Long-lasting rat growth enhancement by an immunoregulating synthetic peptide.

We have studied the long-lasting effects on rat weight gain of an active immunization with a peptide construction consisting of the covalent linkage of the 104-113 GH sequence to the 323-339 sequence of ovalbumin and to adjuvant muramyl dipeptide (MDP). The 104-113 GH sequence has already been identified as a potential epitope capable of enhancing growth hormome (GH) activity when complexed with the specific antibodies. Our results show that: a) 104-113 peptide antibodies after reacting with the endogenous GH produced a weight gain up to 7% higher than that observed in unimmunized rats; and b) the position of the adjuvant sequence in the molecule was critical for the immune response. Antibodies elicited in hypophysectomised rats had no effect on weight gain, thus confirming that the increase in hormonal activity is actually linked to the binding of specific peptide antibodies to endogenous GH.