Angiotensin II modulates arterial baroreflex function via a central alpha 1-adrenoceptor mechanism in rabbits

To test the hypothesis that angiotensin II (ANG II) modulates arterial baroreflex function via a central alpha 1-adrenoceptor mechanism, we examined the effects of intravertebral infusion of ANG II on baroreflex function curves before and after intravertebral administration of the alpha 1-adrenoreceptor antagonist prazosin. Rabbits were chronically instrumented with subclavian and vertebral arterial catheters, venous catheters, and aortic and vena caval occludes. Baroreflex curves were obtained by relating heart rate (HR) to mean arterial pressure during increases and decreases in arterial pressure. Intravertebral infusions of ANG II (5, 10, and 20 ng.kg-1.min-1) produced a dose-dependent shift of the midrange of the curve toward higher pressures (64 +/- 1 to 68 +/- 1, 76 +/- 1, and 85 +/- 2 mmHg, respectively). Pretreatment with prazosin (10 micrograms/kg) via the vertebral artery markedly reduced the shift in the baroreflex curve induced by the highest dose of ANG II (64 +/- 2 to 70 +/- 2 mmHg). These data suggest that ANG II resets the operating point of the HR baroreflex curve to a higher blood pressure and that this effect is mediated via a central alpha 1 mechanism. When the effects of vertebral ANG II on the baroreflex control of renal sympathetic nerve activity (RSNA) were examined, intravertebral administration of ANG II, while reducing the gain and the maximum RSNA, did not reset the RSNA baroreflex curve. These data suggest that ANG II acutely resets the HR baroreflex but not the RSNA baroreflex and that the resetting involves an alpha 1-adrenergic mechanism.

Monoclonal antibody markers for early development of the stereociliary bundles of mammalian hair cells

Two monoclonal antibodies, SC1 and SC2, were raised in vitro against antigens from the stereocilia of guinea-pig hair cells. They both labelled stereociliary antigens that were not detected in any other cell within the cochlear duct or the vestibular epithelial. SC1 cross-reacted with the tectorial membrane in the cochlea and labelled both cochlear and vestibular hair cells from both the mouse and the rat. In the mouse the SC1 antigen was labelled from embryonic days 16-18, coincident with the development of the stereociliary bundles. SC1 cross-reacted with neuromuscular junctions from striated muscle and with basal keratinocytes in skin. SC2 did not cross-react cleanly with hair cells from the mouse or the rat but it cross-reacted with proximal tubules of the guinea-pig kidney. Both antibodies can be used as cellular markers within the guinea-pig cochlea and SC1 should be particularly useful for studies of hair cell differentiation in the mouse.

Umbilical plasma concentration of endothelin-1 in intrapartum fetal stress: effect of fetal heart rate abnormalities

OBJECTIVE

To measure the umbilical plasma concentration of endothelin (ET)-1 in the presence of labor, fetal heart rate (FHR) abnormalities, and fetal hypoxia.

METHODS

Umbilical and maternal plasma concentrations of ET-1 were measured in 100 pregnant women at full-term deliveries (60 with vaginal delivery without induction and 40 with elective cesarean delivery without labor). We assessed the FHR pattern, measured umbilical blood gases and plasma concentration of vasopressin, and investigated the relationships between the umbilical vein-artery ET-1 concentration difference and these variables.

RESULTS

The concentration of ET-1 in the umbilical vein was higher than in the umbilical artery and the maternal vein in all cases. The umbilical vein-artery ET-1 concentration difference (mean +/- standard error of the mean) was significantly greater in the vaginal delivery group (4.5 +/- 2.0 pmol/L) than in those delivered by elective cesarean (1.7 +/- 1.5 pmol/L) (P < .05). The umbilical vein-artery ET-1 concentration difference was significantly greater when more than three episodes of severe variable decelerations occurred during the 30-minute period before delivery (7.0 +/- 2.0 pmol/L) than in the absence of any decelerations (1.6 +/- 1.5 pmol/L) (P < .05). The umbilical vein-artery ET-1 concentration difference correlated positively with the umbilical arterial concentration of vasopressin (r = 0.45, P < .05) and negatively with the umbilical arterial oxygen pressure (r = -0.47, P < .05).

CONCLUSION

In cases of vaginal delivery with FHR abnormalities and with fetal hypoxia, the fetoplacental concentration of ET-1 was increased.

