[Effect of synthetic somatostatin on basal and stimulated growth hormone and prolactin secretion in vitro]

The effect of synthetic somatostatin on the basal and stimulated secretion of growth hormone and prolactin under conditions of incubation of the adenohypophysis (ADH) tissue in vitro was studied. The labeled growth hormones (GH) and prolactin (Pl) secreted was assayed by the method of electrophoresis in polyacrylamide gel as modified by the authors. Synthetic somatostatin (10 and 100 nM) suppressed the basal and stimulated by 2--0-dibutyril AMP, theophylline, and prostaglandins of E series GH labeled secretion. In doses of 100 nM the inhibitor also suppressed the basal and the stimulated by 2--0-dibutyril AMP and theophylline release of labeled Pl. Apparently, the inhibitory action of somatostatin involves the reduction of the ADH activity of adenylatecyclase.

Prostaglandin inhibition of testosterone production induced by luteinizing hormone, dibutyryl cyclic AMP or 3-isobutyl-1-methyl xanthine in dispersed rat testicular interstitial cells

Testicular interstitial cells were utilized to study the effects of prostaglandins (PG) on in vitro testosterone production and to examine the role of cyclic adenosine-3',5'-monophosphate (cAMP) in this process. Testosterone production was assessed after 3 hour incubations while cAMP accumulation was examined after a 0.5 hour incubation period. Testosterone and cAMP were measured by radioimmunoassay. None of the PGs tested (PGA, PGA2, PGB1, PGE1, PGE2, PGF1alpha PGF2alpha) altered basal testosterone production when present in incubates at concentrations of 1.3 X 10(-8) M to 1.3 X 10(-4). However, at concentrations of 1.3 X 10(-4) M all of these PGs were capable of decreasing Luteinizing Hormone (LH; 100ng)-induced testosterone production. The inhibition of LH-induced testosterone production by the B, E and F series PGs was less pronounced than that for the A series. PGA1 and PGA2 exhibited 80% and 95% inhibition, respectively, at 1.3 X 10(4) M. The inhibitory action of 4 X 10(5) M PGA1 or PGA2 was evident within 30 minutes. Preincubation of interstitial cells with indomethacin (10(-5) or 10(-6) M) for 30 minutes did not alter subsequent basal or LH (100ng)-induced testosterone production. Accumulation of cAMP was stimulated by LH (10 microgram) or by PGs (1.3 X 10(-4) M PGA1, PGA2, PGB1, PGE1 or PGF2alpha). The PG-induced cAMP accumulation thus occurred at concentrations where LH-stimulated testosterone production was inhibited. Furthermore, PGA1 and PGA2 (1.3 X 10(-4) M) inhibited testosterone production induced by either 3-isobutyl-1-methyl xanthine (MIX; 10(-4) M or 10(-3) M) or dibutyryl cAMP (dbcAMP; 10(-4) M or 10(-3) M). These results indicate that PGs can block testosterone production by a direct effect on testicular interstitial cells and suggest that PGs exert their inhibitory action distal to stimulation of cAMP formation. PGs do not appear to play a role in the mechanism of LH action.

Rat oocyte maturation in vitro: relief of cyclic AMP inhibition by gonadotropins

The hormone-independent, spontaneous maturation that rat oocytes undergo in vitro can be inhibited by derivatives of cyclic AMP and inhibitors of cyclic nucleotide phosphodiesterase. In this study, we have shown that this inhibition of maturation can be partially relieved by preparations of ovine and rat luteinizing hormone or follicle-stimulating hormone. The ability of gonadotropins to foster the resumption of maturation in cultures of cyclic AMP-inhibited oocytes suggests that this system is suitable for studies of the hormonal control of oocyte development. The dose and time dependency of the response to gonadotropins has been examined in order to study the role of these hormones in oocyte maturation and to compare this effect to other known responses of the cumulus-oocyte complex. These studies show that highly purified preparations of rat gonadotropins are less effective inducers of maturation than the more commonly used, but considerably less purified, preparations of ovine gonadotropins. Almost complete relief of inhibition is observed, however, when the oocytes are exposed to a combination of rat luteinizing hormone and follicle-stimulating hormone. Oocyte maturation was not influenced by the sex steroids progesterone or 17beta-estradiol. Our results suggest that: (i) cyclic AMP is involved in the intrafollicular inhibition of oocyte maturation; (ii) both gonadotropins are required for maximal stimulation of the resumption of oocyte meiosis; and (iii) steroids are not involved in this response to gonadotropins.

