Targeted overexpression of galanin in lactotrophs of transgenic mice induces hyperprolactinemia and pituitary hyperplasia.

We generated transgenic mice that carry 4.6 kb of the mouse galanin gene fused to 2.5 kb of the rat PRL promoter. In all transgenic lines that carried and transmitted the transgene, there were significant increases in galanin messenger RNA and peptide levels in the anterior pituitary in both male and female transgenic mice, and the elevation of galanin was restricted to the anterior lobe. Furthermore, galanin release from pituitary cells in vitro of both male and female transgenic mice was dramatically increased compared with that in control mice. At 2-4 months of age, pituitary PRL contents in female transgenic mice were increased compared with those in normal controls. Moreover, PRL messenger RNA levels were increased in female transgenic mice. However, plasma levels of PRL in female transgenic mice were not significantly higher until 6 months of age. By 11 months of age, cell numbers in the anterior pituitary were increased in female, but not male, transgenic mice. The percentage of lactotrophs in female transgenic mice as well as PRL gene expression per cell were significantly higher. No differences were detected in PRL content, gene expression, or release between normal and transgenic male mice. Six weeks of estrogen treatment significantly increased anterior pituitary weights and PRL secretion in male transgenic mice compared with that in normal male mice. In addition, anterior pituitary weights and PRL secretion were decreased in female transgenic mice compared with controls 6 weeks after ovariectomy. We conclude that overexpression of galanin in lactotrophs stimulates PRL synthesis and secretion and acts as a growth factor resulting in the formation of pituitary hyperplasia and hyperprolactinemia. Furthermore, estrogen appears critical for these galanin-mediated events.     

Structure-activity relationship of pituitary adenylate cyclase activating polypeptide

AIM: To investigate the structure-activity relationship of pituitary adenylate cyclase activating polypeptide (PACAP) in guinea pig gallbladder using a synthetic PACAP/vasoactive intestinal peptide (VIP) hybrid. METHODS: We synthesized PACAP-VIP hybrid peptides using the Fmoc strategy and a simultaneous multiple solid-phase peptide synthesizer. The peptides were tested in isolated guinea pig gallbladders using an improved horizontal type organ bath. RESULTS: VIP induced relaxation of gallbladder smooth muscle strips, while PACAP27 contracted them. Amino acids at positions 4, 5, 9, and 24-26 were replaced without significant loss of activity. [Leu¹³]-PACAP27, a substitution in the α-helix domain, also had no significant loss in activity (P < 0.05). It was more potent than [Gly⁸]- and [DAsp⁸]-PACAP27 and could substitute peptides at position 21. Des-[His¹] and [Ala⁶]-PACAP27 had no activity at 10^-7 mol/L. [Gly⁸]-, [DAsp⁸]-, [Phe²¹]- and [Pro²¹]-PACAP27 at 10^-7 mol/L had about 25% of the activity of PACAP27 at 10^-7 mol/L (P < 0.05). CONCLUSION: The N-terminal disordered region is more important than other regions for determining the physiological activity of PACAP in the guinea pig gallbladder.     

Hypothalamic, pituitary and testicular function during sexual maturation of the male rat.

