ACTIVITY OF A NOVEL NONPEPTIDYL GROWTH-HORMONE SECRETAGOGUE, L-700,653 IN SWINE

L-700,653 is a potent nonpeptidyl GH secretagogue consisting of a benzolactam structure: (4'-[[13(R)-[[3-[(2(S),3-dihydroxypropyl)amino]3-methyl- 1-oxobutyl]amino]2, 3, 4, 5-tetrahydro-2-oxo-1H-1-benzazepin-1-yl]methyl][1, 1'-biphenyl]2-carboxamide hydrochloride). When administered sc by a Medi-Jector device at 0, 0.003, 0.01, 0.03, and 0.1 mg/kg BW to male castrated swine (similar to 50 kg BW), L-700,653 stimulated dose-related increases in peak plasma GH concentrations by 20% (P = NS), 150% (P = NS), 250% (P < 0.05), and 340% (P < 0.05), respectively, over the saline vehicle control value (11.3 +/- 6.5 ng/ml) and stimulated increases in GH areas under the curve (AUCs) by 10% (P = NS), 30% (P = NS), 90% (P < 0.05), and 100% (P < 0.01), respectively, over the saline vehicle control value (799 +/- 145 ng/min.ml). After sc administration of L-700,653, there were no significant changes in plasma LH levels. Subcutaneous dose of 0.03 or 0.1 mg/kg increased plasma cortisol AUCs by 60% (P = NS) and 150% (P < 0.03) over the control value (2461 +/- 935 ng/min.ml) and increased cortisol peaks by 80% (P = NS) and 200% (P < 0.01), respectively, over the control value (38.3 +/- 12.3 ng/ml). Repeated sc administration of L-700,653 (0.03 or 0.1 mg/kg) at 0800, 1400, and 2000 h daily over 3 days consistently increased mean GH peak and GH AUC at each treatment period, with minimal and maximal increases of 40% and 190% in GH peak level at the 0.03 mg/kg dose and 100% and 400% increases in GH peak level at the 0.1 mg/kg dose, respectively. Continuous iv infusion of L-700,653, at either 0.01 or 0.1 mg/kg BW.h over a 180-min period, increased GH AUCs by 60% (P = NS) or 470% (P < 0.01) and GH peaks by 190% (P = NS) or 1520% (P < 0.01), respectively, over the control value (589 +/- 313 ng/min.ml; 7.0 +/- 11.1 ng/ml). After a 180- to 300-min saline infusion, an iv bolus dose of 0.1 mg/kg L-700,653 resulted in GH responses inversely proportional to the previous infusion dose, i.e. 0, 0.01, or 0.1 mg/kg. In a follow-up study, continuous iv infusion of L-700,653 at 12-fold the dose (1.2 mg/kg.h) over a 240-min period resulted in an initial peak of 81.4 +/- 26.1 ng/ml at 15 min and a secondary peak (33.7 +/- 5.9 ng/ml) at 100 min; GH levels remained above the preinfusion baseline value (3 ng/ml) until nearly 60 min post-L-700,653 infusion. After the 240-360 min saline infusion period, an iv bolus challenge of L-700,653 (0.1 mg/kg) at 360 min resulted in little, if any, GH response. The results of these studies indicate that L-700,653 is a potent GH secretagogue in swine when administered sc at 0800, 1400, and 2000 h daily over 3 days or after continuous iv infusion over 3 or 4 h.