Myocardial adenyl cyclase: activation by thyroid hormones and evidence for two adenyl cyclase systems

The mechanism responsible for the hyperdynamic circulatory state in hyperthyroidism has not been defined. Although certain cardiac manifestations resemble those caused by excessive adrenergic stimulation, recent evidence suggests that thyroid hormone exerts an effect on the heart that is independent of the adrenergic system. Since the inotropic and chronotropic effects of norepinephrine appear to be mediated by activation of adenyl cyclase, the possibility that thyroxine and triiodothyronine are also capable of activating adenyl cyclase was examined in the particulate fraction of cat heart homogenates.L-thyroxine and L-triiodothyronine increased the conversion of adenosine triphosphate-(32)P (ATP-(32)P) to cyclic 3',5'-adenosine monophosphate-(32)P (3',5'-AMP-(32)P) by 60 and 45% respectively (P < 0.01). A variety of compounds structurally related to the thyroid hormones, but devoid of thyromimetic activity did not activate adenyl cyclase: these included 3,5-diiodo-L-thyronine, L-thyronine, 3,5-diiodotyrosine, monoiodotyrosine, and tyrosine. D-thyroxine activated adenyl cyclase and half maximal activity was identical to that of the L-isomer. Although the beta adrenergic blocking agent propranolol abolished norepinephrine-induced activation of adenyl cyclase, it failed to alter activation caused by thyroxine. When maximal concentrations of L-thyroxine (5 x 10(-6) moles/liter) and norepinephrine (5 x 10(-5) moles/liter) were incubated together, an additive effect on cyclic 3',5'-AMP production resulted.THIS INVESTIGATION DEMONSTRATES: (a) thyroid hormone is capable of activating myocardial adenyl cyclase in vitro and (b) this effect is not mediated by the beta adrenergic receptor. Moreover, the additive effects of norepinephrine and thyroxine suggest that at least two separate adenyl cyclase systems are present in the heart, one responsive to norepinephrine, the other to thyroid hormone.These findings are compatible with the hypothesis that the cardiac manifestations of the hyperthyroid state may, in part, be caused by the direct activation of myocardial adenyl cyclase by thyroid hormone.     

Decreased myocardial adenyl cyclase activity in hypothyroidism

It has been suggested that hypothyroidism may alter the responsiveness of the heart to sympathetic stimulation. To define more precisely the interrelationship between hypothyroidism and catecholamine responsiveness we: (a) studied the effects of norepinephrine and fluoride on the activation of adenyl cyclase in the particulate fraction of heart homogenates from euthyroid and hypothyroid cats; and (b) assessed the contractile response of isolated right ventricular papillary muscles from the same cats to increasing concentrations of norepinephrine. It was found that maximal accumulation of cyclic 3',5'-adenosine monophosphate (3',5'-AMP) was significantly lower at peak norepinephrine concentrations in the hypothyroid (284 +/-5 pmoles) than in the euthyroid group (326 +/-10 pmoles) (P < 0.02). However, the K(m) for norepinephrine was similar in both groups (1-2 x 10(-5) moles/liter), and there was no apparent change in the threshold concentration. Fluoride-mediated increases in Cyclic 3',5'-AMP accumulation were also significantly lower in the hypothyroid (585 +/-25 pmoles) as compared to the euthyroid group (790 +/-20 pmoles) (P < 0.02). In contrast, norepinephrine produced a similar augmentation of contractility in isolated papillary muscles from the hypothyroid and euthyroid cats. It thus appears that although the hypothyroid state is associated with a decrease in the total amount of myocardial adenyl cyclase per milligram of tissue capable of being activated by norepinephrine or fluoride, there is no change in the sensitivity of the enzyme to norepinephrine stimulation. Moreover, the finding that the inotropic response to norepinephrine is unaltered in hypothyroidism is compatible with the hypothesis that only a fraction of the total intracellular cyclic 3',5'-AMP produced by norepinephrine activation of adenyl cyclase is required to elicit the inotropic response.     

Leukocyte adenyl cyclase activity in human bronchial asthma.

Changes in adenyl cyclase activity of the peripheral blood leukocytes were investigated in patients with bronchial asthma. Estimation of the leukocyte adenyl cyclase activity was carried out following in vitro stimulation by sodium fluoride (NaF) or metaproternol. The NaF-stimulated adenyl cyclase activity was significantly lower during asthmatic attacks. An oral administration of metaproterenol to patients during an attack was found to enhance the activity back to the control levels. Off-attack asthmatic patients showed a normal value which was again elevated considerably when they were administered metaproterenol. In contrast, measurements of adenyl cyclase activity using metaproterenol stimulation showed little change in patients in spite of asthmatic attacks or metaproterenol regimen. The lowering of the NaF-stimulated leukocyte adenyl cyclase activity was inversely proportional to the degree of lymphopenia during attacks and positively correlated with an increasing percentage of neutrophils.     