Inhibition of steroidogenic response to corticotropin in mouse adrenal tumor cells (Y-1) by the ionophore A23187. Role of protein biosynthesis

Addition of the ionophore A23187 to Y-1 mouse adrenal tumor cells in monolayer culture inhibits steroidogenesis and the steroidogenic response to corticotropin (50% inhibition at 1 . 10(-7)M). Inhibition is rapid in onset and is not overcome by addition of external Ca2+. The ionophore also inhibits stimulation of steroid synthesis by cyclic AMP. A23187 inhibits incorporation of the amino acid lysine into protein by Y-1 cells and the dose dependence of this inhibition closely resembles that of the inhibition of the steroidogenic response to corticotropin. Addition of A23187 to a subcellular system for protein synthesis prepared from Y-1 cells, inhibits incorporation of the amino acid phenylalanine into protein and this effect is not overcome by high concentrations of Ca2+. The inhibitory effect of A23187 on the response to corticotropin, like that response itself, takes place at some part of steroid synthesis after entry of cholesterol into the cells and before the side-chain cleavage of cholesterol. These studies confirm the importance of protein synthesis in the response to corticotropin and demonstrate that the effect of protein synthesized under the influence of corticotropin is exerted at some point in the events which bring substrate (cholesterol) to the mitochondrial side-chain cleavage enzyme system. It is also shown that A23187 inhibits protein synthesis, and hence the response to corticotropin, by a mechanism which is independent of the concentration of available Ca2+.

Restoration by levamisole of rosette-forming cells inhibited by histamine, db-CAMP and adenosine

Db-cAMP and adenosine in vitro markedly inhibited the E-rosette formation of peripheral T-cells of healthy subjects. Histamine in vitro also inhibited the E-rosette formation, but only in patients with allergic disorders. Levamisole in vitro significantly restored the E-rosette formation of T-cells inhibited by db-cAMP, adenosine and histamine.

Relationship between dibutyryl cyclic AMP and microtubule organization in contracting heart muscle cells

Rhythmic and synchronous contractions of interconnecting myocyte cultures prepared from fetal rat hearts are arrested upon the addition of 0.2--2.0 mM N6, O2'-dibuturyladenosine 3':5'-cyclic monophosphate (Bt2cAMP). The contractions arrested by Bt2cAMP are restored either by diluting the Bt2cAMP from the media or by adding colchicine. While colchicine restores Bt2cAMP-arrested myocyte contractions at concentrations as low as 1.0 micron, the inactive isomer lumicolchicine shows no effect. Morphologically, Bt2cAMP treatment of myocyte cultures results in the appearance of numerous elongated cellular processes not present in control cultures. Ultrastructural examination indicates that in Bt2cAMP-treated cells the intracellular distribution of microtubules is altered such that these organelles appear to accumulate in parallel arrays. In cells not treated with Bt2cAMP, the microtubules appear randomly oriented, while in cells treated with only colchicine, intact microtubules are not observed. The relationship between microtubules an heart cell contraction is discussed.

Stimulation of colonic glycoprotein synthesis by dibutyryl cyclic AMP and theophylline

The effects of dibutyryl cyclic AMP (B2cAMP) and theophylline on glyoprotein synthesis in rabbit colon were studied in mucosal organ cultures using [3H]glucosamine as a precursor. Addition of B2cAMP (1 mm) to culture medium caused a significant increase in glycoprotein synthesis after 12 and 24 hr compared with biopsies cultured in control medium. The increase in glycoprotein synthesis was observed only if the cyclic nucleotide was present continuously in the incubation medium for at least 12 hr. The stimulatory effect of B2cAMP on [3H]glucosamine incorporation was blocked by cycloheximide. B2cAMP also stimulated mucosal uptake of glucosamine into the intracellular pool and markedly enhanced specific activity of mucosa galactosyltransferase, an enzyme involved in glycoprotein synthesis. Addition of 5mM theophylline caused a greater than 2-fold increase in cAMP levels, which was also accompanied by an increase in glucosamine uptake and incorporation into mucosal glycoproteins. This study demonstrates that elevation of intracellular cAMP concentration in colon epithelium in vitro is associated with an increase in glycoprotein synthesis. These effects may be mediated in part by (1) increased uptake of glycoprotein precursors such as glucosamine, and (2) increased activity of glycoprotein synthetic enzymes.

