Generation and amplification of the cytosolic calcium signal during secretory responses to gonadotropin-releasing hormone

Gonadotropin-releasing hormone (GnRH) stimulates characteristic biphasic increases in cytosolic calcium concentration ([Ca2+]i) and in luteinizing hormone (LH) release in cultured gonadotrophs, with an early peak followed by a prolonged plateau in both responses. Analysis of [Ca2+]i by dual-wavelength fluorimetric assay and of LH release at 5-sec intervals in perifused pituitary cells revealed increases in both responses within a few seconds of exposure to GnRH. The maximum elevation of [Ca2+]i occurred within 20 sec, and the peak gonadotropin release in 35 sec; the total duration of the spike phase for both [Ca2+]i and LH release was 2.5 min. Under extracellular Ca2(+)-deficient conditions, the GnRH-induced peak in [Ca2+]i was reduced by about 20% and the plateau phase was abolished. Concomitantly, the magnitude of the acute phase of LH release was reduced by 40% and that of the second phase by about 90%. Recovery of the plateau phase of LH release occurred within 25 sec after addition of 1.25 mM Ca2+ to Ca2(+)-deficient medium. In a dose-dependent manner, the non-selective Ca2+ channel blockers Co2+ and Cd2+ reduced the Ca2+ current measured by whole-cell recording in pituitary gonadotrophs and abolished the extracellular Ca2(+)-dependent component of LH release. The selective calcium channel blocker, nifedipine, decreased the magnitude of the Ca2+ current and reduced the plateau phase of LH release by 50%; conversely, the dihydropyridine agonist methyl, 1,4,dihydro-2,6-dimethyl 3-nitro-4-(2-trifluorome) (Bay K 8644) consistently enhanced the amplitudes of both Ca2+ current and GnRH-induced LH release. These data reveal a close temporal correlation between changes in [Ca2+]i and LH release during GnRH action, with Ca2+ mobilization during the spike phase and Ca2+ influx through dihydropyridine-sensitive and insensitive sets of receptor-operated calcium channels during the spike and plateau phases. In addition, analysis of the magnitudes of the [Ca2+]i and LH responses to a wide range of GnRH concentrations in the presence and absence of extracellular Ca2+ is consistent with amplification of the [Ca2+]i signal in agonist-stimulated gonadotrops.

Novel gelatin particle agglutination test for serodiagnosis of leprosy in the field

We developed a novel gelatin particle agglutination test (MLPA) for the serodiagnosis of leprosy; this test is especially useful for clinical practice and epidemiological surveys of leprosy in countries in which the disease is endemic. The antigen used in the test is the chemically synthesized trisaccharide moiety of Mycobacterium leprae-specific phenolic glycolipid I. MLPA is a simple and easy technique having sensitivity and specificity comparable to those of the conventional indirect enzyme-linked immunosorbent assay. The new technique was found to be useful for monitoring of chemotherapy and predictive diagnosis of high-risk individuals in contact with persons with leprosy and may be useful for the prediction of relapse. We are now preparing to supply a quality-controlled ready-to-use MLPA kit for leprosy control in countries in which leprosy is endemic.

Cisplatin, adriamycin and ifosfamide-based combination chemotherapy for gynecological cancers derived from the extended müllerian system

Their histogenetic similarity suggests that a group of malignant tumors may have a common sensitivity to a cytotoxic chemotherapy. Seventy patients with a variety of gynecological cancers arising from the uterine cervix, endometrium, ovary and pelvic peritoneum were treated with a combination of cisplatin, adriamycin and ifosfamide (PAI). As schedule modifications, PAI plus bleomycin for cancers containing squamous components and PAI plus etoposide for nonepithelial malignancies were recommended. In twenty-five evaluable cases, including 12 recurrent tumors after previous radiation therapy or PAC (cisplatin, adriamycin and cyclophosphamide) chemotherapy, the total response rate was 95% for epithelial cancers (vaginal cancer: 1/1, cervical: 9/10, endometrial: 2/2, ovarian: 6/6 and peritoneal: 2/2), and 100% for nonepithelial malignancies including one uterine leiomyosarcoma, one uterine mixed Müllerian tumor and one extragonadal mixed Müllerian tumor. The survival rates of patients with non measurable lesion were 100% for cervical cancer (the observation period: 65-879 days), 92.9% for endometrial cancer (96-975 days) and 88.9% for ovarian cancer (148-976 days). The hematological toxicity of this treatment was severe but acceptable. The results obtained indicate that a wide range of gynecological cancers originating in the primary and secondary Müllerian tissues (extended Müllerian system) must have a similar sensitivity to cytotoxic treatment with a PAI-based combination chemotherapy.