Lysosomal enzyme activities in skeletal muscle of patients with neuromuscular diseases

Activities of nine lysosomal enzymes and pH-dependent isozyme patterns of alpha-mannosidase were examined in the skeletal muscle of patients with neuromuscular diseases, and the ratios of these enzyme activities in leukocytes to those in myocytes (L/M ratio) were determined. The activities of enzymes with a high L/M ratio were markedly increased in the muscles of patients with Duchenne muscular dystrophy (DMD), myotonic dystrophy (MyD), or polymyositis (PM). In contrast, those which showed a low L/M ratio were increased in the muscles of amyotrophic lateral sclerosis (ALS) and disuse muscle atrophy (DUA). The isozyme pattern of alpha-mannosidase in DMD muscle resembled that in leukocytes, while those in ALS and DUA muscle resembled that in normal muscle. These results may suggest that the increased activity of lysosomal enzymes in the muscles of patients with DMD, MyD, or PM is due primarily to infiltrating leukocytes, while that in patients with ALS or DUA is due to intramyofiber lysosomes.

Disinfestation of experimentally infested cat fleas, Ctenocephalides felis, on cats and dogs by oral lufenuron

In vivo efficacy of orally administered lufenuron, an insect growth regulator, in disinfesting cat fleas was evaluated, using flea-free cats and dogs which were purchased and infested every 10 days with cat fleas from a colony kept in our laboratory. Lufenuron was orally administered as a single dose of 15, 30, or 60 mg/kg to cats, and 5, 10 or 20 mg/kg to dogs. In cats, adult flea emergence was intensively prevented for 30 days by dosing of 15 mg/kg of lufenuron and 40 days by 30 or 60 mg/kg. The average egg hatch rate in 15 mg/kg group was, however, significantly higher than those in 30 mg/kg or more, suggesting necessity to dose 30 mg/kg to cats to prevent development of cat fleas effectively. In dogs, a lower dose of the drug, 10 mg/kg seemed to be sufficient for the complete prevention of flea development.

Autoantibody to factor VIII that has less reactivity to factor VIII/von Willebrand factor complex

To determine the difference in reactivity of factor VIII (FVIII) inhibitor to FVIII/von Willebrand Factor (vWF) complex and FVIII free of vWF, an autoantibody to FVIII light chain was tested. A patient (1-3) suffered from autoimmune hemolytic anemia with autoantibody to FVIII. Epitope specificity of the patient's IgG (I-3 IgG) was shown to be the C2 domain of FVIII light chain (2170-2332) by Western blotting using recombinant FVIII deletions expressed in Escherichia coli. The inhibitory effect on FVIII procoagulant activity (VIII:C) of I-3 IgG was tested against a conventional FVIII concentrate; Haemate P, a monoclonal antibody-purified FVIII concentrate; Hemofil M, and a recombinant FVIII (rFVIII); Kogenate. I-3 IgG showed only 1.3 BU/mgIgG for Haemate P, in contrast to 20 BU/mgIgG for both Hemofil M and Kogenate. The ratio of VIII:C/vWF:Ag in Haemate P and Hemofil M was 1/3.43 and 1/0.01, respectively, while Kogenate did not contain vWF. The inhibitory effect of the I-3 IgG was then compared with Kogenate and its complex with vWF. The inhibitory effect was decreased against the rFVIII by forming a complex with vWF from 22 BU/mgIgG to 0.5 BU/mgIgG. Fab from the I-3 IgG had the same effect. In addition, vWF showed a protective effect on FVIII inactivation by the I-3 IgG in a dose dependent manner. Fifty-nine percent of residual VIII:C was retained in the presence of 8 U/ml of vWF after 1 hr incubation with I-3 IgG. These results suggested that vWF could compete with the I-3 IgG for binding to FVIII.

[Two-color flow cytometry analysis of lymphocyte subsets in patients with acute myocardial infarction and post-myocardial infarction syndrome]

