent in cultured anterior pituitary cells from neonatal estrogen-treated and control rats, suggesting normal responsiveness of DA receptors on lactotrope cells in both groups. The present results confirm the ability of estradiol treatment or induction of a PRL deficiency during the early neonatal period to induce subsequent hyperprolactinemia in female rats, and further indicate that the hyperprolactinemic conditions resulting from either neonatal manipulation are dependent on the ovary and are associated with decreased levels and turnover of DA in the median eminence during the prepubertal period. Although these findings suggest that increased exposure to estradiol during the neonatal period may underlie the similar effects of neonatal PRL deficiency, the further observations in neonatal estrogen-treated rats that 1) decreased DA turnover in the median eminence persists at Day 60, and 2) lactotrope responsiveness to DA is normal, differ from results obtained previously in PRL-deficient rats. Thus, enhanced exposure to estrogen during the neonatal period does not appear to account for all of the neuroendocrine consequences of neonatal PRL deficiency.

Agouti-related peptide prevents steroid-induced luteinizing hormone and prolactin surges in female rats.

We studied the effect of Agrp (agouti-related peptide) on LH (luteinizing hormone) and PRL (prolactin) surges in ovariectomized rats primed with estradiol and progesterone. The rats displayed characteristic LH and PRL surges that were completely abolished by starving. Injection of either 1 nmol or 3 nmol Agrp (83-132), a potent antagonist of the orexigenic MC3 and MC4 receptors, completely prevented both the LH and PRL surges. We also investigated the effects of either a single or double injection of anti-Agrp serum to fasted animals, which were without LH and PRL surges. A single injection of the antiserum was without effect, but the rats that received double injection of anti-Agrp serum partially reinstated both the LH and PRL surges. Although the onset of LH and PRL surges was significantly delayed in the double treated group, the highest levels of the surges for both hormones were statistically indistinguishable compared with the control group. These data give a clear indication that endogenous Agrp may be involved in LH and PRL surges during starvation, providing further evidence that the melanocortin system is important for these hormonal surges in female rats.

The immunostaining for the hypothalamic vasoactive intestinal peptide, but not for beta-endorphin, dynorphin-A or methionine-enkephalin, is affected by the glucocorticoid milieu in the rat: correlation with the prolactin secretion.

Effects of the glucocorticoid milieu on the basal and ether stress-induced prolactin (PRL) release and on the immunostaining for hypothalamic vasoactive intestinal peptide (VIP), beta-endorphin (beta-EP), dynorphin-A (DYN-A) and methionine-enkephalin (Met-ENK), were examined in separate groups of male rats. After colchicine treatment in intact rats, VIP-containing cell bodies were observed only in the suprachiasmatic nucleus (SCN). Adrenalectomy (ADX), performed 7 days previously, resulted in the additional appearance of VIP-immunoreactive neurons in the parvocellular subdivision of the paraventricular nucleus (PVN), as well as in significantly higher basal and stressed PRL levels than intact values. Treatment of intact rats with a high dose (500 micrograms/kg body weight (s.c.) daily for 7 days) of dexamethasone (DEX), but not with a low dose (50 micrograms/kg) of DEX, significantly reduced both the basal and stressed PRL release. Administration of either the low or high dose of DEX to ADX rats prevented the appearance of the PVN-VIP neurons. In addition, the ADX-induced high basal and stressed PRL levels were restored to intact values by the low dose of DEX, and completely suppressed by the high dose of DEX. The staining of SCN-VIP-, beta-EP-, DYN-A or Met-ENK neurons was not affected by any treatment employed in this study. These results suggest that the appearance of PVN-VIP immunostaining in ADX rats may, at least in part, be responsible for the enhanced PRL secretion observed in this group. However, SCN-VIP-, beta-EP-, DYN-A- or Met-ENK neurons do not seem to play a pivotal role in the glucocorticoid regulation of PRL secretion.

A comparative study of the effects of neonatal androgenization and estrogenization on prolactin secretion in adult female rats.