Hypothalamic content of gonadotrophin-releasing hormone (GnRH), serum LH and FSH, capacity of the testis to synthesize testosterone in vitro, and testicular 5-ene-3 beta-hydroxysteroid dehydrogenase-isomerase and 17 beta-hydroxysteroid dehydrogenase were measured in groups of rats at approximately 5 day intervals from birth to day 64 and at days 74 and 89. The capacity of the testes to synthesize testosterone in vitro was measured in the presence of a saturating dose of rat LH. Gonadotrophin-releasing hormone increased steadily from 0-17 ng per hypothalamus at birth to a maximum of 7 ng at day 52 and then remained constant. LH concentrations were highly variable and often exceeded adult values between days 10 and 32. After day 32 a steady rise was observed which reached adult values between days 37 and 42. FSH concentrations markedly increased from 255 ng/ml observed at birth and day 10 to a peak value of 1000 ng/ml at day 32. Subsequently there was a steady decline in FSH values until day 74 when the concentration returned to values found at birth. 5-ene-3 beta-Hydroxysteroid dehydrogenase-isomerase activity exhibited a rapid increase between days 12 and 19 followed by an even greater rate of increase between days 19 and 32 when adult levels were attained. 17 beta-Hydroxysteroid dehydrogenase activity was very low between birth and day 22. Enzyme activity began to increase at day 22 with a rapid increase in activity observed between days 37 and 58. The increase in capacity to synthesize testosterone closely followed the increase in 17 beta-hydroxysteroid dehydrogenase activity. The study demonstrates that during sexual maturation in the male rat, changes in serum LH and FSH do not reflect changes in hypothalamic GnRH. The appearance of Leydig cells as monitored by 5-ene-3 beta-hydroxysteroid dehydrogenase-isomerase activity precedes by approximately 20 days the increase in testicular capacity to synthesize testosterone in vitro. The latter coincides with the increase in 17 beta-hydroxysteroid dehydrogenase activity. These results suggest that 17 beta-hydroxysteroid dehydrogenase is a limiting factor in the ability of the testis to respond to LH stimulation.     

Stimulatory effect of pituitary adenylate-cyclase activating polypeptide (PACAP) and its PACAP type I receptor (PAC1R) on prolactin synthesis in rat pituitary somatolactotroph GH3 cells

In this present study, we investigated the role of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptor, PACAP type I receptor (PAC1R) on prolactin synthesis in pituitary somatolactotroph GH3 cells. PACAP increased prolactin promoter activity up to 1.3 ± 0.1-fold. This increase, while significant, was less than the increase resulting from thyrotropin-releasing hormone (TRH) stimulation. By transfection of a PAC1R expression vector to the cells, the response to PACAP on prolactin promoter activity was dramatically potentiated to a degree proportional to the amount of PAC1R transfected. In the PAC1R expressing GH3 cells, TRH and PACAP alone increased prolactin promoter up to 3.3 ± 0.3-fold and 4.9 ± 0.2-fold, respectively, and combined treatment with TRH and PACAP further increased prolactin promoters up to 6.8 ± 0.6-fold. PACAP binds both Gs- and Gq-coupled receptors and stimulates adenylate cyclase/cAMP and protein kinase C/extracellular signal-regulated kinase (ERK) signaling pathways. PACAP increased ERK phosphorylation in PAC1R expressing cells to the same degree as TRH. Combined treatment with TRH and PACAP had a synergistic effect on ERK activation. GH3 cells produce both prolactin and growth hormone. Stimulation of GH3 cells with TRH significantly increased the mRNA level of prolactin and attenuated growth hormone mRNA expression. PACAP increased both prolactin and growth hormone mRNA levels, particularly in PAC1R expressing cells. In addition, increasing amount of PAC1R in GH3 cells potentiated the action of TRH on prolactin promoter activity, as well as on ERK phosphorylation. PAC1R was induced by PACAP itself, but not by TRH. Our current study demonstrates that PACAP and its PAC1R, functions as a stimulator of prolactin alone or with TRH in prolactin producing cells.     

Microheterogeneity of anterior pituitary FSH in the male rat: isoelectric focusing pattern throughout sexual maturation

