RESUMEN
Coalescing macroalgae are ecologically important members of intertidal and shallow subtidal communities. However, we still lack quantitative information on the demographic consequences of coalescence. Using demographic models developed for modular invertebrates, we studied the demography of settlement and early recruitment in the coalescing macroalga Mazzaella laminarioides (Bory) Fredericq. Permanently marked microscopic fields on laboratory-incubated and field-incubated plates were monitored regularly (at 15, 30, 45, and 60 d) using image analysis techniques to evaluate the relative importance of settler abundance, mortality, coalescence (fusion), and fission on the changes in size and numbers of recruits. On the plates, spores settled individually or in groups. Over time, spores in close proximity may coalesce, resulting in a mixture of unisporic and multisporic crusts. When new spores arrive, they may or may not coalesce with previously settled crusts. Coalescence and mortality reduce the number of sporelings, but coalescence increases the size of the sporelings, thereby reducing further probability of sporeling mortality. Crust fissions are negligible in frequency, while the frequency of coalescence increases from â¼25% after only 3 d, to â¼75% after 60 d. Thus, as a result of variable settlement, mortality, and coalescence, any area colonized by M. laminarioides would contain a mixture of crusts of different sizes, ages, and genetic constitution. The interactions between the above three processes create a more complex survivorship curve than the ones known for unitary organisms.
RESUMEN
UNLABELLED: The action of adenosine on atrial functional refractory period, as well as on its ability to interrupt atrial flutter is similar to that of digitalis. The latter suggests the possible existence of an adenilic component to digitalis action. To test this possibility, we measured the plasma concentrations of adenosine after ouabain infusion in dogs, and we investigated the effect of digitalis on atrial refractory period and on flutter in conditions of cholinergic inhibition and purinergic blockade. Ouabain was administered until ventricular fibrillation was induced. Blood was obtained from both the coronary sinus and the femoral vein, and adenosine was measured by liquid chromatography. The refractory period was measured by applying an extra stimulus at variable intervals following a train of 10 basic beats. Flutter was induced by stimulation of the posterior internodal pathway. RESULTS: The concentration of adenosine in plasma collected from the coronary sinus increased by more than 100%; the effect of digitalis on atrial refractory period was independent of cholinergic blockade, but it was inhibited by aminophylline; the ability of digitalis to interrupt flutter was modified by aminophylline. CONCLUSION: The antiarrhythmic action of digitalis seems to include an adenilic component, that results from the liberation of adenosine in the heart.
Asunto(s)
Adenosina/farmacología , Antiarrítmicos/farmacología , Glicósidos Digitálicos/farmacología , Adenosina/sangre , Animales , Antiarrítmicos/administración & dosificación , Aleteo Atrial/sangre , Aleteo Atrial/tratamiento farmacológico , Aleteo Atrial/fisiopatología , Perros , Evaluación Preclínica de Medicamentos , Interacciones Farmacológicas , Electrocardiografía/efectos de los fármacos , Atrios Cardíacos/efectos de los fármacos , Atrios Cardíacos/fisiopatología , Masculino , Ouabaína/administración & dosificación , Ouabaína/farmacología , Ouabaína/envenenamiento , Intoxicación/sangre , Intoxicación/fisiopatología , Receptores Purinérgicos P1/efectos de los fármacos , Receptores Purinérgicos P1/fisiologíaRESUMEN
All natural cardiac glycosides (CG) have a hydroxyl (OH) group attached to carbon 14 (C 14) of the steroid nucleus which has been considered important for their pharmacological action. To investigate the relation between chemical structure and biological activity of CG, we studied the cardiac effects of a semisynthetic derivative if gluco-digitoxigenin that lacks the C 14 hydroxyl group; the compound was named Dig-3 and corresponds to the number of a series of semisynthetic glycosides being studied. On the failing heart of the Starling's heart-lung preparation Dig-3 reverts experimental cardiac failure. Electrophysiological experiments in anesthetized dogs (morphine chloralose) have shown that Dig-3 shortens the functional refractory period of the ordinary atrial myocardium (OAM), and lengthens that of the specialized atrial tissue (SAT). The basal excitability is reduced in both tissues, however OAM is more susceptible to Dig-3 action. The conduction velocity of impulses in SAT diminishes 50% with one tenth of the lethal dose (LD) of Dig-3 whereas in the OAM, an equivalent decrease is achieved with 60% of LD. A-V dissociation induced by the infusion of toxic doses of Dig-3 reverted to sinus rhythm in about 6 min after the administration was stopped. We conclude that the presence of the OH group attached to C 14 of digitalis molecule does not constitute a structural requirement for the preservation of its inotropic and electrophysiological actions on the heart, although its potency is greatly diminished.