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Competing Interests: Disclosure The authors report no conflicts of interest in this work.

Background: Muscarinic cholinoceptors have been found in all types of ocular tissue, e.g. in corneal epithelium and endothelium. Latest research has focused only on the m5 cholinoceptor subtype. However, previous studies have also indicated the presence of m2 or m4 receptor subtypes in corneal tissue. The aim of this study was to show the decrease of intracellular cAMP formation and protein kinase A (PKA) activity after stimulation of m2 or m4 cholinoceptors in bovine corneal epithelial and endothelial cells. MATERIALS UND METHODS: Muscarinic cholinoceptors were studied using polyclonal antibodies. The cAMP concentration was determined with an enzyme immunoassay and PKA activity was estimated by the consumption of ATP., Results: Immunocytochemistry, immunofluorescence and immunoblotting revealed the presence of the m4 muscarinic cholinoceptor subtype but not of the m2 receptor subtype in bovine corneal epithelial and endothelial cells. In bovine corneal epithelium and endothelium protein cAMP formation was decreased and PKA activity was inhibited by acetylcholine in a dose-dependent manner (p<0.001)., Conclusion: The findings indicate that stimulation of m4 muscarinic cholinoceptors inhibits the cAMP-PKA pathway in corneal epithelial and endothelial cells resulting in decreased protein kinase A activity. Further work will be needed to clarify the physiological role of this signaling pathway in corneal epithelium and endothelium.

To control the breathing rhythm the medullary respiratory network generates periodic salvo activities for inspiration, post-inspiration and expiration. These are under permanent modulatory control by serotonergic neurons of the raphe which governs the degree of phosphorylation of the inhibitory glycine receptor α3. The specific activation of serotonin receptor type 1A (5-HTR(1A)), which is strongly expressed in the respiratory neurons, functions via inhibition of adenylate cyclase and the resulting reduction of the intracellular cAMP level and a gradual dephosphorylation of the glycine receptor type α3 (GlyRα3). This 5-HTR(1A)-GlyRα3 signal pathway is independent of the µ-opioidergic transduction pathway and via a synaptic inhibition caused by an increase in GlyRα3 stimulates a disinhibition of some target neurons not only from excitatory but also from inhibitory neurons. Our physiological investigations show that this 5-HTR(1A)-GlyRα3 modulation allows treatment of respiratory depression due to opioids without affecting the desired analgesic effects of opioids. The molecular mechanism presented here opens new pharmacological possibilities to treat opioid-induced respiratory depression and respiratory disorders due to disturbed inhibitory synaptic transmission, such as hyperekplexia.

Background: PDE5 inhibitors represent the gold standard in the medical therapy of erectile dysfunction (ED). Promising results have been published regarding further urological indications such as treatment of ureteral colic. The aim of the present study was to evaluate the functional effects of the PDE5 inhibitors sildenafil (SIL), vardenafil (VAR), and tadalafil (TAD) on tissue tension and cyclic nucleotide levels of human ureteral smooth muscle segments in vitro., Methods: Relaxant responses of human ureteral smooth muscle were investigated in vitro using the organ bath technique. Cyclic nucleotides cAMP and cGMP were determined by specific radioimmunoassays., Results: Relaxing effects of ureteral muscle tension were observed in the rank order VAR>SIL>TAD. While only VAR significantly elevated cGMP levels 3.3-fold over control, no increase for cAMP levels was observed., Conclusions: Our data provide evidence that cGMP is involved in the control of the normal function of the smooth musculature of the human ureter. Our findings suggest the potential of using selective inhibitors of PDE isoenzymes in the treatment of ureteral colic.

