In vivo and in vitro actions of low-molecular-weight gonadal peptides

Two low-molecular-weight gonadal peptides, IRRP3 and IRRP5, have been isolated from sheep ovaries having different biological properties in male rats. The peptide IRRP3 has specific effect on FSH secretion as well as release at the pituitary level, in vitro binding of labeled FSH to testicular receptor, and in vivo uptake of labeled FSH by the testis, whereas peptide IRRP5 has specific effect on LH secretion at the pituitary level, in vitro binding of labeled LH to testicular receptor, and in vivo uptake of labeled LH by the testis.