Glucose synthesis by isolated guinea-pig hepatocytes. Effect of cyclic AMP and dibutyryl cyclic AMP.

In isolated guinea-pig hepatocytes, dibutyryl cyclic AMP stimulated gluconeogenesis from 2 mM galactose by 25 and 40% respectively. In the presence of 0.5 mM theophylline, cyclic AMP (0.1 mM) increased glucose synthesis from lactate and galactose by 26 and 34% respectively.     

Endogenous cyclic AMP in thyroid cell culture. Effect of thyroid-stimulating hormone and dibutyryl cyclic AMP

We have studied the variations of endogenous cyclic AMP levels in thyroid cells cultured over a period of 7 days in several conditions: in the presence of thyroid-stimulating hormone or dibutyryl cyclin AMP which both promote the aggregation of isolated cell into follicles, and in their absence when cells develop as a typical monolayer. In follicle-forming cells, the cyclic AMP level was found to rise during the first day of culture, then to fall rapidly. In monolayer-forming cells, the cyclic AMP content slightly increases attaining the same level as found in other cells at the fourth day, which remains stable till the seventh day. We have investigated the response of these cells to the acute effect of thyroid-stimulating hormone: only cells cultured in the presence of dibutyryl cyclic AMP retain the capability of increasing their cycli AMP concentration whereas monolayer-forming cells do not preserve this quality of thyroid cells.     

Endogenous cyclic AMP in thyroid cell culture. Effect of thyroid-stimulating hormone and dibutyryl cyclic AMP.

We have studied the variations of endogenous cyclic AMP levels in thyroid cells cultured over a period of 7 days in several conditions: in the presence of thyroid-stimulating hormone or dibutyryl cyclic AMP which both promote the aggregation of isolated cells into follicles, and in their absence when cells develop as a typical monolayer. In follicle-forming cells, the cyclic AMP level was found to rise during the first day of culture, then to fall rapidly. In monolayer-forming cells, the cyclic AMP content slightly increases attaining the same level as found in other cells at the fourth day, which remains stable till the seventh day. We have investigated the response of these cells cultured in the presence of dibutyryl cyclic AMP retain the capability of increasing their cyclic AMP concentration whereas monolayer-forming cells do not preserve this quality of thyroid cells.     

Heterokaryosis in Microsporum gypseum

The basic properties of heterokaryosis have been studied with the use of morphological and biochemical mutants ofMicrosporum gypseum. A direct proof of heterokaryosis was given with the help of the isolation of hyphal tips. Heterokaryons formed from aconidial components conidiate abundantly. The heterokaryotic constitution is preserved only with the transfer of mycelium; by microconidia the transfer is not effected.     

Diploids in Microsporum gypseum

The paper studies diploids in dermatophyteMicrosporum gypseum. They were isolated as the more rapidly growing sectors from heterokaryons on minimal medium. They are characterized by their wild morphology, conidiation and growth rate, and they are prototrophic. In their genome they contain all the markers present in both mutant components.     

Effect of dibutyryl cyclic AMP on the sulphation of proteoglycans by chondrocytes

An intestinal lipodystrophy induced by dietary fat in female Mongolian gerbils (Meriones unguiculatus) was reversed to normal by myo-inositol given in the diet or by injection within 1-4 days. An increase in plasma chylomicron and lipid concentrations was observed before the occurrence of rapid disappearance of accumulated lipids from the intestine. Dietary myo-inositol also caused an increase in triacylglycerol release from everted gut sacs. Thus, myo-inositol might act on the intestine to stimulate the production and secretion of chylomicrons, travelling via the lymphatic pathway into the bloodstream. The activity of pH 9.0 microsomal lipase (EC 3.1.1.3) of gerbil intestine was decreased due to myo-inositol deficiency. The lowered activity could be restored to high levels by feeding of injecting myo-inositol in vivo. A time-course study during intestinal recovery indicates that the increase in microsomal lipase activity correlated with the rapid lipid removal phase of the intestine, but not the initial increase in plasma chylomicron and triacylglycerol concentrations.     

B-cell amplification by dibutyryl cyclic AMP in mice

Mice injected with N⁶-2′-O-dibutyryl-adenosine 3′,5′ monophosphate (DBcAMP) showed increased anti-sheep erythrocyte (anti-SE) antibody plaque-forming spleen cell (PFC) responses up to 7-fold greater than control mice. The amount of increase was related to the immunizing dose of SE and to the dose of DBcAMP, and it was more pronounced in 19S PFC than in 7S PFC. Mice thymectomized (Tx) within 16 hr after birth and injected with SE and DBcAMP at 40 days showed a 2.7-fold greater anti-SE PFC response than Tx controls injected with SE alone. DBcAMP restored the PFC response of Tx mice to 75% of that seen for sham Tx, DBcAMP-treated controls. These data suggest that a T cell-B cell interaction is not stringently required in mouse anti-SE antibody responses in vivo, since a T cell-like effect may be substituted or a minimal response can be enhanced with a soluble amplifier such as dibutyryl cyclic AMP.     

