Tissue and plasma distribution of exogenous growth hormone-releasing factor analogue (GRF1-29NH2) after intravenous, subcutaneous and intraperitoneal injection in the rat.

1. The administration of 125I-labelled growth hormone-releasing factor (GRF) analogue 1-29NH2 by intravenous, subcutaneous or intraperitoneal injection to rats leads to rapid (i.v.) or slow (s.c. and i.p.) increases in plasma radioactivity followed by extensive breakdown of the peptide. 2. Tissues possessing GRF-like immunoreactivity such as gastric antrum (but not fundus), duodenum and ileum showed in vitro specific uptake of 125I-GRF probably mediated by vasoactive intestinal peptide (VIP) receptors. 3. Pituitary (the primary target organ for GRF) but neither thyroid nor parathyroid exhibited specific uptake of 125I-GRF.