Serial changes in lymphocyte subsets were analyzed in 37 patients with acute myocardial infarction (AMI), in 2 patients with postmyocardial infarction syndrome (PMIS), and in healthy subjects (control group) using two-color flow cytometry to investigate cellular immunity after AMI and PMIS. Peripheral blood lymphocyte subsets were measured on admission and at weeks 2, 4, 8, and 16 after the onset of AMI. The white blood cell count was significantly higher on admission and at week 2 in the AMI group compared with the control group. The percentage of CD4-positive helper T cells was significantly higher on admission and at weeks 2 and 4 in the AMI group compared with the control group, and the percentage of CD8-positive suppressor T cells was significantly lower in the AMI group at week 2 than in the control group. The ratio of helper-to-suppressor T cells peaked 2 weeks after the AMI and then decreased gradually. There were no significant changes in the CD4/CD8 ratio, the percentage of cytotoxic T cells, or the percentage of inducer T cells, throughout the observation period. There were no significant differences in the percentage of T cells, B cells, CD4-positive T cells, CD8-positive T cells, and natural killer cells between AMI patients and control subjects. The percentage of activated CD4- and CD8-positive cells was higher in the AMI group at weeks 4 and 8 than in the control group. There was no significant correlation between changes in lymphocyte subsets and infarct size. The percentage of activated CD8-positive cells was consistently higher in the PMIS group compared with the control and AMI groups. The percentage of cytotoxic T cells in one of the PMIS patients was significantly higher than in the AMI group. There were no significant differences in the proportions of other subsets between PMIS and AMI patients. The changes in lymphocyte subsets observed in patients with AMI suggested that immunological competence was enhanced in these patients. Abnormalities in humoral immunity, such as the appearance of anticardiac antibody, have been observed in patients with PMIS. Our results suggest that PMIS is also associated with changes in cellular immunity.

Changes in calmodulin concentration and cyclic 3',5'-nucleotide phosphodiesterase activity in skeletal muscle of hyper- and hypothyroid rats

Hyper- and hypothyroid states occasionally induce skeletal muscle dysfunction i.e. periodic paralysis and thyroid myopathy. The etiology of these diseases remains unclear, but several findings suggest that the catecholamine-beta-receptor-cAMP system or other messenger systems are disturbed in these diseases. In this context, we evaluated changes in the cyclic 3',5'-nucleotide metabolic enzyme, cyclic 3',5'-nucleotide phosphodiesterase (PDE) and calmodulin concentrations in skeletal muscles of hyper- and hypothyroid rats. Activities of cyclic AMP-PDE were low in skeletal muscle both from hyper- and hypothyroid rats, and calmodulin concentration was high in hyperthyroid and low in hypothyroid rats, as compared with normal rats. DE-52 column chromatographic analysis showed that the cGMP hydrolytic activity in peak I and the cAMP hydrolytic activity in peak II were decreased in hypothyroid rats, whereas cAMP hydrolytic activity in peak III was unchanged. The cAMP hydrolytic activity in peak III was decreased in hyperthyroid rats, but the activities in peaks I and II were unchanged. These findings indicate that cAMP and calmodulin may have some role in skeletal muscle function in the hyperthyroid state, and that cAMP and calmodulin-dependent metabolism may be suppressed in the hypothyroid state.

Dexamethasone-induced changes in glucose transporter 4 in rat heart muscle, skeletal muscle and adipocytes

To clarify the effect of glucocorticoid on glucose transporters (GLUT) in adipocytes and muscle, we examined the changes of GLUT4 in rat heart muscle, skeletal muscle and adipocytes during long-term administration of dexamethasone and the translocation of GLUT4. The levels of GLUT4 in the plasma membrane and the low-density microsome fraction were measured by Western blotting using anti-GLUT4 peptide antibody. The levels of GLUT4 in the heart and skeletal muscles of rat were unchanged by treatment of dexamethasone. In the adipocytes the level of GLUT4 in plasma membrane was changed, but it was decreased in the low-density microsome fraction. Although adipocytes are less involved in blood sugar regulation than skeletal muscle, this finding suggests that glucose metabolism in Cushing's syndrome is affected partly by a decrease of GLUT4 in the adipocytes.

Comparison on reactivity of Fe(III) and Al(III) compounds in the presence of hydrogen peroxide: its relevance to possible origin for central nervous system toxicity by aluminum ion

The iron(III) compounds with several aminocarboxylate chelates containing an aryl or furan substituent exhibit high activity in enhancement of the reactivity of hydrogen peroxide, leading to facile hydroxylation at benzene ring, and to degradation of furan ring, but no such activity was observed for the corresponding Al(III) compounds. These results were interpreted in terms of the molecular orbital consideration, and lack of the activity of the Al(III) complexes was attributed to lack of electrophilic nature of the peroxide adduct due to the absence of a d-orbital; this may explain the fact that there were no tumors in Al-NTA(nitrilotriacetic acid)-treated rats. Based on the facts observed in this study, the decreased function of iron(III) ions for synthesizing neurotransmitters in the brain was assumed to be one of the possible origin for the neurotoxicity by injection of the Al(III) salts in vivo.

