EFFECT OF ARGININE AND ORNITHINE INFUSION S ON SECRETION OF THE GROWTH-HORMONE IN PREPUBERTAL EWES

Twenty five Suffolk ewe lambs, alloted in five groups, were used to te st the effect of Arginine (ARC), or Ornithine (ORN) infusions on pulsa tile growth hormone (GH) secretion. Additionally, plasma glucose (G) a nd urea (U) concentrations were also determined. 15 and 30 g ARG and 1 2 or 24 g ORN dissolved in 500 mt saline were intravenously infused fo r 6 h. Control lambs received 500 mt saline. Blood samples were collec ted from the jugular vein at 15-min intervals for 750 min starting 30 min before infusions. The PULSAR program was used to detect significan t hormone fluctuations. Mean plasma GH concentrations (ng/mL/6 h) incr eased 100 to 400% in ARG and ORN infused animals compared to control e wes during the period of infusions. Amplitude of GH pulses were 13.5 /- 3.8, 79.4 +/- 37.3, 255.3 +/- 158.6, 56.9 +/- 34.9, 15.9 +/- 5.9 in saline, ARG and ORN infused lambs respectively during the infusion pe riod. Number of GH pulses were similar in the five groups during and a fter the infusions (1 pulse/h). Plasma concentrations of G and U remai ned unchanged in control lambs but in those infused with 30 g ARG ther e was a statistically significant decrease in G (P < 0.01) and a stati stical increase in U (P < 0.05). ARG infusions generated 2 different p atterns of GH secretion. One was characterized by 400 fold increases o n the basal GH concentrations at 30-45 min of the start of infusions, and by a second pattern which was characterized by more moderate incre ases. The GH release induced by ARG may be related to the prevalent so matostatinergic tonus present in each animal.