New phorbol and deoxyphorbol esters: isolation and relative potencies in inducing platelet aggregation and erythema of skin

Diester diterpenes based upon phorbol, 4-deoxyphorbol, 4 alpha-deoxyphorbol, 4-deoxy-5-hydroxyphorbol and 4,20-dideoxy-5-hydroxyphorbol were isolated from the fruit oil of Sapium indicum. Corresponding tri- and tetra-esters were produced by acetylation and mono-esters by selective hydrolysis. Twenty-six compounds were tested for production of erythema in vivo and induction of human and rabbit platelet aggregation in vitro. The flatter shape of the AB-ring trans compounds is necessary for interaction of phorbolesters at their receptor in that the cis analogues were inactive. The tertiary C-4 hydroxy group of phorbol was not necessary for activity although the 4-deoxy derivatives were less potent than the 4-hydroxy diterpenes. A primary hydroxy group at C-20 was essential for biological activity because the methyl and aldehyde derivatives of this position were inactive. The C-20 acetates were also inactive on platelets, but they did produce erythema, possibly because of the removal of the ester due to lipase activity in the skin. 5-hydroxy-analogues which undergo intramolecular hydrogen bonding had greatly reduced activities in both systems. Membrane stabilisers, phospholipase A2 and calmodulin inhibitors were antagonists for phorbol esters in platelet aggregation tests, whilst cyclo-oxygenase inhibitors and free radical scavengers had no inhibitory effects. Consequently, one electron withdrawal and free radical formation plays no part in the biological activity of these compounds.

Additional evidence against universal modulation of beta-adrenoceptor responses by excessive thyroxine

1 The effect of prolonged, excessive thyroxine on beta-adrenoceptor-mediated relaxation of guinea-pig trachea was studied. 2 Thyroxine did not significantly affect the potency of the beta 1-adrenoceptor agonist, noradrenaline, or the beta 2-adrenoceptor agonist, terbutaline. 3 Thyroxine did not significantly affect the apparent KB values of the selective beta 1-adrenoceptor antagonist, practolol, or the selective beta 2-adrenoceptor antagonist, butoxamine. 4 Thyroxine did not significantly affect the maximum response to noradrenaline. The maximum response to terbutaline in tissues from the thyroxine-treated animals was only slightly lower than the maximum response in tissues from paired control animals. 5 These results suggest that excessive thyroxine does not significantly affect the beta-adrenoceptor-mediated relaxation of guinea-pig trachea and that the reported modulation of beta-adrenoceptor-mediated responses in other tissues is specific for the given tissue rather than common to all beta-adrenoceptor systems.

Limiting Factors in Photosynthesis: III. Effects of Iron Nutrition on the Activities of Three Regulatory Enzymes of Photosynthetic Carbon Metabolism

When Fe was withheld from sugar beets (Beta vulgaris L. CV F58-44H1), the activities of NADP-glyceraldehyde-3-phosphate dehydrogenase, fructose 1,6-bisphosphatase, and ribulose 5-phosphate kinase were not diminished, while chlorophyll per area was decreased by 75%. On resupplying Fe, chlorophyll per area increased to control levels within 5 days, whereas the activities of the three enzymes remained approximately constant. These results support the view advanced earlier (Terry 1980 Plant Physiol 65: 114-120) that the photosynthetic effects of Fe deprivation are mediated by changes in the lamellar components of chloroplasts and not by changes in stromal enzymes involved in photosynthetic carbon reduction.

Pharmacological isolation of a single beta-adrenoceptor subtype makes Schild plots which have slopes of 1 possible for selective beta-adrenoceptor antagonists in carbachol-contracted guinea-pig trachea

The effects of selective beta-adrenoceptor agonists and antagonists on isometric relaxation of carbachol-contracted, guinea-pig isolated trachea were studied. An attempt was made to pharmacologically isolate the beta 1- and beta 2-adrenoceptors by use of appropriate selective agonists and antagonists. The slopes of the Schild plots for butoxamine vs noradrenaline and terbutaline as well as for practolol vs terbutaline did not differ significantly from 1, the predicted value for a competitive antagonist acting at a single receptor type. These data differ from a previous report suggesting that slopes of less than 1 are characteristic for selective beta-adrenoceptor antagonists in carbachol-contracted guinea-pig trachea. They support the hypothesis that the slopes in this preparation are due to interaction of the agonist with both beta 1- and beta 2-adrenoceptors rather than the state of contraction of the trachea.