To study the role of myocardium beta-adrenoceptors pathway in ventricular remodeling of heart failure patients. beta-adrenegic receptor density (Bmax) and the content of cAMP were measured in the papillae of left ventricle and blood lymphocyte of 20 patients suffered from heart failure (CHF) (NYHZ classification II to III) Bmax were investigated using 3H-dihydroalpheolol as ligand. cAMP were assessed by competitive immunoassay. Left ventricle mass index (LVMI) were measured using echocardiogram. The results showed that the Bmax and cAMP in failing myocardium significantly negatively correlated with LVMI (r = -0.77, P < 0.01 and r = -0.46 P < 0.05 respectively); the Bmax of myocardium and blood lymphocyte in CHF patients with NYHA III (63 +/- 12 fmol/mgpro and 514 +/- 115 fmol/10(7) cell) significantly lowered than that of NYHA II patients (94 +/- 20 fmol/mgpro and 702 +/- 138 fmol/10(7) cell); and the Bmax of myocardium and blood lymphocyte in patients with abnormal LVMI (62 +/- 12 fmol/mgpro and 516 +/- 122 fmol/10(7) cell) decreased more significantly than that with normal LVMI patients; even in nromal LVMI patients (92 +/- 21 fmol/mgpro and 682 +/- 146 fmol/10(7) cell), the Bmax of blood lymphocyte was already decreased (P < 0.01), when comparing with controls. The intralymphocyte cAMP content sygnificantly decreased than that of controls (P < 0.05). These results indicated that Bmax could reflect the severity of ventricle remodeling and the impairment of myocardium. The regulation of myocardium intracellular messenger transduction was earlier than the pathologic structural change of LV remodeling.

Estrogen replacement therapy has been found to reduce the incidence of cardio- and cerebrovascular diseases in postmenopausal women. The mechanisms of this vasoprotection are controversial. In recent years, direct vascular actions of estrogens have been proposed in addition to beneficial effects on cardiac risk factors such as hypercholesterolemia. In an attempt to determine the role of direct hormonal influences on human arteries we analyzed the acute vascular responses to 17 beta-estradiol in a series of in vitro and in vivo studies. A dose-dependent estrogen-induced vasorelaxation was found in human coronary arteries in vitro which was more pronounced in women and associated with a significant increase in cyclic AMP and cyclic GMP content. This vascular response could be confirmed in healthy postmenopausal women during a clinical double-blind cross-over study using a quantitative duplex-sonographic approach. Estradiol induced a significant vasodilation and increase of blood flow in femoral arteries, whereas placebo had no effect. As measured by quantitative coronary angiography, high-dose estradiol application was also followed by a significant dilation of epicardial coronary arteries. These direct vascular actions such as vasodilation and increase of blood flow may contribute to the preventive estrogen effects on cardiovascular diseases in postmenopausal women.

A positive inotropic effect can be achieved by an increase in the intracellular concentration of calcium which interacts with the contractile proteins and/or by an increased sensitivity of the contractile proteins towards calcium. An increase in intracellular calcium concentration can be produced by cAMP-increasing agents. An increase in intracellular cAMP levels can result from stimulation of adenylate cyclase which leads to an increase in cAMP formation or from inhibition of the degradation of cAMP by inhibition of phosphodiesterases. The main effect of cAMP is to increase the calcium inward current during the action potential and to enhance the sequestration of calcium by intracellular calcium stores. This leads to an increase in calcium release and hence to an increase in the calcium concentration in the vicinity of the contractile proteins. PDE inhibitors are independent of receptors and also produce vasodilatation ("inodilators"). However, two potential disadvantages of PDEs must be kept in mind: 1) Positive chronotropy and induction of tachyarrhythmias and 2) tolerance which might be due to a down regulation of beta-adrenoceptors and/or to an increase in inhibitory G-proteins.

When enoximone is acutely administered to patients with stable angina and angiographically proven relevant coronary stenosis i.v. application of 0.75 mg/kg exhibits pronounced antiischemic effects. This could be observed in patients during exercise and in those in whom the ischemia was provoked by rapid cardiac stimulation. The antiischemic effects were documented by relief of symptoms, reduction of ST-depression, improvement of impaired myocardial wall motion, decrease to normalization of pathologically elevated filling pressure, amelioration of coronary blood flow as evidenced by myocard scintigraphy and washout time of an intracoronarily injected echo-contrast medium. There was also a definite improvement of ischemia-caused mitral regurgitation. Similar observations were found when the drug was injected in the diseased coronary arteries in a small dose (0.075 mg/kg) so that peripheral effects were not present. In comparison to the Ca(++)-blocker Gallopamil the antiischemic effects of Enoximone were more pronounced, a synergistic action was, however, observed. Negative dromotropic effects of Gallopamil could be abolished by Enoximone. With oral administration of the drug over a period of one week antiischemic effects could also be documented with Holter monitoring as well as during exercise. There was a reduction of ST-depression both at spontaneously occurring ischemic episodes and during exercise, in the number and duration of episodes of silent ischemia, particularly, however, a decrease in symptomatic episodes. In none of the patients under study proarrhythmic effects were observed.

