Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Actions on αT3-1 Gonadotrophs Show Desensitization

PACAP is a hypothalamic hypophysiotropic factor that acts upon a number of pituitary cells, including gonadotrophs. In the gonadotroph-derived αT3-1 cell line, PACAP acts via PVR1 receptors to stimulate adenylyl cyclase and phosphoinositidase C. PACAP-stimulated cAMP accumulation is inhibited by protein kinase C-activating phorbol esters in these cells and the current work was undertaken primarily to establish whether it is also subject to homologous regulation. In acute experiments, PACAP27-stimulated cAMP accumulation (intracellular plus extracellular) was measured (in the presence of phosphodiesterase inhibitor) both in intact cells and in cell membranes. The peptide increased cAMP accumulation, but initial rates of PACAP27-stimulated cAMP accumulation were reduced to between 10 and 50% within 10 min of stimulation in both cells and membranes. The initial rate of forskolin-stimulated cAMP accumulation was maintained in membranes but not in intact cells (although the deviation from linearity was less pronounced than with PACAP27). Thus, rapid homologous desensitization to PACAP27 occurs in intact αT3-1 cells, but is not entirely receptor specific. Rapid homologous desensitization of PACAP27-stimulated cAMP accumulation also occurred in the presence of a protein kinase C activating phorbol ester, which inhibited cAMP accumulation without altering the kinetics of the PACAP27 effect. Brief pre-treatment (3 min) with PACAP27 also reduced the ability of PACAP27, but not gonadotrophin-releasing hormone, to cause a spike-type elevation of cytosolic Ca²⁺ concentration (a consequence of phosphoinositidase C activation). In chronic desensitization studies, pre-treatment for 6 h with PACAP27 caused a dose-dependent (IC₅₀ approximately 10 nM) reduction of PACAP-stimulated cAMP accumulation and down regulated cell surface PVR1 receptors (to approximately 50%). Thus, it appears that PACAP27-stimulated (PVR-1 receptor mediated) adenylyl cyclase undergoes rapid homologous desensitization in αT3-1 cells, which is paralleled by homologous desensitization of PACAP27-stimulated phosphoinositidase C activity and involves mechanisms distinct from those underlying heterologous desensitization by phorbol esters. Chronic desensitization of PACAP-stimulated cAMP accumulation and down-regulation of cell surface PVR-1 receptors also occurs in these cells although the receptor loss may not entirely explain the observed desensitization.     

老年心功能不全血浆心钠素浓度的变化

采用放射免疫法测定31例老年心功能不全患者血浆心钠素(ANP)浓度,发现老年心功能不全组ANP明显低于对照组(P<0.01)。血浆ANP含量随心功能不全的严重程度而明显减少(P<0.05)。病程与ANP浓度呈负相关 (r=-0.441,P<0.05)。不同病种、不同受累部位及有或无房颤之间ANP差异无显著性(P<0.05)。     

血清TPS浓度在消化道肿瘤中价值的研究

共选择３０例消化道肿瘤病人，其中食管癌，胃癌，大肠癌各１０例，设健康献血者３０例，对两组血清特异型组织多肽抗原浓度进行了检测，结果肿瘤组血清ＴＰＳ浓度明显高于健康人。消化道肿瘤阳性检出经达７０％，其中食管癌８０％，胃癌６０％，大肠癌７０％。消化道肿瘤合并淋巴转移阳性检出率达７６．９％，其中食管癌１００％，胃癌６６．７％，大肠癌７０．０％。随着病程发展，血清ＴＰＳ浓度呈现升高趋势。     

POTASSIUM ACCELERATES URINARY SODIUM EXCRETION DURING SALT LOADING WITHOUT STIMULATING ATRIAL NATRIURETIC POLYPEPTIDE SECRETION

1. Effects of potassium (K) supplementation (100 mEq/day) on urinary sodium (Na) excretion and on the secretion of atrial natriuretic polypeptide (ANP) during salt loading (350 mEq/day) were studied in 12 healthy salt-resistant normotensives under strictly controlled metabolic ward conditions. 2. Urinary volume and Na excretion on the first day of the high salt period (HSP) were significantly greater in the K-supplemented group (KG) than in the control group (CG). 3. There was a significant gain in bodyweight after salt loading in both groups, with a significantly greater gain in CG on the second day of HSP. Haematocrit decreased significantly during salt loading in both groups, the degree of which was significantly greater in CG. 4. Plasma norepinephrine decreased significantly during salt loading in both groups, the degree of which was significantly less in KG than in CG. A significant increase in plasma ANP was observed in CG on and after the second day of HSP, while a significant increase in plasma ANP was observed on the fifth day of HSP in KG. 5. These findings indicate that K supplementation accelerates diuresis and natriuresis, resulting in moderate suppression of volume expansion induced by salt loading and that this accelerated diuresis and natriuresis is not a result of the action of ANP.     