Clinical significance of the number of positive tumor markers in assisting the diagnosis of lung cancer with multiple tumor marker assay

The clinical significance of multiple tumor marker assay in assisting the diagnosis of lung cancer was assessed in 67 patients with primary lung cancer, and 115 with nonmalignant pulmonary disease. The tumor markers studied were carbohydrate antigen 19-9 (CA19-9), carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), squamous cell carcinoma-related antigen (SCC), and tissue polypeptide antigen (TPA). The positive rates for all of the tumor markers were significantly higher in the lung cancer group than in the nonmalignant pulmonary disease group. The sensitivity was 31-66%, the specificity was more than 90% for all five markers, and the accuracy was 69-82%. Among the markers, the positive rate of CEA was best correlated with adenocarcinoma (Ad), NSE with small cell carcinoma (Sm), SCC with squamous cell carcinoma (Sq), CA19-9 with Ad, and TPA with Ad. In multiple tumor marker assay, as the number of combined markers was increased, the sensitivity of the assay became higher and the specificity became lower, resulting in a lower accuracy. However, when more than two markers were positive, the relative possibility of lung cancer was increased 90-100%. The number of positive tumor markers in multiple tumor marker assay indicated that it would be of auxiliary value for the diagnosis of lung cancer.

Calcium mobilization and influx during the biphasic cytosolic calcium and secretory responses in agonist-stimulated pituitary gonadotrophs

Stimulation of enriched pituitary gonadotrophs by gonadotropin-releasing hormone (GnRH) elicits dose-dependent biphasic elevations of cytosolic calcium ([Ca2+]i) and luteinizing hormone (LH) release, with rapid initial peaks followed by sustained plateaus during continued exposure to the agonist. A potent GnRH-antagonist, [N-acetyl-D-p-Cl-Phe1,2,D-Trp3,D-Lys6,D-Ala10]GnRH, prevented the biphasic [Ca2+]i and LH responses when added before GnRH, and rapidly abolished both responses to GnRH when added during the plateau phase. In low Ca2+ medium the LH peak responses to GnRH were reduced and the subsequent sustained responses were almost completely abolished; reduction of extracellular Ca2+ during exposure to GnRH caused a prompt decline of LH release. The initial [Ca2+]i peak is derived largely from intracellular calcium mobilization with a partial contribution from calcium influx, while the sustained phase is dependent on the entry of extracellular Ca2+ through both L-type and dihydropyridine-insensitive channels. The presence of L-type voltage-sensitive calcium channels (VSCC) in pituitary gonadotrophs was indicated by the ability of elevated extracellular [K+] to stimulate calcium influx and LH release, and the sensitivity of these responses to dihydropyridine agonist and antagonist analogs. In cells pretreated with high [K+], the peak [Ca2+]i response to GnRH was enhanced but the subsequent plateau phase was markedly attenuated. This divergent effect of sustained membrane depolarization on the biphasic [Ca2+]i response suggests that calcium entry through VSCC initially potentiates agonist-induced mobilization of Ca2+ from intracellular storage sites. However, established Ca2+ entry through depolarization-activated VSCC cannot be further increased by agonist stimulation because both processes operate through the same channels, probably by changes in their activation-inactivation kinetics. Finally, the reciprocal potentiation by the dihydropyridine agonist, BK 8644, and GnRH of [Ca2+]i and LH responses confirms that both compounds act on the same type of channels, i.e., L-type VSCC, that participate in agonist-mediated calcium influx and gonadotropin secretion.

