EFFECTS OF ALPHA(2)-ADRENOCEPTOR ANTAGONISTS ON METABOLIC PROCESSES OF SWINE - II - NITROGEN-BALANCE RESPONSES

We studied the effects of alpha(2)-adrenoceptor antagonists (A2AA) on nitrogen (N) partitioning. The diets fed contained 19.8% CP and 1.15% lysine. Pigs were fed the diet as a percentage of BW equaling approxim ately 90% of voluntary intake. In Trial 1, pigs (n = 11/treatment) wer e fed a basal diet and injected s.c. at 8-h intervals for 11 d with sa line, RX821002 (25 mg/injection), or cimaterol (.6 mg/injection). Comp ared to saline-treated pigs, urinary N, as a percentage of N eaten, de creased among pigs injected with RX821002 (15%, P < .05) or cimaterol (17%, P < .05). In Trial 2, pigs got saline (n = 6) or 25 mg RX821002 (n = 6) as s.c. injections three times daily, or they were fed a diet containing 150 ppm RX821002 and injected thrice daily with saline (n = 6) for 11 d. The RX821002 lowered apparent DM and N digestibility (P < .05). Compared to controls, RX821002 lowered urinary N, as a percent age of N eaten, 15 and 18% when given by injections or per os, respect ively, but effects were not significant. Trial 3 evaluated the effects of RX821002 fed at levels of 0 (n = 6), 37.5 (n = 5), 75 (n = 6), or 150 ppm (n = 6). Contrasts showed Linear dose-dependent decreases in g ain and apparent N digestibility (P < .05). Compared to untreated cont rols, urinary N, expressed as a percentage of N consumed, decreased 2, 12, and 10% among pigs fed diets with 37.5, 75, or 150 ppm RX821002, respectively, but effects were not significant. Trial 4 compared N bal ance in pigs (n = 6/treatment) fed basal diet or diet with 100 ppm RX8 21002 to that of pigs fed diets with 25 or 100 ppm yohimbine. Treatmen ts reduced apparent N and DM digestibility(P < .05). Urinary N, as a p ercentage of N consumed, decreased 16 (P > .05), 18 (P < .05), and 24% (P < .05) for 100 ppm RX821002, 25 ppm yohimbine, or 100 ppm yohimbin e, respectively. Data from Trials 2, 3, and 4 6 om control pigs (n = 1 8) or pigs fed A2AA (all A2AA sources and doses; n = 41) were pooled a nd analyzed. Feeding A2AA decreased apparent N and DM digestibility (P < .01). The fact that fecal moisture content was higher in pigs fed A 2AA suggests rate of digesta passage increased and offers an explanati on for reduced N and DM digestibility in treated pigs. Despite adverse effects of A2AA, efficiency of postabsorptive N metabolism increased. As a percentage of N consumed and compared to control pigs, urinary N decreased 15% (P < .01) and retained N increased 12% (P < .05) in ani mals fed A2AA. Data from these studies show net efficiency of N metabo lism is improved in swine given A2AA.