Effects of thyroid-stimulating hormone on adenyl cyclase activity and intermediary metabolism of “cold” thyroid nodules and normal human thyroid tissue

"Cold" thyroid nodules do not concentrate (131)I before or after thyrotropin (TSH) administration. In an attempt to elucidate the reason for this TSH unresponsiveness, the effect of TSH in vitro on several metabolic parameters was studied in 11 "cold" thyroid adenomas, 2 medullary carcinomas, and in the surrounding normal thyroid tissue. Basal adenyl cyclase activity, glucose-1-(14)C oxidation, and (32)P incorporation into phospholipids were significantly greater in the adenomas than in the adjacent normal thyroid; basal cyclic 3',5'-adenosine monophosphate (cyclic AMP) concentration and adenine-(3)H incorporation into (3)H-labeled cyclic AMP were not different. In adenomas as well as normal thyroid, all parameters responded significantly to in vitro TSH stimulation. The response to TSH of adenyl cyclase activity and (32)P incorporation was enhanced in adenomas compared with that of the adjacent normal thyroid. These differences were not explained by an increased cellularity of the adenomas. Medullary carcinomas did not respond to TSH in any of the above parameters.The studies demonstrate an intact, TSH-responsive adenyl cyclase-cyclic AMP system in the adenomas and, accordingly, imply the presence of receptor sites for TSH on the cells of the adenoma. The failure of such nodules to concentrate (131)I may be owing to a subsequent impairment in the expression of cyclic AMP action on iodine metabolism.     

Abnormal hormone responses of an adrenocortical cancer adenyl cyclase

Properties of adenyl cyclase of normal adrenals and of a corticosterone-producing adrenal cancer of the rat have been compared. Enzyme activity was found in all particulate fractions of both tissues. The cyclase of the tumor as well as of the adrenals was stimulated by adrenocorticotropic hormone (ACTH) over similar concentration ranges. Unexpectedly, the tumor enzyme was also stimulated by epinephrine, norepinephrine, and thyroid-stimulating hormone (TSH). These hormones produced a dose-related effect over a concentration span that was comparable with that for ACTH. The tumor cyclase was not responsive to angiotensin Il, vasopressin, glucagon, insulin, growth hormone, parathyroid hormone, and thyrocalcitonin. ACTH was the only hormonal preparation that stimulated normal adrenal cyclase. These findings are compatible either with the possibility that the adenyl cyclase receptor of the tumor has undergone structural alteration with a consequent loss of specificity for ACTH or with the possibility that the tumor possesses several cyclase regulatory receptors.     

Stimulation of intestinal mucosal adenyl cyclase by cholera enterotoxin and prostaglandins

The effects of several prostaglandins (PG) and a highly purified preparation of cholera enterotoxin (CT) on intestinal mucosal adenyl cyclase activity and the effect of CT on intestinal mucosal cyclic 3',5'-adenosine monophosphate concentration were determined in guinea pig and rabbit small intestine and were correlated with the effects of the same agents on ion transport. Adenyl cyclase activity, measured in a crude membrane fraction of the mucosa, was found at all levels of the small intestine with the highest activity per milligram protein in the duodenum. The prostaglandins, when added directly to the assay, increased adenyl cyclase activity; the greatest effect (2-fold increase) was obtained with PGE(1) (maximal effect at 0.03 mM) and PGE(2). The prostaglandins also increased short-circuit current (SCC) in isolated guinea pig ileal mucosa, with PGE(1) and PGE(2) again giving the greatest effects. The prior addition of theophylline (10 mM) reduced the subsequent SCC response to PGE(1) and vice versa. It was concluded, therefore, that the SCC response to PGE(1), like the response to theophylline, represented active Cl secretion. CT increased adenyl cyclase activity in guinea pig and rabbit ileal mucosa when preincubated with the mucosa from 1 to 2.5 hr in vitro or for 2.5 hr in vivo but not when added directly to the assay. The increments in activity caused by PGE(1) and NaF were the same in CT-treated and control mucosa. Cyclic 3',5'-AMP concentration in rabbit ileal mucosa was increased 3.5-fold after a 2 hr preincubation with CT in vitro. Phosphodiesterase activity in the crude membrane fraction of the mucosa was unaffected by either CT or PGE(1). A variety of other agents including insulin, glucagon, parathormone, thyroid-stimulating hormone, L-thyroxine, thyrocalcitonin, vasopressin, and epinephrine all failed to change adenyl cyclase activity. It is concluded that CT and certain prostaglandins produce small intestinal fluid secretion by increasing mucosal adenyl cyclase activity, thereby stimulating an active secretory process.     