[In situ localization of mRNA with T-T dimerized DNA probes]

When a particular antigen is immunohistochemically localized at a given site, it is difficult to differentiate whether the antigen was produced at the site or immigrated to the site from elsewhere. If the antigen, e.g. hormone, is synthesized at the site, it indicates that the site is the effector cell and if the antigen is not synthesized at the site, it indicates that the site is the affector cell. Hence this differentiation is essential in order to establish physiological function of the antigen. One way to illustrate in situ synthesis of the antigen is to demonstrate the presence of messenger RNA (mRNA) which encodes the amino acid sequence of the antigen. To localize a particular mRNA at the lavel of cells, recently in situ hybridization techniques are utilized. As a non-radioactive marker for in situ hybridization. We introduced and utilize thymine-thymine dimers. When DNA is irradiated with ultraviolet light, thymine-thymine (T-T) dimer is formed between adjacent thymines. Since the T-T dimer is a well recognized antigen, after hybridization of T-T dimerized DNA with cellular mRNA, the sites of T-T dimer was recognized by routine immunohistochemistry. When the T-T dimerized probe is used, the resolution is high and intracellular sites of the target may be recognized both at the light and electron microscopic levels, and the sensitivity may be elevated by immunohistochemical and enzyme-histochemical procedural modifications.

Mechanism of action of GnRH: the participation of calcium mobilization and activation of protein kinase C in gonadotropin secretion

The role of protein kinase C in luteinizing hormone (LH) release was analyzed in studies on the secretory responses to gonadotropin releasing hormone (GnRH) and phorbol esters in pituitary cell cultures. 12-O-tetradecanoyl-phorbol 13-acetate (TPA), 4 beta-phorbol 12,13-bibenzoate, and 4 beta-phorbol 12,13-diacetate stimulated LH release with ED50s of 5, 10 and 1000 nM, respectively, and with about 70% of the efficacy of GnRH. Phorbol ester-stimulated LH secretion was decreased but not abolished by progressive reduction of [Ca2+] in the incubation medium, and the residual response was identical with that of GnRH in Ca2+-deficient medium. TPA increased [Ca2+]i to a peak after 30 s in normal medium but not in the absence of extracellular Ca2+, indicating that protein kinase C promotes calcium entry but can also mediate secretory responses without changes in calcium influx and [Ca2+]i. The extracellular Ca2+-dependent action of TPA on LH release was blocked by CoCl2 but not by nifedipine. The secretory actions of TPA and GnRH were additive at low doses and converged to a common maximum LH response at high concentrations of the agonists. TPA caused rapid translocation of cytosolic protein kinase C to the particulate fraction, followed by a progressive decrease in total enzyme activity to less than 10% after 6 h. Partial recovery of the cytosolic enzyme (to 20%) occurred after washing and reincubation for 15 h. Such kinase C-depleted cells showed prominent dose-dependent reductions in the actions of both GnRH and TPA on LH release in normal and Ca2+-deficient media. These observations show that the actions of kinase C on LH release include extracellular Ca2+-dependent and independent components, and support the hypothesis that protein kinase C participates in the LH secretory response to GnRH in pituitary gonadotrophs.

Tumor-associated expression of a serum protein, termed aX protein (alpha 1-inhibitor III), and its mRNA in rat liver

A cDNA clone bearing the mRNA sequence for rat alpha X protein (alpha X) was isolated from a cDNA library constructed from rat liver mRNA. The nucleotide sequence of alpha X protein cDNA showed 97% homology with that of the 3'-proximal domain of alpha 1-inhibitor III cDNA. The amino acid sequence deduced from that of alpha X cDNA also exhibited high homology with the primary sequences of alpha 1-inhibitor III and alpha 2-macroglobulin. K231 ascites hepatoma cells were transplanted into male ACI rats, and the level of alpha X mRNA in the liver of the tumor-bearing rats was determined by RNA blot hybridization with the cDNA probe. The serum concentration of alpha X decreased to about 30% of the control value with time after transplantation. The amount of alpha X mRNA in the liver of tumor-bearing rats was proportional to the serum concentration of alpha X. The serum concentrations of transferrin and albumin in the tumor-bearing rats also decreased to about 30 and 60% of the normal levels, respectively. However, the amounts of mRNAs for transferrin and albumin in the liver of tumor-bearing rats did not decrease. These findings indicate that the mechanisms of tumor-associated decrease in the concentrations of different serum proteins in tumor-bearing rats may differ.

