No abstract

S U M M A R YThe effects of plane of nutrition on blood flow in the portal vein (PBF) and on the rate of clearance of progesterone from the circulation (MCR) were measured for 14 or 24 h in six ovariectomized gilts given 1 or 3 kg of food per day. On a body weight basis, PBF was significantly increased by the increase in food intake from a mean for all gilts of 14-9 ml/kg.min (1-34 litres/min) on 1 kg to 21 -6 ml/kg. min (1 -96 litres/min) on 3 kg, a mean increase of 45 %. Metabolic clearance of progesterone was increased by a similar percentage, 4 7 1 % , from 410 ml/kg.min (3-70 litres/min) to 60-3 ml/kg.min (5-67 litres/min) by the increase in food intake. Both MCR and PBF were lowest between 04.00 and 06.00 h, increasing after each feed except that when 3 kg/day was fed the MCR remained high throughout the period between meals. In two gilts, blood flow in both the portal vein and hepatic artery (HAF) was measured. The mean PBF and HAF for each pig were 40-6 and 5-8, and 32-4 and 35 ml/kg, min respectively. HAF was 11-2% of total hepatic blood flow.

Yeast two-hybrid analysis is a valuable approach to the discovery and characterization of protein interactions. We have developed vectors that can indicate the presence of an insert when used in two-hybrid bait and prey construction by gap repair cloning. The strategy uses a recombination cloning site flanked by sequences encoding the GAL4 activation and binding domains. After gap repair cloning in standard hosts carrying an ADE2 reporter gene, disruption of GAL4 by an insert can be identified by the development of red colony color, while empty vector plasmids produce white colonies. Function in yeast two-hybrid applications was initially validated using known interacting proteins in pair-wise analyses, and subsequently, the bait vectors were used in library screens with the mouse Mad212 and human Mccd1 proteins, identifying a number of putative new interactions for these proteins. These vectors should facilitate high-throughput yeast two-hybrid screens in which large numbers of bait and prey constructs may be required.

The mitotic spindle checkpoint arrests cells in metaphase until all kinetochores are correctly attached to spindle fibres. In a search for new components of the spindle checkpoint, based on protein interaction, we have identified mouse Telomeric Repeat Binding Factor 1 (Trf1) as a protein that interacts directly with the spindle checkpoint protein Mad1 and the mitotic kinase Nek2. Trf1 has a role in the regulation of telomere length, but has also been implicated in cell cycle regulation. These interactions now provide a direct link between telomere length regulation and the control of mitotic progression.

One hypothesis for the adverse effect which a high food intake in early pregnancy has on early embryo mortality in gilts is that it increases blood flow through the liver and in consequence the rate of removal of progesterone from the blood. To study this aspect the metabolic clearance rate of progesterone (MCR) from plasma and the rate of blood flow in the portal vein were measured concurrently during 14 hour periods in six ovariectomised gilts, weighing 70 to 80 kg, when their food intake was 1 and 3 kg/day. To determine the MCR, progesterone was infused into a jugular vein at 70 ug/minute for 36 hours. The concentration of progesterone was determined in plasma samples collected from a cannula in the posterior vena cava at 20 minute intervals during the last 14 hours of infusion when an equilibrium had established between the rates of infusion and clearance. Because ovariectomy removed the principal endogenous source of progesterone, body fat became depleted of the steroid. Therefore, a priming dose of approximately 100 mg of progesterone in arachis oil was given intramuscularly 48 and 24 hours before each infusion started.