Effects of neonatal androgenization (NA) and estrogenization (NE) were compared especially in terms of the prolactin (PRL) secretion in female rats. Twenty-four h after birth, a total of seven groups of newborn female rats were treated as follows. Three NA groups received a single s.c. injection of 10, 100 or 1000 micrograms of testosterone, respectively. Similarly, three NE groups received 1, 10 or 100 micrograms of estradiol-17 beta, respectively. The remaining one group was injected with oil vehicle only, and served as controls. At 8 weeks of age, animals were killed by rapid decapitation. PRL, estradiol and progesterone were measured in the plasma. Anterior pituitary (AP) was weighed, and AP PRL content was measured. NA and NE, at the highest doses, resulted in a similar degree of hyperprolactinemia and hyperestrogenemia showing an effect ratio of about 1:10. This ratio was, however, not true with the lower doses. Furthermore, there was no dose-dependency in the effect of NE on the plasma PRL and estradiol levels. In turn, plasma progesterone levels were dose-dependently decreased by both NA and NE. AP PRL content, expressed per AP, was significantly higher than control values in only NA (1000 micrograms) and NE (100 micrograms) groups. AP weight was increased by NA (1000 micrograms) but not by any NE treatment. These results indicate that NA and NE do not always exert similar effects on the PRL secretion or on several other related parameters. Therefore, aromatization of testosterone to estradiol does not appear to be the sole mechanism mediating the neuroendocrine consequences of NA.

A comparative study of adrenocorticotropin-releasing activity of prostaglandins E1, E2, F2 alpha and D2 in the rat.

There is substantial evidence to indicate that prostaglandin (PG) E2 exerts a stimulatory effect on the hypothalamo-pituitary-adrenal axis in rodents. However, little is known regarding the possibility that other PGs play a similar role in regulating the endocrine axis. Therefore, in this study we compared the effects of intravenous administration of PGs E1, E2, F2 alpha and D2 on adrenocorticotropin (ACTH) secretion in conscious male rats. Each PG was administered at two doses of 0.1 and 1.0 mg/kg body weight, and blood samples were collected sequentially up to 120 min postinjection. Although PGD2 was without effect on ACTH secretion at either dose, PGs E1, E2 and F2 alpha all significantly stimulated the hormonal response at both doses. Interestingly, PGs E1, E2 and F2 alpha were largely equipotent in stimulating ACTH release. To the best of our knowledge, this is the first study to demonstrate significant ACTH-releasing activity of intravenously administered PGs E1 and F2 alpha in the rat. These results suggest that PGE2 might not be the only prostanoid playing a role in regulating the hypothalamo-pituitary-adrenal axis and, thus, multiple PGs may be involved in the endocrine axis.

Intravenous administration of tumor necrosis factor-alpha stimulates corticotropin releasing hormone secretion in the push-pull cannulated median eminence of freely moving rats.

Utilizing push-pull perfusion, we examined the effects of intravenous (iv) administration of human recombinant tumor necrosis factor (TNF)-alpha on the levels of plasma adrenocorticotropin (ACTH) and corticotropin releasing hormone (CRH) in the median eminence (ME) of freely moving male rats. The ME was perfused with artificial cerebrospinal fluid between 11:00 and 14:00 h, and perfusates and blood samples were collected every 20 min. TNF-alpha (1.0 microgram), but not vehicle only, given as an iv bolus at 12:00 h significantly stimulated both plasma ACTH and ME-CRH. The increase in ME-CRH clearly preceded that of plasma ACTH. This is the first to characterize the temporal profile of CRH secretion in the ME after iv administration of TNF-alpha to freely moving rats. These in vivo data strongly suggest that TNF-alpha stimulates ACTH secretion, at least in part, by triggering hypothalamic CRH release. In addition, combined with our previous data obtained by iv administration of human recombinant interleukin-1 under the same experimental condition, the present study also suggests that iv injected TNF-alpha and interleukin-1 may share a common site of action in the brain, such as the ME, to stimulate CRH secretion.

A further study on the stimulatory effect of peptide histidine methionine on growth hormone secretion in acromegaly: a dose-related study and a comparison with vasoactive intestinal peptide.