[Experience with surgical therapy in ventricular septal perforation following acute myocardial infarction, with special reference to operative method]

Repair of ventricular septal perforation (VSP) caused by acute myocardial infarction (AMI) has been one of the unsettled subjects in cardiac surgery, because of high mortality. Our patients operated on for VSP during approximately the past 3 1/2 years consisted of five with anteroseptal infarction and one with inferoseptal infarction. Of the former five, four underwent sandwich procedure and one, ventriculoplasty for extensive lesions. The inferoseptal infarction case was treated initially with simple ventricular closure, but subsequently with ventriculoplasty for postoperative false ventricular aneurysm. Operative mortality rate, i.e., within one month was 17%, but the final survival rate was 50% for delayed complications. Various reparative methods were applied. Our impression thus far obtained is as follows. Sandwich procedure should be best for anteroseptal cases unless lesions are extensive, but ventriculoplasty should be of the choice for infero-(or postero-) septal cases or extensive anteroseptal cases. Our reparative method devised to improve closure of VSP is also introduced.

Structure of the gene for the arylphorin-type storage protein SP 2 of Bombyx mori

Two forms of storage proteins termed "SP 1" and "SP 2", respectively, accumulate in a stage-dependent fashion in the larval hemolymph of the silkworm Bombyx mori. We have cloned and analyzed the genomic sequence encoding SP 2, an arylphorin-type storage protein. The SP 2 structural gene contains five exons spanning over 5 kilobases of chromosomal DNA. The transcription initiation site of the SP 2 gene was identified at the nucleotide level and a typical TATA box was located 30 base pairs upstream of the transcription initiation site. The 5'-flanking region of the gene contains a sequence homologous to the SV 40 enhancer "core" structure. A region homologous to the Drosophila enhancer sequence predicted for the fat body specificity of gene expression exists in the 5'-upstream region. Developmental profiles of the SP 2 mRNA and its precursor in the fat body indicate that the biosynthesis of SP 2 is developmentally regulated at the level of transcription. The exon/intron composition of the SP 2 gene is remarkably similar to that of the SP 1 gene. Moreover, the deduced primary structures of SP 1 and SP 2 exhibit nearly 30% homology, implying that two storage protein genes of the B. mori silkworm might have evolved from a common ancestor.

Desensitization of pituitary gonadotropin secretion by agonist-induced inactivation of voltage-sensitive calcium channels

Gonadotropin-releasing hormone (GnRH) stimulates calcium mobilization and influx in pituitary gonadotrophs, and agonist-induced calcium entry through voltage-sensitive channels (VSCC) is required for the maintenance of gonadotropin secretion. However, prolonged or frequent exposure to GnRH attenuates the extracellular Ca2+-dependent cytosolic Ca2+ signal and diminishes hormone secretion. Measurements of membrane Ca2+ currents revealed significant impairment of VSCC activity in gonadotrophs during desensitization by GnRH. VSSC were also inactivated in a calcium-dependent manner during exposure to high K+. Prolonged inactivation of such Ca2+ channels by high K+ reduced the calcium and secretory responses to GnRH and vice versa. The calcium-dependent inactivation of VSCC during GnRH action appears to be a primary factor in the onset of desensitization in pituitary gonadotrophs. This mechanism could also account for the development of agonist-induced refractoriness in other calcium-regulated target cells.

Novel sites of expression of functional angiotensin II receptors in the late gestation fetus

In the adult, the peptide hormone angiotensin II (AII) is primarily known as a regulator of circulatory homeostasis, but recent evidence also suggests a role in cell growth. This study of AII in late gestation rat fetuses revealed the unexpected presence of receptors in skeletal muscle and connective tissue, in addition to those in recognized adult target tissues. The AII receptors in this novel location decreased by 80 percent 1 day after birth and were almost undetectable in the adult. Studies in fetal skin fibroblasts showed that the receptors were coupled to phospholipid breakdown, with concomitant increases in inositol phosphate and cytosolic calcium. The abundance, timing of expression, and unique localization of functional AII receptors in the fetus suggest a role for AII in fetal development.

