HDL-induced cardiac prostacyclin synthesis: relative contribution of HDL apoprotein and lipid

The objective of this study was to determine if the apoprotein or lipid constituents of high density lipoproteins (HDL) mediate HDL-induced prostacyclin synthesis in the Langendorff-perfused rabbit heart. Acetylation, acetoacetylation, or partial removal by trypsin digestion of HDL apoprotein did not reduce the ability of the lipoprotein to stimulate cardiac prostacyclin synthesis. Delipidated apoproteins were less effective in stimulating cardiac prostacyclin synthesis in comparison to intact HDL. In contrast, protein-free lipid vesicles, made from HDL lipids, caused a pronounced stimulation of cardiac prostacyclin synthesis. These results suggest that HDL apoproteins, in their native state, are not essential for HDL-induced cardiac prostacyclin synthesis. The stimulation of cardiac prostacyclin synthesis by HDL may depend on the lipoprotein's lipid rather than on its apoprotein constituents.     

Valproate and copper accelerate TRH-like peptide synthesis in male rat pancreas and reproductive tissues

Treatment with valproate (Valp) facilitates the synthesis of TRH-like peptides (pGlu-X-Pro-NH(2)) in rat brain where "X" can be any amino acid residue. Because high levels of TRH-like peptides occur in the pancreas and pGlu-Glu-Pro-NH(2) (Glu-TRH) has been shown to be a fertilization promoting peptide, we hypothesized that these peptides mediate some of the metabolic and reproductive side effects of Valp. Male WKY rats were treated with Valp acutely (AC), chronically (CHR) or chronically followed by a 2 day withdrawal (WD). AC, CHR and WD treatments significantly altered TRH and/or TRH-like peptide levels in pancreas and reproductive tissues. Glu-TRH was the predominant TRH-like peptide in epididymis, consistent with its fertilization promoting activity. Glu-TRH levels in the epididymis increased 3-fold with AC Valp. Phe-TRH, the most abundant TRH-like peptide in the pancreas, increased 4-fold with AC Valp. Phe-TRH inhibits both basal and TRH-stimulated insulin release. Large dense core vesicles (LDCV's) contain a copper-dependent enzyme responsible for the post-translational processing of precursors of TRH and TRH-like peptides. Copper (500 microM) increased the in vitro C-terminal amidation of TRH-like peptides by 8- and 4-fold during 24 degrees C incubation of homogenates of pancreas and testis, respectively. Valp (7 microM) accelerated 3-fold the processing of TRH and TRH-like peptide precursors in pancreatic LDCV's incubated at 24 degrees C. We conclude that copper, an essential cofactor for TRH and TRH-like peptide biosynthesis that is chelated by Valp, mediates some of the metabolic and reproductive effects of Valp treatment via acceleration of intravesicular synthesis and altered release of these peptides.     

Regulation of lipid synthesis in relation to keratinocyte differentiation capacity

Cultured keratinocytes and squamous carcinoma cells provide a useful model system for studying the processes involved in the regulation of differentiation, as the differentiation capacity of the cells can be modulated experimentally by changing the extracellular calcium concentration. Furthermore, the squamous carcinoma cell lines exhibit a defect in their differentiation capacity which they express to different extents. In this paper, the effect of external lipoproteins has been studied on lipid synthesis in normal keratinocytes and three squamous carcinoma cell (SCC) lines which showed a decreasing capacity to differentiate in the order of normal keratinocytes greater than SCC-12F2 greater than SCC-15 greater than SCC-4. The ability of the cells to form cornified envelopes was taken as a measure of differentiation capacity. The rate of total lipid synthesis as well as the phospholipid-neutral lipid ratio decreased in the order SCC-4 greater than SCC-15 greater than SCC-12F2 greater than or equal to normal keratinocytes, clearly correlating with the differentiation capacity of the cells. Because of the high rate of phospholipid synthesis and the low rate of ceramide synthesis, it is concluded that, under these in vitro conditions used, the maturation of keratinocytes proceeds to a lesser extent than that seen under in vivo conditions. In proliferating cells, in which the low-density lipoprotein (LDL) receptor is operative to a high extent, the rate of lipogenesis, especially that of neutral lipids, responded dramatically to changes of extracellular lipoprotein concentration. In the presence of lipoproteins a marked decrease of cholesterol and triacylglycerol synthesis and an increase of cholesterol ester synthesis has been observed. On the other hand, in differentiating cells lipogenesis appeared to be independent of extracellular lipoproteins, due to the absence of the LDL uptake mechanism, the only exception being the synthesis of triacylglycerols, the rate of which could be modulated to a certain extent by extracellular lipoproteins. The results presented here demonstrate a close inverse relationship between the regulation of lipogenesis by extracellular lipoproteins and the ability of the cells to differentiate.     

Localization of metallothionein in the genital organs of the male rat

We studied the immunohistological localization of metallothionein (MT), a low molecular weight metal binding protein, in male rat genital organs (testis, epididymis, ejaculatory duct, seminal vesicle, coagulating gland, and prostate) by use of the avidin-biotin-peroxidase complex method. MT concentrations in testis, seminal vesicle, and prostate ranged from 15-30 micrograms/g tissue. In testis, seminiferous tubules with mature spermatozoa exhibited weak MT staining, whereas the tubules containing differentiating spermatogenic cells but not containing spermatozoa showed strong MT staining. No MT immunostaining was observed in Leydig cells. In growing rat testes, the pattern of MT immunostaining was found to change with development: MT was found in supporting cells only on Day 7, spermatogonia adjacent to basement membrane on Day 14, and spermatocytes localized in the central part of the tubules on Day 21. Strong MT immunostaining in the basal cells was a common feature in other genital tissues, except the ductus efferentes. In prostate, the strongest MT staining was found in the lateral lobe, and MT was localized in apocrine secretions in the dorsal lobe. The present results suggest a close association of MT with cell proliferation and differentiation, as well as possible involvement of MT in supply or storage of zinc ions.     

Protein synthesis in the organs and tissues of frogs with local exposure to low temperatures]

Intensity of synthesis of total proteins and spectrum of synthesized proteins has been studied in various organs and tissues of sharp-faced frogs during local profound cooling of one of its limbs. It was shown that the effect of low temperatures on a certain part of a body of a poikilothermic animal has induced both a response of the whole organism and a much more acute response of the cooled tissues. The organism responded by a fall of the whole body temperature and a decrease in the activity of synthesis of total proteins of the viscera. Local cooling of a part of the frog body has induced a more significant decrease in the protein synthesis intensity in the cooled tissues alteration in the spectrum of synthesized proteins and appearance of specific proteins.     

Effects of dexamethasone on lipid metabolism in rat organs

Injecting of dexamethasone (10 mg/kg body weight) for 8 days to rats decreased the body weight and feed intake by 29 and 50%, respectively. The increase in weights of liver, heart, kidneys and testes per 100 g body weight was 55, 37, 33 and 13%, respectively. Though, in general, the triglyceride content increased in all the organs, maximum increase (9-fold) was observed in the liver. The plasma showed elevated levels of triglycerides, cholesterol and phospholipids. In hepatic mitochondrial membranes, the content of protein, phospholipids and cholesterol decreased/g tissue. The percent 14C distribution, as a part of total incorporation in nonpolar lipids, of [14C]acetate into triglycerides of liver, kidneys and testes increased significantly. The increased turnover of phospholipids in liver and heart was mainly due to increased turnover of phosphatidyl choline (PC) and phosphatidyl ethanolamine in liver and PC in heart. Turnover of phospholipids of testes was not affected.