Anterior pituitary glands were removed from male rats at 5, 10, 15, 18, 21, 28, 30, 40, 50 and 90 days of age, and the multiple forms of FSH present within them were separated by polyacrylamide gel-isoelectric focusing (PAGE-IEF; pH range 3.0-8.0). Gel eluents were analysed for FSH content by radioimmunoassay (RIA) and a specific radioreceptor assay (RRA). All pituitaries studied exhibited one or more peaks of immunoactive FSH within a pH range of 7.0-3.0; the major peak exhibited an isoelectric point (pI) of 4.9-4.0. Between 25 and 56% of anterior pituitary FSH obtained from rats 5-30 days old focused within a pH range of 4.9-4.5, whilst in older animals (greater than or equal to 40 days) this pH range contained 17-27% of the total FSH recovered. In contrast, in animals 40-90 days old, the greatest proportion of immunoactive FSH (42-62% of the total immunoactivity recovered) focused within a pH range of 4.4-4.0; further, only these groups of animals exhibited a significant proportion of anterior pituitary FSH with a pI less than or equal to 3.9. Between 14 and 21% of total FSH from 5- to 30-day-old rats focused within a pH range of 5.4-5.0, whereas in older animals this pH range contained 6-9% of the total FSH recovered. These shifts in FSH pI occurred at the time of appearance of spermiogenesis, at 45 days of age. Although the ratio of the concentration of FSH measured by RRA to that measured by RIA declined as the pI of the anterior pituitary FSH decreased throughout a pH range of 7.0-4.0, the most acidic FSH molecules (pI less than 4.0) showed an abrupt increase in that ratio. These results demonstrate that the transition from sexual immaturity to adulthood is accompanied by qualitative changes of intracellular pituitary FSH. They contrast with previous findings in female rats in which a shift to less acidic anterior pituitary FSH forms was detected at the time of vaginal opening, thus indicating the existence of a sexual dichotomy in terms of the action of gonadal steroids on the type of FSH molecule synthesized by the anterior pituitary gland.     

Postnatal maturation of gonadotropes in the male rat pituitary

The postnatal maturation of gonadotropes was studied with the use of electron microscopic-immunocytochemical strains for the beta-chains of LH and FSH on serially sectioned fields. A third serially sectioned field was stained with antiserum to ACTH-(17-39). Morphometric studies on semithin and ultrathin plastic sections stained for LH and FSH showed a 200-300% increase in the percentages of LH and FSH cells during the first week of postnatal life. In the 1- to 2-week-old rats, the percentage of gonadotropes in the population was greater than that in the adult. Analysis of the hormone content of serially sectioned gonadotropes showed that storage patterns similar to those in the adult were reached by the seventh day of life. In the neonatal group, 66% of the serially sectioned cells contained both FSH and LH, 20% contained only LH, and 14% contained only FSH. In the 7- to 15-day-old rats, the percentages of gonadotropes containing both hormones increased to 79% while 10-11% of the cells contained only LH or FSH. This is similar to the findings in the adult rat population (75% LH and FSH cells, 14.2% LH cells, and 11% FSH cells). The fields stained for ACTH showed that 35-80% of the gonadotropes contained ACTH-like immunoreactivity during neonatal development, with the highest values seen in the 7- to 15-day-old rats. In the normal adult rats, 2-10% of the gonadotropes contain ACTH activity. Cells containing only ACTH were also seen in all age groups examined. The morphological analysis showed that immature gonadotropic cells contained scattered storage granules, arranged either at the cell periphery or concentrated near the nucleus. They were small, irregularly shaped, and often exhibited a high nucleo-cytoplasmic ratio. They were difficult to distinguish from corticotropes. More mature cell types were found after 1 week of age. These were ovoid and contained numerous large and small granules, features similar to the adult type I cell. The granules, however, were more irregularly shaped (pleomorphic). Immature forms were observed in the gonadotrope population as late as 15 days of age. Most gonadotropes from the 20- to 25-day-old rats resembled those in the adult population. Our findings support the physiological studies which show that the first week of life is an important time for functional and morphological maturation of the gonadotrope population. They also support the finding that immature gonadotropes are larger, more numerous, and more heterogeneous than those in the adult male rat population. Finally, we propose that a subpopulation of gonadotropes may serve as a stem cell or may be involved in the development of adrenal-gonadal interactions.     