[Significance of disturbances of cardiac filling in constrictive pericarditis]

Using pulsed Doppler echocardiography, blood filling patterns of the right atrium and left and right ventricles in constrictive pericarditis were studied to evaluate the physiological role of the pericardium in the hemodynamics of this disease. Thirteen cases were examined including five cases with atrial fibrillation. The control subjects consisted of 16 healthy persons and six cases of lone atrial fibrillation. 1. Peak velocity of the atrial filling wave during ventricular systole was reduced, and the filling time was shortened, suggesting reduced compliance and restricted motion of the atrial wall, because of the thickening and adhesions of the pericardium. Duration of the atrial filling wave during ventricular diastole was also shortened, reflecting disturbance of the early diastolic filling of the right ventricle. 2. In healthy subjects, duration of the rapid filling wave was longer in the right ventricle than in the left ventricle, probably due to the greater compliance of the right ventricular wall as compared to that of the left ventricular wall. In constrictive pericarditis, the rapid filling time of the right ventricle is shortened, so that the difference in this time between the right and left ventricles is minimized, which may be related to a thinner right ventricular wall. Duration of the rapid filling wave of the right ventricle correlated with right ventricular end-diastolic pressure, indicating that the duration of the right ventricular rapid filling wave is proportional to the severity of constrictive pericarditis. In conclusion, constriction of the pericardium definitely influences the hemodynamics of the right side of the heart more than it does the left side in constrictive pericarditis. This difference appears to result from the difference in thickness of the myocardial layers of both ventricles.

[Evaluation of mid-ventricular obstruction of hypertrophic cardiomyopathy by real-time two-dimensional Doppler flow imaging: a case report]

Mid-ventricular obstruction was evaluated in a case of hypertrophic cardiomyopathy using a real-time two-dimensional Doppler flow imaging system. A 60-year-old woman was referred to our hospital because of oppressive precordial sensation., I-mode echocardiography showed asymmetric septal hypertrophy: thickness of the end-diastolic left ventricular posterior wall was 9 mm, and that of the interventricular septum was 19 mm. However, there was no systolic anterior motion of the mitral apparatus. Doppler color flow imaging showed a mid-left ventricular narrowing in late-systole and a mosaic pattern was depicted from the mid-ventricle to the outflow tract. Continuous wave Doppler echocardiography disclosed a peak velocity of 2.0 m/sec (pressure gradient (PG) = 16 mmHg). In the right ventricular outflow tract, a mosaic pattern was also seen and a peak velocity of 1.5 m/sec was detected (PG = 9 mmHg). These results were nearly identical with the data measured by cardiac catheterization. Thus, it was concluded that intraventricular obstruction of hypertrophic cardiomyopathy is diagnosed by observing the flow image and flow velocities in the ventricle using a real-time two-dimensional Doppler flow imaging system.

Ifosfamide, adriamycin and cisplatin (IAP) plus bleomycin (B) combination chemotherapy in patients with recurrent cancer of the uterine cervix

A combination chemotherapy of ifosfamide, adriamycin and cisplatin (IAP) plus bleomycin (IAP plus B) was used to treat nine patients with recurrent cervical cancer of the uterus. All patients had received conventional radiation therapy with or without hydroxyurea as a potential radiation sensitizer, and seven of them had measurable disease in a previous irradiated field (4 cases) or distant area (3 cases). The tumors included 5 squamous cell carcinomas (non keratinizing: 2, keratinizing: 3), two adenosquamous (including one glassy cell carcinoma), one adenocarcinoma (endometrioid type) and one argyrophil cell carcinoma. All histologic type cancers except argyrophil cell carcinoma responded to IAP plus B treatment. In seven evaluable cases, three complete responses (CR) and 3 partial responses (PR) were recorded (response rate was 85.7%), including 3 responded tumors within previously irradiated pelvic tissue. The median duration of CR was over 7 months and that of PR was 3.5 months. Side effects of IAP plus B were severe in hematologic toxicity (100% of grade 4 leucopenia) but acceptable, permitting five courses of treatments at four week intervals. The results obtained were encouraging, although therapeutic benefits of IAP plus B were not evident in a patient with argyrophil cell carcinoma and the intractable nature of this histologic type cancer in the uterine cervix was again emphasized.

