1. Investigación

To study the effect of prolonged diabetes on protein synthesis and on the activities of initiation factors elF-2 and elF-2B in the liver, female rats were treated with streptozotocin. Some animals were mated and studied on day 20 of pregnancy, whereas others were kept virgin and studied in parallel. The protein synthesis rate was measured with an 'in vitro' cellfree system, and was lower in diabetic pregnant and virgin animals than in pregnant and virgin controls (30-60%). The fetuses of diabetic rats had a lower protein synthesis rate than those from controls, although they always showed a higher protein synthesis rate than their mothers or virgin rats. Protein synthesis rate, RNA concentration, and initiation factor 2 activity were higher in pregnant than in virgin rats. Both activity and level of elF-2 factor changed in parallel to the protein synthesis rate, although no differences could be detected between control and diabetic animals. The eIF-2B activity in tissue extracts from diabetic virgin rats and fetuses was lower than in extracts from their controls, whereas no differences could be detected between pregnant and virgin control rats nor between pregnant control and pregnant diabetic animals. The percentage of the phosphorylated form of eIF-2 factor, eIF-2(uP), was slightly lower in virgin than in pregnant rats but was unaffected by the diabetic condition, while in diabetic fetuses this parameter was lower than in their corresponding controls. The cyclic adenosine monophosphate dependent protein kinase level was lower in diabetic rats than in controls, whereas no changes in the activity of casein kinase II were found. The isoelectric forms of the 13 subunit of eIF-2 factor, eIF-213, were different in the diabetic and the control animals, indicating that insulin deficiency modifies the phosphorylation of specific substrates. Since no differences were detected in RNA or eIF-2 content between control and diabetic rats, translation may, at least partly, be inhibited in the liver by an impairment of peptide chain initiation caused by the decreased eIF-2B activity which nevertheless is independent of eIF2u phosphorylation.

Para estudiar el efecto de la gestación y la diabetes sobre la actividad y la expresión (ARNm) de la lipoproteína lipasa (LPL) y de la lipasa sensible a las hormonas (HSL) en tejidos, las ratas recibieron 40 mg de estreptozotocina/kg y se sacrificaron al día 20 de gestación. En el tejido adiposo blanco {T AB), la actividad y el ARNm de la LPL eran más bajos en las ratas preñadas controles (PC) que en las vírgenes controles (VC), siendo también inferior la actividad en las diabéticas (D) que en las controles(C), tanto vírgenes (V) como preñadas (P). En la glándula mamaria (GM), la actividad y el ARNm de la LPL estaban más altos en las PC que en las VC, y disminuyeron en las PD y VD respecto de las C. En el T AB, la actividad HSL estaba más alta en las P que en las V y era similar en las PC y PD, sin cambios en los niveles de ARNm. En la GM, la actividad y el ARNm de la HSL estaban más bajos en las P que en las V y eran menores en las D que en las C. Estos resultados permiten concluir que los mecanismos de regulación de la actividad y de la expresión molecular (ARNm) de la LPL y de la HSL durante la gestación y la diabetes son específicos de cada tejido. El paralelismo en los cambios de la actividad y el nivel de ARNm de la LPL en el T AB y GM, así como entre la actividad y el ARNm de la HSL en la GM, indican que la regulación a nivel transcripcional de la expresión de estos genes es un mecanismo importante para la captación y movilización de los TO en estos tejidos.

To study the effect of diabetes on hepatic protein synthesis and polysomal aggregation in pregnant rats, female rats were treated with streptozotocin prior to conception. Some animals were mated. and studied at day 20 of pregnancy, whereas. others were studied in parallel under non pregnant conditions. The protein synthesis rate measured with an "in l'ITTO .. cell-free system was higher in pregnant than in virgin control rats. It decreased with diahetes in both groups. although values remained higher in diabetic pregnant rats than in the virgin animals. The fetuses of diabetic rats had a lower protein synthesis rate than those from controls, although they showed a higher protein synthesis rate than either their respective mothers or virgin rats. Liver R~A concentration was higher in control and diabetic. pregnant rats than in virgin rats, and the effect of diabetes decreasing this parameter was only significant for pregnant rats. Liver RNA concentration in fetuses was lower than in their mothers, and did not differ between control and diabetic animals. The decreased protein synthesis found in d1ahe11c animals was accompanied by disaggregation of hea,·y polysomes into lighter species, indicating an impairment in peptide-chain initiation.