Some functional aspects of canine corticotrophs

To examine the regulation and functional significance of canine pituitary pars intermedia corticotrophs, ACTH and cortisol responses to CRF were studied in healthy dogs before and after treatment with dexamethasone. In addition the effects of the dopamine agonist bromocriptine and the dopamine antagonist pimozide were investigated. In the latter two instances prolactin concentrations were also measured. Finally the pituitaries were studied immunocytochemically for ACTH and alpha-MSH. No response of ACTH or cortisol to bromocriptine was observed. Pimozide caused a slight rise in ACTH levels in some dogs. However, prolactin levels significantly decreased with bromocriptine and increased with pimozide. Injection of synthetic ovine CRF to dogs was followed by sharp increases in ACTH and cortisol values. These responses were obliterated by prior treatment with dexamethasone. In 1 of 4 dogs given dexamethasone before euthanasia, there were few pars distalis cells with ACTH(1-24) immunopositivity, although persistence of ACTH(1-24) reaction was noted within cells of the pars intermedia. The results indicate that none of the CRF-induced ACTH secretion in dogs is derived from pars intermedia corticotrophs. Dosages of bromocriptine and pimozide that clearly alter prolactin secretion do not consistently affect ACTH levels.     

The in vivo effects of acenocoumarol, phenprocoumon and warfarin on vitamin K epoxide reductase and vitamin K-dependent carboxylase in various tissues of the rat

In rats the in vivo effects of a chronic low-dose treatment (+/- 60 micrograms/rat per day) with different coumarins (acenocoumarol, phenprocoumon and warfarin) on hepatic and non-hepatic vitamin K-dependent enzyme systems were compared. The plasma concentrations of the three coumarins differed largely but these differences were not reflected in the microsomal coumarin contents. The non-hepatic microsomes contained less than 20% of the coumarins found in liver microsomes. No substantial differences were observed between the following effects of the three anticoagulant treatments. The blood coagulation factor activities were about 10% of normal. The hepatic microsomal vitamin K epoxide reductase activity was diminished to about 35% of control values. The vitamin K epoxide reductase activities present in kidney, lung, spleen, testis and brain microsomes were less influenced by the coumarin treatments; activities ranged between 45 and 65% of normal. In the liver microsomes a 15-fold accumulation of non-carboxylated precursor proteins was found; in the non-hepatic microsomes this effect was less pronounced but still present. The hepatic vitamin K-dependent carboxylase activity was enhanced but the corresponding non-hepatic enzyme activities were slightly or not affected. In addition, the effects of a chronic low-dose warfarin treatment were compared with those after an acute high dose of the drug.     

Recovery of Adrenocortical Function during Long-term Treatment with Corticosteroids

The recovery of adrenocortical function during very slow withdrawal of corticosteroids was studied in a homogeneous group of patients suffering from sarcoidosis. All patients had been treated with gradually decreasing doses of prednisone for at least two years. The initial dose had been 40 mg. daily in all cases. Determination of the cortisol production rate and of plasma fluorogenic corticosteroids was done under basal conditions and after tetracosactrin stimulation. There was good correlation between cortisol production rate and plasma fluorogenic corticosteroids throughout all the tests. Cortisol production rate and plasma fluorogenic corticosteroids started to rise when the dosage of prednisone was lowered to 7·5 mg. daily and reached normal values when the dosage was reduced to 2·5 mg. The response to tetracosactrin began to increase at the same dosage level, but was not normal at 2·5 mg., or when prednisone treatment was stopped. At a dosage level of 7·5 mg. of prednisone plasma fluorogenic corticosteroids already showed a nyctohemeral rhythm.It may be calculated that even very low dosages of prednisone given during the last stage of a treatment schedule enhance total corticosteroid activity beyond the normal level, which would account for their therapeutic value.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

Remodeling and spacing factor 1 (RSF1) deposits centromere proteins at DNA double-strand breaks to promote non-homologous end-joining