Macroconidial Germination in Microsporum gypseum

Biochemical events which occur during macroconidial germination have been studied in the dermatophyte Microsporum gypseum. The specific activity levels of various metabolic enzymes have been assayed during germination time periods. The accumulated levels of several of these enzymes, as a function of exogenous carbohydrate source, have been investigated. M. gypseum was found to possess a constitutive glyoxalate shunt, a constitutive glucokinase, a fructose phosphoenolpyruvate transferase, and a mannitol phosphoenolpyruvate transferase. The integration of endogenous reserve utilization during germination is discussed. The purification and properties of an alkaline phosphatase and its possible relationship to sporulation and spore germination also are described.     

Effect of dibutyryl cyclic AMP on collagen synthesis in a clonal osteoblast-like cell line derived from newborn mouse calvaria

The effects of dibutyryl cyclic AMP (DBcAMP) and related compounds on collagen synthesis in a clonal osteoblast-like cell line, MC3T3-E1, were investigated. The addition of DBcAMP to cultures increased the hydroxyproline content of the cells. It also enhanced the incorporation of labeled proline into collagen and elevated the activity of prolyl hydroxylase, an enzyme involved in collagen synthesis. These effects were observed at concentrations of 0.1 to 2 mM DBcAMP. 8-Bromo cyclic AMP also increased the hydroxyproline content of the cells, while sodium butyrate and dibutyryl cyclic GMP had no such effect. These results suggest that the intracellular accumulation of cyclic AMP in osteoblasts leads to their active production of collagen, a major component of the organic matrix of bone.     

Effects of cyclic AMP and dibutyryl cyclic AMP on amino acid transport in the isolated rat ovary.

Prepubertal rat ovaries were incubated in medium containing the non-utilizable amino acids alpha-aminoisobutyric acid (AIB-14C) or 1-aminocyclo-pentane-carboxylic acid (cycloleucine-14C). The rate of uptake of the two amino acids was studied in the isolated ovaries after different incubation periods. Addition of 5mM cyclic AMP (cAMP) caused a slight stimulation of the AIB-transport but in higher concentrations (10-25 mM) an inhibition was noted. With dibutyrl cyclic AMP (dbcAMP) a dose-dependent increase was seen with 0.5-5 mM concentrations with no further effect of higher concentrations. Time course studies were performed with both AIB and cycloleucine in presence of 10 mM dbcAMP and increased uptake values were noted at each time studied (30-240 min). The phosphodiesterase inhibitor aminophyline in lower concentrations did not influence AIB-transport but 5-10 mM caused increased uptake values in the ovaries. The stimulatory action of dbcAMP on amino acid transport was augmented by a low concentration of aminophylline (0.5 mM). Experiments were in addition carried out in the presence of puromycin and under these circumstances it was still possible to enhance amino acid transport by addition of dbcAMP. The results are discussed in relation to earlier reported effects of gonadotropins on ovarian amino acid transport.     

Effect of dibutyryl cyclic AMP on glucose-6-phosphatase activity in human fetal liver explants

Glucose-6-phosphatase (EC 3.1.3.9) activity in human fetal liver remains constant at 8–28 nmoles/min per mg protein from the 8th week of gestation to at least week 28 and this value is approximately 25–35% of that found in the adult. This enzyme activity was well maintained for 2–3 days in organ culture of fetal liver explants. Incubation with dibutyryl cyclic AMP (0.1 mM) and theophylline (0.5 mM) increased glucose-6-phosphatase activity 4–8-fold within 24 h. Theophylline alone was ineffective, but markedly potentiated the effects of dibutyryl cyclic AMP. This increase in enzyme activity was completely abolished by simultaneous incubation with cycloheximide or actinomycin D. Insulin clearly decreased glucose-6-phosphatase activity in control tissues after 24 h incubation and tended to diminish the elevated glucose-6-phosphatase activity which resulted from pre-incubation with dibutyryl cyclic AMP.The smallest specimen obtained (36 mm crown-rump length = 6 weeks gestation) was capable of elevating glucose-6-phosphatase activity more than 3-fold in response to dibutyryl cyclic AMP incubation, suggesting that the human fetal liver has the competence to respond to hormonal agents at a very early stage of development.