Comparative distribution of immunoreactive pituitary adenylate cyclase activating polypeptide and vasoactive intestinal polypeptide in rat forebrain.

Pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are structurally similar, share the same high affinity site in same peripheral tissues and increase the intracellular content of adenylate cyclase. To establish which neural circuits are signaling with each of these two peptides, we systematically compared the immunohistochemical distribution of PACAP and VIP in selected rat forebrain regions using previously characterized antiserum. The PACAP antiserum recognized both PACAP27 and PACAP38, and PACAP immunoreactivity was unaffected by preincubation with various other peptides. PACAP-immunoreactive perikarya and fibers were observed in both hypothalamic and extrahypothalamic regions. In the hypothalamus PACAP perikarya were located in the supraoptic, paraventricular, anterior commissural, periventricular, and perifornical nuclei. In intact rats PACAP immunolabeled fibers were present in the internal zone of the median eminence and posterior pituitary. One week after hypophysectomy the intensity of staining in the internal zone was enhanced and immunoreactive fibers appeared in the external zone of the median eminence. Two or 3 weeks later a dense fiber network was observed around the portal capillaries in the external zone, and immunoreactive material further accumulated in the fibers of the internal zone. PACAP-immunoreactive perikarya and fibers were also observed in several extrahypothalamic regions including central thalamic nuclei, amygdaloid complex, bed nucleus of stria terminalis, septum, hippocampus and cingulate, and entorhinal cortices. In the lateral septum and entorhinal cortex PACAP fibers surrounded unstained neuronal cell bodies and small blood vessels. In intact rats, VIP-immunoreactive perikarya were present in all regions of the cerebral cortex, hippocampus, amygdaloid complexus and in the suprachiasmatic nucleus, but not in the paraventricular and supraoptic nuclei. In colchicine-treated rats the VIP perikarya appeared in the preoptic area and paraventricular nucleus. The fibers were organized in two main pathways: the stria terminalis and an ascending pathway from the suprachiasmatic nucleus to the paraventricular area. Hypophysectomy induced the appearance of VIP-immunoreactive fibers in the internal zone of the median eminence and perikarya in the supraoptic and paraventricular nuclei in addition to the suprachiasmatic nucleus. The dissimilar distributions of PACAP and VIP suggest that PACAP neural circuits are independent of that of VIP in the rat forebrain. These findings support possible multifunctional roles for PACAP as a posterior pituitary hormone, a hypophysiotrophic factor, and a neurotransmitter/neuromodulator.     

Temperature-sensitive phenotype in mice lacking pituitary adenylate cyclase-activating polypeptide

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved hormone. Targeted disruption of the PACAP gene has revealed a role for this peptide in lipid metabolism, carbohydrate metabolism, and the sympathetic response to insulin stress. We report here that PACAP null mice are temperature sensitive. When raised at 21 C, only 11% of the PACAP null mice survived past the first 2 wk after birth, but when raised at 24 C, most (76%) of the PACAP null mice survived. The question is the mechanism by which the absence of PACAP affects thermoregulation. Brown adipose tissue is the major site of adaptive thermogenesis in neonates and rodents. We show that PACAP null mice have brown adipocytes that differentiate normally and express two enzymes involved in thermogenesis, hormone-sensitive lipase and uncoupling protein 1. Likewise, levels of catecholamines in the adrenal medulla and plasma are normal in PACAP null mice raised at a lower temperature. In contrast, norepinephrine and its precursor dopamine extracted from brown adipose tissue are present at significantly lower levels in the PACAP null mice compared with controls. Also, PACAP null mice showed a greater loss of core body temperature compared with wild-type controls at 21 C. We conclude that under prolonged but mild cold stress, lack of PACAP results in inadequate heat production due to insufficient norepinephrine stimulation of brown adipose tissue.     