We examined whether the GH-releasing effect of peptide histidine methionine (PHM) in acromegaly may be mediated by activation of pituitary receptors for vasoactive intestinal peptide (VIP), which is structurally similar to but more powerful than PHM in stimulating GH secretion in acromegaly. VIP (50 or 100 micrograms) or PHM (50, 100, or 200 micrograms) was given as an i.v. bolus to 11 patients with active acromegaly, and plasma GH levels were measured before and at intervals up to 120 min after the injection. A paradoxical GH response (> 50% and > 6 micrograms/l above the basal) to 50 or 100 micrograms of VIP was observed in 4 (36%) or 5 (45%) patients, respectively. 2 (18%) patients showed paradoxical GH responses to both 50 and 100 micrograms of PHM, and, interestingly, as many as 5 (45%) patients showed positive GH responses to 200 micrograms of PHM. 3 of these 5 responders to 200 micrograms of PHM were also responders to both doses of VIP. To add to, one of the responders to 100 micrograms of VIP did not show a positive GH response to even 200 micrograms of PHM. These results may suggest that in at least some acromegalics the PHM stimulation of GH secretion is mediated by activation of pituitary VIP receptors by PHM and/or by PHM binding to its specific receptors which may have appeared concomitantly with VIP receptors. However, the occasional heterogeneity of the VIP- and PHM-induced GH responses may suggest that on some somatotroph adenomas either VIP or PHM receptors may appear independently.

Stimulation by neuropeptide Y of growth hormone secretion in prolactinoma in vivo.

We examined the effects of intravenous bolus injection of human neuropeptide Y (NPY, 100 micrograms) on the plasma growth hormone (GH) and prolactin (PRL) responses in 15 patients with prolactinoma (PRLoma). The GH and PRL responses to NPY were considered positive (a paradoxical increase) when an increase over baseline of at least 100% occurred. Although NPY did not affect PRL secretion in any of the patients examined, 60% (9 of 15) of the patients showed a significant rise in GH secretion after NPY. The presence or absence of the positive paradoxical increase in GH after NPY was not related to the age of the patients, basal PRL levels, the size of the pituitary adenoma (macro- or microadenoma), or the presence or absence of suprasellar extension of the adenoma. Although the underlying mechanism of the NPY stimulation of GH secretion and also its pathophysiological significance in PRLoma are open to question, the present observation may represent another example of paradoxical hormone responses which are occasionally found in functioning pituitary adenomas.

Clinical significance of the growth hormone response to vasoactive intestinal peptide and gonadotropin-releasing hormone in acromegaly.

GH-secreting pituitary adenomas causing acromegaly can be classified into at least two types, i.e. the lactotroph-like adenoma and somatotroph-like adenoma. From a functional point of view, the lactotroph-like adenoma is characterized by positive GH responses to TRH and bromocriptine (Br) with a GH increase or decrease, respectively, whereas the somatotroph-like adenoma is characterized by a high GH response to GHRH and a low GH response to TRH and Br. In this study, we examined whether the loading of vasoactive intestinal peptide (VIP) and GnRH, another hypothalamic hormone capable of stimulating GH secretion in acromegaly, have a pathophysiological significance as TRH, GHRH, and Br tests. In 52 patients with active acromegaly, we performed iv bolus injections of TRH (500 micrograms), GHRH (100 micrograms), VIP (100 micrograms), and GnRH (100 micrograms), and a peroral administration of Br (2.5 mg), in order to compare the GH responses to these loads. There was a significant correlation that the higher was the GH response after TRH the greater was the GH decrease after Br. Although statistically insignificant, there was a trend (0.05 < p < 0.1) that the higher was the GH response after GHRH the smaller was the GH decrease after Br. In addition, as novel findings, we observed that the GH responses to GHRH, VIP, and GnRH were in significant positive correlations to each other, and that the higher were the GH responses after VIP and GnRH the smaller was the GH decrease after Br. In agreement with this, we also found that a simultaneous GH responsivity to VIP and/or GnRH in TRH-responsive acromegalics significantly enhanced the GH response to GHRH and lowered the Br responsiveness compared to the data of pure TRH-responders. From these results, we hypothesize that the positive GH responsiveness to VIP and GnRH, like that to GHRH, may be a feature of the somatotroph-like pituitary adenoma causing acromegaly. The present results appear to be of some help in understanding the basis of the great variabilities in the GH responses to various dynamic testings in acromegaly.

A re-evaluation of the prolactin-releasing activity of growth hormone-releasing hormone in acromegaly in vivo.