Mitochondrial encephalomyopathy with autosomal dominant inheritance: a clinical and genetic entity of mitochondrial diseases

We report a Japanese family with chronic progressive external ophthalmoplegia (CPEO) with autosomal dominant inheritance, and review 54 reported CPEO patients in seven families (including the present family) with autosomal dominant inheritance and mtDNA deletions in the skeletal muscle. Mean age at onset in the CPEO was 26 years, which is older than that in published solitary cases. In addition to blepharoptosis and external opthalmoplegia, proximal muscle atrophy and weakness were found in 62%, hearing loss in 25%, and ataxia in 17% of the patients. Retinal degeneration was not found, and cardiac involvement was very rare. mtDNA deletions in the muscle were multiple and large scale, and all such deletions were located in the non-D-loop region. Autosomal dominant CPEO has unique clinical features which differ from those of solitary CPEO, and is associated with multiple large-scale mtDNA deletions. Thus, autosomal dominant CPEO can be considered a clinical and genetic entity of mitochondrial diseases.

Effects of thyroid hormone on coenzyme Q and other free radical scavengers in rat heart muscle

Active oxygen species are reported to cause organ damage. This study was therefore designed to determine the behaviour of antioxidants and free radical scavengers so as to reveal changes in animals in the hyper- and hypothyroid state. Levels of antioxidant factors (i.e. coenzyme Q (CoQ)10, CoQ9 and vitamin E) and free radical scavengers (catalase, glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD)) were measured in the heart muscles of rats rendered hyper- or hypothyroid by 4 weeks of thyroxine (T4) or methimazol treatment. Serum levels of CoQ9 and total SOD were also measured. A significant reduction in CoQ9 levels was observed in the heart muscles of both hyper- and hypothyroid rats when compared with control hearts. There was no difference in serum CoQ9 levels in thyroid dysfunction when compared with control animals. Levels of vitamin E in the heart muscles of hyperthyroid rats were significantly increased, and there was no reduction in vitamin E levels in hypothyroid rats when compared with control hearts. GSH-PX levels in the heart muscle were reduced in hyperthyroid rats and increased in hypothyroid rats when compared with control hearts. However, there were no differences in catalase levels in heart muscle between hyper- and hypothyroid rats. The concentration of SOD in heart muscle was increased in hyperthyroid rats and was not decreased in hypothyroid rats compared with control rats, suggesting the induction of SOD by excessive production of O2-. These data suggest that the changes in these scavengers have some role in cardiac dysfunction in the hyper- and hypothyroid state in the rat.

[A rare case of a diabetic patient with small cell lung cancer, initially diagnosed as pyogenic vertebral osteomyelitis]

A rare case of a patient with non-insulin-dependent diabetes mellitus (NIDDM) with small cell lung cancer, initially diagnosed as pyogenic vertebral osteomyelitis, was reported. A 40-year-old male patient was diagnosed with NIDDM about 3 years earlier, but he did not receive any treatment. Then, a two-month history of high fever, persistent cough and back pain developed. Chest X-ray film showed a lung infiltrate with a small cavity in the upper portion of the left lung. Computed tomography and magnetic resonance imaging of the chest revealed a tumor mass shadow with osteoclasia along the bodies of the 6th and 7th thoracic vertebral bone. Staphylococcus aureus infection was confirmed by arterial blood culture. Administration of antibiotics resulted in the disappearance of the left lung infiltrate and a slight reduction of the tumor mass in the thoracic vertebral bone, suggesting pyogenic vertebral osteomyelitis as an unusual complication of NIDDM. However, as the tumor mass still remained, needle biopsy for the mass lesion was performed, resulting in the diagnosis of metastasis of small cell carcinoma from the left lung. Gene aberration in this lung disease has been reported recently, and its correlation with NIDDM which may also be induced by genetic abnormality is an interesting question that remains to be resolved.