Effects of gaba, gabob and some anticonvulsant drugs on dibutyryl cyclic AMP evoked seizures

The present experiments were undertaken to study the possible effects of Gaba, Gabob, phenobarbitone, diphenylhydantoin, and diazepam given systemically on convulsant activity evoked in chicks by intrahypothalamic injection of dibutyryl cyclic AMP (cAMP). Diphenylhydantoin and phenobarbitone antagonized the effect of dibutyryl cAMP but unfortunately the effects of Gaba and Gabob were complicated by osmotic effects. Diazepam, an anticonvulsant benzodiazepine, did not affect dibutyryl cAMP-induced electrocortical spiking. The dibutyryl cAMP-induced syndrome seems to be of limited value as a model for assessing the activity of anticonvulsant drugs are present.

[Control of the regeneration of small pieces of the planarian Dugesia tigrina by cylic AMP and GMP nucleotides]

The effects on regeneration of cyclic nucleotides AMP and GMP were studied on small pieces of the planarian worm Dugesia tigrina. db cAMP, 8Br cGMP and substances acting on their metabolism were used in this work (aminophylline, insulin, imidazole). It seems that these second messengers play a role in a mechanism of regulation in which cGMP has a promotive action and cAMP an inhibitive one.

Influence of adenosine, cAMP and db-cAMP on responses of the isolated terminal guinea-pig ileum to electrical stimulation

Adenosine, cAMP and db-cAMP were found to inhibit nerve-mediated contractions of the terminal ileum elicited by electrical stimulation (ES). Responses to ES at 30 Hz, which are believed to be of adrenergic origin, were considerably more affected than the responses to ES at 3 Hz, which may be of purinergic orign. The following order of relative inhibitory potencies was established: adenosine greater than cAMP greater than db-cAMP. Adenosine, cAMP and db-cAMP did not affect the contractile responses of the preparation to histamine, potassium and noradrenaline. Therefore, the observed inhibition of nerve-mediated contractions was thought to be due to an action on presynaptic sites, i.e. on the neural network within the intestine. This action was antagonized by an increase in external calcium and by aminophylline, which is known to increase intracellular calcium. The present experiments suggests that the inhibitory action of adenosine, cAMP and db-cAMP results from a reduction of calcium fluxes across the neural membrane and to a subsequent reduction in the release of neurotransmitter(s). The inhibitory effect of cAMP appeared to be nonspecific and was presumably related to adenosine in its molecule.

Effects of corticosterone on adrenocorticotrophin-induced mitochondrial differentiation with special reference to 11 beta- and 18-hydroxylation

The effects of corticosterone in concentrations found in adrenal venous plasma on ACTH-induced changes in cultured cortical cells derived from foetal rat adrenals were studied. Corticosterone at a concentration of 5-7 X 10(-5) mol/l completely inhibited mitochondrial differentiation to fasciculte-like morphology. The same cultures revealed significant inhibition of 11beta- and 18-hydroxylation compared with cultures treated with ACTH only. This was shown by the reduced formation of corticosterone and 18-OH-deoxycorticosterone (48%, P less than 0-001) and simultaneous enhancement of deoxycorticosterone formation (33%, P less than 0-05) from added [4-14C]progesterone. Similar inhibition was observed when dibutyryl cyclic AMP replaced ACTH as an inducer of differentiation. Lower concentrations of corticosterone (1-2 X 10(-5) and 2-4 X 10(-5) mol/l) inhibited ACTH-stimulated formation of corticosterone and 18-OH-deoxycorticosterone from endogenous precursors. The results demonstrate that corticosterone regulates the stage of differentiation in cultured adrenocortical cells. The possible role of corticosterone in the regulation of growth and steroidogenic capacity of the adrenal cortex is discussed.

