-The aim of the present study was to examine, for the first time in pigs, the dosedependent effect of arginine (ARG) on growth hormone (GH) and insulin release and the effect of the combined ARG and aspartic acid (ASP) treatment on GH and insulin release. ARG (0.5 or 1 g/kg body weight) with or without an equimolar supplement of ASP (0.38 or 0.76 g/kg, respectively) was administered in piglets via the duodenum. ARG

-The novel synthetic growth hormone-releasing heptapeptide GHRP-is reported to be more potent than growth hormone-releasing hormone (GHRH) in eliciting GH release in vivo in rats and man. However, in ovine pituitary cells in primary culture in a perifusion system, GHRP-1 was 10-fold less active than GHRH. The purpose of this work was to study the effect of GHRP-1 in sheep in vivo. Ovine GH release stimulated by either GHRP-1 or GHRH() -29)NH!, in eight pre-ruminant lambs, was determined. GHRP-was administered at doses of 1.2, 2.4 and 6 nmole/kg by i.v. bolus, and GHRH(1-29)NH! at 0.3 nmole/kg. Mean ± s.e.m. peak GH levels in the plasma after injection of saline, 1.2, 2.4, 6 nmole/kg GHRP-and 0.3 nmole/kg GHRH were 2.2 ± 0.9, 9.3 ± 2.5, 8.8 ± 2.4, 35.1 ± 5.8 and 5 I .6 ± 10.5 ng/mL, respectively. As spontaneous 20 ng/mL peaks were observed, only peaks above this level can be considered as significant. The highest dose of GHRP-1 (6 nmole/kg) elicited oGH release, but its action was surpassed by GHRH 0.3 nmole/kg. Furthermore GHRP-1 and GHRH appear to behave inversely when response amplitudes are considered. Animals exhibiting a strong reaction to GHRH-1, show a correspondingly weak reaction to GHRH and vice-versa