Psoriasiform skin eruptions during treatment with beta-adrenergic blocking drugs have recently attracted increasing attention and led the Bundesgesundheitsamt [German Office of Public Health] to publish general information on this issue. Today's knowledge on the clinical picture, pharmacology, and the pathogenesis is discussed, with reference to the latest experimental data. The blockade of keratinocyte beta-adrenergic receptors may play a key role in the aetiopathology of this unwanted side-effect.

The addition of D(+)-glucose (final concentration 50 mM) to a cell suspension of yeasts (wild type and several mutants of the cell cycle, the cAMP-dependent protein kinase system, and a mutant of the adenylate cyclase gene) triggers a rapid increase in the concentrations of cAMP and cGMP in the wild strain. In contrast to cAMP, an increase of cGMP was also found in the mutants. cAMP and cGMP have been characterized as second messengers in eucaryotic cells. Cyclic nucleotide activation of the protein kinases enables them to perform their only known function in eukaryotes, the phosphorylation of substrate proteins. The results, described here by using selected yeast mutants as a model for higher eukaryotes, indicate that there exist two different regulatory systems for the control of the cAMP and cGMP levels.

Prostaglandins (PG) play an important role in the regulation of the renal blood flow and glomerular filtration rate. This study was designed to examine PG synthesis in the presence and absence of the ACE inhibitor captopril, PG binding to specific receptors and the ability of PG to stimulate cAMP accumulation in isolated glomeruli. Glomeruli were isolated from rat kidneys by a passive mechanical sieving technique. PG synthesis was determined by RTLC and RIA. The main eicosanoids synthesized by glomeruli were PGF2 alpha, thromboxane (TX) A2 (measured as TXB2), PGI2 (measured as 6-keto-PGF1 alpha) and PGE2. Binding experiments were performed with PGE1, PGE2 and the PGI2 analogue iloprost. Scatchard analysis revealed that the specific binding was highest for PGE1, followed by iloprost and PGE2. Adenylate cyclase was preferentially stimulated by PGE1 and PGE2, and to a lesser extent by PGI2, whereas PGF2 alpha had almost no effect. Captopril reduced mainly TXB2 concentrations. Glomerular TXB2 reduction, therefore, seems to be an additional hypotensive effect of captopril medication.

Protein kinases represent a diverse family of enzymes that play a critical role in regulation. Among nearly 100 known protein kinases, the cAMP-dependent enzyme is best understood biochemically. Unlike other protein kinases, cAMP-dependent protein kinase consists of two different types of subunits that dissociate, a regulatory subunit (R), which is the receptor for cAMP, and a catalytic subunit (C). In the absence of cAMP, the enzyme exists as an inactive tetramer, R2C2. The binding of intracellular cAMP to the R subunit decreases the affinity of the R subunit for the C subunit by approximately four orders of magnitude and, under physiological conditions, leads to dissociation of the holoenzyme into R2(cAMP)4 dimer and two free C subunits that are catalytically active. Mutants of the cAMP metabolism, adenylate cyclase and cell cycle mutants, provided further information about protein synthesis and cellular growth in Saccharomyces cerevisiae. The purified protein kinases were divided into different types according to their elution profiles from the DEAE-cellulose matrix. Two types of cAMP-dependent and two types of cAMP-independent protein kinases were isolated from the wild strain. Differences in the activities of the kinases in the mutants showed a close relationship to the locus of the respective mutations in the cell-cycle. Some properties of the protein kinases are discussed with respect to individual mutations.

