Hormone-dependent processing of the avian progesterone receptor

Avian progesterone receptor exists as two forms, A and B, with molecular weights of 79,000 and 110,000 daltons, respectively. The origin and significance of these two forms is an area of active investigation and debate. Monoclonal antibodies produced against these two forms were used to examine receptor stability in cytosol and changes in the receptor forms induced by hormone binding. The lability of hormone binding at elevated temperatures is well documented. Analysis by Western blotting showed the receptor was stable in freshly prepared oviduct cytosol for 2 hr at 37°C, while hormone binding was lost within 30 min. However, loss of receptor through degradation was seen when cytosol was prepared from frozen tissue or when homogenization was excessive. Progesterone was injected into diethylstilbestrol-stimulated chicks to examine, in vivo, effects of hormone treatment on receptor forms in the cytosol and nuclear fractions. Progesterone treatment caused a time- and dose-dependent conversion of the A receptor to a form (A′) with a slower electrophoretic mobility. The cytosolic progesterone receptor was divided equally between the B and A forms, while the nuclear receptor was predominantly A′. The amount of nuclear receptor was consistently less than cytosolic receptor. Receptor phosphorylation was analyzed by incubating tissue minces with [³²P]orthophosphate with or without progesterone followed by immune isolation of receptor forms. Progesterone treatment caused a time-dependent increase in cytosol receptor phosphorylation which was evident after 5 min of treatment. This phosphorylation was observed with both the A and B receptor forms. The results indicate that receptor phosphorylation is a very early event during progesterone action.     

Photoreactions of human lens monomeric crystallins

Human lens beta s- and gamma A-crystallins exhibit very similar tryptophan fluorescence emission maxima (329 nm). gamma A isolated from infant human lenses is photo-oxidized by 300 nm irradiation and forms water-insoluble aggregates; beta s or gamma A from young human lenses form a small amount of water-soluble crosslinked species. At least part of the mechanism of photodamage by 300 nm irradiation is photogeneration of the oxidant H2O2 via the generation of O2- radical, this reaction occurs via photosensitization by the tryptophan photo-oxidation product N-formylkynurenine (N-FK) or related species. These results indicate that even though the tryptophan residues of beta s- and gamma A-crystallins are in hydrophobic (buried) microenvironments as compared to those of the alpha- and beta-crystallins, the photogeneration of N-FK is sufficient to produce O2- and H2O2.     

Specific Inhibition of Cell Proliferation In the Mouse Intestine By an Aqueous Extract of Rabbit Colon

Aqueous extracts from rabbit colon, kidney, testis and small intestinal mucosa were prepared by homogenization and centrifugation at 105,000 g. After precipitation with ammonium sulphate. the 0–50 fraction (F₁) and the supernatant (F₂) were collected, dialysed against a phosphate buffer and tested on mice in vivo. 1 hr after a single injection of F₁ (15 mg content) from colon, the uptake of tritiated thymidine was decreased in jejunal and colonic DNA in mice. This effect, maximal after 3 hr and totally reversible after 7 hr, was found in neither the kidney nor the testis. the F₁ fractions of non-digestive organs (kidney, testis) were also found to exert a significant inhibition on thymidine incorporation into intestinal DNA in vivo. F₁ fractions of intestinal contents, prepared under the same conditions, exerted no significant effects on DNA synthesis in mouse intestine. Conversely, the colon F₂ fraction did not inhibit the synthesis of jejunal and colonic DNA in vivo. A slowing of cellular migration was also noticed in the jejunum and colon of mice injected with colon or small intestine F₁, as ascertained radioautographically by determining the position of the leading edge of the labelled cells in jejunal or colonic F₁-injected mice. Our results suggest that the F₁ fraction of the aqueous extract of rabbit colon contains one or more substances, which may act either on intestinal DNA synthesis or on the G₁-S transition of the cellular cycle in the mouse intestine. This reversible and tissue-specific intestinal action appears to inhibit cell proliferation and presents several of the characteristics defining a chalone, as does the action of small intestinal F₁ previously reported (Sassier & Bergeron, 1977). However, because of a relative lack of origin specificity of this effect, the physiological significance of our data remains to be ascertained.     

Plasma catecholamines: effects of footshock level and hormonal modulators of memory storage

Plasma levels of norepinephrine (NE) and epinephrine (EPI) were measured in male Sprague-Dawley rats before and at several times after training injections of agents known to enhance or to impair later retention performance for a one-trial inhibitory (passive) avoidance task. Two days before testing, each animal was surgically prepared with a chronic tail artery catheter that allows for repeated blood sampling in unhandled rats. Exposure to a single, intense training footshock (3.0 mA, 2.0 sec duration) resulted in an immediate but transient increase in plasma levels of EPI and to a lesser extent NE. Plasma levels of both catecholamines did not differ between unshocked controls and animals that received a weak training footshock (0.6 mA, 0.5 sec duration). An injection of EPI at a dose that enhances retention performance (0.1 mg/kg, sc) resulted in increments in plasma EPI levels of 0.8-1.9 ng/ml from 5 to 40 min after injection. An injection of EPI (0.5 mg/kg, sc) at a dose that produces retrograde amnesia resulted in increments in plasma EPI ranging from 3.7 to 4.5 ng/ml during the 40 min after injection. Plasma NE levels were not significantly altered following an EPI injection. A single injection of adrenocorticotropin (ACTH, 0.3 or 3.0 IU per rat) did not alter the plasma catecholamine responses to training with a weak footshock. Similarly, the synthetic ACTH analog, Organon 2766 (125 or 250 mg/Kg) did not affect plasma catecholamines in untrained (unshocked) rats.These results demonstrate that significant increments in plasma levels of NE and EPI occur shortly after inhibitory avoidance training. Furthermore, an injection of EPI that enhances retention of an inhibitory avoidance task mimics the magnitude, though not the temporal characteristics, of the endogenous adrenal medullary response to a training footshock. Other hormonal treatments (ACTH and Organon 2766) which enhance memory storage do not affect plasma levels of NE and EPI.