Levels of cyclic 3',5'-cyclic monophosphate (cAMP) play an important role in the decision to enter the mitotic cycle in the yeast, Saccharomyces cerevisiae. In addition to growth arrest at stationary phase, S. cerevisiae transiently arrest growth as they shift from fermentative to oxidative metabolism (the diauxic shift). Experiments examining the role of cAMP in growth arrest at the diauxic shift show the following: 1) yeast lower cAMP levels as they exhaust their glucose supply and shift to oxidative metabolism of ethanol, 2) a reduction in cAMP is essential for traversing the diauxic shift, 3) the decrease in adenylate cyclase activity is associated with a decrease in the expression of CYRi and CDC25, two positive regulators of cAMP levels and an increase in the expression of IRA1 and IRA2, two negative regulators of intracellular cAMP, 4) mutants carrying disruptions in IRAI and IRA2 were unable to arrest cell division at the diauxic shift and were unable to progress into the oxidative phase of growth. These results indicate that changes cAMP levels are important in regulation of growth arrest at the diauxic shift and that changes in gene expression plays a role in the regulation of the Ras/adenylate cyclase system.

—The stability of the GABA content of synaptosomal‐enriched fractions was evaluated by two approaches. Firstly, the addition of 10−3m‐aminooxyacetic acid to the homogenizing medium totally inhibited the GABA‐degrading enzyme in the fractions but did not affect the GABA levels. This indicated that GABA was not being metabolized during the normal preparation of the synaptosomal‐enriched fraction. Secondly, when synaptosomal‐enriched fractions were re‐fractionated by discontinuous density gradient centrifugation, the GABA contents of the fractions before and after the second fractionation were very similar provided they were expressed on a per mg protein basis. It was therefore concluded that the GABA content of the organelles was not subject to change during the fractionation procedures. On the basis of these findings and others it was suggested that the synaptosomal‐enriched fraction could be used as a model to evaluate drug‐induced changes in GABA levels in nerve endings. In vivo experimentation indicated that the convulsant agents hydrazine, isonicotinic acid hydrazide and aminooxyacetic acid brought about similar decreases in the GABA content of the synaptosomal‐enriched fractions prepared from tissue at the onset of seizures despite the fact that no correlation was observed between seizure activity and whole brain GABA levels.

Propranolol (Inderal; 1) is extensively metabolized in man. Metabolites of interest pharmacologically include ring-hydroxylated propranolols (1a-g). In order to identify these ring-oxidized products and to study the effect of hydroxyl position on biological activity, we have synthesized all seven isomers. With the exception of 1b and 1g, the desired compounds were prepared by alkylation of the respective methoxy-1-naphthols with epichlorohydrin and reaction of the resulting epoxide with isopropylamine. Cleavage og the methyl group in fused pyridine hydrochloride afforded 1a,c-f. 1g was prepared by the direct alkylation of 1,8-naphthalenediol (17) with epichlorohydrin, followed by reaction with isopropylamine. 1b was synthesized by treating 2-naphthol (9) with chlorine gas and then treating the resulting 1,1-dichloronaphthalen-2(1H)-one (10) with sodium allyl oxide. Acetylation of the hydroxy function and epoxidatrion of the allyl group, followed by relation with isopropylamine, gave 3'-hydroxy-4'-chloropropranolol (15). Dechlorination gave 1b. All of the racemic hydroxylated propranolols produced beta blockade and direct vasodilation in anesthetized dogs. The potency is strongly dependent upon the position of the hydroxyl group, i.e., 1e is 4 times as potent as 1 as a beta receptor antagonist, whereas 1a, 1b, and 1g are all significantly less potent than 1. For direct vasodilation, 1a and 1g are equipotent to 1, while 1b-f are much less potent. The potencies of the compounds were also compared with their 1-octanol/pH 7.4 buffer distribution coefficients; the direct vasodilating potency was found to increase with increasing lipophilicity, while the beta-adrenergic antagonist potency decreased.

The intramuscular administration of L-cycloserine, gabaculine, and aminooxyacetic acid caused significant, time-dependent increases in the gamma-aminobutyric acid (GABA) content of both whole brain and synaptosomal-enriched preparations obtained from the tissue, a linear relationship being observed between the two parameters. In contrast, the administration of hydrazine resulted in a large increase in whole brain GABA level, with little change in the synaptosomal GABA content. The key factor in these different responses appeared to be the degree of inhibition of glutamic acid decarboxylase by the drugs. Pretreatment of mice with the GABA-elevating agents resulted in a delay in the onset of seizures, which was related directly to the increase in synaptosomal GABA content. Although the seizures were delayed, they occurred while the GABA content of nerve endings (synaptosomes) was above that in preparations from untreated animals. The decrease in GABA content at the onset of seizures, expressed as a percentage of the level at the time of injection of the convulsant agent, was, however, reasonably constant. A hypothesis to explain these results is proposed.

Cardiac /S-l adrenoceptors respond to sympathetic nerve stimulation (SNS), but it is not clear that SNS evokes fi-2 adrenoceptor-mediated vasodilation. Sensitivity of B adrenoceptors to catecholamines and to SNS was evaluated in dogs. Norepinephrine (NE) and epinephrine (E) were equipotent vasoconstrictors (femoral artery blood flow or gracilis autoperfusion pressure) before aadrenoceptor blockade with dibozane (DIB). After DIB, NE was 1/100 as potent a vasodilator as E, which was equipotent with isoproterenol (ISO). SNS evoked gracilis muscle vasoconstriction before DIB and vasodilation after. Dilation induced by SNS or acetylcholine (ACH) after DIB was blocked by atropine (AT), but that caused by NE was not. Dilation evoked by NE, E, or I after DIB and AT was blocked by propranolol (PROP). Vasoconstrictor responses to NE, E, or SNS in dogs without DIB were not augmented by PROP at a dose that blocked the dilator effect of ISO. NE and E were equipotent and both 1/10 as potent as ISO as positive inotropic and chronotropic agents. Cardiac responses to NE, E, ISO, and SNS were antagonized by PROP. Subclassification of adrenoceptors that subserve cardiac stimulation as fi-1 and that subserve vasodilation as fi-2 was substantiated. Cardiac fi-1 adrenoceptors responded to SNS and to circulating E and NE. Vascular fi-2 adrenoceptors responded to circulating E, to ISO, and to high doses of NE, but not to SNS. fi-2 Adrenoceptors in blood vessels appear not to be innervated and may function as hormone receptors sensitive primarily to E released from the adrenal medulla, rather than to NE released from adrenergic nerves.