Many of newly developed positive inotropic agents are phosphodiesterase inhibitors (PDEI). These are (in contrast to the classical, unselective PDEIs) in most cases selective inhibitors of PDE III which is inhibitable by cGMP. The most important action of PDEIs is a receptor-independent increase in intracellular cAMP, resulting from an inhibition of the degradation of cAMP. An increase in intracellular cAMP levels can also be produced by stimulation of adenylate cyclase, which leads to an increase in cAMP formation. Therefore, the effects of beta-adrenoceptor agonists (e. g., isoprenaline) and PDEIs are rather similar. The main effect of cAMP is to increase the slow Ca inward current during the action potential. This leads to an increase in Ca release from intracellular Ca stores, to an increase in the Ca concentration in the vicinity of the contractile proteins and, hence, to a positive inotropic effect. In addition, PDEIs also produce vasodilatation, which might be of even greater importance than the cardiostimulatory effects of these drugs ("inodilators"). However, two potential disadvantages of PDEIs must also be mentioned: 1) increase in beat frequency and tachyarrhythmias that also result from an increase in intracellular cAMP concentration and 2) decrease in effectiveness or tolerance, which might be due to an increase in inhibitory G proteins.

In heart failure, an increase in the activity of the sympathetic nervous system takes place to maintain perfusion pressure to vital organs, resulting in increased levels of noradrenaline in the blood of these patients. This permanent stimulation produces a down-regulation of cardiac beta-adrenoceptors. Since noradrenaline acts primarily on the cardiac beta 1-adrenoceptor subtype, beta 1-adrenoceptors decrease in number, whereas the beta 2-adrenoceptor subpopulation remains unchanged in most instances. Consequently, the positive inotropic response to beta-adrenoceptor agonists is diminished. However, there is also a decrease in the positive inotropic effect of beta 2-adrenoceptor agonists, histamine and cAMP-phosphodiesterase inhibitors such as milrinone, whereas the positive inotropic effect of cAMP-independent Na(+)-channel activators such as DPI 206-106 and the effects of cardiac glycosides are not diminished. These observations suggest a more generalised alteration of the cAMP-adenylate cyclase system in the failing heart. Stimulatory guanine nucleotide-binding protein (Gs) couples receptors to adenylate cyclase that stimulate cAMP formation, such as beta-adrenoceptors, histamine receptors and glucagon receptors. In the failing human heart, Gs content has been reported to remain unchanged as compared with that in non-failing myocardium. However, there is a 35%-40% increase in inhibitory guanine nucleotide-binding proteins (Gi), which are involved in the receptor-mediated inhibition of adenylate cyclase. Taken together, two defects of the cAMP-adenylate cyclase system have been identified: an increase in Gi content and a decrease in the number of beta-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the effect of thyroxine (T4 0.050 mg/kg/d, i.p.), TSH (0.08 U/kg/d, i.p.) and hypothalamic peptide (HF; 1 mg protein/kg/d, i.p.) given alone or in combination, on the growth of murine (NB C-1300) and human (NB Park) neuroblastoma transplanted onto the nude mouse (nu/nu). Both T4 and TSH caused a significant increase (perchlorate a decrease) of the serum T3. Histologically, the T4 treatment was followed by partial tumor necrosis and a marked growth of connective tissue within the tumors; there was no significant change in tumor weight as compared to the control group. Treatment with HF alone or in combination with T4 inhibited in 30% the invasive growth of the neuroblastoma transplants and a fatty degeneration was found in 25% of the human NB-TX after 28 days of treatment. The measurement of the intratumoral content of the cyclic nucleotides showed a significant increase of the cAMP and a decrease of the cGMP. The morphological and biochemical alteration observed under treatment with thyroid hormone or analogues could possibly be applied for therapeutic purposes.

The effect of triiodothyronine (T3) on the differentiation of cultured neuroblastoma (NB) cells was studied after 9 days of treatment with a dose of 10(-4) M/10(6) cells per day. Using phase contrast microscopy, 30-50% of NB cells showed formation of neurites as a morphological sign of cellular differentiation. The initial rise of the mitosis rate was followed by a plateau. Changes in cyclic nucleotide content, in the triphosphates and in the activity of the enzyme ornithine decarboxylase (ODC) were assessed in 2 human and 2 murine cell lines to serve as biochemical parameters of the cell differentiation induced by T3. Whereas the cAMP level increased significantly (3 to 7 fold compared with its initial value), the cGMP value dropped to 30 to 50% of that of the control group. ATP and GTP increased about 200%, the ODC showed a decrease of about 50%. The present studies show a biphasic effect of T3 on neuroblastoma cells: the initial rise of mitotic activity is followed by increased cell differentiation starting from day 4 of the treatment.