Increased cathepsin L levels in serum in some patients with ovarian cancer: comparison with CA125 and CA72-4

Our purpose was to determine the correlation between cathepsin L mRNA levels and serum cathepsin L levels of patients with ovarian cancer. Moreover, we compared serum cathepsin L levels with cancer antigen 125 (CA125) and cancer antigen 72-4 (CA72-4) levels. Using an ELISA assay, serum samples of 30 patients with gynecological tumors were analyzed for cathepsin L, CA125, and CA72-4. We also examined whether cathepsin L gene expression was enhanced in ovarian cancer samples, by quantitative Northern blot analysis with a human cathepsin L complementary DNA (cDNA) probe. Significantly increased serum levels of cathepsin L in patients with ovarian cancer (P < 0.05) were observed. We also measured serum levels of CA125 and CA72-4 in the same patients. Compared with CA125 and CA72-4, cathepsin L showed a lower false-positive rate (27.2%) in gynecological diseases, and no correlation was observed between cathepsin L and CA125 or CA72-4 values. Moreover, ovarian cancer samples were found to express higher levels of cathepsin L mRNA than those of uterine cancer, benign ovarian tumor, and normal ovary samples. Our data demonstrated that serum cathepsin L may be useful in the early detection of ovarian cancer. Furthermore, the combination assay consisting of cathepsin L, CA125, and CA72-4 may be a more useful method than those currently in use for the detection of ovarian cancer.

Myocardial infarct size by serum troponin T and myosin light chain 1 concentration

The late troponin T (TnT) peak concentration, which is known to be independent of reperfusion of the infarcted zone in acute myocardial infarction (MI), has been suggested to be correlated with clinical estimates of cardiac function and myocardial infarct size. To refine the clinical application of the late TnT peak in infarct sizing, and to examine differences in this estimation in different infarct sites, we measured the serum concentrations of TnT and myosin light chain 1 (MLC1), and compared these values with left ventricular ejection fraction (LVEF) obtained from left ventriculography, and extent score (ES) and severity score (SS) obtained from 201Tl scintigraphy in patients with anterior and inferior myocardial infarction. The late TnT peak concentration was strongly correlated with the MLC1 peak value in patients with anterior MI (r = 0.67, p < 0.05) and in those with inferior MI (r = 0.92, p < 0.0005). Furthermore, there were strong linear correlations between the late TnT peak values and all of the clinical data (LVEF; r = -0.79, p < 0.01, ES; r = 0.75, p < 0.05, SS; r = 0.75, p < 0.05, respectively) in patients with anterior MI. However, these correlations were weak in patients with inferior MI. Similar correlations were observed between MLC1 and the clinical data. Thus, TnT and MLC1 have similar kinetics in the serum at the late phase and can be used to estimate the size of anterior infarct.

Role of homeodomain protein binding region in the expression of Drosophila proliferating cell nuclear antigen gene: analysis with transgenic flies

The regulatory region of Drosophila proliferating cell nuclear antigen (PCNA) gene consists of a promoter region (-168 to +24 with respect to the transcription initiation site) and an upstream region containing three homeodomain protein binding sites (HDB) (-357 to -165). The PCNA gene regulatory regions with HDB (-607 to +137) or without HDB (-168 to +137) were fused with the lacZ and transgenic flies were established by P-element-mediated transformation. Male transgenic flies were crossed with wild-type females, and zygotic expression of the lacZ was monitored by quantitative beta-galactosidase assay, at various stages of development. Expression of the lacZ was high in embryos, first and second instar larvae, and adult females, and low at other stages of development. Only a marginal difference in expression was observed between flies carrying the homeodomain protein binding region and those not carrying it. Spatial pattern of the lacZ expression in the embryo visualized by immunostaining with the anti-lacZ antibody was similar to the distribution of the endogenous PCNA protein. Here, too, only a marginal difference was observed between transgenic flies carrying two different constructs of the PCNA lacZ. In genetic crossing experiments of transgenic flies with those carrying mutation in homeobox genes, no significant change in the lacZ expression pattern was observed. However, when male transgenic flies were crossed with female flies homozygous for a torso gain-of-function allele, repression of the lacZ expression was observed in the central region of the embryo. Because these local changes in the lacZ expression depend on the homeodomain protein binding region, unidentified homeodomain proteins are probably involved. Our results suggest that the promoter region is practically sufficient for expression of the PCNA gene and that the homeodomain protein binding region functions as a silencer when torso is activated ectopically.