The beta adrenergic receptors of chromatophores of the frog, Rana pipiens

The isolated skin of Rana pipiens was found to be a suitable model for the quantitative study of chromatophore beta adrenergic receptors uninfluenced by prejunctional phenomena. Cumulative concentration-response curves for adrenergic agonists were obtained in preparations in which effective alpha adrenergic blockade had been produced with phenoxybenzamine. The beta adrenergic agonists darkened the preparation, as did melanocyte-stimulating hormone, but the maximum effects differed. The maximum of the l-isoproterenol cumulative concentration-response curve was approximately 50% less than that of melanocyte-stimulating hormone, while the maxima for l-epinephrine and l-norepinephrine were significantly less than that for isoproterenol. Microscopic examination revealed a qualitative difference: while maximal darkening produced by melanocyte-stimulating hormone was associated with maximal changes in both interspot melanophores and iridophores, maximal adrenergic-induced darkening was associated with maximal iridophore granule concentration only. No qualitative differences could be observed in the darkening caused by the three adrenergic agonists. The beta adrenergic potencies of l-norepinephrine and l-isoproterenol relative to l-epinephrine were determined by four-point bioassay. Isoproterenol was found to be 138 times as potent as epinephrine, while norepinephrine was 4 times as potent. Similarly, antagonism of isoproterenol-induced darkening of phenoxybenzamine-pretreated skin samples by the beta adrenergic blocking agents dl-propranolol, dl-sotalol, dl-practolol, l-butoxamine and d-butoxamine was studied, and their KB and pA2 values, respectively, were found to be: dl-propranolol (1.44 X 10(-8)M, 7.81); dl-sotalol (7.25 X 10(-8)M, 7.23); l-butoxamine (6.92 X 10(-6)M, 5.10); dl-practolol (1.91 X 10(-5)M, 4.96); d-butoxamine (no activity). Comparison of the potency ratios and pA2 values cited above with similar parameters obtained by other investigators in several mammalian tissues suggests that there is wide variation among beta adrenergic receptors.

A comparison of the effects of quinetholate, lidocaine and procainamide on ouabain-induced ventricular tachycardia and cardiac function

The antiarrhythmic effects of the quinoline derivative, quinetholate, on ouabain-induced tachycardia were compared with those of lidocaine and procainamide in dogs. In addition, the effects of these three agents on cardiac function were compared. Quabain was injected intravenously until ventricular ectopic beats accounted for at least 60% of the heart rate. Then one of the above antiarrhythmic agents was infused until sinus rhythm was reestablished for a minimum of 3 min or until it became evident that successful reversion would not occur. All three agents effectively reversed ouabain-induced ventricular tachycardia in most instances. Quinetholate was especially consistent, causing 16 reversions out of a total of 17 experiments. The relative molar antiarrhythmic potencies of the three agents in responding animals were as follows: lidocaine = 1.0, procainamide = 1.5, and quinetholate = 3.1. Quinetholate caused the longest lasting reversions, i.e. usually lasting at least 30 min after infusion was stopped. The degree of cardiac depression caused by the three agents at their mean effective antiarrhythmic doses was determined using the left ventricular function curve method. Lidocaine produced a significant depression of the ventricular function curve at the antiarrhythmic dose while procainamide and quinetholate did not.

The perception of self and others: acquaintanceship, affect, and actor-observer differences

Three studies were designed to examine how people perceive themselves versus others. The main finding was that people were seen as causing positive behaviors, and situational factors were regarded as causing negative behaviors (positivity effect). This positivity effect was found to operate most strongly for perceptions of intimate others, such as spouse and friends, and less strongly for strangers and liked and disliked acquaintances. There was little support for the actor-observer difference that people view their own behavior more situationally than they do other people's behavior. It was concluded that both cognitive and motivational factors must be considered in predicting how people perceive and describe others.

The perception of self and others: Acquaintanceship, affect, and actor-observer differences

Three studies were designed to examine how people perceive themselves versus others. The main finding was that people were seen as causing positive behaviors, and situational factors were regarded as causing negative behaviors (positivity effect). This positivity effect was found to operate most strongly for perceptions of intimate others, such as spouse and friends, and less strongly for strangers and liked and disliked acquaintances. There was little support for the actor-observer difference that people view their own behavior more situationally than they do other people's behavior. It was concluded that both cognitive and motivational factors must be considered in predicting how people perceive and describe others.