Feeding and metabolism in mice lacking pituitary adenylate cyclase-activating polypeptide

Disruption of the pituitary adenylate cyclase-activating polypeptide (PACAP) gene in mice has demonstrated a role for this highly conserved neuropeptide in the regulation of metabolism and temperature control. Localization of PACAP neurons within hypothalamic nuclei that regulate appetite suggest PACAP may affect feeding and thus energy balance. We used PACAP-null mice to address this question, examining both food intake and energy expenditure. PACAP-null mice were leaner than wild-type littermates due to decreased adiposity and displayed increased insulin sensitivity. The lean phenotype in the PACAP-null mice was completely eliminated if animals were fed a high-fat diet or housed near thermoneutrality (28 C). Further metabolic analyses of PACAP-null mice housed at 21 C indicated that the reduced body weight could not be explained by decreased food intake, increased metabolic rate, or increased locomotor activity. The thyroid hormone axis of PACAP-null mice was affected, because mRNA levels of hypothalamic TRH and brown adipose tissue type 2 deiodinase were reduced in PACAP-null mice housed at room temperature, and brain deiodinase activity was lower in PACAP-null mice after an acute cold challenge compared with wild-type controls. These results demonstrate that PACAP is not required for the regulation of food intake yet is necessary to maintain normal energy homeostasis, likely playing a role in central cold-sensing mechanisms.     

Effect of sexual maturation and androgens on prostaglandin levels in tissues of the male reproductive system in mice.

Prostaglandins E and F were measured in the testis, epididymis, vas deferens, and seminal vesicles of CD-1 mice from 2 to 8 weeks of age. The concentration of PGF was higher than that of PGE in all organs studied, except for the vas deferens. The concentration of prostaglandins (PGs) was age-dependent, showing a progressive decline from immaturity to adulthood. However, in the testis, there was an apparent transient increase in the concentration of PGs in the seminal vesicle changed very little between the ages of 5 and 8 weeks. The vas deferens had a significantly higher PG concentration than any of the organs studied, and a unique pattern of changes in the levels of PGE and PGF with age. In the vas deferens of two- and three-week-old mice, the concentration of PGF was higher than the concentration of PGE, but after 4 weeks of age PGE became somewhat more abundant than PGF. Treatment of immature mice with testosterone propionate (TP) produced significant changes in PG concentrations, resulting in PG levels resembling those of adult animals. The treatment also changed the ratio of PGE to PGF in the vas deferens (from 1:2 to 1:1). Hereditary dwarf mice had higher levels of PGs in the tissues of the male reproductive system than did their normal littermates. The treatment of dwarf mice with TP generally reduced the concentration of PGs in their reproductive system and resulted in a PG pattern more characteristic of normal adult males of the same strain. The data demonstrate pronounced changes in PG levels in the tissues of the male reporductive system of mice during sexual maturation. From the present study and from previous findings, it can be concluded that these changes can be accounted for by an increase in testicular testosterone secretion.     

Hypogonadism alters cecal and fecal microbiota in male mice

Low testosterone levels increase the risk for cardiovascular disease in men and lead to shorter life spans. Our recent study showed that androgen deprivation via castration altered fecal microbiota and exacerbated risk factors for cardiovascular disease, including obesity, impaired fasting glucose, excess hepatic triglyceride accumulation, and thigh muscle weight loss only in high-fat diet (HFD)-fed male mice. However, when mice were administered antibiotics that disrupted the gut microbiota, castration did not increase cardiovascular risks or decrease the ratio of dried feces to food intake. Here, we show that changes in cecal microbiota (e.g., an increased Firmicutes/Bacteroidetes ratio and number of Lactobacillus species) were consistent with changes in feces and that there was a decreased cecal content secondary to castration in HFD mice. Castration increased rectal body temperature and plasma adiponectin, irrespective of diet. Changes in the gut microbiome may provide novel insight into hypogonadism-induced cardiovascular diseases.     