Inhibitory effect of somatostatin on dibutyryl cyclic AMP-induced insulin and growth hormone release in human subjects

The effect of somatostatin on the responses of blood glucose, plasma immunoreactive insulin (IRI), growth hormone (GH), and free fatty acids (FFA) to the injection of dibutyryl cyclic AMP (DBC) was studied in six normal volunteers. DBC, when injected alone, induced a rapid increase in blood glucose and plasma IRI levels, while GH concentrations showed a less marked and more delayed increase and plasma FFA showed a clear downtrend. Somatostatin infusion suppressed the GH and IRI release induced by DBC, potentiated its hyperglycemic effect and changed the pattern of FFA. These results suggest that somatostatin inhibits hormone secretion distal to the generation of cyclic AMP.

Ability of various factors to oppose the stimulatory effect of dibutyrylcyclic AMP on the release of melanocyte-stimulating hormone by the rat pituitary in vitro

Various agents were tested for their ability to oppose the stimulatory effect of dibutyryl cyclic AMP on the release of the melanocyte-stimulating hormone from the rat neuro intermediate lobe in vitro. Only dopamine exhibited an inhibitory effect; serotonin, gamma-amino-butyric acid, tocinoic acid, tocinamide, the tripeptide Pro-Leu-Gly-NH2 and dibutyryl cyclic GMP were all ineffective.

[Protective effect of thymidine in relation to the cytostatic action of cyclic adenosine-3', 5'-monophosphate in mammalian cell cultures]

Under the action of lmM of cyclic adenosine-3',5'-monophosphate (cAMP) the survival and the rate of reproduction of the cells of Chinese hamster in the culture decreased in comparison with control to 27 and 42%, respectively. Addition of 0.02 mM thymidine together with cAMP almost completely eliminated the cytostatic action of the latter. Thymidine also prevented the cytostatic effect of noncyclic 5'-AMR, but failed to influence the death of the cells with the action of dibutyril cAMP and theophylline. Thymidine failed to prevent the inhibitory action of cAMP on the mutant strains of mouse cells defective by thymidinekinase. A conclusion was drawn that in the concentrations under study thecytostatic action of the exogenous cAMP on the cells of mammals served as the sequence of splitting to 5'-AMP in the culture medium and was realized by blocking one of the stages of TMP synthesis.

Direct effects of cyclic AMP and dibutyryl cyclic AMP on renal blood flow

The direct effects of adenosine 3',5'-cyclic monophosphate (cAMP) and dibutyryl adenosine 3',5'-cyclic monophosphate (D-cAMP) on renal blood flow were studied in dogs under renal perfusion with constant pressure. Cyclic AMP caused a marked phasic decrease in renal blood flow in doses more than 1 mg, while D-cAMP produced a slight increase in that in doses more than 10 mg. The vasoconstrictive effect of cAMP was not blocked by the pretreatment with phenoxybenzamine, but was markedly depressed during the infusion of aminophylline. On the other hand, the vasodilative effect of D-cAMP was not affected either by the pretreatment with propranolol or during the infusion of aminophylline. These findings indicate that cAMP and D-cAMP have an opposite direct effect on the renal artery, independently of the adrenergic receptors. However, there may be a possibility that cAMP produces its vasoconstrictive effect on the renal artery partly through the action of its metabolites.

The hyperthermic effect of intracerebroventricular cholera enterotoxin in the unanaesthetized cat

1. Cholera enterotoxin was used to evaluate a possible role of endogenous cyclic AMP in production of hyperthermia. Injection of purified toxin (0.10-1.0 mug in 0.10 ml.) into the lateral cerebral ventricle of unanaesthetized cats caused dose-related hyperthermic responses. Heating the toxin for 40 min at 90 degrees C abolished its hyperthermic activity.2. Intraventricular administration of dibutyryl cyclic AMP (250-1000 mug) also caused hyperthermia which, however, was preceded by transient periods of hypothermia and/or excitation in about half of the tests.3. Paracetamol, indomethacin and sodium salicylate inhibited hyperthermic responses to cholera enterotoxin. Paracetamol and indomethacin also inhibited hyperthermia induced by dibutyryl cyclic AMP (sodium salicylate was not tested).4. It is likely that the hyperthermic effect of cholera enterotoxin in the cat is mediated via endogenous cyclic AMP and that the antipyretics inhibit this effect by an action subsequent to the increase in cyclic AMP.5. It is unlikely that prostaglandin-induced hyperthermia in the cat is mediated via cyclic AMP since these antipyretics do not inhibit this response to prostaglandin E(1).