Inhibitory effect of thyroid hormones on pituitary cyclic AMP phosphodiesterase activity in vitro

Thyroid hormones effectively inhibited partially purified cyclic AMP phosphodiesterase from the anterior and posterior lobes of bovine pituitary gland competitively with the substrate, but thyronine, diiodotyrosine, monoiodotyrosine, thyrotropin, thyrotropin releasing hormone, dexamethasone, and luteinizing hormone releasing hormone did not inhibit this enzyme activity.K _i values were found to be 1.0 and 2.5 M for thyroxine, and 8.0 and 13.5 M for triiodothyronine in the anterior and posterior lobes, respectively.     

Rate of inactivation of adenyl cyclase and phosphodiesterase: determinants of brain cyclic AMP

In order to assess the effects of time requirements of different tissue inactivation methods, concentrations of cyclic adenosine monophosphate in rat brain were determined. Fixation of tissues was obtained by the following methods: decapitation with removal of brain and freezing in liquid nitrogen; decapitation into liquid nitrogen; whole animal immersion in liquid nitrogen; 1.5 kW maximal field strength microwave irradiation for 8 seconds; and, 5 kW maximal field strength microwave irradiation for 2 seconds. Results of these studies indicate that as the time is reduced for inactivation of brain adenyl cyclase and phosphodiesterase, levels of cyclic adenosine monophosphate become progressively lower. This same correlation is also evident in studies of regional brain concentrations of cyclic adenosine monophosphate after 1.5 kW and 5 kW microwave inactivation. It is concluded that 5 kW maximal field strength microwave exposure is the most rapid means of enzyme inactivation permitting a more accurate estimation of endogenous cyclic adenosine monophosphate concentrations. Its use offers rapid inactivation with minimization of trauma and facilities the study of regional metabolites through ease of dissection.     

An ATP pool associated with adenyl cyclase of brain tissue

R adioactive adenine has been frequently used to label cyclic adenosine 3', 5'-monophosphate (cAMP) in diverse cells and tissues (K uo and D e R enzo , 1969; S himizu , D aly and C reveling , 1969, B rooker , 1971). We have previously reported that cAMP from the guinea-pig cerebral cortex is derived from a precursor pool of adenine nucleotides which is more highly labelled than the bulk cellular ATP (S himizu , C reveling and D aly , 1970a). The present study was carried out to throw additional light on the property of the precursor pool. Levels of cAMP and ATP and specific activities of [¹⁴C]cAMP and [¹⁴C]ATP were determined simultaneously in cerebral slices which were prelabelled with [¹⁴C]adenine and subsequently incubated with veratridine, histamine or adenosine.     

Effect of Vibrio cholerae filtrate on the adenyl cyclase system in vitro]

An in vitro model using homogenates of the rat intestine and liver for studying the V. Cholerae culture filtrate effect on the adenylate cyclase system is proposed. Optimal conditions for the adenylate cyclase functioning have been investigated for this model. It was shown that V. Cholerae filtrate induces a stable activation of adenylate cyclase and does not change the activity of cyclic AMP phosphodiesterase. It was also established that the activity of phosphodiesterase in the intestinal homogenate is about 2.5 fold higher than that in the liver homogenate. The model may be considered promising for investigation of the mechanism of cholerae toxin action.     

Effect of the linoleic acid concentration of mother's diet on adenyl cyclase activity of fetal and neonatal rat brown adipose tissue

An adenyl cyclase activity was measurable in the brown adipose tissue of fetal rat, and could be stimulated in vitro by noradrenaline during the last 3 days of fetal life. The stimulating effect of noradrenaline was maximal at birth and decreased during the first days of extrauterine life. Ingestion by mother of a high lipid diet modified the developmental pattern of fetal adenyl cyclase. The linoleic acid content of mother's diet had no effect on the noradrenaline- or fluoride-stimulated specific activities except on the day 22 of gestation. Relative noradrenaline-stimulated activity, expressed as a fraction of the maximal activity, was significantly increased in fetuses and 1-day-old newborns from mothers fed a high linoleic acid diet, but no effect was observed in suckling newborns.