The study maps how the GH‑releasing peptide pralmorelin (GHRP‑2) moves through a rat’s body after an IV dose. It disappears from the blood quickly, is mostly cleared into bile within an hour, and spreads to organs either by blood flow (liver) or by crossing membranes (other tissues). The researchers built a computer model that predicts these levels over time.

Pralmorelin hydrochloride (pralmorelin), consisting of six amino acid residues, is a growth hormone-releasing peptide. The aim of this study is to analyze the pharmacokinetics of pralmorelin after intravenous bolus administration to rats, and to develop a physiologically based pharmacokinetic (PB-PK) model to describe and predict the concentrations of pralmorelin in blood and tissues. Pralmorelin (3 mg/kg) was administered intravenously to 24 Sprague-Dawley rats. Groups of three rats were sacrificed by decapitation at each designated time point (up to 4 h), and plasma and tissues (brain, lung, heart, liver, kidney, small intestine, muscle, adipose, and skin) were collected. Bile was also pooled until decapitation. The concentration of pralmorelin in samples was determined by liquid chromatography-tandem mass spectrometry. Plasma concentrations of pralmorelin declined rapidly in a biexponential manner. Biliary excretion of pralmorelin was so rapid that 80% of the dose was recovered unchanged in the bile within 1 h after administration. The distribution parameters in each tissue were obtained by using a hybrid model and an integration plot. They revealed that the distribution of pralmorelin into liver was blood flow-limited, and its distribution was permeability-limited in all other tissues. The PB-PK model developed in this study well described the time courses of pralmorelin concentration in the blood and tissues of rats.