Transient Inhibitory Effect Research Articles

Phytochrome and binding site interaction: Transient inhibitory effect of azide

Summary Phytochrome pelletability was substantially reduced when red light irradiated maize coleoptiles were incubated with azide or cyanide in the dark. The inhibition is transient in the case of azide but persists in the case of cyanide. Thus, during prolonged dark incubation of red irradiated coleoptiles with azide there is a gradual increase of phytochrome pelletability while the total cellular phytochrome decreases only slightly. The phenomenon is only seen when phytochrome remains in the Pfr form during dark incubation. Recovery did not occur in coleoptiles irradiated with red/far red in which the phytochrome is in the Pr form

Effects of anesthesia and surgical procedures on intestinal myoelectric activity in rats.

Electrical spiking activity of the duodenum and jejunum was recorded from chronically implanted electrodes in rats during volatile or barbiturate anesthesia and following laparotomy. The normal pattern of electrical spiking activity in the fasted rat, with myoelectric complexes at 15-min intervals, was transiently replaced by quiescence during ethyl ether anesthesia. A slight increase in irregular spiking activity occurred after induction with pentobarbital, and the only effect of thiopental anesthesia was a reduction in the velocity of propagation of the complexes by 20%. Under barbiturate anesthesia, incision of the skin did not inhibit myoelectric activity, but incision of each abdominal muscle layer had an immediate and transient inhibitory effect; the deeper the layer, the longer was the inhibition. Peritoneal incision consistently produced inhibition of spiking activity which was prolonged by exposure of the bowel to air and intestine handling. The inhibitory effects produced by surgery persisted after vagotomy or transection of the spinal cord at the thoracic level but disappeared after splanchnicectomy. The above results suggest that a somatovegetative reflex with efferent pathways in the splanchnic nerves is involved in the first stage of operative inhibition of intestinal myoelectric complexes.

Inhibition of X-ray-induced Protection ofEscherichia ColiK-12 Cells against the Lethal Effects of Ultra-violet Light by Nitrofurantoin

Wild-type cells of E. coli K-12 showed increasing U.V. resistance if they were X-irradiated and incubated at 37 degrees C in growth medium before the U.V. exposure. Development of higher U.V. resistance could be inhibited by incubating the X-irradiated cells either at temperatures below 15 degrees C, or in the presence of 0.01 M KCN. Nitrofurantoin (NF), which was recently found specifically to inhibit inducible enzyme synthesis, had only a transient inhibitory effect on X-ray-induced U.V. resistance. Cells grown in glucose medium showed less inhibition by NF of X-radiation-induced resistance to U.V.-radiation than did cells grown in glycerol, or in glucose medium with added cyclic AMP. It is suggested that X-ray-induced U.V. resistance requires active cellular metabolism, but it is not subject to catabolite repression. The following hypothesis is offered to explain the action of NF: Under de-repressed conditions (without catabolite repression by glucose) nitrofurantoin could counteract the radiation-induced inhibition of a repair inhibitor (such as post-irradiation DNA degradation).

Effects of scopolamine, d-amphetamine and other drugs affecting catecholamines on spontaneous alternation and locomotor activity in mice

Locomotor activity and Y-maze spontaneous alternation were examined in three strains of inbred mice (A/J, DBA/2J and C57BL/6J) following various drug treatments. Although the strains exhibited different levels of locomotor activity, the level of spontaneous alternation was comparable among the strains. Scopolamine produced dose dependent increases in locomotor activity in the A and DBA/2 strains, but produced a transient inhibitory effect upon locomotor activity in C57BL/6. Nevertheless, spontaneous alternation was eliminated equally, regardless of strain. d-Amphetamine increased locomotor activity and reduced alternation significantly below chance levels (perseveration). α-Methyl-p-tyrosine (α-MpT) and FLA-63 reduced the locomotor stimulating effects of d-amphetamine; however, the effectiveness of these agents was found to be strain dependent. Neither α-MpT nor FLA-63 reduced the perseverative behavior. A subsequent study employing Swiss-Webster mice revealed that with pretreatment of reserpine, both α-MpT and FLA-63 eliminated the amphetamine-induced perseverative behavior. Results were interpreted in terms of (a) the role of cholinergic and catecholaminergic systems in modulating alternation behavior, (b) qualitative differences in the behavioral effects elicited by scopolamine and d-amphetamine, (c) strain-specificity regarding pharmacological effects, and (d) role of newly synthesized norepinephrine and dopamine in subserving amphetamine-induced locomotor activity and perseveration.

Role of complement in guinea pig skin allograft rejection: 1. Effect of cobra venom C3 inactivator and fumaropimaric acid on rejection

Two complement (C) inhibitors, the cobra venom C3 inactivator and fumaropimaric acid were used to study skin allograft rejection in the guinea pig. The cobra venom inactivator markedly lowered C activity. When injected on Day 5 post-allograft, the venom factor induced a 2- to 3-day prolongation of allograft survival. Fumaropimaric acid, a reversible inhibitor of C1, C2, C3, C 567 is known to have only a transient complement inhibitory effect. When injected in divided doses from Days 5–7, little if any prolongation of allograft rejection was noted. Serum hemolytic complement activity was not reduced during normal allograft rejection, nor could C3 be found bound to allograft rejection sites by immunofluorescence. It is suggested that the cobra venom C3 inactivator prolongs allograft survival by alteration of complement-dependent inflammation.