The cellular response to ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) in native chromatin requires a tight coordination between the activities of DNA repair machineries and factors that modulate chromatin structure. SMARCA5 is an ATPase of the SNF2 family of chromatin remodeling factors that has recently been implicated in the DSB response. It forms distinct chromatin remodeling complexes with several non-canonical subunits, including the remodeling and spacing factor 1 (RSF1) protein. Despite the fact that RSF1 is often overexpressed in tumors and linked to tumorigenesis and genome instability, its role in the DSB response remains largely unclear. Here we show that RSF1 accumulates at DSB sites and protects human cells against IR-induced DSBs by promoting repair of these lesions through homologous recombination (HR) and non-homologous end-joining (NHEJ). Although SMARCA5 regulates the RNF168-dependent ubiquitin response that targets BRCA1 to DSBs, we found RSF1 to be dispensable for this process. Conversely, we found that RSF1 facilitates the assembly of centromere proteins CENP-S and CENP-X at sites of DNA damage, while SMARCA5 was not required for these events. Mechanistically, we uncovered that CENP-S and CENP-X, upon their incorporation by RSF1, promote assembly of the NHEJ factor XRCC4 at damaged chromatin. In contrast, CENP-S and CENP-X were dispensable for HR, suggesting that RSF1 regulates HR independently of these centromere proteins. Our findings reveal distinct functions of RSF1 in the 2 major pathways of DSB repair and explain how RSF1, through the loading of centromere proteins and XRCC4 at DSBs, promotes repair by non-homologous end-joining.     

A model of erythropoiesis in adults with sufficient iron availability

In this paper we present a model for erythropoiesis under the basic assumption that sufficient iron availability is guaranteed. An extension of the model including a sub-model for the iron dynamics in the body is topic of present research efforts. The model gives excellent results for a number of important situations: recovery of the red blood cell mass after blood donation, adaptation of the number of red blood cells to changes in the altitude of residence and, most important, the reaction of the body to different administration regimens of erythropoiesis stimulating agents, as for instance in the case of pre-surgical administration of Epoetin-α. The simulation results concerning the last item show that choosing an appropriate administration regimen can reduce the total amount of the administered drug considerably. The core of the model consists of structured population equations for the different cell populations which are considered. A key feature of the model is the incorporation of neocytolysis.     

Enhanced endothelin-1-mediated leg vascular tone in healthy older subjects.

Advanced age is associated with a decreased leg blood flow and reduced physical activity. Endothelin (ET-1), a powerful vasoconstrictor, may play a role in the increased leg vascular tone in older men. objectives: to assess the ET-1-mediated vascular tone in the legs of healthy sedentary older men, both before and after 8 wk of exercise training. methods: in 8 younger subjects (19-50 yr) and 8 older men (67-76 yr), bilateral leg blood flow was measured using venous occlusion plethysmography before and after antagonizing ET-1 (using selective ET(A/B)-receptor antagonists). In older men, reversibility of the observations was assessed after 8 wk of cycling. results: ET-receptor inhibition increased leg blood flow significantly more in older men compared with younger individuals (29 +/- 9% and 10 +/- 4%, respectively, P < 0.05). Eight-week cycling training increased baseline blood flow in older men. The blood flow response to ET-receptor inhibition in older men was not affected by the training program (25 +/- 8%, P > 0.05 for comparison with pretraining). The flow ratio (blood flows infused leg/noninfused leg) decreased significantly by training from 26 +/- 8% to 7+3% (P < 0.05). CONCLUSION: the increased baseline vascular tone in aging is at least in part mediated by the endothelin. Eight-weeks cycling training in older sedentary men decreased leg vascular tone and seems to partly decrease the ET-1-mediated vascular tone.     

What can we learn from noncoding regions of similarity between genomes?

Background  

In addition to known protein-coding genes, large amounts of apparently non-coding sequence are conserved between the human and mouse genomes. It seems reasonable to assume that these conserved regions are more likely to contain functional elements than less-conserved portions of the genome.