5 alpha-Reductase type 1 is localized to the outer nuclear membrane.

The subcellular distribution of the two isozymes of 5 alpha-reductase has been controversial. To resolve this issue which could provide clues about the respective functions of the two isozymes, two antisera were generated, one which was specific for the Type 1 5 alpha-reductase and one which recognized both isozymes. In COS cells transfected separately with the Type 1 or Type 2 cDNA, both isozymes were detected on Western blots at an M(r) of 26,000. Subfractionation of the COS cells resulted in the partitioning of both isozymes between the crude nuclear and cytosolic fractions, while cytoimmunofluorescence localized both reductases to the nuclear periphery. In rat liver homogenate, the 5 alpha-reductase was also detected at M(r) 26,000. The 5 alpha-reductase immunoreactivity was increased after castration of the animals with no further effect when castrated animals were treated with androgens. Although the rat liver expresses only the Type 1 5 alpha-reductase, the 5 alpha-reductase was distributed about equally between crude nuclear and cytosolic subfractions; this distribution could be shifted to the cytosolic fractions with harsher homogenization procedures. Further extensive subfractionation and extraction studies identified the rat liver Type 1 5 alpha-reductase as an integral membrane protein present in the outer nuclear membrane of the nuclear envelope and in rough endoplasmic reticulum. Thus, the subfractionation and cytoimmunofluorescence studies are consistent with the localization of the Type 1 5 alpha-reductase to the outer nuclear membrane of the nuclear envelope which is continuous with and indistinguishable from the endoplasmic reticulum. This study is the first to localize rat liver Type 1 5 alpha-reductase to the nuclear envelope to which the prostatic 5 alpha-reductase activity previously had been localized. We conclude that, contrary to previous tissue distribution studies, but consistent with investigations in transfected cells, both isozymes are similarly localized to the nuclear periphery.

Plasma flow and net nutrient flux across gut and liver of cattle fed twice daily.

The objectives of this study were 1) to quantify daily patterns of plasma flow and metabolite flux through portal-drained viscera (PDV) and liver in cattle fed twice daily and 2) to identify an interval for blood sampling that would approximate the average daily plasma flow and nutrient flux values. Data are from three experiments in which multicatheterized cattle were fed at or near ad libitum intake twice daily. Five lactating primiparous Holstein cows (506 kg, fed at 0730 and 1930) ate 17.3 kg DM/d as chopped alfalfa hay:corn grain plus supplement (urea and minerals) 50:50 (Exp 1). Five beef steers (474 kg, fed at 0900 and 2100) ate 8.3 kg DM/d as chopped switchgrass hay:corn grain plus supplement 37:63 (Exp 2). Six beef steers (306 kg fed at 0900 and 2100) ate 6.9 kg DM/d as chopped alfalfa hay (Exp 3). Plasma flow (by dilution of para-aminohippurate) was measured hourly for 24 h. Plasma flows (mean +/- SE) through PDV were 1,264 +/- 147, 538 +/- 56, and 499 +/- 26 L/h for Exp. 1, 2, and 3, respectively. Corresponding liver flows were 1,662 +/- 216, 642 +/- 41, and 591 +/- 30 L/h. The within-animal differences from their respective daily means were estimated as a function of time of day using nonparametric smoothing. Across experiments, PDV and liver flows were above the daily mean from 1200 to 1400, were not different from the daily mean from 1600 to 1700, and were below the daily mean from 1930 to 2130. Metabolites measured were ammonia, urea, alpha-amino N, and glucose. In general, metabolite flux was not different from the average daily mean values between 1200 and 1600. Blood sampling over 12 h or one 12-h feeding cycle is sufficient for daily plasma flow and metabolite flux estimation in cattle fed twice daily.

Effect of mesenteric vein infusion of propionate on splanchnic metabolism in primiparous Holstein cows.

Our objective was to assess the effects of increased propionate supply on gut and liver function in lactating cows. Four multicatheterized, primiparous cows (30.4 +/- .5 kg/d of milk) were fed for ad libitum intake a diet of 50% alfalfa hay and 50% concentrate (20.6 +/- 1.9 kg/d of DM, 226 +/- 21 MJ/d of metabolizable energy, and 611 +/- 56 g/d of N). Each cow received intramesenteric infusions of NaCl (control) or Na-propionate (150 mmol/h of a 2.5 M solution) in a reversal design. After 72 h of infusion, blood flow (by indicator dilution) and net flux (venoarterial differences multiplied by blood flow) were measured across portal-drained viscera and the liver. Energy supply from feed consumed and from infusion was similar between treatments. Energy that was excreted as milk decreased with propionate infusion. Propionate infusion increased arterial concentration of propionate; decreased absorption of acetate, butyrate, and valerate; and decreased hepatic removal of L-lactate, butyrate, valerate, NEFA, and oxygen. Propionate infusion decreased splanchnic release of glucose and increased splanchnic release of acetate and alanine. Net flux of urea, BHBA, insulin, or glucagon was unaffected by treatments. Our data show a link between a greater proportion of energy supplied as propionate and decreased energy excreted as milk. This response was associated with decreased net removal of glucogenic and ketogenic substrates by the liver and increased supply of acetate for use by peripheral tissues.