[Cell mediated immune response in leprosy lesions]

Five biopsies from 2 leprosy patients, tuberculoid (TT), and polar lepromatous (LLp), were studies using immunoperoxidase procedures with monoclonal antibodies. Immunohistochemical patterns of them were remarkably different. In a TT patient, epithelioid cells and helper/inducer T (Leu 3a+) cells made the central core of a granuloma surrounded by suppressor/cytotoxic T (T8+) cells and B cells, indicating a possible immune-mediated cell response. The distribution of B cells suggests that not only T but also B cells may take part in the formation of the granuloma. In contrast, helper/inducer cells, suppressor/cytotoxic cells, and macrophages of a LLp patient were admixed uniformly at the site of the lesion, indicating a poor immune response. Although the ENL skin lesion of this LLp patient did not eliminate the bacilli, HLA-DR expression by keratinocytes and increased numbers of helper/inducer cells found in an ENL lesion, comparable to the findings of TT leprosy, suggests that a cell mediated immune response may play some role in the pathogenesis of ENL reaction.

Mechanisms of secretory responses to gonadotropin-releasing hormone and phorbol esters in cultured pituitary cells. Participation of protein kinase C and extracellular calcium mobilization

The role of protein kinase C in luteinizing hormone (LH) release was analyzed in studies on the actions of gonadotropin releasing hormone (GnRH) and phorbol esters in cultured pituitary cells. During incubation in normal medium, GnRH stimulated LH release with an ED50 of 0.35 nM. Incubation in Ca2+-deficient medium (Ca2+-free, 10 microM) substantially decreased but did not abolish the LH responses to GnRH. The extracellular Ca2+-dependent component of GnRH action could be mimicked by high K+ concentrations, consistent with the presence of voltage-sensitive calcium channels (VSCC) in pituitary gonadotrophs. Ca2+ channel agonist (Bay K 8644) and antagonist (nifedipine) analogs, respectively, enhanced or partially inhibited LH responses to GnRH and also to K+, the latter confirming the participation of two types of VSCC (dihydropyridine-sensitive and -insensitive) in K+-induced secretion. Phorbol esters, including 12-O-tetradecanoylphorbol-13-acetate (TPA), 4 beta-phorbol-12,13-dibenzoate, and 4 beta-phorbol-12,13-diacetate, stimulated LH release with ED50s of 5, 10, and 1000 nM, respectively, and with about 70% of the efficacy of GnRH. Phorbol ester-stimulated LH secretion was decreased but not abolished by progressive reduction of [Ca2+]e in the incubation medium, and the residual LH response was identical with that elicited by GnRH in Ca2+-deficient medium. TPA increased [Ca2+]i to a peak after 20 s in normal medium but not in the absence of extracellular Ca2+, indicating that protein kinase C (Ca2+/phospholipid-dependent enzyme) promotes calcium entry but can also mediate secretory responses without changes in calcium influx and [Ca2+]i. The extracellular Ca2+-dependent action of TPA on LH release was blocked by Co2+. However, nifedipine did not alter TPA action on [Ca2+]i and LH release. These observations indicate that protein kinase C can participate in GnRH-induced LH release that is independent of Ca2+ entry, but also promotes the influx of extracellular Ca2+ through dihydropyridine-insensitive Ca2+-channels.

Localization in situ of c-myc mRNA and c-myc protein in adult mouse testis

It has been suggested that c-myc, one of the proto-oncogenes, plays a role in normal somatic cell proliferation and differentiation. To define whether c-myc is only expressed during somatic cell division or is also expressed during meiotic cell division, the production of c-myc mRNA and protein were investigated in the mouse testis by using in situ hybridization with non-radioactive DNA probes and enzyme immunohistochemistry respectively. For in situ hybridization, T-T dimerized DNA probes were used and DNAs hybridized in situ were detected immunohistochemically using specific antibody against T-T dimer. The results indicate that c-myc mRNA and protein are expressed in a cell-cycle-dependent manner only in spermatogonia and not in spermatocytes and spermatids.