心脏病患者血浆心钠素浓度初探

本文报道了采用放射免疫分析法检测的136例健康人和95例心脏病患者血浆心钠素含量的结果。健康人血浆心钠素含量为460．86±23．68ng／L，男女之间，年龄之间无明显差异。心脏病患者的血浆心钠素浓度均高于健康人，心脏病患者心功能越差，血浆心钠素浓度越高，其中以肺心病组变化最为明显。     

双功能域重组FN多肽抑制癌细胞浸润能力的研究

在制备了两个Cell Ⅰ-Hep Ⅱ 双结构域重组FN多肽(CH50和CH56)的基础上,研究其抑制肿瘤细胞浸润能力的作用。两个多肽的结构差异是CH50中删除了Cell I和HepⅡ之间的Ⅲ-11和ED-A结构顺序。CH50(ED_(50)为30.2 nmol/L)结合细胞的能力略高于CH56(ED_(50)为45.4 nmol/L)。两种多肽均可显著抑制黑色素瘤B16/F1细胞结合层粘素的能力,抑制作用相同。在体内肿瘤浸润抑制试验中,两种多肽均可显著抑制癌细胞浸润能力,使肺转移结节数降低80％左右。结果提示:Ⅲ-11和ED-A结构顺序对Cell Ⅰ-Hep Ⅱ 双结构域多肽结合细胞的能力有一定的影响,但删除Ⅲ-11和ED-A不是重组多肽抑制肿瘤转移的决定因素,Cell I和Hep Ⅱ 这两个结构域单独连接在一起是其抑制肿瘤细胞转移的结构基础。     

Similarities between the relaxations induced by vasoactive intestinal peptide and by stimulation of the non-adrenergic non-cholinergic neurons in the rat stomach

Summary The characteristics of the non-adrenergic, noncholinergic inhibitory response of the rat stomach fundus to transmural nerve stimulation were compared with the relaxation induced by vasoactive intestinal polypeptide (VIP). Treatment with -chymotrypsin (5 U/ml) or VIP antiserum (1:200) significantly reduced the relaxation induced by transmural nerve stimulation at 30 Hz, indicating that the possible transmitter in the non-adrenergic, non-cholinergic nerves is a peptide and may be VIP or a closely related peptide. VIP was able to relax, fully and dose-dependently, the stomach fundus that had previously been constricted by treatment with 10^–6 M serotonin, and the IC₅₀ value for VIP was 2.4 × 10^–9 M. VIP elevated levels of cyclic AMP in a dose-dependent manner and the EC₅₀ value was 2.8 × 10^–9 M in the presence of 10^–6 M atropine and 10^–6 M guanethidine. The stomach fundus was relaxed by transmural nerve stimulation (30 Hz, 50 mA) and transmural nerve stimulation also caused production of cyclic AMP in the rat stomach in the presence of atropine and guanethidine. The basal level of cyclic AMP in the stomach was 8.7 ± 0.26 pmole/mg protein. When transmural nerve stimulation was applied for 5 min, the contraction of the stomach, induced by 10^–6 M serotonin, was inhibited by 54% in the presence of atropine and guanethidine and the level of cyclic AMP was increased to 13.0 ± 0.73 pmol/mg protein. Apamin inhibited the transmural nerve stimulation-induced relaxation and shifted the dose-response curve for VIP to the right. These results suggest that one of the putative neurotransmitter from non-adrenergic, non-cholinergic nerves in the rat stomach is VIP and that VIP-induced relaxation may be mediated by the production of cyclic AMP and by the opening of apamin-sensitive K⁺-channels.Send offprint requests to K. Kamata at the above address     

Human isolated small intestine: motor responses of the longitudinal muscle to field stimulation and exogenous neuropeptides

Summary (1) Longitudinal muscle strips from the human small intestine (jejunum/ileum) responded to electrical field stimulation (1–50 Hz) with frequency-related primary contractions which were largely atropine- (3 M) sensitive. When the tone was raised by addition of galanin (0.3 – 1 M), prostaglandin (PG) E₂ (1–10 M) or neurokinin A (NKA, 0.1 M), a frequency-related relaxation was evident which was potentiated by atropine. All the responses to field stimulation were abolished by tetrodotoxin (1 M), thus indicating their neural origin. (2) The atropine-sensitive primary contraction to field stimulation was virtually abolished by omega conotoxin fraction GVIA (CTX, 0.1–0.3 M) while the relaxations were CTX-resistant. The field stimulation-induced relaxations, which were observed in the presence of atropine and guanethidine (3 M), were also unaffected by apamin (0.1 M). (3) NKA and substance P (SP) produced a concentration- (1 nM–1 M for both peptides) related contraction, NKA being about 53 times more potent than SP. [Pro⁹]SP sulphone and [MePhe⁷]-NKB, selective agonists of the NK-1 and NK-3 receptor, respectively, were barely effective. On the other hand, [\Ala⁸]NKA(4–10), a selective NK-2 receptor agonist, had a potent contractile activity, similar to that of NKA. (4) Galanin (1 nM–1M) produced an atropine- and tetrodotoxin-resistant concentration-related contraction of longitudinal muscle of human isolated small intestine. The response to galanin did not show any sign of fading and was particularly suitable to study the evoked relaxations. (5) Calcitonin gene-related peptide (CGRP) (10–100 nM) consistently inhibited the nerve-mediated contractions of strips from the ileum while the effect on the jejunum was less pronounced. Vasoactive intestinal polypeptide (VIP, 0.1–1 M) inhibited nerve-mediated contractions both in the ileum and the jejunum. (6) These experiments indicate that both cholinergic excitatory and non-adrenergic non-cholinergic nerves affect motility of the longitudinal muscle of the human small intestine. Furthermore, several neuropeptides produce potent motor effects, the contractile response to tachykinins being apparently mediated by activation of NK-2 receptors.