Protective effects of pituitary adenylate cyclase activating polypeptide in endothelial cells against oxidative stress-induced apoptosis

Pituitary adenylate cyclase activating polypeptide (PACAP) is a widely distributed neuropeptide that has various different functions in the nervous system and in non-neural tissues. Little is known about the effects of PACAP in endothelial cells. The aim of the present study was to investigate the effects of PACAP on endothelial cell survival and apoptotic signaling pathways under oxidative stress. Mouse hemangioendothelioma (EOMA) cells were exposed to 0.5mM H(2)O(2) which resulted in a marked reduction of cell viability and a parallel increase of apoptotic cells assessed by MTT test and flow cytometry. Co-incubation with 20nM PACAP1-38 increased cell viability and reduced the percentage of apoptotic cells. Flow cytometry analysis showed that oxidative stress reduced the phosphorylation of the anti-apoptotic ERK and increased the phosphorylation of the pro-apoptotic JNK and p38 MAP kinases. PACAP1-38 treatment ameliorated these changes: levels of phospho-ERK were elevated and those of phospho-JNK and p38 were decreased. All these effects were abolished by simultaneous treatment with the PACAP antagonist PACAP6-38. In summary, our results show that PACAP effectively protects endothelial cells against the apoptosis-inducing effects of oxidative stress.     

Targeted overexpression of parathyroid hormone-related protein (PTHrP) to vascular smooth muscle in transgenic mice lowers blood pressure and alters vascular contractility

PTH-related protein (PTHrP) and its receptor are expressed in vascular smooth muscle cells and are believed to participate in the local regulation of vascular tone. To explore the function of locally produced PTHrP in vascular smooth muscle in vivo, we developed transgenic mice that overexpress PTHrP in smooth muscle using a smooth muscle alpha-actin promoter to direct expression of the transgene. In the PTHrP-overexpressing mice, messenger RNA expression was mainly restricted to smooth muscle-containing tissues. Several founders also expressed the transgene in bone and heart and exhibited striking abnormalities in the development of these tissues. In PTHrP-overexpressing mice, blood pressure was significantly lower than that in wild-type controls (121 +/- 3 vs. 135 +/- 2 mm Hg; P < 0.01). Moreover, the magnitude of the vasorelaxant response to iv infusions of PTHrP-(1-34)NH2 was significantly attenuated in the transgenic animals. A similar desensitization to PTHrP was observed in aortic ring and portal vein preparations. Surprisingly, PTHrP-overexpressing mice were also significantly less responsive to the hypotensive action of infused acetylcholine in vivo and to the relaxant actions of acetylcholine on aortic vessel preparations in vitro. In summary, we have successfully targeted overexpression of PTHrP to the smooth muscle of transgenic mice. When expressed in its normal autocrine/paracrine setting, PTHrP lowers systemic blood pressure and decreases vascular responsiveness to further relaxation by PTHrP and other endothelium-dependent vasorelaxants such as acetylcholine. We postulate that the heterologous desensitization to acetylcholine-induced relaxation in PTHrP-overexpressing blood vessels involves desensitization of second messenger/effector signaling pathways common to PTHrP and acetylcholine.     

Gonadal regulation of pituitary gonadotropin-releasing hormone receptors during sexual maturation in the rat