High performance liquid chromatography allows a simultaneous determination of ATP, CTP, GTP, and the cyclic nucleotides. During cell differentiation initiated by DBcAMP, we observed an increase in ATP, cAMP, GTP and an decrease in CTP, cCMP, and cGMP levels. It is being discussed the changes of relation between the triphosphates their corresponding cyclic nucleotides during the differentiation of NB cells.

D-glucose stimulates the accumulation of cyclic AMP in isolated islets of Langerhans in a dose-dependent manner. This effect is present as long as the sugar remains elevated in the incubate. Under present experimental conditions the stimulation of cyclic AMP precedes insulin release. Islet or medium cyclic AMP, and insulin secretion are closely correlated at various incubation times. We conclude that the beta-cell cyclic AMP system is one of the major mediators of the glucose signal to insulin secretion. Tolbutamide and glibenclamide have similar effects in the absence or with low concentrations of glucose. These results may indicate that these sulfonylurea derivates act at sites where glucose exerts its effect.

Bencyclane (N-[3-(1-benzyl-cycloheptyloxy)-propyl]-N,N-dimethyl-amine-hydrogenfumarate, Fludilat), inhibits phosphodiesterase(PDE)-activity in vitro similarly to several other smooth muscle relaxants. Compared with papaverine this inhibitory effect of bencyclane on PDE is weak despite of its strong relaxant effect on smooth muscle, which is about equal to that of papaverine. 14C-Bencyclane is accumulated 8-fold in the smooth muscle tissue of bovine coronary arteries, indicating that relaxation is caused by 8-fold higher concentrations in the tissue than in the organ bath. A comparison of (corrected) ED50-values for relaxation with Ki-values for PDE-inhibition obtained with several PDE-inhibitors, including bencyclane, yields a significant correlation between both parameters. Since in subsequent studies in isolated tracheal muscle strips bencyclane at maximum relaxing concentrations did not increase cAMP, which was in contrast to the actions of papaverine or aminophylline, it is likely that bencyclane-induced smooth muscle relaxation is unrelated to inhibition of PDE or cAMP. In the same dose range in which bencyclane relaxes smooth muscles it exerts a non-specific antiadrenergic inhibitory effect, possibly due to its local anesthetic action at the cell membrane. It is also possible that the myocardial inhibitory effect of bencyclane is caused by a direct Ca++-antagonistic mechanism (Fleckenstein et al. 1971).

The tissue changes in osteogenesis imperfecta apparently lie in the collagen and in the glycosaminoglycans. The collagen shows structural development disturbance and incomplete calcification. The tissue glycosaminoglycans are increased. The basis probably lies in a disturbed ATP metabolism (Solomons and Millar, 1973). An increased pyrophosphate concentration explains the decreased calcification and the structural changes. The increased osteolysis could be explained by increased quantities of cAMP.

Using pregnant Wistar rats a comparative study was carried out, which was aimed to investigate the effect of long-term tocolysis (second half of gestation) with fenoterol alone as well as in combination with the cardioselective beta-blocker metoprolol (Beloc) upon the level of beta-adrenoceptor stimulation in maternal pulmonal, myocardial and myometrial tissue and in the myocardium of the fetuses. Radioimmunologic assessment of cyclic AMP tissue concentrations was used to obtain a parameter for beta-adrenoceptor stimulation. During treatment with fenoterol alone a significant rise of cyclic-AMP could be observed in all tissues, fetal myocardium showing the most pronounced rise. When combining fenoterol and metoprolol no derangement of the desired therapeutical beta 2-effect upon myometrium and lung could be found. Cyclic-AMP concentration in the maternal myocardium, however, was reduced significantly after combination therapy as compared to the monotherapy group, stressing the cardioprotective effect of metoprolol during beta 2-mimetic therapy, which yet has been demonstrated by means of other experimental models. As a similar tendency could be found in fetal myocardium, the conclusion may be drawn that combining metoprolol with fenoterol exerts also a fetal cardioprotection during beta 2-mimetic therapy of pregnant individuals. Furthermore possible effects of this combined therapy upon fetal beta-adrenergic reactions in general are discussed in this study.

