Biphasic effect of the alpha-adrenolytic phentolamine on hormone-stimulated formation of cyclic adenosine-3',5'-monophosphate in isolated fat cells of rats.

Isolated fat cells from rat epididymal adipose tissue were incubated with various lipolytic hormones in the absence and presence of the alpha-adrenergic blocking agent phentolamine. Lipolysis, stimulated by noradrenaline, isoproterenol, or ACTH, was inhibited dose-dependently by phentolamine. At concentrations of phentolamine where lipolysis was already inhibited, phentolamine had a biphasic effect on hormone-stimulated formation of cAMP. Low concentrations of phentolamine enhanced cAMP formation, while high concentrations inhibited cAMP. The additional increase of cAMP formation by phentolamine was only seen with maximally effective concentrations of noradrenaline, isoproterenol, and ACTH. Half-maximally effective concentrations were invariably inhibited by phentolamine. The activity of noradrenaline-stimulated adenylate cyclase of fat-cell plasma membranes was inhibited by phentolamine, whereas cAMP phosphodiesterase activity was unaffected.     

Splenic regeneration and blood flow after ligation of the splenic artery or partial splenectomy

In normal, young miniature piglets, either the major arteries and the veins were ligated or three quarters of the spleen was resected using three different techniques. These techniques served as an animal model for splenic salvage in human subjects. After arterial ligation, no signs of infarction could be seen 1 and 4 weeks later, and after 6 months, normal sized spleens with enlarged vessels in the gastrolienal ligaments were found. When the splenic remnant was left at the main vessels, no obvious growth could be demonstrated after 6 months. The splenic tissue left at the smaller vessels, however, increased in size. Measurements of splenic blood flow in unanesthetized piglets 6 months after operation resulted in greater differences in perfusion per gram among the experimental groups. Not only splenic mass, but also blood flow to the whole splenic tissue seems to be an important factor in the protective function of the spleen.     

Oncogenic transformation and the reductions of insulin secretion and proliferative calcium dependence during repeated passage of pancreatic islet cells in vitro

Islet cells were isolated from 2 fetal bovine pancreas glands and cultivated in vitro. During the course of repeated passage in vitro, the B-cells in these cultures retained the ability to synthesize insulin, but rapidly lost the ability to secrete it. The cells also became progressively more able to proliferate in calcium-deficient medium which did not support the proliferation of cells from primary cultures. The reductions of insulin secretion and proliferative calcium dependence were accompanied by the acquisition of the ability to produce tumors in nude mice.     

Induction of characteristic hepatocyte proliferative lesion with dietary exposure of Wistar Hannover rats to tocotrienol for 1 year

Tocotrienol is an antioxidant which has found commercial application as a food additive and health supplement all over the world. Since there have been no reports regarding toxicological effects of long-term exposure, we performed a 52-week chronic study using Wistar Hannover rats of both sexes given the compound at doses of 0, 0.08, 0.4 or 2% in powdered basal diet. Since 6 animals in the 2% male group died of hemorrhage of several organs by week 50, the maximum dose level was changed to 1% in both sexes for the last 2 weeks. Decrease of body weight gain was observed in the 2% males from week 5 and females from week 10, this persisting to the end of the study. With the high dose, prolongation of prothrombin time and increase of serum ALT in males, and increase of serum ALP in both sexes were observed with statistical significance. In male and female rats receiving 0.4% or less, there were no toxicological changes in any of the parameters examined. At necropsy, multiple cyst-like nodules on the liver surface were macroscopically pronounced in both sexes receiving 2%. On histopathological examination, hepatocellular nodules were evident with distortion of hepatic cords and compression of the surrounding tissue, almost all including areas of spongiosis hepatis. The constituent hepatocytes were immunohistochemically stained with proliferation cell nuclear antigen at high rates. Nevertheless, they did not exhibit overt atypia and the basic lobular architecture remained intact. Additionally, they were consistently negative for glutathione S-transferase placental form (GST-P). Accordingly, we propose the newly categorized but previously used name 'nodular hepatocellular hyperplasia', which may not necessarily have a neoplastic or regenerative nature. However, quantitative GST-P analysis of the liver sections overall showed numbers of GST-P foci in the high dose females to be significantly elevated as compared to the control value. Based on the present data demonstrating nodular liver lesions only at the high dose of both sexes, we conclude that the no-observed-adverse-effect level (NOAEL) is 0.4% (303mg/kg/day for males, and 472mg/kg/day for females).     

Differences in spontaneous fetal abnormalities among three outbred stocks of Wistar Hannover rats in Japan

Wistar Hannover rats, which are maintained by three animal breeders in Japan, were examined to obtain basic data on reproductive and developmental parameters. Untreated pregnant females were terminated on gestational day 20, and the fetuses were removed by cesarian section. The fetuses were counted, weighed and examined for morphological abnormalities. There were few differences among the three stocks of Wistar Hannover rats on the numbers of implantations and live fetuses, sex ratio and fetal weights. The most common fetal abnormalities were the presence of left-sided umbilical arteries, supernumerary ribs and wavy ribs. The incidences of these abnormalities were different among the three stocks of Wistar Hannover rats. Our results provide important data which should be considered in the determination of which stock of rat is used in developmental studies.