The number of pituitary GnRH receptors increases during sexual maturation in rats. In females, GnRH receptor content (GnRH-RC, femtomoles bound per gland) rises to a plateau (50 +/- 9 fmol) between 15-30 days of age before increasing further to 107 +/- 19 at 50 days. In males, GnRH-RC rises gradually to 140 +/- 9 fmol at 35 days, then remains stable through 60 days. Administration of estradiol or testosterone to immature females and males, respectively, inhibits the early rise in GnRH-RC. GnRH given for 2 days to steroid-treated immature animals restores receptor content to control levels. Neonatal castration in both sexes rapidly increases GnRH-RC and this response is maintained through 60 days of age. Castrations performed at different ages between 5-60 days showed a sex difference in GnRH-RC responses. Females exhibited a 2-fold increase in GnRH-RC by 5 days post castration at all ages studied. In males a similar increase in GnRH-RC was seen up to 25 days, but later diminished and no receptor response occurred when castration was performed between 30-45 days of age. Orchidectomy after 50 days again resulted in a 2-fold rise in GnRH-RC. GnRH injections (20 micrograms/day in divided doses) increased GnRH-RC in intact males at all ages studied. The same dosage did not increase GnRH receptors in 35-45 day male castrates and 5- to 10-fold higher doses were required to increase GnRH-RC indicating reduced receptor responsiveness to GnRH. Serum gonadotropins increased in response to castration at all ages in both sexes and did not parallel receptor responses in males. These data indicate that pituitary GnRH receptors are modulated by gonadal steroids from day 10 of life in both sexes and that the mechanism involves modification of hypothalamic GnRH secretion. Additionally, factor(s) other than gonadal steroids are operative in males during maturation which alter pituitary receptor responses to GnRH and result in discordant receptor and gonadotropin responses to GnRH.     

A novel role for endogenous pituitary adenylate cyclase activating polypeptide in the magnocellular neuroendocrine system

Central release of vasopressin (VP) by the magnocellular neuroendocrine cells (MNCs) responsible for systemic VP release is believed to be important in modulating the activity of these neurons during dehydration. Central VP release from MNC somata and dendrites is stimulated by both dehydration and pituitary adenylate cyclase activating polypeptide (PACAP). Although PACAP is expressed in MNCs, its potential role in the magnocellular response to dehydration is unexplored. The current study demonstrates that prolonged dehydration increases immunoreactivity for PACAP-27, PACAP-38, and the type I PACAP receptor in the supraoptic nucleus (SON) of the rat. In addition, PACAP stimulates local VP release in the euhydrated rat SON in vitro, and this effect is reduced by the PACAP receptor antagonist PAC(6-27) (100 nm), suggesting the participation of PACAP receptors. Concomitant with its effects on local VP release, PACAP also reduces basal glutamate and aspartate release in the euhydrated rat SON. Furthermore, somatodendritic VP release elicited by acute dehydration is blocked by PAC(6-27), suggesting that endogenous PACAP participates in this response. Consistent with this, RIA revealed that local PACAP-38 release within the SON is significantly elevated during acute dehydration. These results suggest that prolonged activation of hypothalamic MNCs is accompanied by up-regulation of PACAP and the type I PACAP receptor in these cells and that somatodendritic VP release in response to acute dehydration is mediated by activation of PACAP receptors by endogenous PACAP released within the SON. A potential role for PACAP in promoting efficient, but not exhaustive, systemic release of VP from MNCs during physiological challenge is discussed.     

动脉粥样硬化形成过程中内皮功能的变化及垂体腺苷酸环化酶激活肽的干预作用

目的动态、系统地观察家兔实验性动脉粥样硬化(AS)进程中内皮功能的变化及垂体腺苷酸环化酶激活肽(PACAP)的干预作用。方法新西兰雄性家兔60只,随机等分为两组AS模型组(AS组)及PACAP干预组(干预组)。分别于实验的第0、2、4、8、12周末测定血脂、血清一氧化氮(NO)含量及一氧化氮合酶(NOS)活性,同时处死每组兔5～6只,取其胸主动脉做形态学观察。结果①AS组4周末时内皮细胞(EC)出现脱落;4周末后NO及cNOS活性有所增高,最终两者呈总体下降的趋势;iNOS活性8周末前持续上升,其后下降。②干预组EC形态改变出现较晚;12周末时NO含量及4周末时cNOS活性、2周末时iNOS活性均高于AS组(P<0.05)。结论AS进程中NO水平及NOS活性是一个不断变化的动态过程,PACAP可通过提高NOS活性等途径增加血清NO含量,保护EC,这可能是PACAP抗AS的重要机制之一。