Myocardial beta-adrenoceptors mediate physiological effects of the agonists noradrenaline und adrenaline and stimulant effects of related amines and beta-blockers. At least 2 beta-adrenoceptor subtypes appear to contribute to the mediation of physiological effects. beta-adrenoceptor subtypes have recently been found with selective beta-blockers and nonphysiological agonists in several heart regions. However, no evidence has yet been reported that the affinity of a physiological agonist for cardiac beta-adrenoceptor subtypes differs. The possibility is discussed that an agonist may cause greater conformational change of one subtype than of another while binding to the same extent to both beta-adrenoceptor populations. The affinity of catecholamines for beta-adrenoceptors is low. Marked positive inotropic and chronotropic effects occur with catecholamine concentrations causing low beta-adrenoceptor occupancy and barely suprathreshold stimulation of the adenylyl cyclase. The large beta-adrenoceptor reserve and adenylyl cyclase reserve enable the regulation of the sinoatrial pacemaker activity and of ventricular and atrial contractility. Thus exposure to high catecholamine concentrations causes a pronounced decrease of Vmax for the adenylyl cyclase with a concurrent decrease in inotropic and chronotropic potencies, but without decreasing maximum inotropic and chronotropic effects of catecholamines. Data from isolated human myocardium suggest that the intropic potency of catecholamines is lower and the adenylyl cyclase reserve smaller than in other species. Pindolol, its derivatives, and some other partial agonists only cause positive chronotropic effects at concentrations considerably higher than those required to half-saturate cardiac beta-receptors.

During animal experiments two substances, which are used for tocolysis (Fenoterol and Clenbuterol) have been compared regarding their tocolytic efficiency (determinations of myometrial cyclic AMP after long term treatment of the pregnant rat), their effects upon myocardial high energy phosphates (determinations of maternal myocardial high energy phosphates as well as of maternal and fetal myocardial cyclic AMP after long term treatment of the pregnant rat) and upon the hemodynamic situation (acute experiments with thoracotomized dogs). While significant hemodynamic derangements could be stated when using Fenoterol, no significant evidence for such alterations could be found during Clenbuterol administration during acute experiments. Determinations of myocardial high energy phosphates however reflected an augmented myocardial workload, both after Fenoterol and Clenbuterol administration. As by means of myometrial cyclic AMP determinations Clenbuterol proved to be at least as efficient as Fenoterol, concerning the tocolytic effect, Clenbuterol can be recommended as an oral tocolytic because of its pharmaco-cinetic advantages and the encouraging results from our hemodynamic investigations. According to results from chronical experiments an additional cardioprotection by means of magnesium substitution and eventually beta 1-blockade is still recommended.

1. Total lipids, total cholesterol, cholesterol esters, phospholipids, triglycerides and free fatty acids as well as the fatty acids profiles of the different lipid classes were determined in serum, lipomatous and normal adipose tissue. Triglycerides were elevated in patient L's serum. The distribution of serum lipoproteins in this patient's serum showed a type IV according to Fredrickson. All other lipid parameters were within the normal range. Palmitoleic acid was increased nearly in all lipid fractions of the patients' sera as well as in the lipids of lipomatous subcutaneous adipose tissue. 2. The lipomatous adipose tissues of the patients showing no histological abnormalities revealed higher levels of cyclic AMP than normal subcutaneous adipose tissue. 3. Serum uric acid was normal (patient E.), between the normal and pathological range (patient L.) and elevated (patient W.). Urinary uric acid excretion was increased in all three patients. 4. 14C-glycine was overincorporated into urinary uric acid in all three patients. 5. Adenine phosphoribosyltransferase activities in the hemolysates were within the normal range. A decrease of hypoxanthine-guanine phosphoribosyltransferase activities could be demonstrated in two patients' (e., w.) erythrocytes. Erythrocyte phosphoribosylpyrophate synthetase activity was slightly increased in patient L.'s and twice the normal value in patient W.'s erythrocytes.