Human gastric mucosal adenylate cyclase activity: effects of various cytoprotective prostaglandins

Several prostaglandins prevent ulcer formation (called cytoprotection) by a mechanism other than inhibition of gastric acid secretion. One suggestion is that they increase cyclic AMP in non-parietal cells. A variety of prostaglandins with potent cytoprotective properties were tested for their capacity to modulate adenylate cyclase activity in homogenates of human gastric mucosa. Prostaglandin E2, prostacyclin (PGI2) and 15(S)-methyl-PGE2 stimulated the cyclase in human gastric mucosal biopsy specimens in a dose-dependent manner. Cytoprotective prostaglandins without antisecretory properties such as PGF2 beta were also able to activate the enzyme system dose-dependently. In contrast, cytoprotective prostaglandins such as PGD2, the PGE1-analogue, SC-29333, and the prostaglandin-like compound C83 did not stimulate human gastric adenylate cyclase. Whereas PGD2 did not modulate enzyme activity at all, SC-29333 and C83, at concentrations greater than 10 mumol/l, inhibited basal and PGE2-stimulated enzyme activities. These studies suggest that cyclic AMP is not directly related to the cytoprotective effect of prostaglandins, at least in human gastric mucosa.     

Effects of beta-adrenergic stimulating and blocking agents on the adrenaline response and adenyl cyclase activity of leukocyte in monkey and human being.

Using the method in which leukocyte suspensions were incubated with NaF or metaproterenol at 30 degrees C for 15-30 min to allow them to convert 3H-ATP (10 muCi) to 3H-cyclic AMP, followed by separation of the formed 3H-cyclic AMP by common chromatography, the leukocyte adenyl cyclase activity of monkeys and human beings was measured with high reproducibility. The oral administration of metaproterenol increased the leukocyte adenyl cyclase activity which was stimulated by NaF and decreased the count of peripheral eosinophils in some of the monkeys. In the beta-adrenergic blockade of the monkey which was made by administration of propranolol, the leukocyte adenyl cyclase activity significantly decreased. The leukocyte adenyl cyclase from patients with coronary heart disease also decreased after oral medication with propranolol.     

The various assays for measuring activity states of factor VIIa in plasma and therapeutic products: Diagnostic value and analytical usefulness in various pathophysiological states

The key coagulation factor FVII, and its activated form FVIIa, present a major interest for their role at the initiation phase of blood coagulation, and because they can activate all blood coagulation cascade, through the extrinsic, but also the intrinsic pathway. Blood activation initiated through FVII is first presented, as it is understood nowadays. Measurement of FVII and FVIIa were of main interest for epidemiological studies, but FVIIa contribution to assay results was only deduced. The introduction of specific FVIIa assays, functional or immunoassays, allowed measuring directly FVIIa without any interference of non-activated FVII, or other coagulation factors or their activated forms. The various methods available, and their characteristics are presented, with a special focus on two assays developed by our group for FVIIa (a clotting one and a chromogenic one). The FVIIa clotting assay shows evident superiority for measuring its activity in plasma, in pathophysiological conditions. The normal range is <2.5 ng/ml, which represents less than 0.5% of the FVII protein. FVIIa is elevated in some pathological states. The chromogenic assay is of interest for assigning the potency of FVIIa concentrates, as it has a higher dynamic range. Both assays are fully automatable on laboratory instruments, and standardized in a satisfactory manner thanks to the use of the FVIIa concentrate WHO International Standard (NIBSC). The various applications and usefulness of FVIIa laboratory assays are discussed, for the measurement of therapeutic products, or for following recoveries in treated patients, including hemophiliacs with inhibitors, patients with severe bleeding risk (liver diseases, surgery, trauma, …), and lastly for measurement of its activity in therapeutic products.     

Effects of dopamine on kidney function and on the adenyl cyclase phosphodiesterase system in man.

Clearance studies were made to determine the influence of intravenous infusions of dopamine (between 2.5 and 3.5 mug.kg.-1min.-1) on renal function and on the adenyl cyclase phosphodiesterase system in eleven patients with chronic renal disease. Glomerular filtration rate (+ 19%), effective renal plasma flow )+ 29%), sodium (+ 199%) and potassium (+ 40%) clearances were significantly increased. These effects were associated with a stimulation of the adenyl cyclase phosphodiesterase system demonstrated by an increase of cyclic adenosine 3'5'-monophosphate in plasma and urine. The results suggest that dopamine probably affects renal function by activating the adenyl cyclase phosphodiesterase system.     