In 1985, Losa et al reported that an i.v. bolus injection of GH-releasing hormone (GHRH) was able to paradoxically stimulate PRL secretion in more than half of their acromegalic patients. However, this observation was not generally accepted since several other investigators have concluded that such an anomalous PRL response to GHRH was an extremely rare phenomenon in acromegaly. Therefore, in this study we examined a large number (51 patients) of active acromegalics in order to obtain more reliable data on the incidence of the paradoxical PRL response to GHRH in this disorder. Each patient underwent i.v. bolus injections of GHRH (100 micrograms) and thyrotropin-releasing hormone (TRH, 500 micrograms) on separate days, and plasma levels of GH and PRL were measured. The plasma PRL response to GHRH was considered positive (a paradoxical increase) when an increase over baseline of at least 50% occurred. We found that only 6 patients (12%) showed a positive PRL response to GHRH. These PRL-responders to GHRH had higher GH responses to this peptide than PRL-non-responders to GHRH. Although PRL-responders and non-responders to GHRH had a similar PRL responsiveness to TRH, the GH response to TRH was lower in PRL-responders to GHRH than PRL-non-responders to this peptide. In addition, PRL-non-responders to GHRH had lower basal GH and higher basal PRL levels than PRL-responders to GHRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulatory and inhibitory effects of neuropeptide Y on growth hormone secretion in acromegaly in vivo.

It has been reported that neuropeptide Y (NPY) affects growth hormone (GH) secretion in several animal species. With respect to the role of NPY in regulating GH release in humans, one previous study has reported that NPY inhibited GH secretion from cultured GH-secreting pituitary adenoma cells in vitro. However, since it has yet to be explored whether NPY affects GH secretion in acromegaly in vivo, in this study we attempted to examine the effect of intravenous (i.v.) bolus injection of 100 microg of human NPY on plasma GH levels in 15 patients with active acromegaly, trying to find a possible correlation among GH responses to NPY, thyrotropin-releasing hormone (TRH;500 microg, i.v.), luteinizing hormone-releasing hormone (LHRH;100 microg, i.v.), and bromocriptine (Br;2.5 mg, per os). NPY significantly increased GH secretion (more than twice the basal level) in 4 (27%) patients, and all of them were responsive to LHRH and non-responsive to Br. In contrast, 3 (20%) acromegalics showed a significant decrease in GH levels (less than half the baseline) after NPY, and all these patients were responsive to both TRH and Br. From these results, we hypothesize that the NPY-induced increase in GH release may be a feature of somatotroph-like pituitary adenoma causing acromegaly, whereas the NPY-induced decrease in GH secretion may be a feature of lactotroph-like adenoma.

A suppressive effect of dexamethasone (DEX) on adrenocorticotropin (ACTH) response to vasoactive intestinal peptide (VIP) in Cushing's disease: a parallel modulation by DEX of ACTH responses to VIP and corticotropin-releasing hormone.

We have previously reported and confirmed that vasoactive intestinal peptide (VIP) is a significant stimulator of ACTH and cortisol secretion in at least some patients with Cushing's disease. We have also found that the hormonal responses to corticotropin-releasing hormone (CRH) in VIP-responsive patients with Cushing's disease were higher than those in VIP non-responders, which suggested a linkage between the actions of CRH and VIP in this disorder. Therefore, in the present study we examined whether this linkage also exists after glucocorticoid treatment by testing the effect of dexamethasone (DEX) pretreatment (1.0 mg, intravenous bolus, 60 min before) on ACTH and cortisol responses to CRH (100 microg, i.v. bolus) and VIP (100 microg, i.v. bolus) in 7 patients with Cushing's disease who were responsive to both neuropeptides while under no DEX pretreatment. The results were that in 5 patients, DEX was able to significantly suppress the ACTH and cortisol responses to both CRH and VIP, and in the remaining 2 patients, DEX did not significantly affect the action of either CRH or VIP. This study is the first to demonstrate the parallel inhibition by DEX of ACTH and cortisol responses to CRH and VIP in Cushing's disease. Although the possibility cannot be excluded that VIP may act on CRH receptors in corticotropinomas as a partial agonist, it seems more likely that specific receptors for CRH and VIP, respectively, may concurrently express in substantial quantity in those corticotropinomas that are responsive to both neuropeptides.