Age caused concurrent changes in the activation of the adenylate-cyclase activity by dopamine in the diencephalon and the stimulation of the basal level of cAMP by isoproterenol in the lymphocytes were demonstrated in the spontaneously tumor producing C3H mice. These changes may be related to the occurrence of tumors in these animals. The above-mentioned changes in the cAMP system were not found in AB mice. By treating the adult C3H mice with substances which increase the cAMP level, it was possible to achieve a renewed stimulation of the cAMP system as seen in young mice. With this treatment the spontaneous tumor-induction rate was also reduced. In the adenocarcinomas of the C3H mice a decrease in the level of prostaglandin E and an increase in the level of prostaglandin F2 alpha was observed.

1. It is becoming increasingly clear that besides traditional immunosuppressive agents, an array of miscellaneous influences and conditions, as well as drugs used for other purposes, can affect the immune system. The potential pathogenetic role of immunity in an ever growing number of diseases, including infections, cancer, and autoimmune processes, confers on the concept of concomitant immunosuppression or immunotoxicology its due place in the discipline of immunopharmacology. 2. Microorganisms such as viruses, bacteria, and protozoa (and their products), as well as parasites, may depress immune reactivity. The mechanism of action, dose-response dependency, effect of timing, and relation to bacterial adjuvanticity need more thorough exploration. 3. The efficacy of immunosuppressive drug protocols can be improved by combining immunosuppressants without bone marrow toxicity, such as niridazole or free fatty acids, with the standard antiproliferative immunosuppressive agents. 4. Prostaglandin is a likely candidate for an essential role as an immunosuppressive effector. Its release from T-suppressor cells is triggered for example by microorganisms. Moreover, dietetic and metabolic factors, such as free fatty acids, and nervous impulses affect prostaglandin formation. If thus constitutes a link between the nervous system and, on the other hand, immunity and possibly cancer.

Up to 4 weeks after partial hepatectomy the concentrations of immunoreactive insulin and glucagon in the blood plasma of rats were determined. Furthermore we measured the activity of acid phosphatase in the serum, the concentration of cyclic AMP in liver cells, the activities of acid phosphatase in whole liver cells and in the cytosol of liver cells after partial hepatectomy. 2 h after partial hepatectomy there was a decline of the concentration of insulin in the plasma to about 13% of the initial value. 12 h after surgery a 5-fold increase of glucagon was found in the plasma. Shortly after this cyclic AMP reached its highest concentration. The activity of acid phosphatase in the whole liver cells and in the cytosol decreases slightly in the first 24 h after surgery whereas there is an increase of the activity of acid phosphatase in the serum.

Loss of appetite, strongly reduced feed intake, and stop in weight gain are characteristic signs of alimentary zinc deficiency. The present paper investigates some parameters of the energy metabolism of Zn-deficient rats in order to obtain information on possible disturbances. The blood of Zn-deficient rats showed an increased activity of adenosine triphosphatase (ATPase) in comparison to ad-libitum- and pair-fed control animals. Therefore the concentration of adenosine triphosphate (ATP) was reduced and the concentration of adenosine diphosphate (ADP) increased in deficient animals. As a consequence, the ratio ATP/ADP was strongly reduced in Zn-deficient rats compared with both control groups. The concentration of adenosine monophosphate (AMP) was reduced in the blood of Zn-deficient rats. The levels of c-AMP in serum and urine were markedly increased in Zn-deficient rats in comparison with both control groups. Key enzymes of energetic utilization of carbohydrates such as fructose-1.6-biphosphatase and glucose-6-phosphate dehydrogenase were reduced in their activities in livers and kidneys of Zn-deficient animals. The results show that alimentary Zn deficiency impairs some parameters of the energy metabolism. The problems of reduced feed intake in Zn deficiency still remain unsolved.

