The step response: a method to characterize mechanisms of renal blood flow autoregulation

Response of renal vasculature to changes in renal perfusion pressure (RPP) involves mechanisms with different frequency characteristics. Autoregulation of renal blood flow (RBF) is mediated by the rapid myogenic response, by the slower tubuloglomerular feedback (TGF) mechanism, and, possibly, by an even slower third mechanism. To evaluate the individual contribution of these mechanisms to RBF autoregulation, we analyzed the response of RBF to a step increase in RPP. In anesthetized rats, the suprarenal aorta was occluded for 30 s, and then the occlusion was released to induce a step increase in RPP. Three dampened oscillations were observed; their oscillation periods ranged from 9.5 to 13 s, from 34.2 to 38.6 s, and from 100.5 to 132.2 s, respectively. The two faster oscillations correspond with previously reported data on the myogenic mechanism and the TGF. In accordance, after furosemide, the amplitude of the intermediate oscillation was significantly reduced. Inhibition of nitric oxide synthesis by Nomega-nitro-l-arginine methyl ester significantly increased the amplitude of the 10-s oscillation. It is concluded that the parameters of the dampened oscillations induced by the step increase in RPP reflect properties of autoregulatory mechanisms. The oscillation period characterizes the individual mechanism, the dampening is a measure for the stability of the regulation, and the square of the amplitudes characterizes the power of the respective mechanism. In addition to the myogenic response and the TGF, a third rather slow mechanism of RBF autoregulation exists.

[The content of the DNA, the RNA and the wet weight and the RNA:DNA and the wet weight:DNA ratio in different tissues during the growth of chickens. 2. Analysis of the kidney, the spleen, the gizzard and the M. pectoralis superficialis]

At chicken of the race "White Leghorn" the content of nuclei in the kidney was highest (14.60 x 10(9)) on the 203rd, in the spleen on the 112th (14.85 x 10(9)), in the gizzard on the 112th (18,24 x 10(9)) and in the M. pectoralis superficialis on the 168th day (36.42 x 10(9)) after hatching. The biggest fresh weight:DNA-ratio was determined in the kidney on the 203rd (285), in the spleen on the 28th (92) and in the gizzard (694) and in the M. pectoralis superficialis (1984) on the 203rd day. The DNA-concentration on the 2nd day after hatching in the kidney was 4,56 +/- 0,36, in the spleen 11.49 +/- 0.84, in the gizzard 1.85 +/- 0.13 and in the M. pectoralis superficialis 2.96 +/- 0.18 mg/g wet weight respectively the RNA:DNA-ratio in these tissues 1.00, 0.88, 1.70 and 0.85. The growth of tissues by the increase of the number of cells (hyperplasia) and of the volume of cells (hypertrophy) is described.

[The effect of a different level of crude protein in the feed of chickens from 1 to 14 days after hatching on the development of body weight, the biochemical parameters of the liver and breast muscle and the serum level of total protein and albumin]

The effect of a concentration of crude protein of 170 or of 227 g/kg in the ration of chicken from the 1st to the 14th day after hatching on biochemical values of the liver, the M. pectoralis superficialis and the serum was analysed. The significance of developmental investigations in domestic animals under normal and pathological conditions is discussed.

[Joint utilization of glucose and n-alkanes in citric acid synthesis by Saccharomycopsis lipolytica]

Fermentations for the overproduction of citrate and isocitrate with S. lipolytica in media containing both glucose and n-alkanes as mixed C-source have been performed. Biomass and product yields strongly depend on the C-source of the inoculation culture. If the inoculation culture had been taken from media containing glucose as sole C-source both glucose and n-alkanes were utilized for cell growth in the main culture whereas only glucose was utilized if the inoculation medium contained only n-alkanes. For idiophasic citrate and isocitrate production both glucose and n-alkanes were consumed independently of the C-source of the inoculum but that C-source was preferentially utilized which has been the C-source of the inoculation culture. These findings are reflected by the activities of the isocitrate lyase and the pyruvate carboxylase, respectively. In S. lipolytica both anaplerotic pathways are coexisting but the C-source of the inoculation culture determines the level of the specific activities even if the ratio of the cell-mass of the inoculum to the cell mass of the main culture at the end of the growth phase is about 1:35.