Studies on human iodide peroxidase: its activity in various thyroid disorders.

Iodide peroxidase activities in the human thyroid gland were measured in various thyroid disorders. The peroxidase activities in the thyroid gland revealed high values in Graves' disease, normal levels in thyroid adenoma and low values in thyroid carcinoma as compared to those in normal thyroid glands. A high activity of this enzyme was observed in toxic adenoma. The same results were observed whether 10% (W/V) homogenate or mitochondrial and microsomal fractions of the thyroid gland were used.     

Activation of myocardial adenyl cyclase by histamine in guinea pig, cat, and human heart

Histamine has positive inotropic and chronotropic effects on the heart which are not abolished by beta adrenergic-blocking agents. Since the positive inotropic and chronotropic effects of other hormones on the heart are thought to be mediated by cyclic 3',5'-AMP, we examined the effect of histamine on adenyl cyclase in particulate preparations of guinea pig, cat, and human myocardium. Histamine at the peak of its dose-response curve, 3 x 10(-4)moles/liter, produced approximately a 300% increase in cyclic 3',5'-AMP accumulation in the guinea pig, 60% in the cat, and 90% in the human heart particles. Half-maximal activity for the histamine mediated activation of adenyl cyclase in the guinea pig was 9 x 10(-6)moles/liter, almost identical with that observed for norepinephrine in the same preparation. DL-Propranolol, 1 x 10(-5)moles/liter, did not abolish the activation of adenyl cyclase produced by histamine but did abolish the activation produced by norepinephrine. In contrast, diphenhydramine hydrochloride, Benadryl, 8 x 10(-5)moles/liter, abolished the activation of adenyl cyclase by histamine but not that produced by norepinephrine. These data suggest that there are at least two receptor sites in guinea pig heart mediating the activation of adenyl cyclase, one responsive to histamine, the other to norepinephrine. In addition, combined maximal doses of histamine and norepinephrine produced completely additive effects on the activation of adenyl cyclase, which suggests that at least two separate adenyl cyclase systems are present in the heart, each responsive to one of these hormones. However, definitive proof would require physical separation of the two enzymes.     

Collagenase activity in the granulocytes of patients with various liver diseases

Studies were conducted on collagenase activity on peripheral granulocytes of patients with various liver diseases. Total collagenase activity increased significantly in chronic active hepatitis (CAH) and in liver cirrhosis (LC), and, in these disorders, it correlated with the extent to which hepatic fibrosis has progressed. Active collagenase activity increased in CAH, but no differences from normal controls were found in other liver diseases. These results suggest that total collagenase may reflect the degree of hepatic fibrosis, and that active collagenase may be related to chronic active hepatitis lesions.     

Effects of Ca++ and prostaglandin E1 on vasopressin activation of renal adenyl cyclase

Adenyl cyclase activity was assayed in crude homogenates of the renal cortex, medulla, and papilla of the golden hamster. The specific activity (moles C-AMP/unit of time per mg protein of tissue) of the enzyme under basal conditions, was greatest in papilla, somewhat lower in medulla, and least in cortex. On an absolute scale, the sensitivity to vasopressin was greater in the medullary and papillary than in the cortical homogenates. In addition, at concentrations of 0.1-1.0 mm, CaCl(2) inhibited the enzyme in the order papilla > medulla > cortex. These results imply the existence of distinct differences in the composition of the adenyl cyclase-receptor complex in various parts of the kidney. We proposed that Ca(++) inhibits the core enzyme directly since at the minimally inhibitory concentration (0.1 mm), CaCl(2) reduced to an equivalent extent (a) basal activity, (b) the response to graded doses of vasopressin (0.5 to 50.0 mU/ml) and (c) the response to maximal stimulatory concentrations of NaF (10 mm). Prostaglandin E(1) (PGE(1) = 10(-7)m) had no effect on either basal adenyl-cyclase activity or the response to 10 mm NaF in medullary and papillary homogenates. 7-Oxa-13-prostynoic acid (10(-4)m) similarly had no effect under basal conditions or on stimulation with NaF in medullary homogenates. Both fatty acids, however, inhibited the enzymic response to vasopressin, particularly at low concentrations of the peptide. The straight-chain fatty acid, 11-eicosanoic acid (10(-7)m), was inactive on basal activity or on the response to vasopressin. The possibility that PGE(1) modifies the coupling mechanism between the core enzyme and the hormone-specific receptor is discussed.