Participation of voltage-sensitive calcium channels in pituitary hormone release

The role of extracellular Ca2+ in pituitary hormone release was studied in primary cultures of rat anterior pituitary cells. The basal levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyrotropin (TSH), and adrenocorticotropin (ACTH) secretion were independent of extracellular Ca2+ concentration ([Ca2+]e). In contrast, the basal levels of growth hormone (GH) and prolactin (PRL) release showed dose-dependent increases with elevation of [Ca2+]e, and were abolished by Ca2+-channel antagonists. Under Ca2+-deficient conditions, BaCl2 mimicked the effects of calcium on PRL and GH release but with a marked increase in potency, and also increased basal LH and FSH release in a dose-dependent manner. In the presence of normal [Ca2+]e, depolarization with K+ maximally increased cytosolic [Ca2+] ([Ca2+]i) from 100 to 185 nM and elevated LH, FSH, TSH, ACTH, PRL, and GH release by 7-, 5-, 4-, 3-, 2-, and 1.5-fold, respectively. These effects of KCl were abolished in Ca2+-deficient medium or in the presence of the Ca2+-channel antagonist, Co2+, and were diminished by the dihydropyridine Ca2+-channel antagonist, nifedipine. The Ca2+-channel agonist BK 8644 (100 nM) enhanced the hormone-releasing actions of 25 mM KCl upon PRL, LH, FSH, GH, TSH, and ACTH by 2.3-, 2.0-, 1.8-, 1.7-, 1.6-, and 1.4-fold, respectively. The dose- and voltage-dependent actions of BK 8644 were specific for individual cell types; BK 8644 enhanced GH, PRL, TSH, LH, and ACTH secretion in the absence of any depolarizing stimulus, with ED50 values of 8, 10, 150, 200, and 400 nM, respectively. However, in the presence of 50 mM KCl, the ED50 values for BK 8644 were 1.5, 2, 3, 5, and 7 nM for GH, PRL, ACTH, TSH, and LH, respectively. [3H]BK 8644 bound specifically to pituitary membranes with Kd values of 0.8 nM and concentrations of about 900 channels per cell. These observations provide evidence for the presence and participation of voltage-sensitive calcium channels in the secretion of all five populations of anterior pituitary cells.

Biphasic activation of cytosolic free calcium and LH responses by gonadotropin-releasing hormone

Gonadotropin-releasing hormone (GnRH) stimulates rapid peak increases in [Ca2+]i and LH release, followed by lower but sustained elevations of both [Ca2+]i and hormone secretion. Omission of extracellular Ca2+ only slightly decreased the peak of [Ca2+]i, but reduced the peak LH response by 40% and prevented the prolonged increases in [Ca2+]i and LH release. Dihydropyridine calcium antagonists did not affect the peak [Ca2+]i and LH responses, but reduced the sustained increases by up to 50%. Whereas GnRH-induced mobilization of intracellular calcium initiates the LH peak, and Ca2+ entry through dihydropyridine-insensitive channels contributes to the peak and plateau phases of LH release, dihydropyridine-sensitive L-type Ca2+ channels participate only in the sustained phase of gonadotropin secretion.

Abnormal blood pathways in left ventricular cavity in acute myocardial infarction. Experimental observations with special reference to regional wall motion abnormality and hemostasis

To elucidate the mechanism of regional hemostasis in the left ventricular (LV) cavity during myocardial infarction, the blood pathway in LV cavity was examined with contrast echocardiography injected from the left atrium before and after coronary ligation in nine canines. Before coronary ligation, contrast echoes spread over LV cavity with one rush. After ligation, smokelike echoes indicating hemostasis were observed at the apical middle of the LV cavity in five dogs with apical akinesis and at the apical area in four dogs with apical dyskinesis. The contrast echoes did not reach the apex within one diastolic period but turned upward to the outflow tract in the middle of the cavity in all dogs. In the cardiac beats that followed, some contrast echoes spread slowly toward the apex, forming a thin layer along the posterior wall in cases with akinesis but not in cases with dyskinesis. The area separated from the blood pathway developed where the smokelike echoes had been developed. Tachycardia exaggerated the abnormality of blood pathway and widened the contrast echo-free area. The abnormal pathway of the blood in apical myocardial infarction develops hemostasis in the apex. This should be one of the mechanisms of thrombus formation in myocardial infarction.