Cell proliferation and advancement of hepatocarcinogenesis in the rat are associated with a decrease in connexin 32 expression

The expression of connexin 32 (Cx32), a major liver gap junction protein, after partial hepatectomy (PH) and during development and progression of hepatocarcinogenesis was studied in the rat. Cx32 was quantitatively analyzed by counting immunohistochemically demonstrated protein spots on the membranes of hepatocytes. Livers were sequentially examined after PH to assess the correlation with cell proliferation. For the analysis of different stages in carcinogenesis, Cx32 was assayed in N-ethyl-N-hydroxyethylnitrosamine-induced enzyme altered foci (EAF), hyperplastic nodules (HN), hepatocellular carcinomas (HCC), pulmonary metastatic HCC and transplanted HCC in relation to their degree of altered enzyme expression. Cx32 showed: (i) a rapid decrease after PH to its lowest levels during and 12 h after the S phase of cell proliferation when 5-bromo-2'-deoxyuridine (BrdU) labeling indices were examined; (ii) a progressive decrease from early preneoplasia EAF to HN and HCC, values for pulmonary metastatic and transplanted HCC being 0; (iii) clearly inverse correlations with increased BrdU index and degree of altered enzyme expression in HN, indicating that these, with the lowest Cx32 count, are closest to HCC. Therefore, the observed decrease appears linked to cell proliferation and progression of hepatocarcinogenesis, providing a reflection of cellular independence and growth advantage.

Role of endogenous opioids and central opioid receptors in cerebral cortical blood flow autoregulation

To examine the role of endogenous opioids in autoregulatory maintenance of cerebral cortical blood flow (CoBF), CoBF was measured continuously by laser-Doppler flowmetry during changes in arterial pressure. Experiments were conducted on pentobarbital sodium-anesthetized adult mongrel dogs. Mean arterial pressure (MAP) was decreased or increased by inflating a perivascular occluder placed around the inferior vena cava or the thoracic descending aorta, respectively. To exclude the influence of the baroreceptor reflex on the autoregulatory maintenance of CoBF, all experiments were conducted on dogs with bilateral carotid sinus denervation plus vagotomy. CoBF was well maintained within its normal range despite large changes in MAP. Intravenous injection of naloxone (2.5 mumol/kg), an opioid receptor antagonist, significantly impaired the autoregulatory maintenance of CoBF during the decrease in MAP. On the other hand, intravenous injection of methyl naloxone (2.5 mumol/kg), which does not cross the blood-brain barrier, did not exert any significant effect on the MAP-CoBF relationship. Furthermore, intracerebroventricular injection of a smaller dose of naloxone (2.5 nmol/kg) significantly impaired the autoregulatory maintenance of CoBF during the decrease in MAP, as the larger dose of intravenous naloxone (2.5 mumol/kg) did. On the other hand, intravenous injection of the smaller dose of naloxone did not exert any significant effect on the MAP-CoBF relationship. These findings suggest that endogenous opioids and central opioid receptors may be partly involved in the CoBF autoregulatory mechanism. The endogenous opioids may modulate the autoregulatory vasodilation of the cerebral cortex during the decrease in MAP.

Angiotensin II-dependent hypertension and the arterial baroreflex

Angiotensin II (ANG II)-dependent hypertension involves the resetting of the heart rate (HR) and sympathetic baroreflex toward higher pressures in conscious rabbits. The resetting of the HR baroreflex function occurs within minutes of the administration of ANG II, while the resetting of the sympathetic baroreflex requires several days. In conscious rabbits, an intact area postrema (AP) is required for the resetting of either the HR or sympathetic baroreflex function. Data is also presented showing that pretreatment with an alpha-1 adrenergic receptor antagonist prevents the early resetting of the HR baroreflex.

Changes of calmodulin concentration and cyclic 3',5'-nucleotide phosphodiesterase activities in cardiac muscle of hyper- and hypothyroid rats

To investigate the effect of thyroid hormone on cardiac muscle dysfunction in hyper- and hypothyroid states, we evaluated cyclic 3',5'-nucleotide metabolism by measuring cyclic 3',5'-nucleotide phosphodiesterase activity and calmodulin concentrations in the cardiac muscles of hyper- and hypothyroid rats. Cyclic AMP (cAMP) concentration was significantly high in the cardiac muscle of hyperthyroid rats and low in that from hypothyroid rats compared with control rats. Cyclic AMP and cyclic GMP phosphodiesterase activities were significantly decreased in the soluble fraction of cardiac muscle from hyperthyroid rats and markedly increased in this fraction in hypothyroid rats compared with normal animals. Calmodulin concentration was high in hyperthyroid and low in hypothyroid rats. It was concluded from these findings that low cAMP-phosphodiesterase activity might, in part, bring about the high concentration of cAMP. Calmodulin was significantly high in the cardiac muscle of hyperthyroid rats and the reverse was the case in hypothyroid rats compared with normal rats. The implication is that, in hyper- and hypothyroid states, these changes may play an important role in cardiac function via their effect on cyclic nucleotide and Ca2+ metabolism.