Vascular endothelium is not only a mechanical, non-thrombogenetic barrier in the blood vessel wall, but probably plays a substantial role in the regulation of vascular smooth muscle tone. Besides the ability to metabolize vasoactive compounds like catecholamines and angiotensins, endothelial cells possess an active biochemical machinery for the production of vasoactive compounds (e.g. prostacyclin). During recent years it has become apparent that a large variety of vasodilator compounds require intact endothelial cells to exert their relaxing action. These endothelium-dependent relaxations are not mediated by prostacyclin of endothelial origin, but by an unknown substance that is referred to as endothelium-derived relaxing factor (EDRF). EDRF is a chemically unstable humoral substance and has a biological half-life in the range of seconds. Although EDRF is not a prostaglandin or leukotriene, several findings suggest possible relationships of its production with the eicosanoid system. Both stimulation of phospholipase A2 and inhibition of lysolecithin acyltransferase induce the production of EDRF. This suggests that cleavage of phospholipids may be an important step in the formation of EDRF. EDRF-mediated vascular relaxations (like relaxations induced by nitrovasodilators) were found to be associated with increases in cyclic GMP in vascular smooth muscle. Endothelial cells produce a factor that directly stimulates the enzymatic activity of soluble guanylate cyclase. Several points of evidence indicate that this factor may be identical with EDRF. Thus the mechanism of action of the EDRF formed endogenously may be similar to that of nitrovasodilators.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of methylbenzimidazol-2-yl carbamate (MBC) on the cyclic nucleotide system of germinating Aspergillus nidulans conidia has been investigated throughout the cell cycle. The content in cyclic adenosine 3',5'-monophosphate (cAMP) and cyclic guanosine 3',5'-monophosphate (cGMP) is rapidly decreased in the course of conidia swelling and has been found not to be influenced by MBC. On the other hand, influence of MBC leads, in inhibited nuclear division, to a significant increase of the intracellular cAMP level in the G2-period between the eighth and tenth hour after incubation. The adenylate cyclase activity has not been significantly influenced during this period by MBC treatment. On the contrary, the cAMP-specific phosphodiesterase activity has been decreased. The cGMP content of germinating conidia decreased, contrary to cAMP by MBC treatment between the seventh and twelfth hour. Activity of guanylate cyclase has been generally stimulated in the presence of MBC, whereas that of the cGMP-specific phosphodiesterase as a result of mitosis inhibition has been blocked. the influence of the cyclic nucleotide system on mitosis is discussed in terms of a hypothetical model.

Deeper insight into the pharmacodynamics and pharmacokinetics of theophylline during the past 10 years led to the wide-spread use of the substance in the treatment of obstructive airway diseases. The effect of theophylline can be explained by different mechanisms of action, namely increase in cAMP and prostaglandins, redistribution of calcium, and blockade of purinergic receptors. Besides the known antiobstructive activity of theophylline ethylenediamine, its influence on the respiratory muscles is an essential clinical quality. The results of pharmacokinetic studies and routine determination of theophylline levels contributed to greatly improve the efficacy of theophylline therapy. At adequate doses, theophylline or theophylline ethylenediamine in sustained-release form constitutes the most effective long-term treatment of chronic asthma today. The pharmacological properties of ethylenediamine reinforce some of the more important effects of theophylline and improve tolerance. Combining the substance with beta-sympathomimetics elicits additive effects, while side effects are kept low.

The effect of lithium on the cAMP metabolism was studied in rat brain. It was shown that: 1. Acute and subacute doses of lithium have no effect on the cAMP content of the forebrain of rats while chronic administrations significantly reduce the cAMP level in the brain by 30%; 2. the activities of the cerebral cAMP and cGMP phosphodiesterases are not affected by lithium in vitro; 3. the adenyl cyclase in rat brain homogenates stimulated by sodium fluoride and noradrenaline is inhibited dose-dependently in the mM range and 4. adenyl cyclase in isolated cells from the rat forebrain is very sensitive to inhibition by lithium in the therapeutically relevant microM range. With all due caution in transferring experimental results to the mechanisms of action of drugs in humans, it is obvious from these results in comparison with the effect of lithium on hormone-sensitive adenyl cyclases from extracerebral tissues that the effect of lithium salts in manic psychoses may be due to inhibition, and their prophylactic action probably to a "stabilizing" of cerebral adenyl cyclases.